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Digital transistor?

Started by Sylvia Else ●March 25, 2022
Reply by piglet ●March 26, 20222022-03-26
On 26/03/2022 4:35 am, Sylvia Else wrote:

> On 26-Mar-22 2:40 pm, jlarkin@highlandsniptechnology.com wrote:
>> On Sat, 26 Mar 2022 14:16:46 +1100, Sylvia Else <sylvia@email.invalid>
>> wrote:
>>
>>> On 26-Mar-22 11:32 am, John Larkin wrote:
>>>> On Sat, 26 Mar 2022 10:52:34 +1100, Sylvia Else <sylvia@email.invalid>
>>>> wrote:
>>>>
>>>>> https://www.farnell.com/datasheets/2353855.pdf
>>>>>
>>>>> I bought a few of these. I don't know what is intended by "digital
>>>>> transistor" since the charge storage time defeats any attempt to use
>>>>> them at a high frequency, and there's no way to add a Schottky 
>>>>> diode to
>>>>> prevent saturation, or a speed-up capacitor across the base resistor.
>>>>>
>>>>> I'm using this and the corresponding PNP type to do level shifting of
>>>>> both high and low levels (*). At 25 kHz it's OK, albeit with a
>>>>> significant change in duty cycle, and is adequate for my purpose, 
>>>>> but I
>>>>> wouldn't want to push it much higher.
>>>>>
>>>>> I suppose the lack of description of the switching characteristics
>>>>> should have been a give-away.
>>>>>
>>>>> Sylvia.
>>>>>
>>>>> (*) Whether I needed to do that is a different discussion.
>>>>
>>>> The idea was to drive them from TTL without a base resistor. I suppose
>>>> some people liked not having to do the required higher-level math.
>>>>
>>>> Logic-level mosfets made these mostly obsolete. FDV301 costs us 3
>>>> cents.
>>>
>>> LTSpice shows me 0.7V of undershoot when driving it with 3V pulses, 10ns
>>> rise time, using Onsemi's model, and 10K load resistor.
>>>
>>> https://www.onsemi.com/design/resources/design-resources/models?rpn=FDV301N 
>>>
>>>
>>> Limiting that with a Schottky diode then gives me 22 mA spikes through
>>> the diode.
>>>
>>> Taming it with a 1K gate resistor helps, at the expense of slowing the
>>> output, but now we're back to needing an extra component.
>>>
>>> Not that such spikes always matter.
>>>
>>> Sylvia.
>>
>> 10K load implies very low current, so if you want less spikes you'd
>> need a part witn low Cg-d, namely a wimpier smaller-geometry device.
>>
>> An open-drain cmos gate might work, for whatever you are doing.
>>
>> Got a schematic?
>>
>>
>>
> 
> Below is my LTSpice version of the bit of the circuit concerned, to 
> change levels up and down.
> 
> The actual version implemented using the digital transistors performs 
> fairly closely to the simulation. As I've said, it's sufficient for my 
> requirements.
> 
> I originally used a digital isolator but I've already destroyed two, one 
> through carelessness, and one possibly through static discharge while 
> trying to understand why one channel was behaving oddly. They're rather 
> expensive to buy in excess of what is required in case they break.
> 
> Version 4
> SHEET 1 1268 680
> WIRE 432 -752 432 -784
> WIRE 784 -752 432 -752
> WIRE 192 -704 192 -784
> WIRE 784 -672 784 -752
> WIRE 432 -656 432 -752
> WIRE 528 -656 432 -656
> WIRE 528 -608 528 -656
> WIRE -112 -592 -160 -592
> WIRE 192 -592 192 -624
> WIRE 192 -592 -112 -592
> WIRE 192 -544 192 -592
> WIRE 432 -544 432 -656
> WIRE 736 -512 640 -512
> WIRE 784 -512 784 -592
> WIRE 784 -512 736 -512
> WIRE -32 -496 -80 -496
> WIRE 80 -496 48 -496
> WIRE 128 -496 80 -496
> WIRE 528 -496 528 -528
> WIRE 528 -496 496 -496
> WIRE 560 -496 528 -496
> WIRE 640 -496 640 -512
> WIRE 80 -448 80 -496
> WIRE 432 -448 416 -448
> WIRE 80 -320 80 -368
> WIRE 80 -320 -144 -320
> WIRE 192 -320 192 -448
> WIRE 192 -320 80 -320
> WIRE -80 -272 -80 -496
> WIRE 416 -272 416 -448
> WIRE 416 -272 -80 -272
> WIRE 416 -128 352 -128
> WIRE 416 -80 416 -128
> WIRE 176 -48 176 -96
> WIRE 176 -48 -256 -48
> WIRE 352 -48 352 -128
> WIRE 352 -48 176 -48
> WIRE -256 16 -256 -48
> WIRE 416 32 416 0
> WIRE 416 32 -96 32
> WIRE 176 48 176 -48
> WIRE 176 48 64 48
> WIRE 64 80 64 48
> WIRE -240 96 -256 96
> WIRE 176 144 176 48
> WIRE 416 144 416 32
> WIRE 672 176 624 176
> WIRE 768 176 672 176
> WIRE -96 192 -96 32
> WIRE -48 192 -96 192
> WIRE 64 192 64 160
> WIRE 64 192 32 192
> WIRE 112 192 64 192
> WIRE 512 192 480 192
> WIRE 544 192 512 192
> WIRE 624 192 624 176
> WIRE 512 224 512 192
> WIRE 416 240 400 240
> WIRE -336 256 -384 256
> WIRE 176 256 176 240
> WIRE 176 256 -336 256
> WIRE 400 320 400 240
> WIRE 512 320 512 304
> WIRE 512 320 400 320
> WIRE -256 368 -256 96
> WIRE 176 368 176 336
> WIRE 176 368 -256 368
> FLAG 176 -176 0
> FLAG 400 320 0
> FLAG 768 256 0
> FLAG 192 -864 0
> FLAG -144 -320 0
> FLAG 432 -864 0
> FLAG 416 -192 0
> FLAG -112 -592 OUT1
> FLAG 736 -512 IN1
> FLAG 672 176 IN2
> FLAG -336 256 OUT2
> SYMBOL npn 480 144 M0
> SYMATTR InstName Q1
> SYMATTR Value 2N3904
> SYMBOL pnp 112 240 M180
> SYMATTR InstName Q2
> SYMATTR Value 2N3906
> SYMBOL res 496 208 R0
> SYMATTR InstName R1
> SYMATTR Value 47K
> SYMBOL res 48 64 R0
> SYMATTR InstName R2
> SYMATTR Value 47K
> SYMBOL res 48 176 R90
> WINDOW 0 0 56 VBottom 2
> WINDOW 3 32 56 VTop 2
> SYMATTR InstName R3
> SYMATTR Value 10K
> SYMBOL res 640 176 R90
> WINDOW 0 0 56 VBottom 2
> WINDOW 3 32 56 VTop 2
> SYMATTR InstName R4
> SYMATTR Value 10K
> SYMBOL res 160 240 R0
> SYMATTR InstName R5
> SYMATTR Value 10K
> SYMBOL voltage 176 -80 R180
> WINDOW 0 24 96 Left 2
> WINDOW 3 24 16 Left 2
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V1
> SYMATTR Value 14
> SYMBOL voltage 768 160 R0
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V3
> SYMATTR Value PULSE(0 3.3 0 1e-8 1e-8 2e-5 4e-5 10)
> SYMBOL voltage -256 0 R0
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V4
> SYMATTR Value 4
> SYMBOL npn 128 -544 R0
> SYMATTR InstName Q3
> SYMATTR Value 2N3904
> SYMBOL pnp 496 -448 R180
> SYMATTR InstName Q4
> SYMATTR Value 2N3906
> SYMBOL res 512 -624 R0
> SYMATTR InstName R6
> SYMATTR Value 47K
> SYMBOL res 64 -464 R0
> SYMATTR InstName R7
> SYMATTR Value 47K
> SYMBOL res 64 -512 R90
> WINDOW 0 0 56 VBottom 2
> WINDOW 3 32 56 VTop 2
> SYMATTR InstName 10K
> SYMATTR Value 10K
> SYMBOL res 656 -512 R90
> WINDOW 0 0 56 VBottom 2
> WINDOW 3 32 56 VTop 2
> SYMATTR InstName R9
> SYMATTR Value 10K
> SYMBOL voltage 192 -768 R180
> WINDOW 0 24 96 Left 2
> WINDOW 3 24 16 Left 2
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V2
> SYMATTR Value 3.3
> SYMBOL voltage 784 -688 R0
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V5
> SYMATTR Value PULSE(0 4 0 1e-8 1e-8 25e-6 50e-6 10)
> SYMBOL res 176 -720 R0
> SYMATTR InstName R10
> SYMATTR Value 10K
> SYMBOL voltage 432 -768 R180
> WINDOW 0 24 96 Left 2
> WINDOW 3 24 16 Left 2
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V6
> SYMATTR Value 14
> SYMBOL res 432 -176 R180
> WINDOW 0 36 76 Left 2
> WINDOW 3 36 40 Left 2
> SYMATTR InstName R8
> SYMATTR Value 10K
> SYMBOL res 400 -96 R0
> SYMATTR InstName R11
> SYMATTR Value 10K
> TEXT -288 376 Left 2 !.tran 2E-4
> 


You might not need R8 and R11?

piglet
Reply by Sylvia Else ●March 26, 20222022-03-26
On 27-Mar-22 2:38 am, piglet wrote:

> On 26/03/2022 4:35 am, Sylvia Else wrote:
>> On 26-Mar-22 2:40 pm, jlarkin@highlandsniptechnology.com wrote:
>>> On Sat, 26 Mar 2022 14:16:46 +1100, Sylvia Else <sylvia@email.invalid>
>>> wrote:
>>>
>>>> On 26-Mar-22 11:32 am, John Larkin wrote:
>>>>> On Sat, 26 Mar 2022 10:52:34 +1100, Sylvia Else <sylvia@email.invalid>
>>>>> wrote:
>>>>>
>>>>>> https://www.farnell.com/datasheets/2353855.pdf
>>>>>>
>>>>>> I bought a few of these. I don't know what is intended by "digital
>>>>>> transistor" since the charge storage time defeats any attempt to use
>>>>>> them at a high frequency, and there's no way to add a Schottky 
>>>>>> diode to
>>>>>> prevent saturation, or a speed-up capacitor across the base resistor.
>>>>>>
>>>>>> I'm using this and the corresponding PNP type to do level shifting of
>>>>>> both high and low levels (*). At 25 kHz it's OK, albeit with a
>>>>>> significant change in duty cycle, and is adequate for my purpose, 
>>>>>> but I
>>>>>> wouldn't want to push it much higher.
>>>>>>
>>>>>> I suppose the lack of description of the switching characteristics
>>>>>> should have been a give-away.
>>>>>>
>>>>>> Sylvia.
>>>>>>
>>>>>> (*) Whether I needed to do that is a different discussion.
>>>>>
>>>>> The idea was to drive them from TTL without a base resistor. I suppose
>>>>> some people liked not having to do the required higher-level math.
>>>>>
>>>>> Logic-level mosfets made these mostly obsolete. FDV301 costs us 3
>>>>> cents.
>>>>
>>>> LTSpice shows me 0.7V of undershoot when driving it with 3V pulses, 
>>>> 10ns
>>>> rise time, using Onsemi's model, and 10K load resistor.
>>>>
>>>> https://www.onsemi.com/design/resources/design-resources/models?rpn=FDV301N 
>>>>
>>>>
>>>> Limiting that with a Schottky diode then gives me 22 mA spikes through
>>>> the diode.
>>>>
>>>> Taming it with a 1K gate resistor helps, at the expense of slowing the
>>>> output, but now we're back to needing an extra component.
>>>>
>>>> Not that such spikes always matter.
>>>>
>>>> Sylvia.
>>>
>>> 10K load implies very low current, so if you want less spikes you'd
>>> need a part witn low Cg-d, namely a wimpier smaller-geometry device.
>>>
>>> An open-drain cmos gate might work, for whatever you are doing.
>>>
>>> Got a schematic?
>>>
>>>
>>>
>>
>> Below is my LTSpice version of the bit of the circuit concerned, to 
>> change levels up and down.
>>
>> The actual version implemented using the digital transistors performs 
>> fairly closely to the simulation. As I've said, it's sufficient for my 
>> requirements.
>>
>> I originally used a digital isolator but I've already destroyed two, 
>> one through carelessness, and one possibly through static discharge 
>> while trying to understand why one channel was behaving oddly. They're 
>> rather expensive to buy in excess of what is required in case they break.
>>
>> Version 4
>> SHEET 1 1268 680
>> WIRE 432 -752 432 -784
>> WIRE 784 -752 432 -752
>> WIRE 192 -704 192 -784
>> WIRE 784 -672 784 -752
>> WIRE 432 -656 432 -752
>> WIRE 528 -656 432 -656
>> WIRE 528 -608 528 -656
>> WIRE -112 -592 -160 -592
>> WIRE 192 -592 192 -624
>> WIRE 192 -592 -112 -592
>> WIRE 192 -544 192 -592
>> WIRE 432 -544 432 -656
>> WIRE 736 -512 640 -512
>> WIRE 784 -512 784 -592
>> WIRE 784 -512 736 -512
>> WIRE -32 -496 -80 -496
>> WIRE 80 -496 48 -496
>> WIRE 128 -496 80 -496
>> WIRE 528 -496 528 -528
>> WIRE 528 -496 496 -496
>> WIRE 560 -496 528 -496
>> WIRE 640 -496 640 -512
>> WIRE 80 -448 80 -496
>> WIRE 432 -448 416 -448
>> WIRE 80 -320 80 -368
>> WIRE 80 -320 -144 -320
>> WIRE 192 -320 192 -448
>> WIRE 192 -320 80 -320
>> WIRE -80 -272 -80 -496
>> WIRE 416 -272 416 -448
>> WIRE 416 -272 -80 -272
>> WIRE 416 -128 352 -128
>> WIRE 416 -80 416 -128
>> WIRE 176 -48 176 -96
>> WIRE 176 -48 -256 -48
>> WIRE 352 -48 352 -128
>> WIRE 352 -48 176 -48
>> WIRE -256 16 -256 -48
>> WIRE 416 32 416 0
>> WIRE 416 32 -96 32
>> WIRE 176 48 176 -48
>> WIRE 176 48 64 48
>> WIRE 64 80 64 48
>> WIRE -240 96 -256 96
>> WIRE 176 144 176 48
>> WIRE 416 144 416 32
>> WIRE 672 176 624 176
>> WIRE 768 176 672 176
>> WIRE -96 192 -96 32
>> WIRE -48 192 -96 192
>> WIRE 64 192 64 160
>> WIRE 64 192 32 192
>> WIRE 112 192 64 192
>> WIRE 512 192 480 192
>> WIRE 544 192 512 192
>> WIRE 624 192 624 176
>> WIRE 512 224 512 192
>> WIRE 416 240 400 240
>> WIRE -336 256 -384 256
>> WIRE 176 256 176 240
>> WIRE 176 256 -336 256
>> WIRE 400 320 400 240
>> WIRE 512 320 512 304
>> WIRE 512 320 400 320
>> WIRE -256 368 -256 96
>> WIRE 176 368 176 336
>> WIRE 176 368 -256 368
>> FLAG 176 -176 0
>> FLAG 400 320 0
>> FLAG 768 256 0
>> FLAG 192 -864 0
>> FLAG -144 -320 0
>> FLAG 432 -864 0
>> FLAG 416 -192 0
>> FLAG -112 -592 OUT1
>> FLAG 736 -512 IN1
>> FLAG 672 176 IN2
>> FLAG -336 256 OUT2
>> SYMBOL npn 480 144 M0
>> SYMATTR InstName Q1
>> SYMATTR Value 2N3904
>> SYMBOL pnp 112 240 M180
>> SYMATTR InstName Q2
>> SYMATTR Value 2N3906
>> SYMBOL res 496 208 R0
>> SYMATTR InstName R1
>> SYMATTR Value 47K
>> SYMBOL res 48 64 R0
>> SYMATTR InstName R2
>> SYMATTR Value 47K
>> SYMBOL res 48 176 R90
>> WINDOW 0 0 56 VBottom 2
>> WINDOW 3 32 56 VTop 2
>> SYMATTR InstName R3
>> SYMATTR Value 10K
>> SYMBOL res 640 176 R90
>> WINDOW 0 0 56 VBottom 2
>> WINDOW 3 32 56 VTop 2
>> SYMATTR InstName R4
>> SYMATTR Value 10K
>> SYMBOL res 160 240 R0
>> SYMATTR InstName R5
>> SYMATTR Value 10K
>> SYMBOL voltage 176 -80 R180
>> WINDOW 0 24 96 Left 2
>> WINDOW 3 24 16 Left 2
>> WINDOW 123 0 0 Left 0
>> WINDOW 39 0 0 Left 0
>> SYMATTR InstName V1
>> SYMATTR Value 14
>> SYMBOL voltage 768 160 R0
>> WINDOW 123 0 0 Left 0
>> WINDOW 39 0 0 Left 0
>> SYMATTR InstName V3
>> SYMATTR Value PULSE(0 3.3 0 1e-8 1e-8 2e-5 4e-5 10)
>> SYMBOL voltage -256 0 R0
>> WINDOW 123 0 0 Left 0
>> WINDOW 39 0 0 Left 0
>> SYMATTR InstName V4
>> SYMATTR Value 4
>> SYMBOL npn 128 -544 R0
>> SYMATTR InstName Q3
>> SYMATTR Value 2N3904
>> SYMBOL pnp 496 -448 R180
>> SYMATTR InstName Q4
>> SYMATTR Value 2N3906
>> SYMBOL res 512 -624 R0
>> SYMATTR InstName R6
>> SYMATTR Value 47K
>> SYMBOL res 64 -464 R0
>> SYMATTR InstName R7
>> SYMATTR Value 47K
>> SYMBOL res 64 -512 R90
>> WINDOW 0 0 56 VBottom 2
>> WINDOW 3 32 56 VTop 2
>> SYMATTR InstName 10K
>> SYMATTR Value 10K
>> SYMBOL res 656 -512 R90
>> WINDOW 0 0 56 VBottom 2
>> WINDOW 3 32 56 VTop 2
>> SYMATTR InstName R9
>> SYMATTR Value 10K
>> SYMBOL voltage 192 -768 R180
>> WINDOW 0 24 96 Left 2
>> WINDOW 3 24 16 Left 2
>> WINDOW 123 0 0 Left 0
>> WINDOW 39 0 0 Left 0
>> SYMATTR InstName V2
>> SYMATTR Value 3.3
>> SYMBOL voltage 784 -688 R0
>> WINDOW 123 0 0 Left 0
>> WINDOW 39 0 0 Left 0
>> SYMATTR InstName V5
>> SYMATTR Value PULSE(0 4 0 1e-8 1e-8 25e-6 50e-6 10)
>> SYMBOL res 176 -720 R0
>> SYMATTR InstName R10
>> SYMATTR Value 10K
>> SYMBOL voltage 432 -768 R180
>> WINDOW 0 24 96 Left 2
>> WINDOW 3 24 16 Left 2
>> WINDOW 123 0 0 Left 0
>> WINDOW 39 0 0 Left 0
>> SYMATTR InstName V6
>> SYMATTR Value 14
>> SYMBOL res 432 -176 R180
>> WINDOW 0 36 76 Left 2
>> WINDOW 3 36 40 Left 2
>> SYMATTR InstName R8
>> SYMATTR Value 10K
>> SYMBOL res 400 -96 R0
>> SYMATTR InstName R11
>> SYMATTR Value 10K
>> TEXT -288 376 Left 2 !.tran 2E-4
>>
> 
> You might not need R8 and R11?
> 
> piglet >


Indeed, as originally conceived there weren't there, but they speed it 
up somewhat.

Sylvia.
Reply by Sylvia Else ●March 26, 20222022-03-26
On 27-Mar-22 2:32 am, piglet wrote:

> On 26/03/2022 2:54 pm, jlarkin@highlandsniptechnology.com wrote:
>> On Sat, 26 Mar 2022 15:35:12 +1100, Sylvia Else <sylvia@email.invalid>
>> wrote:
>>
>>> On 26-Mar-22 2:40 pm, jlarkin@highlandsniptechnology.com wrote:
>>>> On Sat, 26 Mar 2022 14:16:46 +1100, Sylvia Else <sylvia@email.invalid>
>>>> wrote:
>>>>
>>>>> On 26-Mar-22 11:32 am, John Larkin wrote:
>>>>>> On Sat, 26 Mar 2022 10:52:34 +1100, Sylvia Else 
>>>>>> <sylvia@email.invalid>
>>>>>> wrote:
>>>>>>
>>>>>>> https://www.farnell.com/datasheets/2353855.pdf
>>>>>>>
>>>>>>> I bought a few of these. I don't know what is intended by "digital
>>>>>>> transistor" since the charge storage time defeats any attempt to use
>>>>>>> them at a high frequency, and there's no way to add a Schottky 
>>>>>>> diode to
>>>>>>> prevent saturation, or a speed-up capacitor across the base 
>>>>>>> resistor.
>>>>>>>
>>>>>>> I'm using this and the corresponding PNP type to do level 
>>>>>>> shifting of
>>>>>>> both high and low levels (*). At 25 kHz it's OK, albeit with a
>>>>>>> significant change in duty cycle, and is adequate for my purpose, 
>>>>>>> but I
>>>>>>> wouldn't want to push it much higher.
>>>>>>>
>>>>>>> I suppose the lack of description of the switching characteristics
>>>>>>> should have been a give-away.
>>>>>>>
>>>>>>> Sylvia.
>>>>>>>
>>>>>>> (*) Whether I needed to do that is a different discussion.
>>>>>>
>>>>>> The idea was to drive them from TTL without a base resistor. I 
>>>>>> suppose
>>>>>> some people liked not having to do the required higher-level math.
>>>>>>
>>>>>> Logic-level mosfets made these mostly obsolete. FDV301 costs us 3
>>>>>> cents.
>>>>>
>>>>> LTSpice shows me 0.7V of undershoot when driving it with 3V pulses, 
>>>>> 10ns
>>>>> rise time, using Onsemi's model, and 10K load resistor.
>>>>>
>>>>> https://www.onsemi.com/design/resources/design-resources/models?rpn=FDV301N 
>>>>>
>>>>>
>>>>> Limiting that with a Schottky diode then gives me 22 mA spikes through
>>>>> the diode.
>>>>>
>>>>> Taming it with a 1K gate resistor helps, at the expense of slowing the
>>>>> output, but now we're back to needing an extra component.
>>>>>
>>>>> Not that such spikes always matter.
>>>>>
>>>>> Sylvia.
>>>>
>>>> 10K load implies very low current, so if you want less spikes you'd
>>>> need a part witn low Cg-d, namely a wimpier smaller-geometry device.
>>>>
>>>> An open-drain cmos gate might work, for whatever you are doing.
>>>>
>>>> Got a schematic?
>>>>
>>>>
>>>>
>>>
>>> Below is my LTSpice version of the bit of the circuit concerned, to
>>> change levels up and down.
>>>
>>> The actual version implemented using the digital transistors performs
>>> fairly closely to the simulation. As I've said, it's sufficient for my
>>> requirements.
>>>
>>> I originally used a digital isolator but I've already destroyed two, one
>>> through carelessness, and one possibly through static discharge while
>>> trying to understand why one channel was behaving oddly. They're rather
>>> expensive to buy in excess of what is required in case they break.
>>
>> Interesting schematic style.
>>
>> You might accomplish the same function with a dual optoisolator or a
>> dual opamp.
>>
>>
>>
>>
> 
> The sim used 50:50 square waves, if the duty cycle is not too far from 
> that then the level shift could be reduced to just two capacitors or 
> even pulse transformers for a 1950s vibe :)
> 
> piglet


I did look at a capacitive solution. But then one gets issues with 
overshoots/undershoots, especially during power up/down. So one adds 
diodes and resistors, and the component count goes up again.

The solution using the digital transistors involves only four components 
per level change - two digital transistors and two additional resistors.

Sylvia.
Reply by Uwe Bonnes ●March 27, 20222022-03-27
John Larkin <jlarkin@highland_atwork_technology.com> wrote:
... 

> Logic-level mosfets made these mostly obsolete. FDV301 costs us 3
> cents.

For interfacing woth uCs, the bipolar digital transisors are
guaranteed off while a MOSFET requires a pulldown while the UC boots

-- 
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 1623569 ------- Fax. 06151 1623305 ---------