SMPS just finished

[Ford_V6]

Hy huys.

I have just built a SMPS using the attached shematic.

The problem is that instead of +/- 37 v i have +/- 60 v on the output.

R5 smokes up every time i power on the smps.

R5 is 460 ohm instead of 510 on the schematic
R7,15 are 1.8 ohm instead of 2 ohm on the schematic.

This 3 components i could not find like in the shematic. The rest is just like in the schematic diagram.

Could those 3 values that are not exact cause the fault ???

Thanks in advance for help.

[RobM]

Try a larger value for R5 (two 1-1.2k in parallel?) and make sure to load the outputs with something.

[JOE DIRT®]

definately put a permanent load on the output or else you will get oscillations

[jackinnj]

well, you have a lot of current going through that poor diode, no wonder it's smoking. You want the diode in the optocoupler to pass just enough current to get the duty cycle correct for the LM3524.

Make sure that the transformer is hooked up correctly. It's not hard to screw up the orientation of the leads in an SMPS power transformer unless you have wound it yourself.

If you are not going to isolate the primary and secondary -- you have them connected through 150R, you might just want to abandon the optocoupler anyway and feed the error amp from a resistive voltage divider attached to the positive leg.

[Ford_V6]

well, you have a lot of current going through that poor diode, no wonder it's smoking. You want the diode in the optocoupler to pass just enough current to get the duty cycle correct for the LM3524.

The resistor is smoking not the diode. The transformer is home made so it's hooked up well.

If you are not going to isolate the primary and secondary -- you have them connected through 150R, you might just want to abandon the optocoupler anyway and feed the error amp from a resistive voltage divider attached to the positive leg.

Can you detail this to me ? A schematic or something ??

Thanks in advance.

[MaXiZ]

I'm not sure to be of aid but try to contact me privately i've just build this SMPS with some variation...
Mail: maxiz@inwind.it
ICQ: 47573544
DIY thread: SMPS problem

[Ford_V6]

Any other ideeas or help ??

Thanks

[jackinnj]

first, I drew in a couple black circles to indicate the polarity of the transformer windings.
second -- there should be a resistor on the compensation network -- poles and zeroes you know
third -- the divider to the inverting input of the error amp should provide (you can adjust it) 2.5V at 37 volts, equalling the 2.5V from the reference voltage divider
fourth -- forget about isolating the two halves, use the same ground (I didn't take it out)

[MaXiZ]

The major changes that i've doneis remove the 150ohm resistor on transformer and remove pin10 from ground... try this before!

[MaXiZ]

If you don't have haste i'll post the schematic tonoght (for me) modifyed that i've build and run correctly.. anyway check if the buz become very hot in few second if so the problem is on the transformer.. Check that the winding are winded correctly, to cover all the surface.
Don't think i'm an expert but with the experience i've learned something... :P
I hope to be of help!
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