Bipolar transistor bias question

. _________+ . | | . R2 R3 | | . | |/ . --R1-+---| Q1 . |>. . | . ___________| 0v

Then you could use NT's circuit, but replace R1 with a schottky.

That does exactly what you want, temperature-compensated for free.

Cheers, James

Yes, that might work R2 is fairly high at 100K or more so the drop on a schottky is only 150mV. If I use 1N4148, the drop is about right at 450mV at room temp.I can get it down to 400mV if R2 is 200K. But it looks ok at 450mV and switches the transistor rail to rail with a 250mV input. It's something to play with But right now I have to get Xmas out of the way and get my relatives something so I can show up at Xmas dinner carrying at least 2 gifts. I'm considering a large box of chocolates, or a Hickory Farm box of sausage and cheese, or a box of egg rolls from an Asian market. Plus a gift card of some value. I sent my grand Niece and Nephew each a 50 dollar bill in a card. I hope the postman doesn't rip it off.

A small-signal schottky will have a higher Vf at low current than that

1n5823 you're thinking of using :-).

But yes, you could also use a 'fat' diode (such as a 1n4001) at low current instead of a small-signal schottky, and get a suitably smaller Vf.

Don't forget, there's always room for Jello!

Cheers, James Arthur

That circuit is a fantasy...

wrote in message news: snipped-for-privacy@googlegroups.com...

I think I have a working modle using just two transistors. The pulse shape is not the best, but better than the original magazine circuit. .Total part count is 10 verses 12 with the old circuit so I saved 2 parts. And it triggers on 250mV. Haven't built it yet, I'll wait until I sell one of the old ones at Doc's. I sold my original for $25 a couple weeks ago. I think I've sold 6 for around $20 each, so I'm ahead $120 in a couple years.

Version 4 SHEET 1 992 680 WIRE 176 -48 80 -48 WIRE 288 -48 176 -48 WIRE 464 -48 288 -48 WIRE 544 -48 464 -48 WIRE 544 -16 544 -48 WIRE -64 0 -208 0 WIRE -16 0 -64 0 WIRE 464 0 464 -48 WIRE 80 16 80 -48 WIRE -208 32 -208 0 WIRE 176 48 176 32 WIRE 208 48 176 48 WIRE 288 48 288 32 WIRE 288 48 272 48 WIRE 304 48 288 48 WIRE 400 48 384 48 WIRE -64 96 -64 64 WIRE -16 96 -16 80 WIRE -16 96 -64 96 WIRE 176 96 176 48 WIRE -16 144 -16 96 WIRE -16 144 -32 144 WIRE 0 144 -16 144 WIRE 80 144 80 96 WIRE 80 144 64 144 WIRE 112 144 80 144 WIRE -176 192 -176 144 WIRE -16 240 -16 144 WIRE 464 240 464 96 WIRE 464 240 -16 240 FLAG 544 64 0 FLAG 176 192 0 FLAG -176 272 0 FLAG -208 32 0 SYMBOL pnp 400 96 M180 WINDOW 3 -24 -21 Left 0 WINDOW 0 -264 -273 Left 0 SYMATTR Value 2N3906 SYMATTR InstName Q1 SYMBOL npn 112 96 R0 WINDOW 0 324 -47 Left 0 WINDOW 3 35 47 Left 0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL voltage 544 -32 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 3.2 SYMBOL diode 64 128 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL voltage -176 176 R0 WINDOW 3 53 98 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 57 124 Left 0 WINDOW 0 -73 49 Left 0 SYMATTR Value PULSE(0 4.5 0 1e-6 1e-6 .001 .3 5) SYMATTR SpiceLine Rser=0 SYMATTR InstName V2 SYMBOL res 160 -64 R0 WINDOW 0 -63 435 Left 0 WINDOW 3 37 57 Left 0 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL cap 272 32 R90 WINDOW 0 -99 47 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C1

SYMBOL res 64 0 R0 WINDOW 0 154 371 Left 0 WINDOW 3 39 50 Left 0 SYMATTR InstName R3 SYMATTR Value 220k SYMBOL res -16 128 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R4 SYMATTR Value 1000k SYMBOL cap -112 128 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C2

SYMBOL res 272 -64 R0 WINDOW 0 -256 433 Left 0 WINDOW 3 38 55 Left 0 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL ind -32 -16 R0 WINDOW 0 216 386 Left 0 WINDOW 3 41 49 Left 0 SYMATTR InstName L1 SYMATTR Value .3 SYMATTR SpiceLine Rser=300 SYMBOL diode -80 0 R0 WINDOW 3 -90 38 Left 0 WINDOW 0 331 372 Left 0 SYMATTR Value 1N4148 SYMATTR InstName D2 SYMBOL res 400 32 R90 WINDOW 0 352 328 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R1 SYMATTR Value 2k TEXT -120 328 Left 0 !.tran 2s

On Tuesday, December 27, 2016 at 9:02:21 PM UTC-5, Bill Bowden wrote:

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That's cute. And power consumption is down below 1mA. Is your coil really 300mH?

A nice feature is how easily you can set the output pulse width to minimize power usage.

For your amusement, here's a version of your circuit with a MOSFET output. (I injected the simulated coil pick-up voltage slightly differently.)

Cheers, James Arthur

Version 4 SHEET 1 992 680 WIRE 176 -80 80 -80 WIRE 288 -80 176 -80 WIRE 400 -80 288 -80 WIRE 480 -80 400 -80 WIRE 480 -64 480 -80 WIRE 176 -48 176 -80 WIRE 288 -48 288 -80 WIRE -64 0 -208 0 WIRE -16 0 -64 0 WIRE 80 16 80 -80 WIRE 480 32 480 16 WIRE 400 48 400 -80 WIRE 176 64 176 32 WIRE 208 64 176 64 WIRE 288 64 288 32 WIRE 288 64 272 64 WIRE 352 64 288 64 WIRE -208 80 -208 0 WIRE -64 96 -64 64 WIRE -16 96 -16 80 WIRE -16 96 -64 96 WIRE 176 96 176 64 WIRE -16 144 -16 96 WIRE 0 144 -16 144 WIRE 80 144 80 96 WIRE 80 144 64 144 WIRE 112 144 80 144 WIRE -208 192 -208 160 WIRE 176 208 176 192 WIRE -16 256 -16 144 WIRE 400 256 400 144 WIRE 400 256 -16 256 FLAG 480 32 0 FLAG 176 208 0 FLAG -208 192 0 SYMBOL npn 112 96 R0 WINDOW 0 79 44 Left 2 WINDOW 3 60 73 Left 2 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL voltage 480 -80 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 3 SYMBOL diode 64 128 R90 WINDOW 0 56 32 VBottom 2 WINDOW 3 54 29 VTop 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL voltage -208 64 R0 WINDOW 3 -108 162 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 -112 76 Left 2 WINDOW 0 -73 49 Left 2 SYMATTR Value PULSE(0 300mV 0 1e-6 1e-6 .001 .3) SYMATTR SpiceLine Rser=0 SYMATTR InstName V2 SYMBOL res 160 -64 R0 WINDOW 0 43 32 Left 2 WINDOW 3 37 57 Left 2 SYMATTR InstName R2 SYMATTR Value 22k SYMBOL cap 272 48 R90 WINDOW 0 58 33 VBottom 2 WINDOW 3 56 27 VTop 2 SYMATTR InstName C1

SYMBOL res 64 0 R0 WINDOW 0 46 23 Left 2 WINDOW 3 39 50 Left 2 SYMATTR InstName R3 SYMATTR Value 220k SYMBOL res 272 -64 R0 WINDOW 0 41 29 Left 2 WINDOW 3 38 55 Left 2 SYMATTR InstName R5 SYMATTR Value 22k SYMBOL ind -32 -16 R0 WINDOW 0 38 18 Left 2 WINDOW 3 41 49 Left 2 SYMATTR InstName L1 SYMATTR Value .3 SYMATTR SpiceLine Rser=300 Cpar=300pF SYMBOL diode -80 0 R0 WINDOW 3 -90 38 Left 2 WINDOW 0 -61 13 Left 2 SYMATTR Value 1N4148 SYMATTR InstName D2 SYMBOL pmos 352 144 M180 SYMATTR InstName M1 SYMATTR Value Si1555DL_P TEXT 440 160 Left 2 !.tran 2s TEXT -240 -112 Left 2 ;Bill Bowden's pendulum driver, with MOSFET output 2

8-Dec-2016

Well, your OP indicated you wanted to use one transistor and that the input voltage would be 300mV. So, the specs have changed now?

Where can I find the 250mV trigger in the simulation?

(Snip LTSpice listing)

The OP just concerned switching the first transistor.I didn't care much about the second. The way I tested for 250mV was to disconnect the 4.7u capacitor and apply a 250mV sine at 20 hertz directly to the cathode of the diode, Then look at the collector of the 3904 and it will swing almost rail to rail (3.2 to .0.15)

This has become completely ridiculous.

Yes, you're right. An easier way to see the 250mV trigger is to disconnect the 4.7u cap and then just look at the trigger at the cathode of the diode. I'm reading 235mV.

That's cute. And power consumption is down below 1mA. Is your coil really 300mH?

A nice feature is how easily you can set the output pulse width to minimize power usage.

For your amusement, here's a version of your circuit with a MOSFET output. (I injected the simulated coil pick-up voltage slightly differently.)

Cheers, James Arthur

Interesting, and you saved another part. But it doesn't seem to work on a 2 volt battery. I'm figuring a couple AA cells will be close to dead at 1 volt each, so I need the thing to operate on 2 volts..

The coil inductance may be lower at 150mH. I just looked at this air core inductance calculator and plugged in the appriximate values of 150mH and 1/4 inch for both inner coil diameter and length.and wire gauge of #38. It shows

3300 turns and about 300 ohms of resistance, which is about what I have. So, the inductance may be lower at 150mH.

The air core calculator is here:

.

Just tried it--works fine for me @ 1.0 V. But you'll prefer the jellybean BJT's; this was just for fun.

The key thing will be whether the new coil gives the pendulum enough of a 'push' to keep 'er going. Then you can tweak the drive pulse width to save power.

Cheers, James Arthur

So,what am I doing wrong? All I changed was V1 to 2 volts and I get an output pulse of 200mV and a width of 1mS. That won't work.

Confusing time and conductance?

With V1=2V I get a 2V x 17mS pulse at the coil.

Did you change FETs? The PMOS has to be a low Vgs(th) type. Or maybe you're measuring at the wrong place? Or disconnecting the positive feedback loop like you were before, for measuring?

The output pulse width is down to 2mS @ V1=1V. It's obviously running out of gas--I wasn't trying to make it work at 0.5V/cell--but it is still *running*, and not laying idle.

Ideally pulse-width would vary inversely with Vcc, providing constant mechanical drive over the battery life. But that takes more parts. :-) Besides--you might want reduced swing as a battery-state indication so the user can see when his batteries are running out of steam.

Cheers, James Arthur

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It's not for a magazine project AFAIK, though Bill has published projects in hobby magazines.

Bill's experimenting with a perpetual pendulum and with a one-pole motor based on similar coils / drivers, both(?) inspired by a solar-powered device described in an article Bill listed above(*) (from Nuts N Volts magazine). He's optimizing, improving, and adapting.

(*)

Bill demonstrates these to kids and the general public for the sheer pleasure, inspiring, fascinating and delighting folks, introducing them to the magic of electronics.

His hobby website is bowdenshobbycircuits.info, full of great projects for young electrophiles.

Cheers, James Arthur

On Thursday, December 29, 2016 at 9:56:11 AM UTC-5, snipped-for-privacy@yahoo.com wr ote:

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Okay, thanks- saw that one earlier, looks fun.

Yes, I think you are right. I just tried the sim again and it works fine on

2 volts. I think I had disconnected the cap for some reason and forgot to reattach it. I did have several adult beverages last night, so my focus wasn't the best.