Some unreasonable fraction of the population loves current mirrors and diff pairs. Neither of which is usually appropriate, especially when designing with discretes.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Like this ...
. Vcc . -+-----+-----+-- . | | | . R1 | } . | |/ | . +---| | . | |>, | . | | |/ | . | +---| } . | | |>, ||--' . | | | ||
Take 2...Here's the output of the "Tringlotron" at 20kHz; even with jellybean transistors it should go to 100 or 200kHz:
Thanks
I little bit hard to tell the components. Can you post the ASC file?
Thanks
Klaus
Sure thing, I made a couple changes...Don't know if component values are optimal, probably have to adjust for a particular load but the idea is pretty simple; positive-going pulse at the base of Q2 shuts down Q3 and then current source involving J1 and R2 shoves current into the base of driver Q1, negative-going pulse at Q2 turns on Q3 which strongly pulls down and turns off Q1, C1 and D1 generate a boost voltage to increase compliance (C1 should probably have been connected to the switching node)
I think this 20kHz square wave into 1k at the output looks pretty nice:
Version 4 SHEET 1 1708 1608 WIRE 112 -496 112 -592 WIRE 720 -496 112 -496 WIRE 976 -496 976 -592 WIRE 112 -416 112 -496 WIRE 976 -352 976 -416 WIRE -368 -272 -960 -272 WIRE -128 -272 -368 -272 WIRE 112 -272 112 -352 WIRE 112 -272 -128 -272 WIRE 336 -272 112 -272 WIRE -368 -192 -368 -272 WIRE -960 -128 -960 -272 WIRE -368 -32 -368 -112 WIRE 336 -32 336 -272 WIRE -128 0 -128 -272 WIRE -128 0 -320 0 WIRE -960 112 -960 -48 WIRE 112 112 112 -272 WIRE -896 160 -912 160 WIRE -368 160 -368 64 WIRE -368 160 -896 160 WIRE 48 160 -368 160 WIRE 720 224 720 -496 WIRE 112 304 112 208 WIRE 464 304 112 304 WIRE 672 304 544 304 WIRE 112 416 112 304 WIRE -960 464 -960 208 WIRE 48 464 -960 464 WIRE -368 624 -368 160 WIRE 112 672 112 512 WIRE 112 672 -304 672 WIRE 112 816 112 672 WIRE -368 992 -368 720 WIRE 112 992 112 896 WIRE 112 992 -368 992 WIRE 336 992 336 32 WIRE 336 992 112 992 WIRE 720 992 720 320 WIRE 720 992 336 992 WIRE 896 992 720 992 WIRE 1120 992 960 992 WIRE -480 1024 -1600 1024 WIRE -1296 1120 -1424 1120 WIRE -1120 1120 -1232 1120 WIRE 720 1184 720 992 WIRE 1120 1184 1120 992 WIRE -960 1248 -960 464 WIRE -480 1264 -480 1024 WIRE 432 1264 -480 1264 WIRE 672 1264 512 1264 WIRE -1600 1296 -1600 1024 WIRE -1424 1296 -1424 1120 WIRE -1424 1296 -1600 1296 WIRE -1312 1296 -1424 1296 WIRE -1120 1296 -1120 1120 WIRE -1120 1296 -1232 1296 WIRE -1024 1296 -1120 1296 WIRE -1600 1376 -1600 1296 WIRE 1120 1536 1120 1264 WIRE -1600 1552 -1600 1456 WIRE 720 1552 720 1280 WIRE -960 1568 -960 1344 FLAG -960 1568 0 FLAG 720 1552 0 FLAG 112 -592 Vdd FLAG 976 -592 Vdd FLAG 976 -352 0 FLAG -1600 1552 0 FLAG 1120 1536 0 SYMBOL npn 48 112 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL pnp 48 512 M180 SYMATTR InstName Q2 SYMATTR Value 2N3906 SYMBOL npn -304 624 M0 SYMATTR InstName Q3 SYMATTR Value 2N3904 SYMBOL pjf -320 64 R180 SYMATTR InstName J1 SYMATTR Value LSJ689B SYMBOL res -384 -208 R0 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL res 96 800 R0 SYMATTR InstName R1 SYMATTR Value 220 SYMBOL schottky 96 -416 R0 SYMATTR InstName D1 SYMATTR Value 1N5817 SYMATTR Description Diode SYMATTR Type diode SYMBOL nmos 672 224 R0 SYMATTR InstName M1 SYMATTR Value BSP89 SYMBOL cap 320 -32 R0 SYMATTR InstName C1 SYMATTR Value 1n SYMBOL nmos 672 1184 R0 SYMATTR InstName M2 SYMATTR Value BSP89 SYMBOL npn -1024 1248 R0 WINDOW 0 124 48 Left 2 WINDOW 3 118 19 Left 2 SYMATTR InstName Q4 SYMATTR Value 2N3904 SYMBOL res -976 -144 R0 SYMATTR InstName R3 SYMATTR Value 220 SYMBOL res 560 288 R90 WINDOW 0 -7 53 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 1 SYMBOL res 528 1248 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 1 SYMBOL res -1216 1280 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 1k SYMBOL cap -1232 1104 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 47 33 VTop 2 SYMATTR InstName C2 SYMATTR Value 1n SYMBOL voltage 976 -512 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 24 SYMBOL voltage -1600 1360 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V3 SYMATTR Value PULSE(0 6 0 100n 100n 0.00002 0.00005) SYMBOL cap 960 976 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 2.2?F SYMBOL res 1104 1168 R0 SYMATTR InstName R7 SYMATTR Value 1k SYMBOL pnp -896 208 R180 SYMATTR InstName Q5 SYMATTR Value 2N3906 TEXT -1216 1592 Left 2 !.tran 0.1 TEXT -1856 464 Left 7 ;TRINGLOTRON
My intuition is that when going for speed when need low parts count/cost with jellybean devices, one must crush things like too high Cob etc. into submission with brute force (current), not try to finesse the parts into being something they are not.
ote:
mgh current is running and a low side FET is turned off, the current mirror (BJT, R1 and R2) cannot keep up due to limited GBW of the BJT
BW?
that,
atically
volt
tt in the
ly,
to much (to many parameters to convey)
FET (so the input impedance is very high, so I just need a voltage that ra mps fast)
o come down to 200ns max
Nice, thanks
Well, the whole current-mode ('translinear') circuitry thing is pretty cool. You used to be able to get monolithic current mirrors for cheap--I still have some of the TL011/41 series that I'll probably never use because I can't replace them. :(
Even the BCV61 and 62 went away--they weren't much to write home about, but worked okay up to maybe a milliamp.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net https://hobbs-eo.com
This isn't as fast as John's but it's simple, has a 250nS risetime, and doesn't over-voltage the output FET's gate.
+5V -+- | v D1 --- | +----------+-------. | | | C1 [R1] 560 | ---10n Vdd | |/ Q1 --- -+- +---+----| 2n3904 | | | | |>. | | | | | | ||--' M1 | | | | || output ||2100 amps peak in D1!
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Eh? I see some spikes of about 400mA that don't last much more than a microsecond, average of 6mA
Really? I'm just seeing half an amp.
Cheers, James Arthur
Ya, a 1N5187 is probably overkill.
Is the price really that much dependent on conductivity? I have several
1.8mOhm power PFETs and the price wasn't that much different than that of a similarly sized NFET. They are just much rarer and the spectrum is limited.Best regards, Piotr
Also, if it enables d.c. operation and eliminates a floating +12V supply, a PFET more than pays for itself.
Cheers, James Arthur
. | | |/ | . | +---| | . | | |>, ||--' . | | | ||
The OP had a series gate resistor, so ending the PNP at ground is better than connecting it to the mosfet source, if you want a fast fall.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Maybe my Spice defaults are different.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
FYI, MOS are a really bad option in this kind of circuit. Why?
You can get ~arbitrarily small BJTs. Low voltage, low current, low capacitance, high fT.
You can't get arbitrarily small MOSFETs. 2N7002 is a huge device, about 4 x
2N4401's worth. Even RUM001L02T2CL is 2N3904 sized (but at a fraction of the voltage rating, so it's probably not a candidate here).The only smaller MOSFETs out there, are the ever-rarer dual gate kind (sold as RF FETs). I guess all the small [regular] MOS disappeared because they're inferior to GaAsFETs, PHEMTs and such.
Replacing M3 with, say, MMBTH10 (and D2 with a '3906 follower), will show immediate gains as the gain node capacitance is reduced to less than half. Alternately, R1 can be made larger, or turned into a current source (which also as I discussed before, can be a switched current source, in differential mode operation, at the expense of even more transistors of course).
The same goes for low power circuitry; AoE2 had a section discussing this, and recommended MOSFETs and RF BJTs at low currents (where they're less squirrely). Emphasis on BJTs, it seems to me. If you need MOS, best to keep it inside an integrated circuit (CMOS gates, or for anything of scale these days, micropower FPGA or MCU).
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/
PMOS are about 4x worse performance than NMOS. They're well worth removing from a design, if you have the option to. Bootstrap supplies are cheap.
As for driving, I've got that covered:
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/
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