DPA switch--duty cycle changes only with line voltage only ...?
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
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.
Voutput2 = 6.13 V @ 0.4A@40v INPUT and 8.17v @ 0.4a @70v input...
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...?
Comments
I will check what are all the parameters u said. And pls find the attached for your reference .Incase if any issue in schematic,pls let me know sir...
I quickly checked the schematic, it really looks fine for me. But I also noticed that no soft finish cap (C10 in Datasheet Fig 26) in the circuit, hopefully this is the root cause. The soft finish cap can ensure some current through the opto during initial start up. If the board not work with soft finish cap, it is highly possible that the issue is caused by the wrong transformer.
Hi,
As per your instruction, i have added the soft-start capacitor at the output and tested it. It was working well at half of the load in each windings .
ie..,
Vout = 4.85V @ 0.5A @ all range of inputs(50% of load)
Vout2 = 13.25 @ 0.25A @ all range of inputs (50% of load)
Then i increased the main load as 0.8 A and i tested it, the DPA425PN gets heating at minimum voltage and also there is a HIGH oscillation in the input side and blown out after few seconds .
Why the dpa425pn blown out ,what will be the reason.... ?
Based on your description,the blew up should be caused by thermal. I guess the root cause is the snubber; Reverse recovery time of the IN4935 maybe too long for this application. Try to use a diode with ultra fast reverse recovery time. I guess this issue should be much better with a faster recovery diode. A resistor around 10 ohm may help too, place the resistor in series with VR1 and D1. Voltage stress will be higher for sure, but the thermal problem should be better.
0.1uF for C1 is too low for this application, i guess at least 4.7uF should be used for your design.Higher value input cap can improve the blew up issue too.
I have designed dc-dc converter input 18v to 30v using dpa426 -output 5v -1 amps, 12,-12v .0.3a 15v -100mA, 8v ,300mA during ON 18v gets oN . when i reduce supply 17.7 gets unstable. 17v to 18v gets unstable output means. i guess dpa switch trying to build the ouput voltage not could so it went soft start then gets error. how do resolve linse sensing
linse sensing increased 20v because i thought energy not enough to build the output voltage. but still isues 19v to 20v getting auto restarting happening. how do resolve the issues.
Hi gopu,
Thank you for your interest of using Power Integrations' part.
You can vary line sensing with Lresistor value. You can also connect Lpin to ground to disable line sensing. Can you send me your schematic so I can figure out better your problem. Thanks.
no doubt that something wrong in your circuit. Check the line sense resistor, modify the X pin resistor to increase the current limt, make sure the transformer is what you want, and also make sure the primary side bias voltage is high enough. I guess the problem is really caused by the wrong direction of your transformer or the too low primary side bias.If the issue can not be fixed after these corrections/modifications, PLS upload a schematic.