High Voltage at no load; ver 2

Posted by: rpaitich@gmail.com on 05/10/2009

I have a problem similar to the one described by jquintela a few days ago.

My supply is 600 vdc, switchable to 140 vdc.

I tried the wired diode-OR suggested in jquintela's thread. It works well to 100 VAC input; above 100 VAC, the 140 vdc mode goes too high. Any other suggestions? My schem is attached. (to configure for 600 vdc, connect TP6 to 5 vdc))

Ron

Files

600_140VDC.pdf (47.73 KB)

Comments

Hi,

Please provide us detailed description of the problem that you are experiencing and the results of any experiments that you may have conducted.

Regards

PI-Sarek

Hi, and thanks again, Sarek.

Details:

If I configure the supply for 600 VDC (conn Q5 gate/TP6 to +5) I get 600 VDC with light to max load (10 W).

If I config the supply for 140 VDC (open Q5 gate) and load it lightly (100 mW), the ouput goes above the target 140 VDC, maybe to 200 VDC.

Also, if i run it on 240 VAC input, the TOPSW vaporizes with a pop. I don't have a 100:1 'scope probe yet, so I can't assess what's wrong - I suspect it has to do with the P6KE200 and MUR160 snubber. The probe will be in this week, and I'll take a look.

I'm beginning to conclude that the wide range of voltage of power is not a good match for TOPSW designs. I'm about to try it with a UC3526 and a 24 VDC xfmr. I had good results with this approach for a 50 W 8 kV supply. ...but I love the unviersal off-line designs, so if you have more that I should try, pls let me know.

FWIW, I've had a great deal of success with your parts in 15-24 VDC supplies, so I'm not a novice. But this is my first effort at high voltage.

Best regards,

Ron

Hi,

Could you please provide us some details of your transformer as well? Specifically I will need the turns ratio and the inductance of the primary winding. If you have any design calculations or PIExpert/PIXLs files that will be very useful.

Please also attach a copy of your board layout.

Thank you,

Regards

PI-Sarek