SG3524

[Marco_Mar]

Hi All!
Just for fun and education about DC/DC converters, I made up this circuit where IC1 is SG3524 (REGULATING PULSE WIDTH MODULATOR).
Well, it does not work because R10 can't set Vout but I got a hint I'd like to share.

Troubleshooting tests:
- VREF at PIN 16 (5V) -> OK
- Pulses on PIN3         -> OK
- between PIN 1 and PIN2 (IN- and IN+ inputs of internal error amplifier) there is a voltage drop of about 1 V. . Do you think is ok? I expected to read 0V.


Thank you for your help

[strawberry]

IC hit duty cycle limit or feedback oscillation

[Marco_Mar]

Thank you.
Pulses on PIN3 are very narrow (Duty Cycle around 0,4%) whilst outputs (PIN11 and PIN14) are always at 50% DC.
Can't detect any oscillation on the feedback path.
Do you suspect a bad IC1?

Bye

[eblc1388]

SG3524 is perfectly fine and working correctly.

Is the wanted output voltage too low? If yes, then the pri/sec turn ratio of the transformer is incorrect. Where did you get the transformer or have you DIY it yourself?

If the output voltage is too high, then the value of resistors in the feedback path is wrong.

[Marco_Mar]

Thank you.
Your hints make me suspect about transformer (got from surplus).
As soon as I can, I'll check it out.

Bye