Simple transistor NOT gate

Started by Allen Bong February 3, 2008
Hi,

Is it possible to construct a simple inverter gate using 1 or 2
transistors and resistors?

I tried the circuit below but it doesn't work at all.




                             VCC
                              +
                              |
                              |
                             .-.
                             | |
                             | |4K7
                             '-'
                              |
                              +------o OUTPUT
                              |
                1K_         |/
       INPUT o-|___|----+---|
                        |   |>
                       .-.    |
                       | |    |
                    4K7| |    |
                       '-'    |
                        |     |
                        |     |
                       ===   ==                       GND   GND


Allen









(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
"Allen Bong" <allenbsf6502@gmail.com> wrote in message 
news:c561da52-94da-4ae7-8d64-8e19ddc3fbf6@v67g2000hse.googlegroups.com...
> Hi, > > Is it possible to construct a simple inverter gate using 1 or 2 > transistors and resistors?
Allen, Yes, it is possible, and your circuit should work. When you ground the input, the transistor should be in cut-off and the collector voltage should be at Vcc. When you apply Vcc to the input, the transistor should saturate and the collector voltage should be at zero. Check all connections and check you transistor. If your ciruit still does not work, in what way is it not working? What type of transistor are you using? What value of Vcc? Other options? Google: transistor not gate Richard
Allen Bong wrote:
> > Hi, > > Is it possible to construct a simple inverter gate using 1 or 2 > transistors and resistors? > > I tried the circuit below but it doesn't work at all. > > VCC > + > | > | > .-. > | | > | |4K7 > '-' > | > +------o OUTPUT > | > 1K_ |/ > INPUT o-|___|----+---| > | |> > .-. | > | | | > 4K7| | | > '-' | > | | > | | > === ==> GND GND
What do you get at the output when input is at ground? At Vcc? What kind of transistor? How many volts is Vcc? You may need to select different resistor values for a particular transistor type, but it should work. The overall circuit is a classic inverting amplifier, used just about everywhere.
On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote:
> Hi, > > Is it possible to construct a simple inverter gate using 1 or 2 > transistors and resistors? > > I tried the circuit below but it doesn't work at all. > >                              VCC >                               + >                               | >                               | >                              .-. >                              | | >                              | |4K7 >                              '-' >                               | >                               +------o OUTPUT >                               | >                 1K_         |/ >        INPUT o-|___|----+---| >                         |   |> >                        .-.    | >                        | |    | >                     4K7| |    | >                        '-'    | >                         |     | >                         |     | >                        ===   === >                        GND   GND > > Allen > > (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)
You've described a perfect transistor inverter, that should work for logic level inputs. A couple of things to check: * Make sure you're using an NPN transistor instead of a PNP, a MOSFET, or something else. * Recheck your wiring, looking particularly at the pinout of the transistor. It's easy to assume EBC when it's ECB, or vice versa. * Use a voltmeter to actually measure the voltage at the input. If you're driving the input from an open collector transistor or gate output, no current will be injected into the base of your transistor when your logic level is "high". If you run through these three, the transistor has to be defective. Replace it. You've got the right answer right in front of you. Make it work. Cheers Chris
On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris <cfoley1064@yahoo.com>
wrote:

>On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote: >> Hi, >> >> Is it possible to construct a simple inverter gate using 1 or 2 >> transistors and resistors? >> >> I tried the circuit below but it doesn't work at all. >> >>                              VCC >>                               + >>                               | >>                               | >>                              .-. >>                              | | >>                              | |4K7 >>                              '-' >>                               | >>                               +------o OUTPUT >>                               | >>                 1K_         |/ >>        INPUT o-|___|----+---| >>                         |   |> >>                        .-.    | >>                        | |    | >>                     4K7| |    | >>                        '-'    | >>                         |     | >>                         |     | >>                        ===   ==>>                        GND   GND >> >> Allen >> >> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) > >You've described a perfect transistor inverter, that should work for >logic level inputs. A couple of things to check: > >* Make sure you're using an NPN transistor instead of a PNP, a MOSFET, >or something else. > >* Recheck your wiring, looking particularly at the pinout of the >transistor. It's easy to assume EBC when it's ECB, or vice versa. > >* Use a voltmeter to actually measure the voltage at the input. If >you're driving the input from an open collector transistor or gate >output, no current will be injected into the base of your transistor >when your logic level is "high". > >If you run through these three, the transistor has to be defective. >Replace it. > >You've got the right answer right in front of you. Make it work. > >Cheers >Chris
Classic RTL gate: should work. But if you used this to drive another such gate, the second gate would serious load down the output voltage of the first one. You could juggle the resistor values to reduce this effect. Like maybe...
>>                              VCC >>                               + >>                               | >>                               | >>                              .-. >>                              | | >>                              | | 1K >>                              '-' >>                               | >>                               +------o OUTPUT >>                               | >>                 10K         |/ >>        INPUT o-|___|----+---| >>                         |   |> >>                        .-.    | >>                        | |    | >>                    open| |    | >>                        '-'    | >>                         |     | >>                         |     | >>                        ===   ==>>                        GND   GND >>
John
On Feb 4, 2:29 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris <cfoley1...@yahoo.com> > wrote: > > > > > > >On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote: > >> Hi, > > >> Is it possible to construct a simple inverter gate using 1 or 2 > >> transistors and resistors? > > >> I tried the circuit below but it doesn't work at all. > > >>                              VCC > >>                               + > >>                               | > >>                               | > >>                              .-. > >>                              | | > >>                              | |4K7 > >>                              '-' > >>                               | > >>                               +------o OUTPUT > >>                               | > >>                 1K_         |/ > >>        INPUT o-|___|----+---| > >>                         |   |> > >>                        .-.    | > >>                        | |    | > >>                     4K7| |    | > >>                        '-'    | > >>                         |     | > >>                         |     | > >>                        ===   === > >>                        GND   GND > > >> Allen > > >> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) > > >You've described a perfect transistor inverter, that should work for > >logic level inputs.  A couple of things to check: > > >* Make sure you're using an NPN transistor instead of a PNP, a MOSFET, > >or something else. > > >* Recheck your wiring, looking particularly at the pinout of the > >transistor.  It's easy to assume EBC when it's ECB, or vice versa. > > >* Use a voltmeter to actually measure the voltage at the input.  If > >you're driving the input from an open collector transistor or gate > >output, no current will be injected into the base of your transistor > >when your logic level is "high". > > >If you run through these three, the transistor has to be defective. > >Replace it. > > >You've got the right answer right in front of you.  Make it work. > > >Cheers > >Chris > > Classic RTL gate: should work. > > But if you used this to drive another such gate, the second gate would > serious load down the output voltage of the first one. You could > juggle the resistor values to reduce this effect. Like maybe... > > > > > > >>                              VCC > >>                               + > >>                               | > >>                               | > >>                              .-. > >>                              | | > >>                              | | 1K > >>                              '-' > >>                               | > >>                               +------o OUTPUT > >>                               | > >>                 10K         |/ > >>        INPUT o-|___|----+---| > >>                         |   |> > >>                        .-.    | > >>                        | |    | > >>                    open| |    | > >>                        '-'    | > >>                         |     | > >>                         |     | > >>                        ===   === > >>                        GND   GND > > John- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -
Thanks very much Richard, Randy, Chris & John, The gate was used to replace a 74LS04 TTL inverter used between the output of 74LS138 and the LE input of a 74LS373 latch. The clock was about 1.8Mhz. During a high the transistor conducts fine but during a low input of short duration, I would not be able to get a high with my logic probe nor the LE is triggered. The Vcc is 5V and the transistor is a Japanese 2SC945 general purpose transistor. I checked with google for a transistor NOT gate and it used 1K at collector and 10K for the base and input. There was no resistor between Base and Emitter. And I tried that circuit, it doesn't work too. Where can I get the schematics for a RTL or DTL not gate? TIA and regards, Allen
On Feb 4, 8:54 am, Allen Bong <allenbsf6...@gmail.com> wrote:
> On Feb 4, 2:29 am, John Larkin > > > > > > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > > On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris <cfoley1...@yahoo.com> > > wrote: > > > >On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote: > > >> Hi, > > > >> Is it possible to construct a simple inverter gate using 1 or 2 > > >> transistors and resistors? > > > >> I tried the circuit below but it doesn't work at all. > > > >>                              VCC > > >>                               + > > >>                               | > > >>                               | > > >>                              .-. > > >>                              | | > > >>                              | |4K7 > > >>                              '-' > > >>                               | > > >>                               +------o OUTPUT > > >>                               | > > >>                 1K_         |/ > > >>        INPUT o-|___|----+---| > > >>                         |   |> > > >>                        .-.    | > > >>                        | |    | > > >>                     4K7| |    | > > >>                        '-'    | > > >>                         |     | > > >>                         |     | > > >>                        ===   === > > >>                        GND   GND > > > >> Allen > > > >> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) > > > >You've described a perfect transistor inverter, that should work for > > >logic level inputs.  A couple of things to check: > > > >* Make sure you're using an NPN transistor instead of a PNP, a MOSFET, > > >or something else. > > > >* Recheck your wiring, looking particularly at the pinout of the > > >transistor.  It's easy to assume EBC when it's ECB, or vice versa. > > > >* Use a voltmeter to actually measure the voltage at the input.  If > > >you're driving the input from an open collector transistor or gate > > >output, no current will be injected into the base of your transistor > > >when your logic level is "high". > > > >If you run through these three, the transistor has to be defective. > > >Replace it. > > > >You've got the right answer right in front of you.  Make it work. > > > >Cheers > > >Chris > > > Classic RTL gate: should work. > > > But if you used this to drive another such gate, the second gate would > > serious load down the output voltage of the first one. You could > > juggle the resistor values to reduce this effect. Like maybe... > > > >>                              VCC > > >>                               + > > >>                               | > > >>                               | > > >>                              .-. > > >>                              | | > > >>                              | | 1K > > >>                              '-' > > >>                               | > > >>                               +------o OUTPUT > > >>                               | > > >>                 10K         |/ > > >>        INPUT o-|___|----+---| > > >>                         |   |> > > >>                        .-.    | > > >>                        | |    | > > >>                    open| |    | > > >>                        '-'    | > > >>                         |     | > > >>                         |     | > > >>                        ===   === > > >>                        GND   GND > > > John- Hide quoted text - > > > - Show quoted text -- Hide quoted text - > > > - Show quoted text - > > Thanks very much Richard, Randy, Chris & John, > > The gate was used to replace a 74LS04 TTL inverter used between the > output of 74LS138 and the LE input of a 74LS373 latch.  The clock was > about 1.8Mhz.  During a high the transistor conducts fine but during a > low input of short duration, I would not be able to get a high with my > logic probe nor the LE is triggered.  The Vcc is 5V and the transistor > is a Japanese 2SC945 general purpose transistor. > > I checked with google for a transistor NOT gate and it used 1K at > collector and 10K for the base and input.  There was no resistor > between Base and Emitter.  And I tried that circuit, it doesn't work > too.  Where can I get the schematics for a RTL or DTL not gate? > > TIA and regards, > > Allen- Hide quoted text - > > - Show quoted text -
I have got the datasheet of 2sc945 at http://www.ortodoxism.ro/datasheets2/8/0u9h25xojqxp8qwzrfi8kxtjsswy.pdf and the RTL inverter gate at http://www.play-hookey.com/digital/experiments/rtl_inverter.html Should I used HFE1 or HFE2 for the current gain of the 2sc945 or should I get a 2N4124 to make the circuit work? Allen
On Sun, 03 Feb 2008 16:54:44 -0800, Allen Bong wrote:

> On Feb 4, 2:29 am, John Larkin > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris <cfoley1...@yahoo.com> >> wrote: >> >> >> >> >> >> >On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote: >> >> Hi, >> >> >> Is it possible to construct a simple inverter gate using 1 or 2 >> >> transistors and resistors? >> >> >> I tried the circuit below but it doesn't work at all. >> >> >>                              VCC >> >>                               + >> >>                               | >> >>                               | >> >>                              .-. >> >>                              | | >> >>                              | |4K7 >> >>                              '-' >> >>                               | >> >>                               +------o OUTPUT >> >>                               | >> >>                 1K_         |/ >> >>        INPUT o-|___|----+---| >> >>                         |   |> >> >>                        .-.    | >> >>                        | |    | >> >>                     4K7| |    | >> >>                        '-'    | >> >>                         |     | >> >>                         |     | >> >>                        ===   ==>> >>                        GND   GND >> >> >> Allen >> >> >> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) >> >> >You've described a perfect transistor inverter, that should work for >> >logic level inputs.  A couple of things to check: >> >> >* Make sure you're using an NPN transistor instead of a PNP, a MOSFET, >> >or something else. >> >> >* Recheck your wiring, looking particularly at the pinout of the >> >transistor.  It's easy to assume EBC when it's ECB, or vice versa. >> >> >* Use a voltmeter to actually measure the voltage at the input.  If >> >you're driving the input from an open collector transistor or gate >> >output, no current will be injected into the base of your transistor >> >when your logic level is "high". >> >> >If you run through these three, the transistor has to be defective. >> >Replace it. >> >> >You've got the right answer right in front of you.  Make it work. >> >> >Cheers >> >Chris >> >> Classic RTL gate: should work. >> >> But if you used this to drive another such gate, the second gate would >> serious load down the output voltage of the first one. You could juggle >> the resistor values to reduce this effect. Like maybe... >> >> >> >> >> >> >>                              VCC >> >>                               + >> >>                               | >> >>                               | >> >>                              .-. >> >>                              | | >> >>                              | | 1K >> >>                              '-' >> >>                               | >> >>                               +------o OUTPUT >> >>                               | >> >>                 10K         |/ >> >>        INPUT o-|___|----+---| >> >>                         |   |> >> >>                        .-.    | >> >>                        | |    | >> >>                    open| |    | >> >>                        '-'    | >> >>                         |     | >> >>                         |     | >> >>                        ===   ==>> >>                        GND   GND >> >> John- Hide quoted text - >> >> - Show quoted text -- Hide quoted text - >> >> - Show quoted text - > > Thanks very much Richard, Randy, Chris & John, > > The gate was used to replace a 74LS04 TTL inverter used between the > output of 74LS138 and the LE input of a 74LS373 latch. The clock was > about 1.8Mhz. During a high the transistor conducts fine but during a > low input of short duration, I would not be able to get a high with my > logic probe nor the LE is triggered. The Vcc is 5V and the transistor > is a Japanese 2SC945 general purpose transistor. > > I checked with google for a transistor NOT gate and it used 1K at > collector and 10K for the base and input. There was no resistor between > Base and Emitter. And I tried that circuit, it doesn't work too. Where > can I get the schematics for a RTL or DTL not gate? > > TIA and regards, > > Allen
Plain 'ol transistor circuits can be slooow if you aren't careful. You should either use a smaller (220 ohm?) resistor on the base, or you should use a 220 in series with a 1k in parallel with a cap -- something between 100pF and 1nF should do, but I refuse to go through the math in my head. You can get Tiny Logic inverters -- I assume you are purposely avoiding surface mount parts? -- Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
On Feb 4, 9:19 am, Tim Wescott <t...@seemywebsite.com> wrote:
> On Sun, 03 Feb 2008 16:54:44 -0800, Allen Bong wrote: > > On Feb 4, 2:29 am, John Larkin > > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris <cfoley1...@yahoo.com> > >> wrote: > > >> >On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote: > >> >> Hi, > > >> >> Is it possible to construct a simple inverter gate using 1 or 2 > >> >> transistors and resistors? > > >> >> I tried the circuit below but it doesn't work at all. > > >> >>                              VCC > >> >>                               + > >> >>                               | > >> >>                               | > >> >>                              .-. > >> >>                              | | > >> >>                              | |4K7 > >> >>                              '-' > >> >>                               | > >> >>                               +------o OUTPUT > >> >>                               | > >> >>                 1K_         |/ > >> >>        INPUT o-|___|----+---| > >> >>                         |   |> > >> >>                        .-.    | > >> >>                        | |    | > >> >>                     4K7| |    | > >> >>                        '-'    | > >> >>                         |     | > >> >>                         |     | > >> >>                        ===   === > >> >>                        GND   GND > > >> >> Allen > > >> >> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) > > >> >You've described a perfect transistor inverter, that should work for > >> >logic level inputs.  A couple of things to check: > > >> >* Make sure you're using an NPN transistor instead of a PNP, a MOSFET, > >> >or something else. > > >> >* Recheck your wiring, looking particularly at the pinout of the > >> >transistor.  It's easy to assume EBC when it's ECB, or vice versa. > > >> >* Use a voltmeter to actually measure the voltage at the input.  If > >> >you're driving the input from an open collector transistor or gate > >> >output, no current will be injected into the base of your transistor > >> >when your logic level is "high". > > >> >If you run through these three, the transistor has to be defective. > >> >Replace it. > > >> >You've got the right answer right in front of you.  Make it work. > > >> >Cheers > >> >Chris > > >> Classic RTL gate: should work. > > >> But if you used this to drive another such gate, the second gate would > >> serious load down the output voltage of the first one. You could juggle > >> the resistor values to reduce this effect. Like maybe... > > >> >>                              VCC > >> >>                               + > >> >>                               | > >> >>                               | > >> >>                              .-. > >> >>                              | | > >> >>                              | | 1K > >> >>                              '-' > >> >>                               | > >> >>                               +------o OUTPUT > >> >>                               | > >> >>                 10K         |/ > >> >>        INPUT o-|___|----+---| > >> >>                         |   |> > >> >>                        .-.    | > >> >>                        | |    | > >> >>                    open| |    | > >> >>                        '-'    | > >> >>                         |     | > >> >>                         |     | > >> >>                        ===   === > >> >>                        GND   GND > > >> John- Hide quoted text - > > >> - Show quoted text -- Hide quoted text - > > >> - Show quoted text - > > > Thanks very much Richard, Randy, Chris & John, > > > The gate was used to replace a 74LS04 TTL inverter used between the > > output of 74LS138 and the LE input of a 74LS373 latch.  The clock was > > about 1.8Mhz.  During a high the transistor conducts fine but during a > > low input of short duration, I would not be able to get a high with my > > logic probe nor the LE is triggered.  The Vcc is 5V and the transistor > > is a Japanese 2SC945 general purpose transistor. > > > I checked with google for a transistor NOT gate and it used 1K at > > collector and 10K for the base and input.  There was no resistor between > > Base and Emitter.  And I tried that circuit, it doesn't work too.  Where > > can I get the schematics for a RTL or DTL not gate? > > > TIA and regards, > > > Allen > > Plain 'ol transistor circuits can be slooow if you aren't careful.  You > should either use a smaller (220 ohm?) resistor on the base, or you > should use a 220 in series with a 1k in parallel with a cap -- something > between 100pF and 1nF should do, but I refuse to go through the math in > my head. > > You can get Tiny Logic inverters -- I assume you are purposely avoiding > surface mount parts? > > -- > Tim Wescott > Control systems and communications consultinghttp://www.wescottdesign.com > > Need to learn how to apply control theory in your embedded system? > "Applied Control Theory for Embedded Systems" by Tim Wescott > Elsevier/Newnes,http://www.wescottdesign.com/actfes/actfes.html- Hide quoted text - > > - Show quoted text -
Is this the circuit you have in mind? VCC | .-. | | | |1K '-' | 10k +------o ___ |/ o-|___|-+ -| | |> .-. | | | | 220| | === '-' GND | +---+ | | .-. | | | --- 1k| | ---1n '-' | | | +---+ | === GND (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de) Yes, this is just a hobby & fun project and I dont have the gears to solder a SMD. I am constructing the circuit on a breadboard and if it works, I would solder it onto a stripboard. I saw the inverter SMD on the back of the databook. It was made by Toshiba and part number is TC4S69F. It was a 1989 databook. Allen
Alan:
   Your transtor is saturating when on, and it is probably very slow to come 
out of saturation. Try putting a diode from base to collector; that will 
keep it from saturating. Here is the circuit:

VCC --------------------------.
                              |
                              |
                             .-.
                             | | 10k
                             | |
                             '-'
                              |
                              |
                    .--->|----o----- out
                    |         |
                    |         |
                    |         |
            1k      |         |
            ___     |       |/
 in -------|___|----o-------|
                            |>
                              |
                              |
GND --------------------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

This trick is called a 'baker clamp' for some reason. The diode prevents the 
transistor from saturating, thereby increasing the speed at which it can 
turn off. This circuit probably won't do more than a few MHz, but you never 
know.

Regards,
 Bob Monsen 

On Feb 4, 1:55 pm, Tim Wescott <t...@seemywebsite.com> wrote:
> On Sun, 03 Feb 2008 17:46:02 -0800, Allen Bong wrote: > > On Feb 4, 9:19 am, Tim Wescott <t...@seemywebsite.com> wrote: > >> On Sun, 03 Feb 2008 16:54:44 -0800, Allen Bong wrote: > >> > On Feb 4, 2:29 am, John Larkin > >> > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> >> On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris > >> >> <cfoley1...@yahoo.com> wrote: > > >> >> >On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote: > >> >> >> Hi, > > >> >> >> Is it possible to construct a simple inverter gate using 1 or 2 > >> >> >> transistors and resistors? > > >> >> >> I tried the circuit below but it doesn't work at all. > > >> >> >>                              VCC > >> >> >>                               + > >> >> >>                               | > >> >> >>                               | > >> >> >>                              .-. > >> >> >>                              | | > >> >> >>                              | |4K7 > >> >> >>                              '-' > >> >> >>                               | > >> >> >>                               +------o OUTPUT > >> >> >>                               | > >> >> >>                 1K_         |/ > >> >> >>        INPUT o-|___|----+---| > >> >> >>                         |   |> > >> >> >>                        .-.    | > >> >> >>                        | |    | > >> >> >>                     4K7| |    | > >> >> >>                        '-'    | > >> >> >>                         |     | > >> >> >>                         |     | > >> >> >>                        ===   === > >> >> >>                        GND   GND > > >> >> >> Allen > > >> >> >> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) > > >> >> >You've described a perfect transistor inverter, that should work > >> >> >for logic level inputs.  A couple of things to check: > > >> >> >* Make sure you're using an NPN transistor instead of a PNP, a > >> >> >MOSFET, or something else. > > >> >> >* Recheck your wiring, looking particularly at the pinout of the > >> >> >transistor.  It's easy to assume EBC when it's ECB, or vice versa. > > >> >> >* Use a voltmeter to actually measure the voltage at the input.  If > >> >> >you're driving the input from an open collector transistor or gate > >> >> >output, no current will be injected into the base of your > >> >> >transistor when your logic level is "high". > > >> >> >If you run through these three, the transistor has to be defective. > >> >> >Replace it. > > >> >> >You've got the right answer right in front of you.  Make it work. > > >> >> >Cheers > >> >> >Chris > > >> >> Classic RTL gate: should work. > > >> >> But if you used this to drive another such gate, the second gate > >> >> would serious load down the output voltage of the first one. You > >> >> could juggle the resistor values to reduce this effect. Like > >> >> maybe... > > >> >> >>                              VCC > >> >> >>                               + > >> >> >>                               | > >> >> >>                               | > >> >> >>                              .-. > >> >> >>                              | | > >> >> >>                              | | 1K > >> >> >>                              '-' > >> >> >>                               | > >> >> >>                               +------o OUTPUT > >> >> >>                               | > >> >> >>                 10K         |/ > >> >> >>        INPUT o-|___|----+---| > >> >> >>                         |   |> > >> >> >>                        .-.    | > >> >> >>                        | |    | > >> >> >>                    open| |    | > >> >> >>                        '-'    | > >> >> >>                         |     | > >> >> >>                         |     | > >> >> >>                        ===   === > >> >> >>                        GND   GND > > >> >> John- Hide quoted text - > > >> >> - Show quoted text -- Hide quoted text - > > >> >> - Show quoted text - > > >> > Thanks very much Richard, Randy, Chris & John, > > >> > The gate was used to replace a 74LS04 TTL inverter used between the > >> > output of 74LS138 and the LE input of a 74LS373 latch.  The clock was > >> > about 1.8Mhz.  During a high the transistor conducts fine but during > >> > a low input of short duration, I would not be able to get a high with > >> > my logic probe nor the LE is triggered.  The Vcc is 5V and the > >> > transistor is a Japanese 2SC945 general purpose transistor. > > >> > I checked with google for a transistor NOT gate and it used 1K at > >> > collector and 10K for the base and input.  There was no resistor > >> > between Base and Emitter.  And I tried that circuit, it doesn't work > >> > too.  Where can I get the schematics for a RTL or DTL not gate? > > >> > TIA and regards, > > >> > Allen > > >> Plain 'ol transistor circuits can be slooow if you aren't careful.  You > >> should either use a smaller (220 ohm?) resistor on the base, or you > >> should use a 220 in series with a 1k in parallel with a cap -- > >> something between 100pF and 1nF should do, but I refuse to go through > >> the math in my head. > > >> You can get Tiny Logic inverters -- I assume you are purposely avoiding > >> surface mount parts? > > >> -- > >> Tim Wescott > >> Control systems and communications > >> consultinghttp://www.wescottdesign.com > > >> Need to learn how to apply control theory in your embedded system? > >> "Applied Control Theory for Embedded Systems" by Tim Wescott > >> Elsevier/Newnes,http://www.wescottdesign.com/actfes/actfes.html-Hide > >> quoted text - > > >> - Show quoted text - > > > Is this the circuit you have in mind? > > >                  VCC > >                   | > >                  .-. > >                  | | > >                  | |1K > >                  '-' > >                   | > >         10k       +------o > >         ___     |/ > >      o-|___|-+ -| > >              |  |> > >             .-.   | > >             | |   | > >          220| |  === > >             '-'  GND > >              | > >              +---+ > >              |   | > >             .-.  | > >             | | --- > >           1k| | ---1n > >             '-'  | > >              |   | > >              +---+ > >              | > >             === > >             GND > > > (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) > > > Yes, this is just a hobby & fun project and I dont have the gears to > > solder a SMD.  I am constructing the circuit on a breadboard and if it > > works, I would solder it onto a stripboard. > > > I saw the inverter SMD on the back of the databook.  It was made by > > Toshiba and part number is TC4S69F.  It was a 1989 databook. > > > Allen > > No no!  You want the capacitor in the path from the drive to the gate, to > speed up the current into and out of the base: > >                470pF? >      ___   .----||-----. > o---|___|--+    ___    +--- to base of xistor >      220   '---|___|---' >                  1k > > If you have enough drive this will even forcibly de-saturate a transistor > -- look around on the Zetex web site & you'll find some app notes on this. > > -- > Tim Wescott > Control systems and communications consultinghttp://www.wescottdesign.com > > Need to learn how to apply control theory in your embedded system? > "Applied Control Theory for Embedded Systems" by Tim Wescott > Elsevier/Newnes,http://www.wescottdesign.com/actfes/actfes.html- Hide quoted text - > > - Show quoted text -
Hi Tim, I've found the application notes on the zetex web site. It was on P2 & P4 of the pdf file which explains the speeding up of switching, both the capacitor speedup and baker clamp methods are described. http://www.zetex.com/3.0/appnotes/apps/an22.pdf Allen
On Feb 7, 8:25 am, Rich Grise <r...@example.net> wrote:
> On Mon, 04 Feb 2008 17:54:09 -0800, Allen Bong wrote: > > Hi, you're right! My copy of AoE does have a description on Baker > > Clamp on Page 584 and also a full chapter on the 8085 micro too.  What > > a find!  Looks like the book was sitting in my book shelf for toooooo > > long and I'm going to reread it from the begining again. > > If you want even faster switching, try this: > [Bob Monsen drew, but I've modified:] > > >> >>                    VCC > >> >>                     | > >> >>                    .-. > >> >>                    | | 10k > >> >>        added       | | > >> >>          v         '-' > >> >>        ~1nF         | > >> >>     .---||---o-->|--o----- out > >> >>     |        |      | > >> >>     |  1K    |      | > >> >>     |  ___   |    |/ > >> >> in -o-|___|--o----| > >> >>                   |> > >> >>                     | > >> >>                    GND > > Cheers! > Rich
Thanks Rich, I do have an 8051 and a PIC16F877 SBC working at 12Mhz and 20Mhz resp. I will try out the circuit there. Rgds, Allen
On Mon, 04 Feb 2008 17:54:09 -0800, Allen Bong wrote:
 
> Hi, you're right! My copy of AoE does have a description on Baker > Clamp on Page 584 and also a full chapter on the 8085 micro too. What > a find! Looks like the book was sitting in my book shelf for toooooo > long and I'm going to reread it from the begining again.
If you want even faster switching, try this: [Bob Monsen drew, but I've modified:]
>> >>                  VCC >> >>                   | >> >>                  .-. >> >>                  | | 10k >> >>        added       | | >> >>          v       '-' >> >>        ~1nF       | >> >>   .---||---o-->|--o----- out >> >>    |    |      | >> >>    |  1K   |      | >> >>     | ___  |    |/ >> >> in -o-|___|--o----| >> >>                 |> >> >>                   | >> >>                  GND
Cheers! Rich
On Feb 5, 8:40 am, JeffM <jef...@email.com> wrote:
> Bob Monsen wrote: > >>Your [transistor] is saturating when on, > >>and it is probably very slow to come out of saturation. > > >>                  VCC > >>                   | > >>                  .-. > >>                  | | 10k > >>                  | | > >>                  '-' > >>                   | > >>            .->|---o----- out > >>       1k   |      | > >>       ___  |    |/ > >> in --|___|-o----| > >>                 |> > >>                   | > >>                  GND > > Man, Monson put a lot of empty space in his art > ...and Google added a lot of crap to it when it got a hold of it.http://groups.google.com/group/sci.electronics.basics/msg/30d98ef099b... > Could Bob be using an oddball font / character set? > ..or is Google "improving" things again? > > >>This trick is called a 'baker clamp' for some reason. > >>The diode prevents the transistor from saturating, > >>thereby increasing the speed at which it can turn off. > > Allen Bong wrote: > >Your circuit works like magic.  I am going to read more > >about this 'baker clamp' diode.  Was it mentioned in the AoE? > > Yup.http://books.google.com/?q=Art-of-Electronics+Baker-clamp+saturation > "Sorry, this page's content is restricted" > I tried anyway so I wouldn't have to walk to the shelf > and the F1_1(|<1/\/6 page crashed Gecko.http://validator.w3.org/check?uri=http://books.google.com/books?id=bk... > Failed validation, 579 Errors > > Opera opened it, but it's true: there's nothing to see there. 8-( > > Dead-tree version:  It's listed in the index: clamp, Baker; page 908.- Hide quoted text - > > - Show quoted text -
Hi, you're right! My copy of AoE does have a description on Baker Clamp on Page 584 and also a full chapter on the 8085 micro too. What a find! Looks like the book was sitting in my book shelf for toooooo long and I'm going to reread it from the begining again. Cheers, Allen
Bob Monsen wrote:
>>Your [transistor] is saturating when on, >>and it is probably very slow to come out of saturation. >> >> VCC >> | >> .-. >> | | 10k >> | | >> '-' >> | >> .->|---o----- out >> 1k | | >> ___ | |/ >> in --|___|-o----| >> |> >> | >> GND >>
Man, Monson put a lot of empty space in his art ...and Google added a lot of crap to it when it got a hold of it. http://groups.google.com/group/sci.electronics.basics/msg/30d98ef099b975e9?dmode=source Could Bob be using an oddball font / character set? ..or is Google "improving" things again?
>>This trick is called a 'baker clamp' for some reason. >>The diode prevents the transistor from saturating, >>thereby increasing the speed at which it can turn off. >>
Allen Bong wrote:
>Your circuit works like magic. I am going to read more >about this 'baker clamp' diode. Was it mentioned in the AoE?
Yup. http://books.google.com/?q=Art-of-Electronics+Baker-clamp+saturation "Sorry, this page's content is restricted" I tried anyway so I wouldn't have to walk to the shelf and the F1_1(|<1/\/6 page crashed Gecko. http://validator.w3.org/check?uri=http://books.google.com/books?id=bkOMDgwFA28C&pg=PP1&dq=Art-of-Electronics+baker-clamp&eieqnR6WkAYHgiQH5zr3QBA&sig=jQFnkt5lCVmTHOpUcItQnM-lVVw Failed validation, 579 Errors Opera opened it, but it's true: there's nothing to see there. 8-( Dead-tree version: It's listed in the index: clamp, Baker; page 908.
On Mon, 04 Feb 2008 04:40:07 -0800, Allen Bong wrote:

It sounds like Bob Monsen's solution worked for you.  I've done this with 
74HC logic, but I'll be damned if I can remember the specific resistor 
and capacitor values I used.

-- 
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
On Feb 4, 1:55 pm, Tim Wescott <t...@seemywebsite.com> wrote:
> On Sun, 03 Feb 2008 17:46:02 -0800, Allen Bong wrote: > > On Feb 4, 9:19 am, Tim Wescott <t...@seemywebsite.com> wrote: > >> On Sun, 03 Feb 2008 16:54:44 -0800, Allen Bong wrote: > >> > On Feb 4, 2:29 am, John Larkin > >> > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> >> On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris > >> >> <cfoley1...@yahoo.com> wrote: > > >> >> >On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote: > >> >> >> Hi, > > >> >> >> Is it possible to construct a simple inverter gate using 1 or 2 > >> >> >> transistors and resistors? > > >> >> >> I tried the circuit below but it doesn't work at all. > > >> >> >>                              VCC > >> >> >>                               + > >> >> >>                               | > >> >> >>                               | > >> >> >>                              .-. > >> >> >>                              | | > >> >> >>                              | |4K7 > >> >> >>                              '-' > >> >> >>                               | > >> >> >>                               +------o OUTPUT > >> >> >>                               | > >> >> >>                 1K_         |/ > >> >> >>        INPUT o-|___|----+---| > >> >> >>                         |   |> > >> >> >>                        .-.    | > >> >> >>                        | |    | > >> >> >>                     4K7| |    | > >> >> >>                        '-'    | > >> >> >>                         |     | > >> >> >>                         |     | > >> >> >>                        ===   === > >> >> >>                        GND   GND > > >> >> >> Allen > > >> >> >> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) > > >> >> >You've described a perfect transistor inverter, that should work > >> >> >for logic level inputs.  A couple of things to check: > > >> >> >* Make sure you're using an NPN transistor instead of a PNP, a > >> >> >MOSFET, or something else. > > >> >> >* Recheck your wiring, looking particularly at the pinout of the > >> >> >transistor.  It's easy to assume EBC when it's ECB, or vice versa. > > >> >> >* Use a voltmeter to actually measure the voltage at the input.  If > >> >> >you're driving the input from an open collector transistor or gate > >> >> >output, no current will be injected into the base of your > >> >> >transistor when your logic level is "high". > > >> >> >If you run through these three, the transistor has to be defective. > >> >> >Replace it. > > >> >> >You've got the right answer right in front of you.  Make it work. > > >> >> >Cheers > >> >> >Chris > > >> >> Classic RTL gate: should work. > > >> >> But if you used this to drive another such gate, the second gate > >> >> would serious load down the output voltage of the first one. You > >> >> could juggle the resistor values to reduce this effect. Like > >> >> maybe... > > >> >> >>                              VCC > >> >> >>                               + > >> >> >>                               | > >> >> >>                               | > >> >> >>                              .-. > >> >> >>                              | | > >> >> >>                              | | 1K > >> >> >>                              '-' > >> >> >>                               | > >> >> >>                               +------o OUTPUT > >> >> >>                               | > >> >> >>                 10K         |/ > >> >> >>        INPUT o-|___|----+---| > >> >> >>                         |   |> > >> >> >>                        .-.    | > >> >> >>                        | |    | > >> >> >>                    open| |    | > >> >> >>                        '-'    | > >> >> >>                         |     | > >> >> >>                         |     | > >> >> >>                        ===   === > >> >> >>                        GND   GND > > >> >> John- Hide quoted text - > > >> >> - Show quoted text -- Hide quoted text - > > >> >> - Show quoted text - > > >> > Thanks very much Richard, Randy, Chris & John, > > >> > The gate was used to replace a 74LS04 TTL inverter used between the > >> > output of 74LS138 and the LE input of a 74LS373 latch.  The clock was > >> > about 1.8Mhz.  During a high the transistor conducts fine but during > >> > a low input of short duration, I would not be able to get a high with > >> > my logic probe nor the LE is triggered.  The Vcc is 5V and the > >> > transistor is a Japanese 2SC945 general purpose transistor. > > >> > I checked with google for a transistor NOT gate and it used 1K at > >> > collector and 10K for the base and input.  There was no resistor > >> > between Base and Emitter.  And I tried that circuit, it doesn't work > >> > too.  Where can I get the schematics for a RTL or DTL not gate? > > >> > TIA and regards, > > >> > Allen > > >> Plain 'ol transistor circuits can be slooow if you aren't careful.  You > >> should either use a smaller (220 ohm?) resistor on the base, or you > >> should use a 220 in series with a 1k in parallel with a cap -- > >> something between 100pF and 1nF should do, but I refuse to go through > >> the math in my head. > > >> You can get Tiny Logic inverters -- I assume you are purposely avoiding > >> surface mount parts? > > >> -- > >> Tim Wescott > >> Control systems and communications > >> consultinghttp://www.wescottdesign.com > > >> Need to learn how to apply control theory in your embedded system? > >> "Applied Control Theory for Embedded Systems" by Tim Wescott > >> Elsevier/Newnes,http://www.wescottdesign.com/actfes/actfes.html-Hide > >> quoted text - > > >> - Show quoted text - > > > Is this the circuit you have in mind? > > >                  VCC > >                   | > >                  .-. > >                  | | > >                  | |1K > >                  '-' > >                   | > >         10k       +------o > >         ___     |/ > >      o-|___|-+ -| > >              |  |> > >             .-.   | > >             | |   | > >          220| |  === > >             '-'  GND > >              | > >              +---+ > >              |   | > >             .-.  | > >             | | --- > >           1k| | ---1n > >             '-'  | > >              |   | > >              +---+ > >              | > >             === > >             GND > > > (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) > > > Yes, this is just a hobby & fun project and I dont have the gears to > > solder a SMD.  I am constructing the circuit on a breadboard and if it > > works, I would solder it onto a stripboard. > > > I saw the inverter SMD on the back of the databook.  It was made by > > Toshiba and part number is TC4S69F.  It was a 1989 databook. > > > Allen > > No no!  You want the capacitor in the path from the drive to the gate, to > speed up the current into and out of the base: > >                470pF? >      ___   .----||-----. > o---|___|--+    ___    +--- to base of xistor >      220   '---|___|---' >                  1k > > If you have enough drive this will even forcibly de-saturate a transistor > -- look around on the Zetex web site & you'll find some app notes on this. > > -- > Tim Wescott > Control systems and communications consultinghttp://www.wescottdesign.com > > Need to learn how to apply control theory in your embedded system? > "Applied Control Theory for Embedded Systems" by Tim Wescott > Elsevier/Newnes,http://www.wescottdesign.com/actfes/actfes.html- Hide quoted text - > > - Show quoted text -
HI Tim, I tried out the circuit but it doesnt work in my application. What do you meant by "if you have enough drive"? I am driving the circuit with the output of a 74LS138. Does the 74LS138 have enough drive to unsaturate the transistor? I am going to google the Zetex web site to get more info as suggested. Thanks. Allen
On Feb 4, 11:21 am, "Bob Monsen" <rcmon...@gmail.com> wrote:
> Alan: >    Your transtor is saturating when on, and it is probably very slow to come > out of saturation. Try putting a diode from base to collector; that will > keep it from saturating. Here is the circuit: > > VCC --------------------------. >                               | >                               | >                              .-. >                              | | 10k >                              | | >                              '-' >                               | >                               | >                     .--->|----o----- out >                     |         | >                     |         | >                     |         | >             1k      |         | >             ___     |       |/ >  in -------|___|----o-------| >                             |> >                               | >                               | > GND --------------------------' > (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) > > This trick is called a 'baker clamp' for some reason. The diode prevents the > transistor from saturating, thereby increasing the speed at which it can > turn off. This circuit probably won't do more than a few MHz, but you never > know. > > Regards, >  Bob Monsen
Hi Bob, Your circuit works like magic. I am going to read more about this 'baker clamp' diode. Was it mentioned in the AoE? Thanks again for your help! Allen
On Sun, 03 Feb 2008 17:46:02 -0800, Allen Bong wrote:

> On Feb 4, 9:19 am, Tim Wescott <t...@seemywebsite.com> wrote: >> On Sun, 03 Feb 2008 16:54:44 -0800, Allen Bong wrote: >> > On Feb 4, 2:29 am, John Larkin >> > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> >> On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris >> >> <cfoley1...@yahoo.com> wrote: >> >> >> >On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote: >> >> >> Hi, >> >> >> >> Is it possible to construct a simple inverter gate using 1 or 2 >> >> >> transistors and resistors? >> >> >> >> I tried the circuit below but it doesn't work at all. >> >> >> >>                              VCC >> >> >>                               + >> >> >>                               | >> >> >>                               | >> >> >>                              .-. >> >> >>                              | | >> >> >>                              | |4K7 >> >> >>                              '-' >> >> >>                               | >> >> >>                               +------o OUTPUT >> >> >>                               | >> >> >>                 1K_         |/ >> >> >>        INPUT o-|___|----+---| >> >> >>                         |   |> >> >> >>                        .-.    | >> >> >>                        | |    | >> >> >>                     4K7| |    | >> >> >>                        '-'    | >> >> >>                         |     | >> >> >>                         |     | >> >> >>                        ===   ==>> >> >>                        GND   GND >> >> >> >> Allen >> >> >> >> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) >> >> >> >You've described a perfect transistor inverter, that should work >> >> >for logic level inputs.  A couple of things to check: >> >> >> >* Make sure you're using an NPN transistor instead of a PNP, a >> >> >MOSFET, or something else. >> >> >> >* Recheck your wiring, looking particularly at the pinout of the >> >> >transistor.  It's easy to assume EBC when it's ECB, or vice versa. >> >> >> >* Use a voltmeter to actually measure the voltage at the input.  If >> >> >you're driving the input from an open collector transistor or gate >> >> >output, no current will be injected into the base of your >> >> >transistor when your logic level is "high". >> >> >> >If you run through these three, the transistor has to be defective. >> >> >Replace it. >> >> >> >You've got the right answer right in front of you.  Make it work. >> >> >> >Cheers >> >> >Chris >> >> >> Classic RTL gate: should work. >> >> >> But if you used this to drive another such gate, the second gate >> >> would serious load down the output voltage of the first one. You >> >> could juggle the resistor values to reduce this effect. Like >> >> maybe... >> >> >> >>                              VCC >> >> >>                               + >> >> >>                               | >> >> >>                               | >> >> >>                              .-. >> >> >>                              | | >> >> >>                              | | 1K >> >> >>                              '-' >> >> >>                               | >> >> >>                               +------o OUTPUT >> >> >>                               | >> >> >>                 10K         |/ >> >> >>        INPUT o-|___|----+---| >> >> >>                         |   |> >> >> >>                        .-.    | >> >> >>                        | |    | >> >> >>                    open| |    | >> >> >>                        '-'    | >> >> >>                         |     | >> >> >>                         |     | >> >> >>                        ===   ==>> >> >>                        GND   GND >> >> >> John- Hide quoted text - >> >> >> - Show quoted text -- Hide quoted text - >> >> >> - Show quoted text - >> >> > Thanks very much Richard, Randy, Chris & John, >> >> > The gate was used to replace a 74LS04 TTL inverter used between the >> > output of 74LS138 and the LE input of a 74LS373 latch.  The clock was >> > about 1.8Mhz.  During a high the transistor conducts fine but during >> > a low input of short duration, I would not be able to get a high with >> > my logic probe nor the LE is triggered.  The Vcc is 5V and the >> > transistor is a Japanese 2SC945 general purpose transistor. >> >> > I checked with google for a transistor NOT gate and it used 1K at >> > collector and 10K for the base and input.  There was no resistor >> > between Base and Emitter.  And I tried that circuit, it doesn't work >> > too.  Where can I get the schematics for a RTL or DTL not gate? >> >> > TIA and regards, >> >> > Allen >> >> Plain 'ol transistor circuits can be slooow if you aren't careful.  You >> should either use a smaller (220 ohm?) resistor on the base, or you >> should use a 220 in series with a 1k in parallel with a cap -- >> something between 100pF and 1nF should do, but I refuse to go through >> the math in my head. >> >> You can get Tiny Logic inverters -- I assume you are purposely avoiding >> surface mount parts? >> >> -- >> Tim Wescott >> Control systems and communications >> consultinghttp://www.wescottdesign.com >> >> Need to learn how to apply control theory in your embedded system? >> "Applied Control Theory for Embedded Systems" by Tim Wescott >> Elsevier/Newnes,http://www.wescottdesign.com/actfes/actfes.html- Hide >> quoted text - >> >> - Show quoted text - > > Is this the circuit you have in mind? > > > > > VCC > | > .-. > | | > | |1K > '-' > | > 10k +------o > ___ |/ > o-|___|-+ -| > | |> > .-. | > | | | > 220| | ==> '-' GND > | > +---+ > | | > .-. | > | | --- > 1k| | ---1n > '-' | > | | > +---+ > | > ==> GND > > > (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de) > > Yes, this is just a hobby & fun project and I dont have the gears to > solder a SMD. I am constructing the circuit on a breadboard and if it > works, I would solder it onto a stripboard. > > I saw the inverter SMD on the back of the databook. It was made by > Toshiba and part number is TC4S69F. It was a 1989 databook. > > Allen
No no! You want the capacitor in the path from the drive to the gate, to speed up the current into and out of the base: 470pF? ___ .----||-----. o---|___|--+ ___ +--- to base of xistor 220 '---|___|---' 1k If you have enough drive this will even forcibly de-saturate a transistor -- look around on the Zetex web site & you'll find some app notes on this. -- Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
Alan:
   Your transtor is saturating when on, and it is probably very slow to come 
out of saturation. Try putting a diode from base to collector; that will 
keep it from saturating. Here is the circuit:

VCC --------------------------.
                              |
                              |
                             .-.
                             | | 10k
                             | |
                             '-'
                              |
                              |
                    .--->|----o----- out
                    |         |
                    |         |
                    |         |
            1k      |         |
            ___     |       |/
 in -------|___|----o-------|
                            |>
                              |
                              |
GND --------------------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

This trick is called a 'baker clamp' for some reason. The diode prevents the 
transistor from saturating, thereby increasing the speed at which it can 
turn off. This circuit probably won't do more than a few MHz, but you never 
know.

Regards,
 Bob Monsen