I don't know what that means.
Yes, I have looked at them, and they should work okay.
The MOSFET is rated for 20A.
That's why I asked for the node voltages to see if I could determine what might be wrong.
They should be fairly close to those shown in post #15.
That's a very small current.
Are you sure you don't mean 500mA and 900mA.

Yes, it's 500mA-900mA. I'm gonna just build a new one from scratch tomorrow or Sunday. I'm using used parts so something may be bad. I'll let you know immediately how it went. Thanks again! I'm glad you are helping folks like this. Very .

 

Yes, it's 500mA-900mA. I'm gonna just build a new one from scratch tomorrow or Sunday. I'm using used parts so something may be bad. I'll let you know immediately how it went. Thanks again! I'm glad you are helping folks like this. Very .

I'm going to use the N channel this time. It's rated for 64 Amps, so maybe it will let more current through? It seems to me with these FETs that the supply voltage and gate voltage play together as far as how much current it will let through.
Like my supply voltage is 12.5V. So 12.5V at the gate will let it all out. But 5V, nowhere near as much? But it should let one lousy Amp through I would think!

 

I'm going to use the N channel this time. It's rated for 64 Amps, so maybe it will let more current through? It seems to me with these FETs that the supply voltage and gate voltage play together as far as how much current it will let through.
Like my supply voltage is 12.5V. So 12.5V at the gate will let it all out. But 5V, nowhere near as much? But it should let one lousy Amp through I would think!

This schematic for the N channel does have the output at the source!And the supply at the drain

I'm going to use the N channel this time. It's rated for 64 Amps, so maybe it will let more current through? It seems to me with these FETs that the supply voltage and gate voltage play together as far as how much current it will let through.
Like my supply voltage is 12.5V. So 12.5V at the gate will let it all out. But 5V, nowhere near as much? But it should let one lousy Amp through I would think!

This schematic you gave me for the N channel has the supply voltage at the drain and output at the source. That seems to be the only difference. But the output voltage is one tenth less than the other. I'm assuming this is still enough for a full charge?

 

That seems to be the only difference.

No.
The gate is connected to the opposite NPN collector.

 

No.
The gate is connected to the opposite NPN collector.

Yes. I saw that too. The N channel is 35 Amps continuous and has a minimum Rds on at 5V. 10 Max. It's a power mosfet STD30NF 06LT4 60V 70 watts of dissipation. 175 Deg C.
I'm putting it together tomorrow.

 

No.
The gate is connected to the opposite NPN collector.

Ok. I switched the P channel FET with the N channel, as well as swapped the collector wires over to one another, and made sure the N channel was output 5V from the source.
Still only putting out a little over 200mA?
would putting on an additional parralell FET double the current? Or would it stay the same?

 

Here's a sim of a crude buck converter.
A standard multivibrator comprising two L6s drives a P-MOSFET to chop the 12V supply . The chopped supply has an average voltage set by the duty cycle of the multivibrator and is smoothed by L1 and C3 to give 5V out to the load. The duty cycle is adjusted by varying R2 or R3.
View attachment 187395

I would not recommend this for driving critical loads, since there is no negative feedback to regulate the output voltage.

I built this on my sim. The voltage is not changing by adjusting R2 or any for that matter?

 

I can't read the component values you used in that sim.

 

I built this on my sim. The voltage is not changing by adjusting R2 or any for that matter?

The image was virtually unreadable. This might be a little better:


You don't have any feedback to control the voltage.

 

Rather than trying to make your schematic more readable, I redrew it:


It shouldn't work. You have the wrong polarity of MOSFET and the one you have is connected wrong; the body diode will always be conducting.

I couldn't make out the value for R5 or the supply voltage.

 

Rather than trying to make your schematic more readable, I redrew it:
View attachment 192274

It shouldn't work. You have the wrong polarity of MOSFET and the one you have is connected wrong; the body diode will always be conducting.

I couldn't make out the value for R5 or the supply voltage.

It's not my design, the supply voltage is 12.5V

Rather than trying to make your schematic more readable, I redrew it:
View attachment 192274

It shouldn't work. You have the wrong polarity of MOSFET and the one you have is connected wrong; the body diode will always be conducting.

I couldn't make out the value for R5 or the supply voltage.

It's not my design and I don't know why the sim copy looks so bad here. It's crystal on my phone. But the supply voltage is 12.5V and the R5 value is 100 ohm.
I've been using the Crutschow differential regulator, but I'm only getting 250mA.I need at least 1000mA or more. Power supply is rated at 5.2A. The sim always shows it putting out over 1A. But it's not doing it. I was thinking buck converter may be the proper way to go.
There is a third wire coming off the power supply. I'm wondering if the cpap is telling the supply how much current to put out? Maybe I should either unhook, or hardwire?
Do you know how to build a regulated buck converter so I can set the voltage to 5V!
.

 

I can't read the component values you used in that sim.

Look down a little further. D1234 redrew the thing with values. R5 is 100 ohm, and he has the polarity reversed. The. Arrow on the FET should be pointing up instead of down. It works on the sim, but puts out 10.28V instead of 5V. No adjustment in this design. Or feedback.

 

Look down a little further. D1234 redrew the thing with values. R5 is 100 ohm, and he has the polarity reversed. The Arrow on the FET should be pointing up instead of down.

This is what it looked like when I zoomed in on the MOSFET;


Corrected schematic:

It works on the sim, but puts out 10.28V instead of 5V. No adjustment in this design. Or feedback.

The output voltage will depend on the frequency of the oscillator and the load.