On 19/12/2016 00:41, billbowden wrote:> I have a switching application where a single bipolar transistor might be > used. The AC input is about 300mV and the transistor needs about 700 mV to > switch on. My idea is to construct a voltage divider using a diode which > will produce about a 600mV drop across the diode and a voltage divider of 2 > equal resistors to set the transistor base voltage at about 300 mV so the > transistor will switch on with an additional 300mV. I understand the > temperature problems, but it seems to be minimal. What am I missing? > >When you say the AC input is 300mV is that pk-pk or rms? If the latter then the 840mV pk-pk may be enough without pre-biasing. Capacitor couple the input and use diode anti-parallel to base-emitter to serve as voltage doubler. piglet
Bipolar transistor bias question
Started by ●December 18, 2016
Reply by ●December 19, 20162016-12-19
Reply by ●December 19, 20162016-12-19
On Mon, 19 Dec 2016 09:32:14 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On Sun, 18 Dec 2016 16:41:42 -0800, "billbowden" ><bperryb@bowdenshobbycircuits.info> wrote: > >>I have a switching application where a single bipolar transistor might be >>used. The AC input is about 300mV and the transistor needs about 700 mV to >>switch on. My idea is to construct a voltage divider using a diode which >>will produce about a 600mV drop across the diode and a voltage divider of 2 >>equal resistors to set the transistor base voltage at about 300 mV so the >>transistor will switch on with an additional 300mV. I understand the >>temperature problems, but it seems to be minimal. What am I missing? >> >> > ><http://www.analog-innovations.com/SED/ThresholdAmp_Bowden_SED_2016-12-19.png> > >(Pardon my snarky response last night... I fell asleep watching a >movie on TV and didn't read your post carefully :-) > > ...Jim ThompsonIf you want to really square it up.... <http://www.analog-innovations.com/SED/ThresholdAmp_Bowden_SED_2016-12-19_10-58-28.png> ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 |
Reply by ●December 19, 20162016-12-19
and a voltage divider of 2> equal resistors to set the transistor base voltage at about 300 mV so the > transistor will switch on with an additional 300mV.if you want the transistor to switch there is no reason to REDUCE the input level swing keep the swing as large as possible and figure out how to shift that level as needed. m
Reply by ●December 19, 20162016-12-19
On Mon, 19 Dec 2016 10:55:28 -0800 (PST), makolber@yahoo.com wrote:> and a voltage divider of 2 >> equal resistors to set the transistor base voltage at about 300 mV so the >> transistor will switch on with an additional 300mV. > >if you want the transistor to switch >there is no reason to REDUCE the input level swing >keep the swing as large as possible and figure out >how to shift that level as needed. >mFor an ideal transistor, Ib (and Ic) increase a decade per 60 mV of base voltage. So 300 mv p-p can swing Ic over 5 decades of current. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●December 19, 20162016-12-19
On Monday, December 19, 2016 at 11:46:21 AM UTC-8, John Larkin wrote:> On Mon, 19 Dec 2016 10:55:28 -0800 (PST), makolber@yahoo.com wrote: > > > and a voltage divider of 2 > >> equal resistors to set the transistor base voltage at about 300 mV...> For an ideal transistor, Ib (and Ic) increase a decade per 60 mV of > base voltage. So 300 mv p-p can swing Ic over 5 decades of current.Easiest way to bias it, is with a second matched transistor, in current-mirror fashion; add in base resistors and a capacitive coupling to the active transistor's base. The thing still isn't an ideal switch, though. For one thing, the base current into the active transistor can do some bias damage, by charging up the coupling capacitor during saturation.
Reply by ●December 19, 20162016-12-19
On 12/19/2016 11:32 AM, Jim Thompson wrote:> On Sun, 18 Dec 2016 16:41:42 -0800, "billbowden" > <bperryb@bowdenshobbycircuits.info> wrote: > >> I have a switching application where a single bipolar transistor might be >> used. The AC input is about 300mV and the transistor needs about 700 mV to >> switch on. My idea is to construct a voltage divider using a diode which >> will produce about a 600mV drop across the diode and a voltage divider of 2 >> equal resistors to set the transistor base voltage at about 300 mV so the >> transistor will switch on with an additional 300mV. I understand the >> temperature problems, but it seems to be minimal. What am I missing? >> >> > > <http://www.analog-innovations.com/SED/ThresholdAmp_Bowden_SED_2016-12-19.png> > > (Pardon my snarky response last night... I fell asleep watching a > movie on TV and didn't read your post carefully :-) > > ...Jim Thompson >Didn't I see something like that in: http://www.analog-innovations.com/SED/HearingAidSlidingClassA.pdf
Reply by ●December 19, 20162016-12-19
"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message news:q0de5ct1a14ppo9ooehjv8g32vk467bk0u@4ax.com...> On Sun, 18 Dec 2016 16:41:42 -0800, "billbowden" > <bperryb@bowdenshobbycircuits.info> wrote: > >>I have a switching application where a single bipolar transistor might be >>used. The AC input is about 300mV and the transistor needs about 700 mV to >>switch on. My idea is to construct a voltage divider using a diode which >>will produce about a 600mV drop across the diode and a voltage divider of >>2 >>equal resistors to set the transistor base voltage at about 300 mV so the >>transistor will switch on with an additional 300mV. I understand the >>temperature problems, but it seems to be minimal. What am I missing? >> > > More detail would help. What is the drive waveform like? What is the > load? Got a schematic? > > A PNP emitter follower can be a neat way to drive an NPN transistor. > It moves the effective threshold near zero volts and does some > temperature compensation. > > Or just add an IC, an opamp or a comparator. > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics >All I want to do is detect a positive half cycle going sine wave at about 20Hz and 300mV peak and produce a negative rectified DC change of about 3 volts. I figure I can do this with one transistor. I'm not interested in adding more parts. I can easily do it with more parts. All I want to know is the circuit stability of biasing a transistor near it's conduction point so it works under all conditions of temperature and supply voltage. It needs to work between a supply voltage of 2 to 3.2 volts. Here's a typical circuit using LTSpice. . Version 4 SHEET 1 880 680 WIRE 208 0 32 0 WIRE 336 0 208 0 WIRE 32 32 32 0 WIRE 128 64 96 64 WIRE 208 128 208 80 WIRE 32 176 32 112 WIRE 128 176 128 144 WIRE 128 176 112 176 WIRE 144 176 128 176 WIRE 128 208 128 176 WIRE 32 224 32 176 WIRE 128 288 128 272 FLAG 336 80 0 FLAG 208 224 0 FLAG 128 368 0 FLAG 32 288 0 FLAG 96 64 0 SYMBOL npn 144 128 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL res 192 -16 R0 WINDOW 0 -400 416 Left 0 WINDOW 3 39 52 Left 0 SYMATTR InstName R1 SYMATTR Value 2k SYMBOL voltage 336 -16 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 2 SYMBOL res 128 160 R90 WINDOW 0 257 402 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 15k SYMBOL res 48 128 R180 WINDOW 0 269 -273 Left 0 WINDOW 3 39 61 Left 0 SYMATTR InstName R3 SYMATTR Value 5.1k SYMBOL diode 16 224 R0 WINDOW 0 -100 172 Left 0 WINDOW 3 -103 34 Left 0 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL cap 112 208 R0 WINDOW 0 -238 190 Left 0 WINDOW 3 -22 55 Left 0 SYMATTR InstName C1 SYMATTR Value 2� SYMBOL voltage 128 272 R0 WINDOW 0 36 87 Left 0 WINDOW 3 94 53 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 94 81 Left 0 SYMATTR InstName V2 SYMATTR Value SINE(0 .3 20 0 0 0 15) SYMATTR SpiceLine Rser=1k SYMBOL res 112 48 R0 WINDOW 0 -281 351 Left 0 WINDOW 3 -45 65 Left 0 SYMATTR InstName R4 SYMATTR Value 51k TEXT -32 396 Left 0 !.tran 1.5
Reply by ●December 20, 20162016-12-20
On 12/19/2016 8:41 PM, billbowden wrote:> "John Larkin" <jjlarkin@highlandtechnology.com> wrote in message > news:q0de5ct1a14ppo9ooehjv8g32vk467bk0u@4ax.com... >> On Sun, 18 Dec 2016 16:41:42 -0800, "billbowden" >> <bperryb@bowdenshobbycircuits.info> wrote: >> >>> I have a switching application where a single bipolar transistor might be >>> used. The AC input is about 300mV and the transistor needs about 700 mV to >>> switch on. My idea is to construct a voltage divider using a diode which >>> will produce about a 600mV drop across the diode and a voltage divider of >>> 2 >>> equal resistors to set the transistor base voltage at about 300 mV so the >>> transistor will switch on with an additional 300mV. I understand the >>> temperature problems, but it seems to be minimal. What am I missing? >>> >> >> More detail would help. What is the drive waveform like? What is the >> load? Got a schematic? >> >> A PNP emitter follower can be a neat way to drive an NPN transistor. >> It moves the effective threshold near zero volts and does some >> temperature compensation. >> >> Or just add an IC, an opamp or a comparator. >> >> -- >> >> John Larkin Highland Technology, Inc >> >> lunatic fringe electronics >> > > All I want to do is detect a positive half cycle going sine wave at about > 20Hz and 300mV peak and produce a negative rectified DC change of about 3 > volts. I figure I can do this with one transistor. I'm not interested in > adding more parts. I can easily do it with more parts. All I want to know is > the circuit stability of biasing a transistor near it's conduction point so > it works under all conditions of temperature and supply voltage. It needs to > work between a supply voltage of 2 to 3.2 volts. Here's a typical circuit > using LTSpice.(snip) Okay. Add the following to your schematic using the LTSpice directives: .step v1 list 2 3.2 .step temp list -40 25 70 This will give you V1 steps of 2 to 3.2 And temperature in 3 steps from -40 to 70C Check the help section to refine your desired range.
Reply by ●December 20, 20162016-12-20
On Monday, December 19, 2016 at 9:41:11 PM UTC-5, Bill Bowden wrote:> "John Larkin" <jjlarkin@highlandtechnology.com> wrote in message > news:q0de5ct1a14ppo9ooehjv8g32vk467bk0u@4ax.com... > > On Sun, 18 Dec 2016 16:41:42 -0800, "billbowden" > > <bperryb@bowdenshobbycircuits.info> wrote: > > > >>I have a switching application where a single bipolar transistor might be > >>used. The AC input is about 300mV and the transistor needs about 700 mV to > >>switch on. My idea is to construct a voltage divider using a diode which > >>will produce about a 600mV drop across the diode and a voltage divider of > >>2 > >>equal resistors to set the transistor base voltage at about 300 mV so the > >>transistor will switch on with an additional 300mV. I understand the > >>temperature problems, but it seems to be minimal. What am I missing? > >> > > > > More detail would help. What is the drive waveform like? What is the > > load? Got a schematic? > > > > A PNP emitter follower can be a neat way to drive an NPN transistor. > > It moves the effective threshold near zero volts and does some > > temperature compensation. > > > > Or just add an IC, an opamp or a comparator. > > > > -- > > > > John Larkin Highland Technology, Inc > > > > lunatic fringe electronics > > > > All I want to do is detect a positive half cycle going sine wave at about > 20Hz and 300mV peak and produce a negative rectified DC change of about 3 > volts. I figure I can do this with one transistor. I'm not interested in > adding more parts. I can easily do it with more parts. All I want to know is > the circuit stability of biasing a transistor near it's conduction point so > it works under all conditions of temperature and supply voltage. It needs to > work between a supply voltage of 2 to 3.2 volts. Here's a typical circuit > using LTSpice. >[snip LTSpice] +2V +2V -+- -+- | | .-. R1 .-. RL | | 5.6k | | 2k '-' '-' | | | R2 |/ +--15k--+--| Q1 | | |>. D1 V C1 --- | --- 2uF--- === | | === ^ Vin Six parts. This has almost zero offset, is drift-compensated, and uses two fewer parts: +2V +2V -+- -+- | | .-. R1 .-. RL | | 5.6k | | 2k '-' '-' | | | |/ +----------| Q1 | |>. 2n3904 |< | Vin>--| Q2 === |\ 2n3906 | === Version 4 SHEET 1 880 680 WIRE 208 0 32 0 WIRE 336 0 208 0 WIRE 208 16 208 0 WIRE 32 32 32 0 WIRE 336 32 336 0 WIRE 336 128 336 112 WIRE 32 144 32 112 WIRE 32 144 0 144 WIRE 144 144 32 144 WIRE 0 176 0 144 WIRE -64 224 -112 224 WIRE 208 224 208 192 WIRE -112 240 -112 224 WIRE 0 304 0 272 WIRE -112 336 -112 320 FLAG 336 128 0 FLAG 208 224 0 FLAG -112 336 0 FLAG 0 304 0 SYMBOL npn 144 96 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL res 192 0 R0 WINDOW 0 -42 44 Left 2 WINDOW 3 -37 73 Left 2 SYMATTR InstName R1 SYMATTR Value 2k SYMBOL voltage 336 16 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 2 SYMBOL res 48 128 R180 WINDOW 0 46 90 Left 2 WINDOW 3 39 61 Left 2 SYMATTR InstName R3 SYMATTR Value 5.1k SYMBOL voltage -112 224 R0 WINDOW 0 36 87 Left 2 WINDOW 3 34 115 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 37 140 Left 2 SYMATTR InstName V2 SYMATTR Value SINE(0 .3 20 0 0 0 15) SYMATTR SpiceLine Rser=1k SYMBOL pnp -64 272 M180 SYMATTR InstName Q2 SYMATTR Value 2N3906 TEXT -32 400 Left 2 !.tran 1.5 Cheers, James Arthur
Reply by ●December 20, 20162016-12-20
On Mon, 19 Dec 2016 21:15:45 -0800 (PST), dagmargoodboat@yahoo.com wrote:>On Monday, December 19, 2016 at 9:41:11 PM UTC-5, Bill Bowden wrote: >> "John Larkin" <jjlarkin@highlandtechnology.com> wrote in message >> news:q0de5ct1a14ppo9ooehjv8g32vk467bk0u@4ax.com... >> > On Sun, 18 Dec 2016 16:41:42 -0800, "billbowden" >> > <bperryb@bowdenshobbycircuits.info> wrote: >> > >> >>I have a switching application where a single bipolar transistor might be >> >>used. The AC input is about 300mV and the transistor needs about 700 mV to >> >>switch on. My idea is to construct a voltage divider using a diode which >> >>will produce about a 600mV drop across the diode and a voltage divider of >> >>2 >> >>equal resistors to set the transistor base voltage at about 300 mV so the >> >>transistor will switch on with an additional 300mV. I understand the >> >>temperature problems, but it seems to be minimal. What am I missing? >> >> >> > >> > More detail would help. What is the drive waveform like? What is the >> > load? Got a schematic? >> > >> > A PNP emitter follower can be a neat way to drive an NPN transistor. >> > It moves the effective threshold near zero volts and does some >> > temperature compensation. >> > >> > Or just add an IC, an opamp or a comparator. >> > >> > -- >> > >> > John Larkin Highland Technology, Inc >> > >> > lunatic fringe electronics >> > >> >> All I want to do is detect a positive half cycle going sine wave at about >> 20Hz and 300mV peak and produce a negative rectified DC change of about 3 >> volts. I figure I can do this with one transistor. I'm not interested in >> adding more parts. I can easily do it with more parts. All I want to know is >> the circuit stability of biasing a transistor near it's conduction point so >> it works under all conditions of temperature and supply voltage. It needs to >> work between a supply voltage of 2 to 3.2 volts. Here's a typical circuit >> using LTSpice. >> >[snip LTSpice] > > +2V +2V > -+- -+- > | | > .-. R1 .-. RL > | | 5.6k | | 2k > '-' '-' > | | > | R2 |/ > +--15k--+--| Q1 > | | |>. >D1 V C1 --- | > --- 2uF--- === > | | > === ^ > Vin >Six parts. >Remove D1 and R2: four parts. -- John Larkin Highland Technology, Inc lunatic fringe electronics
