P-channel MOSFET model

What's your application? If it's plain vanilla slow switching, one of the library parts will work fine, something with similar Rds-on maybe.

LED lighting.

I was thinking of doing some thing similar to this.

But with a FET and a more symmetrical drive circuit such as an NCS2250 comparator capacitively coupled to the FET.

So I can perhaps make it switch faster and more efficiently and with a smaller inductor.

I'm aware that this might sound crazy but it's just for fun and no-one will die if it doesn't work.

Since the parts aren't very expensive in small quantities I might get a board made if a simulation says it has a chance of working.

It will be powered from a 12V lead acid battery.

Why not just ask Torex for a Spice model?

You'd have to type or paste it into your simulation, but that's easy enough. I've done it with some Philips parts, and some of the of the .asc files have been posted here.

gets you the data sheet, but that doesn't include a Spice model.

I might just do that. They'll probably ask how many hundred thousand parts I want. This page might be useful for making an approximate model from the data sheet.

Infineon BSS215P might be more suitable for the FET. That does have a simulation model.

'll have to look into how compatible the model is with LTspice.

Microchip TC105 is also interesting but a bit pricey. However it does lead to CD54NP as a possible choice for the inductor. MA737 doesn't seem to be easily available but a suitable shottky diode shouldn't be hard to find.

Vishay SI2371EDS-T1-GE3 looks interesting too. Not too pricey for lower on resistance.

Some of the TI TPS5- series buck switchers are 19 cents.

Your circuit looks like a good way to blow up transistors.

If you mean the circuit on this page

it is but that's not my circuit it's just a site I found showing the concept I'm looking into. I'll let you know if I manage to simulate anything which might have a chance of working.

>

May need to fix line wraps too.

That works in simulation, but the hazard of ac coupling into the fet gate is that it has a hangup state, the fet on hard forever and nothing limiting the current but 12 volts into the load.

It also grunts at startup, fet full on until the +5 settles. That could cave in a wimpy +12 supply, and it may never run right. The diode will leak more than the fet gate, so the static default is fet on. Just remove "startup" to see the hang state.

You could power a comparator from +12, dc couple into the gate, and slow down the startup. Something like that. Using all discrete transistors would be fun too.

You could just buy a switcher chip and copy the appnotes, as many people do, but you wouldn't learn anything. I know a guy who started a pretty cool company just copying eval boards, but then he started day trading....

The Brat assigned me to do a giant Spice sim this weekend, a dual isolated buck switching power supply that's in trouble, so I'm almost Spiced out.

The sim is all analog, but the actual control loop will be digital, in a small FPGA. One tricky part is that the two supples can be used independently or in parallel, and the loads can be anything, with remote sense.

...

I agree that there's plenty of scope to get 12V out instead of 5V. I had the comparator with it's own 5V source for a while so it wasn't dependent on creating its own supply rail. I also agree that a real circuit may not behave like the simulation and may just sit there producing 12V. But that's a useful lesson in the difference between the simulation model and the real thing. A crowbar and a fuse is one way to fix the hanging fet problem. And if it's an LED lighting circuit it's likely no-one would care. You just have to buy a new unit. Either that or just a suitable fuse should take care of over current as is sometimes done to stop people paralleling too many christmas tree lights.

One of the goals is to see what the minimum component count/cost is. Putting in a beefier inductor and schottky says it can do 5V at 5A no problem as long as the fet doesn't stick on all the time. I haven't looked at the efficiency but it looks like it's reasonably high. I probably will do the comparator discrete to see what the minimum comparator I can get away with is.

There's no fun in going back to the way I did most designs 20 years ago.

Your circuit also looks like it takes a while to get going. And plenty of post filtering. I always took the view that if it can be done perfectly fine without digits then leave the digits those who can't cope with anything other than digits. But I have done power supplies with digital control loops before.

What I really want is a low cost 12V to LED current converter but then where would I get the comparator supply from? Maybe directly from the input side, or another winding on the inductor.

It would be interesting to put two of my circuits in parallel. I think they would auto synchronize.

One of the issues with my circuit is what happens with no load.

68 ohm half watt fixes it in simulation but what happens in reality is anybody's guess.

On 06/05/2024 06:58, Edward Rawde wrote:

LED loads shouldn't care if ground referenced or not so you could use a N-channel MOSFET instead - saves a cent and gives more choice of device.

LEDs shouldn't mind if the current is not smooth. If the inductor is big enough the current can be kept approximately continuous and you can save the output capacitor - perhaps the least long lived part in real life.

Here is my idea of a simple converter, biggest efficiency hit is probably the sense resistor R5. I think the hysteresis determined by R3 may need fine tuning. This circuit has no capacitors, timing is dictated by the inductor solely. I think adding a small capacitor from M1 drain to Q1 collector could extend on-time and improve gate drive? Lots of scope for fiddling.

Version 4 SHEET 1 1256 680 WIRE 64 -112 -144 -112 WIRE 256 -112 64 -112 WIRE 496 -112 256 -112 WIRE 752 -112 496 -112 WIRE 752 -96 752 -112 WIRE 64 -32 64 -112 WIRE 752 16 752 -16 WIRE 752 16 128 16 WIRE 256 64 256 -112 WIRE 64 96 64 64 WIRE 496 96 496 -112 WIRE 752 96 752 16 WIRE -144 144 -144 -112 WIRE 64 192 64 176 WIRE 128 192 64 192 WIRE 496 192 496 160 WIRE 496 192 208 192 WIRE 496 224 496 192 WIRE 544 224 496 224 WIRE 752 224 752 160 WIRE 752 224 624 224 WIRE 496 240 496 224 WIRE 256 320 256 144 WIRE 448 320 256 320 WIRE 256 336 256 320 WIRE 64 384 64 192 WIRE 192 384 64 384 WIRE 64 400 64 384 WIRE -144 496 -144 224 WIRE 64 496 64 480 WIRE 64 496 -144 496 WIRE 256 496 256 432 WIRE 256 496 64 496 WIRE 496 496 496 336 WIRE 496 496 256 496 WIRE -144 560 -144 496 FLAG -144 560 0 SYMBOL voltage -144 128 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL nmos 448 240 R0 SYMATTR InstName M1 SYMATTR Value FDS6612A SYMBOL schottky 512 160 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value 1N5817 SYMATTR Description Diode SYMATTR Type diode SYMBOL ind 640 208 R90 WINDOW 0 5 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName L1 SYMATTR Value 220µ SYMBOL LED 736 96 R0 SYMATTR InstName D2 SYMATTR Value LXK2-PW14 SYMATTR Description Diode SYMATTR Type diode SYMBOL res 736 -112 R0 SYMATTR InstName R5 SYMATTR Value 1.2 SYMBOL res 240 48 R0 SYMATTR InstName R4 SYMATTR Value 3k SYMBOL pnp 128 64 R180 SYMATTR InstName Q1 SYMATTR Value 2N3906 SYMBOL res 48 384 R0 SYMATTR InstName R2 SYMATTR Value 3k SYMBOL res 224 176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 62k SYMBOL npn 192 336 R0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 48 80 R0 SYMATTR InstName R1 SYMATTR Value 3k TEXT 736 560 Left 2 !.tran 10m TEXT 664 400 Left 2 ;EPW SED May 2024 TEXT 624 448 Left 2 ;Simple LED buck smps

piglet

<snip>

Cutting and pasting piglet's .asc file into my version of LTSpice gave a circuit that didn't do anything useful. M1 turns off after 2.67usec., and that's it.

Damn! You are right, some thing strange happened with L1 value. The mu symbol comes out wrong on a second system. Either retype as 220u or as

0.22m and see if that works better?

On 09/05/2024 02:21, Edward Rawde wrote:

I thought you wanted to drive LEDs? But if you really wanted 12V to ground referenced 5V then here is my offering ...

Version 4 SHEET 1 912 680 WIRE -496 -160 -720 -160 WIRE -224 -160 -496 -160 WIRE -48 -160 -224 -160 WIRE 176 -160 -48 -160 WIRE -224 -80 -224 -160 WIRE -48 -80 -48 -160 WIRE -496 -32 -496 -160 WIRE -128 -32 -160 -32 WIRE -112 -32 -128 -32 WIRE -128 32 -128 -32 WIRE -48 32 -48 16 WIRE -48 32 -128 32 WIRE 176 48 176 -160 WIRE -224 64 -224 16 WIRE 128 64 -224 64 WIRE -720 160 -720 -160 WIRE -336 160 -368 160 WIRE 176 160 176 144 WIRE 176 160 -256 160 WIRE 176 208 176 160 WIRE 256 208 176 208 WIRE 416 208 336 208 WIRE 512 208 416 208 WIRE 704 208 512 208 WIRE -224 224 -224 64 WIRE -48 224 -48 32 WIRE 512 240 512 208 WIRE -496 272 -496 48 WIRE -464 272 -496 272 WIRE -368 272 -368 160 WIRE -368 272 -384 272 WIRE -288 272 -368 272 WIRE 416 272 416 208 WIRE 416 272 16 272 WIRE 704 288 704 208 WIRE -496 336 -496 272 WIRE -224 336 -224 320 WIRE -144 336 -224 336 WIRE -48 336 -48 320 WIRE -48 336 -144 336 WIRE 512 336 512 304 WIRE 176 352 176 208 WIRE -144 384 -144 336 WIRE -720 496 -720 240 WIRE -496 496 -496 400 WIRE -496 496 -720 496 WIRE -144 496 -144 464 WIRE -144 496 -496 496 WIRE 176 496 176 416 WIRE 176 496 -144 496 WIRE 512 496 512 416 WIRE 512 496 176 496 WIRE 704 496 704 368 WIRE 704 496 512 496 WIRE -720 544 -720 496 FLAG -720 544 0 SYMBOL pmos 128 144 M180 SYMATTR InstName M1 SYMATTR Value RRR030P03 SYMBOL schottky 192 416 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D2 SYMATTR Value 1N5817 SYMATTR Description Diode SYMATTR Type diode SYMBOL ind 240 224 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L1 SYMATTR Value 0.047m SYMBOL cap 496 240 R0 SYMATTR InstName C1 SYMATTR Value 0.1m SYMBOL res 496 320 R0 SYMATTR InstName Resr SYMATTR Value 0.1 SYMBOL npn -288 224 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL npn 16 224 M0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL pnp -160 16 R180 SYMATTR InstName Q3 SYMATTR Value 2N3906 SYMBOL pnp -112 16 M180 SYMATTR InstName Q4 SYMATTR Value 2N3906 SYMBOL zener -480 400 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value UMZ5_1N SYMBOL res -160 368 R0 SYMATTR InstName R4 SYMATTR Value 330 SYMBOL res -368 256 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 1.5k SYMBOL res -480 64 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R1 SYMATTR Value 1.5k SYMBOL res 720 384 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName Rload SYMATTR Value 5 SYMBOL voltage -720 144 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res -240 144 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 150k TEXT 494 552 Left 2 !.tran 10m TEXT 496 -160 Left 2 ;EPW SED MAY 2024 TEXT 440 -112 Left 2 ;SIMPLE BUCK 12V TO 5V

piglet

Switching to 220u did solve the problem. I should have noticed.

Radiating 150kHz from a remote lamp isn't great idea.

This variation on the circuit slows the switching to 16kHz, but doesn't do anything for the amplitude. Some gain along the feedback path would cut the reduce the current excursions through D2 and the radiated noise.

Replacing Q2 with an LM358 might do it.

Version 4 SHEET 1 1340 680 WIRE 64 -112 -144 -112 WIRE 256 -112 64 -112 WIRE 496 -112 256 -112 WIRE 1008 -112 496 -112 WIRE 1008 -96 1008 -112 WIRE 64 -32 64 -112 WIRE 1008 16 1008 -16 WIRE 1008 16 128 16 WIRE 256 64 256 -112 WIRE 64 96 64 64 WIRE 496 96 496 -112 WIRE 1008 96 1008 16 WIRE -144 144 -144 -112 WIRE 64 192 64 176 WIRE 128 192 64 192 WIRE 496 192 496 160 WIRE 496 192 208 192 WIRE 496 224 496 192 WIRE 544 224 496 224 WIRE 656 224 624 224 WIRE 736 224 720 224 WIRE 752 224 736 224 WIRE 864 224 816 224 WIRE 880 224 864 224 WIRE 1008 224 1008 160 WIRE 1008 224 944 224 WIRE 496 240 496 224 WIRE 256 320 256 144 WIRE 448 320 256 320 WIRE 736 320 736 224 WIRE 864 320 864 224 WIRE 1008 320 1008 224 WIRE 256 336 256 320 WIRE 64 384 64 192 WIRE 192 384 64 384 WIRE 64 400 64 384 WIRE -144 496 -144 224 WIRE 64 496 64 480 WIRE 64 496 -144 496 WIRE 256 496 256 432 WIRE 256 496 64 496 WIRE 496 496 496 336 WIRE 496 496 256 496 WIRE 736 496 736 384 WIRE 736 496 496 496 WIRE 864 496 864 384 WIRE 864 496 736 496 WIRE 1008 496 1008 384 WIRE 1008 496 864 496 WIRE -144 560 -144 496 FLAG -144 560 0 SYMBOL voltage -144 128 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL nmos 448 240 R0 SYMATTR InstName M1 SYMATTR Value FDS6612A SYMBOL schottky 512 160 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value 1N5817 SYMATTR Description Diode SYMATTR Type diode SYMBOL ind 640 208 R90 WINDOW 0 5 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName L1 SYMATTR Value 220µ SYMATTR SpiceLine Cpar=1p SYMBOL LED 992 96 R0 SYMATTR InstName D2 SYMATTR Value LXK2-PW14 SYMATTR Description Diode SYMATTR Type diode SYMBOL res 1008 -64 R0 SYMATTR InstName R5 SYMATTR Value 1.2 SYMBOL res 256 96 R0 SYMATTR InstName R4 SYMATTR Value 3k SYMBOL pnp 128 64 R180 SYMATTR InstName Q1 SYMATTR Value 2N3906 SYMBOL res 64 432 R0 SYMATTR InstName R2 SYMATTR Value 3k SYMBOL res 176 192 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 62k SYMBOL npn 192 336 R0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 64 128 R0 SYMATTR InstName R1 SYMATTR Value 3k SYMBOL FerriteBead 688 224 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L2 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f SYMBOL polcap 992 320 R0 WINDOW 3 24 56 Left 2 SYMATTR InstName C1 SYMATTR Value 22µ SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=16 Irms=0 Rser=1.6 Lser=0 mfg="AVX" pn="TAJC226K016" type="Tantalum" SYMBOL FerriteBead 784 224 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L3 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f SYMBOL polcap 720 320 R0 WINDOW 3 24 56 Left 2 SYMATTR InstName C2 SYMATTR Value 22µ SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=16 Irms=0 Rser=1.6 Lser=0 mfg="AVX" pn="TAJC226K016" type="Tantalum" SYMBOL FerriteBead 912 224 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L4 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f SYMBOL polcap 848 320 R0 WINDOW 3 24 56 Left 2 SYMATTR InstName C3 SYMATTR Value 22µ SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=16 Irms=0 Rser=1.6 Lser=0 mfg="AVX" pn="TAJC226K016" type="Tantalum" TEXT 736 560 Left 2 !.tran 10m TEXT 1112 232 Left 2 ;EPW SED May 2024 TEXT 1072 280 Left 2 ;Simple LED buck smps

If you add a small resistance in series with the inductor, the loop is forced to run semi current mode, which will also help on startup behaviour:

Version 4 SHEET 1 912 680 WIRE -496 -160 -720 -160 WIRE -224 -160 -496 -160 WIRE -48 -160 -224 -160 WIRE 176 -160 -48 -160 WIRE -224 -80 -224 -160 WIRE -48 -80 -48 -160 WIRE -496 -32 -496 -160 WIRE -128 -32 -160 -32 WIRE -112 -32 -128 -32 WIRE -128 32 -128 -32 WIRE -48 32 -48 16 WIRE -48 32 -128 32 WIRE 176 48 176 -160 WIRE -224 64 -224 16 WIRE 128 64 -224 64 WIRE -720 160 -720 -160 WIRE -336 160 -368 160 WIRE 176 160 176 144 WIRE 176 160 -256 160 WIRE 176 208 176 160 WIRE 256 208 176 208 WIRE 384 208 336 208 WIRE 400 208 384 208 WIRE 608 208 480 208 WIRE 800 208 608 208 WIRE -224 224 -224 64 WIRE -48 224 -48 32 WIRE 608 240 608 208 WIRE -496 272 -496 48 WIRE -464 272 -496 272 WIRE -368 272 -368 160 WIRE -368 272 -384 272 WIRE -288 272 -368 272 WIRE 384 272 384 208 WIRE 384 272 16 272 WIRE 800 288 800 208 WIRE -496 336 -496 272 WIRE -224 336 -224 320 WIRE -144 336 -224 336 WIRE -48 336 -48 320 WIRE -48 336 -144 336 WIRE 608 336 608 304 WIRE 176 352 176 208 WIRE -144 384 -144 336 WIRE -720 496 -720 240 WIRE -496 496 -496 400 WIRE -496 496 -720 496 WIRE -144 496 -144 464 WIRE -144 496 -496 496 WIRE 176 496 176 416 WIRE 176 496 -144 496 WIRE 608 496 608 416 WIRE 608 496 176 496 WIRE 800 496 800 368 WIRE 800 496 608 496 WIRE -720 544 -720 496 FLAG -720 544 0 SYMBOL pmos 128 144 M180 SYMATTR InstName M1 SYMATTR Value RRR030P03 SYMBOL schottky 192 416 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D2 SYMATTR Value 1N5817 SYMATTR Description Diode SYMATTR Type diode SYMBOL ind 240 224 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L1 SYMATTR Value 0.047m SYMBOL cap 592 240 R0 SYMATTR InstName C1 SYMATTR Value 0.1m SYMBOL res 592 320 R0 SYMATTR InstName Resr SYMATTR Value 0.1 SYMBOL npn -288 224 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL npn 16 224 M0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL pnp -160 16 R180 SYMATTR InstName Q3 SYMATTR Value 2N3906 SYMBOL pnp -112 16 M180 SYMATTR InstName Q4 SYMATTR Value 2N3906 SYMBOL zener -480 400 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value BZX84C6V2L SYMBOL res -160 368 R0 SYMATTR InstName R4 SYMATTR Value 330 SYMBOL res -368 256 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 1.5k SYMBOL res -480 64 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R1 SYMATTR Value 1.5k SYMBOL res 816 384 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName Rload SYMATTR Value 5 SYMBOL voltage -720 144 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res -240 144 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 150k SYMBOL res 496 192 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 0.1 TEXT 496 552 Left 2 !.tran 10m TEXT 496 -160 Left 2 ;EPW SED MAY 2024 TEXT 440 -112 Left 2 ;SIMPLE BUCK 12V TO 5V