top switch doesnt make switching...

Posted by: instinct on 05/26/2009

ı designed a high voltage output flyback. my feedback circuit
is primary enh.ı used top244y, eı35 transformer. 2 Mohm for L pin,12 kohm for X pin, f and c pin short cut(66 kHZ).on bias winding ı used uf4005 and 0.1 uF capacitor.on secondary winding ı used ux-fob diode.on primary ı used bvy26c and p6ke180 zener diode.

the problem is that topswitch doesn't make switching. we have a short time to make this circuit. we maker your helps.

thanks..

Comments

Using an oscilloscope, verify that the control pin voltage is between 5.8 and 6.3 Volts. If it is below 5.8 volts, check to see if the control pin is being loaded down by a short or by an external circuit. Check to see if the drain voltage is between 36 VDC to 400 VDC. Verify that the source pin is not open. Verify that the L pin is getting the proper current. You can connect the L pin to the source pin to disable the UVP/OVP function to see if the power supply starts. Verify that the X and F pins are properly connected.

If the power supply still doesn't not start, monitor the drain voltage and current with an oscilloscope and apply power. If the power supply begins to switch and then stops and repeats this operation. The device is in auto-restart mode. Verify that the feedback current into the control pin is greater than 2 mA.
Viewing the drain current, verify that the transformer primary winding is not saturating or shorted.

I hope this will help you troubleshoot your power supply.

Z. Cochrane

this is the problem: power supply makes switching then stops and repeats this operation...the current into the control pin must be greater than 2mA..ı will apply that..

thanks for your helps...

the current into the control pin must be greater than 2mA..ı will apply that..
what is the upper limit for the current into the c pin...

The operation you described is called auto-restart. If the control pin does not sense a feedback signal (feedback current less than 2 mA), the controller will go into the auto-restart mode.

Z. Cochrane

My desing still have same problem. i changed bias resistor (10 ohm, 30 ohm, 6.8ohm) but still it works for 2-3 seconds than stop for 2-3 seconds... i couldn't see that my circuit works continously... is it auto-restart problem or else? i have changed all my components on my circuit but i couldnt solve my problem...

Can you send me the schematic (in PDF) so that I can review it? Also send me oscilloscope photos of the drain voltage and drain current of the switching waveforms. I would like to see the on/off ratio of the auto-restart operation. Also the waveforms of individual switch cycle of the drain waveform.

Z. Cochrane

my circuit is same with pri. enh. feedback circuit in app. note 32. page 6 figure4.. I watched drain-source voltage on my circuit. Sometimes it starts to switching(about 4-5 seconds) but than suddenly it stops. After 5-6 seconds it starts again. I measured C pin voltage it was about 6 V when it is switching.. when it stops, C pin voltage drops to 5.2V...

I am giving all my component's name on my circuit; 1N4007 bridge diode, 47uf 450v electrolytic cap, P6KE180 zener diode, BVY26C diode, TOP244Y switch, UX-FOB diode for seconder wind, 47 nF 2000V cap not electrolytic for seconder cap, UF4005 for bias diode, 0.1uF cap (not electrolytic) for bias cap, 15 ohm resistor, 0.1uF cap under the resistor on bias, 0.1 cap between C pin and source,6.8 ohm resistor and 47 uf 50V electrolytic cap between C pin and source... I connected F and C pin for 66khz and connected x and S pin short-circuit, 1.8Mohm for L pin...

waiting for your advices,

thanks.

Try using a larger output and bias winding capacitors. Try 680 uF for the output capacitor and a 100 uF for the bias winding capacitor. If your problem goes away, then you need larger capacitors for loop stability.

Z. Cochrane