Can anyone help with this?

So that we all know what FET we're talking about, please assume the P-channel one in this package.

It is not a jfet - insulated gate

Nice - Thanks. Ed

The OT uses enhancement mosfets, not depletion jfets. Mosfets have insulated gates, occasionally with ESD protection zeners to the source. I blew out a 2N7000 yesterday that doesn't have gate protection.

Most all mosfets have a s-d substrate diode.

There are some small-signal mosfets that are symmetric, but they are very rare. Those ususlly have a discrete substrate pin with substrate diodes to both the source and drain.

Most semiconductors nowadays have diodes to the substrate from most everything.

google mosfet substrate diode

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Did you miss on my picture that the p fet is AO3047 and the n fet is

Right now, there's nothing connected to the output, save a 1K resistor to provide a bit of a load. D2/R3 is out nowm, as the battery will vever gt 'disconnected' Apparently they are there for the case where the supply is a PSU thatcan be switched off...

In the field that I'm looking at, all devices use a micro as it is the simplest solution to achieve the desired result. A polled push button switch contact, whilst in deep sleep mode, is the obvious solution.The switches are invariable the 5mmx5mm tactile buttons that cost a couple of pence ( compared to a toggle switch @£1 plus.) copule of options for me... try piglets on /hold off or consider a latched push button.Try some low vGs fets... Downside is I already have PCBs and I don't like to be beaten by something I don't really understand- burried diodes? I spent 50+ years in the digital domain ( ever since RTL/DTL>TTL.) Analogue I just don't get :(

No but I couldn't find any such FET. Did you mean AO3407 ?

Changing TR2 to 2N7002 doesn't seem to make any difference to the simulation.

Cool, but what happens if I push the switch and hold it down ?

It is not a serious circuit! The floating gate will pickup all sorts of static from people and charged objects just approaching the device without even mechanically activating the switch. Hold a cellphone nearby and you have wireless control!

Yes, sorry, AO3407 :(

Apart from that, it will auto switch between on and off.... I guess 100k (?) source to gate will stop the 'noise'. Not sure I could tell someone ' don't hold the switch down too long'....LOL

"TTman" snipped-for-privacy@gmail.com wrote in message news:10vqaf5$14pb$ snipped-for-privacy@dont-email.me...

I can't find a model of AO3407 I would trust but if all you care about is turn on voltage, and if you trust google AI (which I don't), then you arrive at the following simulation which says it still works down to 2V input.

Version 4.1 SHEET 1 2776 2100 WIRE -1008 -480 -1168 -480 WIRE -896 -480 -1008 -480 WIRE -720 -480 -800 -480 WIRE -640 -480 -720 -480 WIRE -528 -480 -640 -480 WIRE -448 -480 -528 -480 WIRE -448 -448 -448 -480 WIRE -448 -320 -448 -368 WIRE -1008 -304 -1008 -480 WIRE -720 -304 -720 -480 WIRE -640 -288 -640 -480 WIRE -1008 -160 -1008 -224 WIRE -880 -160 -880 -432 WIRE -880 -160 -1008 -160 WIRE -1008 -96 -1008 -160 WIRE -880 48 -880 -160 WIRE -720 128 -720 -224 WIRE -720 128 -832 128 WIRE -640 128 -640 -224 WIRE -640 128 -720 128 WIRE -576 128 -640 128 WIRE -208 128 -576 128 WIRE -1168 256 -1168 -480 WIRE -1008 288 -1008 -16 WIRE -608 288 -1008 288 WIRE -560 288 -608 288 WIRE -512 288 -560 288 WIRE -608 352 -608 288 WIRE -720 368 -752 368 WIRE -656 368 -720 368 WIRE -1008 416 -1008 288 WIRE -656 416 -672 416 WIRE -752 448 -752 368 WIRE -1168 624 -1168 336 WIRE -1008 624 -1008 480 WIRE -1008 624 -1168 624 WIRE -880 624 -880 144 WIRE -880 624 -1008 624 WIRE -752 624 -752 528 WIRE -752 624 -880 624 WIRE -672 624 -672 416 WIRE -672 624 -752 624 WIRE -608 624 -608 432 WIRE -208 624 -208 128 WIRE -208 624 -608 624 WIRE -1168 672 -1168 624 WIRE -512 832 -512 288 WIRE -512 832 -624 832 WIRE -624 896 -624 832 WIRE -672 912 -688 912 WIRE -672 960 -768 960 WIRE -768 992 -768 960 WIRE -768 1104 -768 1072 WIRE -688 1104 -688 912 WIRE -688 1104 -768 1104 WIRE -624 1104 -624 976 WIRE -208 1104 -208 624 WIRE -208 1104 -624 1104 WIRE -768 1152 -768 1104 WIRE -512 1184 -512 832 WIRE -560 1200 -576 1200 WIRE -560 1248 -656 1248 WIRE -656 1280 -656 1248 WIRE -656 1424 -656 1360 WIRE -576 1424 -576 1200 WIRE -576 1424 -656 1424 WIRE -512 1424 -512 1264 WIRE -208 1424 -208 1104 WIRE -208 1424 -512 1424 WIRE -656 1472 -656 1424 FLAG -1168 672 0 FLAG -768 1152 0 FLAG -656 1472 0 FLAG -528 -480 sw FLAG -448 -320 0 FLAG -576 128 button1 FLAG -560 288 button2 FLAG -720 368 pb SYMBOL sw -608 448 M180 SYMATTR InstName S1 SYMATTR Value SWCH SYMBOL voltage -752 432 R0 WINDOW 3 -366 360 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 2 {1/4/F} 10u 10u {1/4/F} {1/F} 5) SYMATTR InstName V1 SYMBOL voltage -1168 240 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 4 SYMBOL sw -624 880 R0 SYMATTR InstName S2 SYMATTR Value SWCH SYMBOL voltage -768 976 M0 WINDOW 3 43 129 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 2 {.245/F} 1u 1u 1m 2m 5) SYMATTR InstName V3 SYMBOL sw -512 1168 R0 SYMATTR InstName S3 SYMATTR Value SWCH SYMBOL voltage -656 1264 M0 WINDOW 3 59 141 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 2 {.501/F} 1u 1u 1m 2m 5) SYMATTR InstName V4 SYMBOL res -992 -320 M0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res -992 -112 M0 SYMATTR InstName R2 SYMATTR Value 100k SYMBOL cap -992 480 R180 WINDOW 0 24 56 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C1 SYMATTR Value 1000n SYMBOL nmos -832 48 M0 SYMATTR InstName TR2 SYMATTR Value 2N7002 SYMBOL res -704 -320 M0 SYMATTR InstName R3 SYMATTR Value 10k SYMBOL pmos -800 -432 M270 WINDOW 0 73 1 VRight 2 WINDOW 3 -21 -49 VRight 2 SYMATTR InstName TR1 SYMATTR Value AO3407 SYMBOL schottky -656 -224 M180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D2 SYMATTR Value BAT54 SYMATTR Description Diode SYMATTR Type diode SYMBOL res -464 -464 R0 SYMATTR InstName R4 SYMATTR Value 1k TEXT -1376 584 Left 2 !.tran 10 startup TEXT -1120 704 Left 2 !.param F=0.5 TEXT -1120 744 Left 2 !.MODEL SWCH SW(Ron=.1 Roff=100Meg Vt=1) TEXT -1168 -552 Left 2 ;TOGGLE POWER ON PUSH BUTTON TEXT -488 936 Left 2 ;BOUNCE ON MAKE TEXT -448 1216 Left 2 ;BOUNCE ON BREAK TEXT -520 -136 Left 2 !.model AO3407 PMOS(Level=3 Vto=-1.9\n+ Kp=15.5 Rs=35m Rd=15m Cgso=1.1n\n+ Cgdo=0.15n CBD=1.1n Is=1e-12 Vds=-30)

If you already have PCBs and if you've managed to reverse D and S for the AO3407 (which will be tricky because you can't just solder it on upside down) then there is likely and error somewhere else.

As well as the reversed D and S, the capacitor C1 look like it could be either short or open circuit. If that was carried to the layout then in either case the output won't turn on.

As far as I can tell the simulation works fine with a 2N7002 for TR2 and an AO3407 model with Vth = -1.9V

Half bright. That's the dimmer function.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

I have one running in my office. Works fine.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

I'll check that and let you know. Thx for confirming sim result !