Thread: Presslab a problem... again

Dude its not going to work without optocoupler... The IC requires a feedback voltage to make any corrections as required if the voltage goes up or down...
Most PSU do have optocoupler no days it also used for seperation the primery section from the secondary incase of high voltage spikes.
So either you need to install an optocoupler in your PS or find a PS that has one on board.

The ATX PSU i bought has 3 instead of one.

fosgate, I'm not worried about the voltage feedback. I'll see about that when I know it works, also on the sec. side of my PSU there is also a PWM, so I suppose thatt this will regulate the voltage also.

What I am worried about is wether my circuit will work atall. So for now I don't care if it outputs a wrong voltage, as long as it outputs anything, right now that's not the case, I'm thinking it has something to do with the on/off opto lead.

To put it in simple words... With the current design that circut wont work without opticoupler.
Basically the IC wont run as it should without feedback signal/voltage.

Marsjell,

The way the circuit is set up now it requires an optocoupler set up for the best regulation. You can connect the voltage feedback lead to one of the outputs (perhaps 3.3V or 5V) and that will work as well. You may have to change the resistor values in the feedback divider, so you get the input in range for the PWM IC. I found that this does not lend to as good of regulation, because they have some compensation circuit on the secondary that averages all the output voltages for the feedback. This circuit connects to the opto coupler, and that is why I used that for regulation.

The on/off lead can be connected to ground, for testing, but if you want the ATX power on/off to function you'll need some way to hook it up to an open collector driver, that goes low when the supply is turned on.

Presslab

presslab,

The supply seems to work, well sort of.. I have a perfect 3.3V & -5.0V output, +12V, +5V & -12V are way off, both -12V is at -26V, +12V at +26, +5 at +8,5.
Do you what this could be? I'm guessing I did something wrong winding the sec. side. I hope this is not the case, as I didn't much enjoy winding the transformer....

2nd question, the transformer humms, can this do any harm? do you know why it does that?

Hmmm seems that the humming came from a supply that didn't have enough power. I tried the circuit using an old AT supply, this seemed to stop the humming but...

using this at supply the two irf540 got very very hot very quick, is this normal? I haven't attached them to a heatsink yet, but they got so damn hot, without any device connected, will they get hotter once there are devices connected?
Also while using the at supply, the +8V & +26V seemed to drop pretty quick, I don't know if they will drop to 5V & 12V, something started smoking so I shutdown the at supply. If they drop to the voltages required, I don't think the devices will be able to handle the voltages as it takes several seconds to drop, or will they?


thanks,
Marcel

[ 12-15-2001: Message edited by: marsjell ]