A PNP-NPN output with common-base level shifting

People tend to not like to leave bases open. A resistor would speed up turnoff and increase the breakdown voltage of the PNP. BVcer > BVceo. And reduce leakage, except that silicon transistors don't leak much.

Looks OK. It is hard to find decent low-voltage zeners.

These are sort of cute:

Or buy a logic-level mosfet!

Lose all but Q1 and Q2 and turn Q1 into a PMOS and Q2 into an NMOS and you have a classic CMOS inverter.

What you have there in bipolar will not be particularly fast.

What do you have in mind for the "low voltage" section, 5V?

Larkin's "TTL_to_HV.JPG" is the same as my MC1554 output stage (yet another coffee bet with Tom Frederiksen :-) But is not particularly fast on the upstroke. The MC1554 was designed for audio.

Sort of looks like my MC1554 output stage from the '60's...

...Jim Thompson

Indeed. I forgot to say that I have seen this configuration with mosfets, but not with bjts. Here is an explicit example:

On page 12 there is a normal non-inverting bipolar push-pull driver (NPN-PNP), and on the next page there is a mosfet variant, which is otherwise the same except it's inverting. There is no explanation why the bipolar variant couldn't be inverting as well!

Because the transistors get saturated? The slower switching is the price for less conduction loss (compared to standard push-pull)? I don't think I'm going to need frequencies beyond, say, 50 kHz, so this probably won't be an issue.

Probably, since I'll mostly be using cheapo TTL ICs. Of course if I use a microcontroller I could go as low as 1.8 V...

The turnoff speed is probably the only relevant issue here. Thanks.

Is this really a problem? Once you go beyond 2.4 V (the minimum for zeners, I gather), can't you just stack p-n diodes (and maybe a Schottky) to get the desired voltage drop?

Too high voltage drops to my taste.

This is quite pretty. Useless for me, but still.

That wouldn't solve the issue of driving a p-channel at high side. Besides, it is my understanding that a mosfet's gate requires not only voltage, but also a large momentary current (larger than control devices can supply) in order to minimize the switching time and the losses incurred during it. If this is true, then it seems that a driver circuit would still be required even if gate voltage wasn't an issue.

Lauri

Any time you connect a PNP to an NPN collector to collector there's a risk of turning both transistors on at the same time. Shoot-through can get ugly.

For low-power design, just slap a tiny-logic buffer on the board. For high power -- I dunno, maybe it'll work, but as mentioned there are speed issues.

Here's a version of a gate driver using NPN and PNP transistors that will drive a large MOSFET with a gate resistor of 2 ohms and an extra 3800 pF

gate capacitance, with less than 100 nSec rise and fall times (according to LTSpice). The constant current stage of Q4, D1, D2, R4, and R7 can be replaced with just a 5k resistor at the expense of switching time, although you can probably use a lower value that would just draw higher current. The constant current stage allows this to be used on a variety of voltages with similar performance. For low frequency switching it can be made quite efficient by changing the current.

Paul

========================= ========================= ========================= ========= Version 4 SHEET 1 1172 680 WIRE -32 -144 -32 -160 WIRE -32 -144 -192 -144 WIRE 112 -144 -32 -144 WIRE 144 -144 112 -144 WIRE 224 -144 144 -144 WIRE 384 -144 224 -144 WIRE 768 -144 384 -144 WIRE 912 -144 768 -144 WIRE 896 -64 768 -64 WIRE 912 -64 896 -64 WIRE 112 -48 112 -144 WIRE 384 -48 384 -144 WIRE 160 -16 144 -16 WIRE 896 -16 896 -64 WIRE 960 -16 896 -16 WIRE -192 0 -192 -144 WIRE 768 0 768 -64 WIRE 832 0 768 0 WIRE -32 16 -32 -144 WIRE 224 32 224 0 WIRE 224 64 224 32 WIRE 320 64 320 0 WIRE 320 64 224 64 WIRE 384 80 384 48 WIRE 480 80 384 80 WIRE 512 80 480 80 WIRE 640 80 640 -16 WIRE 640 80 592 80 WIRE 656 80 640 80 WIRE 720 80 656 80 WIRE 224 112 224 64 WIRE 384 112 384 80 WIRE 960 144 960 48 WIRE 1024 144 960 144 WIRE 1056 144 1024 144 WIRE -80 160 -112 160 WIRE 0 160 -80 160 WIRE 112 160 112 32 WIRE 112 160 80 160 WIRE 160 160 112 160 WIRE 320 160 320 64 WIRE 656 160 656 80 WIRE 1056 176 1056 144 WIRE 144 224 144 -16 WIRE -192 304 -192 80 WIRE -112 304 -112 240 WIRE -112 304 -192 304 WIRE -32 304 -32 80 WIRE -32 304 -112 304 WIRE 144 304 -32 304 WIRE 224 304 224 208 WIRE 224 304 144 304 WIRE 384 304 384 208 WIRE 384 304 224 304 WIRE 656 304 656 224 WIRE 656 304 384 304 WIRE 768 304 768 96 WIRE 768 304 656 304 WIRE 960 304 960 208 WIRE 960 304 768 304 WIRE 1056 304 1056 256 WIRE 1056 304 960 304 WIRE 224 320 224 304 FLAG 224 320 0 FLAG 832 0 Vsw FLAG 640 -16 Vg FLAG -80 160 Vin FLAG 480 80 Vdrv FLAG 1024 144 Vout SYMBOL voltage -112 144 R0 WINDOW 0 37 59 Left 2 WINDOW 3 -109 182 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value PULSE(0 5 10u 10n 10n 2u 10u 1000) SYMBOL npn 160 112 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL pnp 320 208 M180 WINDOW 0 49 26 Left 2 WINDOW 3 38 52 Left 2 SYMATTR InstName Q2 SYMATTR Value 2N4403 SYMBOL res 96 144 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 200 SYMBOL res 128 48 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R2 SYMATTR Value 4.99k SYMBOL res 240 -48 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R4 SYMATTR Value 27 SYMBOL res 496 96 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R5 SYMATTR Value 10 SYMBOL voltage -192 -16 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value 15 SYMBOL nmos 720 0 R0 SYMATTR InstName M1 SYMATTR Value STB120NF10 SYMBOL res 752 -160 R0 SYMATTR InstName R6 SYMATTR Value 100k SYMBOL npn 320 -48 R0 SYMATTR InstName Q3 SYMATTR Value 2N3904 SYMBOL ind 896 -160 R0 SYMATTR InstName L1 SYMATTR Value 10u SYMATTR SpiceLine Ipk=10 Rser=0.0172 Rpar=32450 Cpar=5.52p mfg="Wurth Elektronik" pn="7445710 WE-PD4 XL" SYMBOL schottky 944 -16 R0 SYMATTR InstName D3 SYMATTR Value MBRS360 SYMATTR Description Diode SYMATTR Type diode SYMBOL polcap 944 144 R0 WINDOW 3 24 64 Left 2 SYMATTR Value .47u SYMATTR InstName C1 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=50 Irms=210m Rser=0.45 MTBF=1000 Lser=0 ppPkg=1 SYMBOL res 1040 160 R0 SYMATTR InstName R3 SYMATTR Value 50 SYMBOL cap -48 16 R0 SYMATTR InstName C2 SYMATTR Value 1u SYMBOL cap 640 160 R0 SYMATTR InstName C3 SYMATTR Value 3800p SYMBOL pnp 160 32 M180 WINDOW 0 49 26 Left 2 WINDOW 3 38 52 Left 2 SYMATTR InstName Q4 SYMATTR Value 2N4403 SYMBOL res 160 320 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R7 SYMATTR Value 1k SYMBOL diode 128 -80 R0 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode 128 -144 R0 SYMATTR InstName D2 SYMATTR Value 1N4148 TEXT -224 504 Left 2 !.tran 200u startup

...Jim Thompson