dc/dc converter --testing issue- suggest ur points
Hi,
I have designed 17W DC to DC power supply using DPA425PN switch. The specification are
Input Voltage : 32 -72Vdc
Output 1 : 5V @ 1A ( REGULATED )
Output 2 : +12V , -12V @ 0.5A
Now testing is going on process. when we power up the device ,at no load,the mains windings gives 4.99V and other windings gives +27V and -27V ( rather than 12V ).
How to solve this issue. How to reduce this voltage level at no load?. I think i should use bleeder resistor across the 12V output windings to make as dummy load at no load condition ... (when we put the load,the voltage being reduced to 13v )
Is that ok ...? What should be allowable current to calculate bleeder resistance....?
And also I didnt add a SOFT-FINISH network at the feedback circuit..Is that ok ..? or i should add it....?
Comments
Hi,
I have loaded the outputs gradually.. when the load increase ,the regulated output voltage (5V) decreasing..
Vout = 2V @ 0.8A load @ 40v INPUT and 3.08V@0.8A @ 70V input...((actual voltage 5V @ 1A maximum load))
Voutput2 = 6.13 V & 0.4A@40v INPUT AND 8.17v @ 0.4a @70v input...
(( actual voltage +12V,-12V @ 0.5A maximum load))
WHATEVER MAY BE THE LOAD, THE DUTY CYCLE SHOULD CONTROL THE OUTPUT AND SHOULD GIVE THE REGULATED 5V BY INCREASING DUTY CYCLE...BUT HERE,NOTHING LIKE THAT.. THE DUTY CYCLE CHANGES WITH RESPECT TO LINE VOLTAGE ...
HOW TO SOLVE THIS ISSUE AND HOW TO MAKE THE CONSTANT REGULATED VOLTAGE AT THE OUTPUT SIDE... ?
WHY THE OUTPUT VOLTAGE GETTING DECREASE IF WE INCREASE THE LOAD...?
Can i have your schematic?
it is normal that the unregulated output is higher at no load. The worst case always happens at 5V1A and +-12v no load. This cross regulation issue can be improved with more dummy load and better transformer design. Dummy load is a choice if your efficiency and no load power can meet SPEC, and try different transformer configurations to see if the problem can be improved too.
Soft finish is used for monotonically start up. If no over shoot at output and no voltage stress issue during start up, then soft finish circuit is not necessary.
Thanks for using PI part.