Digital transistor?...

S

Sylvia Else

Guest
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.
 
lørdag den 26. marts 2022 kl. 00.52.43 UTC+1 skrev Sylvia Else:
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.
Click to expand...

it saves a couple of resistors, I don\'t think it ever promised anything else
 
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.
Click to expand...

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.

I bet that base resistor has a radical tempco.

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon
 
lørdag den 26. marts 2022 kl. 01.32.51 UTC+1 skrev John Larkin:
On Sat, 26 Mar 2022 10:52:34 +1100, Sylvia Else <syl...@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.
Click to expand...

more like less parts and less space

Logic-level mosfets made these mostly obsolete. FDV301 costs us 3
cents.
Click to expand...

quite few \"digital transistors\" here for less than half that
https://lcsc.com/products/Digital-Transistors_562.html

but also for fets
https://lcsc.com/products/MOSFETs_381.html
 
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.
Click to expand...

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.
 
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.
Click to expand...

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?



--

I yam what I yam - Popeye
 
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?
Click to expand...

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
 
Lasse Langwadt Christensen wrote:

> it saves a couple of resistors, I don\'t think it ever promised anything else

And they are quite useful, especially the PNP/NPN+resistors pairs in
SOT-23-6/SC-70. Save a lot of board space.

Best regards, Piotr
 
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.
Click to expand...

Interesting schematic style.

You might accomplish the same function with a dual optoisolator or a
dual opamp.




--

I yam what I yam - Popeye
 
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.
Click to expand...

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
 
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
Click to expand...

You might not need R8 and R11?

piglet
 
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
Click to expand...

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

Sylvia.
 
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
Click to expand...

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.
 
John Larkin <jlarkin@highland_atwork_technology.com> wrote:
....
Logic-level mosfets made these mostly obsolete. FDV301 costs us 3
cents.
Click to expand...
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 ---------
 
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