Variation in External current limit value varies turn on & over voltage cut off values. Please guide me to modify circuit.
Dear sir,
By using Top259 we designed 60W flyback converter of 24Vdc, 2.5A with input range 85 Vac -300Vac. With X pin resistor value of 8.2k ohm. Power supply turns on at 75 Vac and input over voltage cut off at 300 Vac with 2.5A load with output voltage of 24Vdc. But over load cut off occur at 5A. But we need over load cut off at 3A. By varying X pin resistor value to 20k ohm, now overload cut off takes place at 3A. But power supply turns on at 150 Vac and over voltage cut off is occur at 320. over voltage recovery delays very much. And increase in Top259 heat sink temperature upto 80 deg cent. we used 27V Zener with 5.1k ohm at bias winding connected to V pin, 1.8M ohm in series with1.5M ohm connected to V pin. Please give me suggestions and what changes we need to do.
Thank you...
Comments
Ok i ll refer it.. Thank you very much..
Dear sir,
Ok i ll refer it, Thank you very much.
From the sounds of it, you're probably going to need to implement the current limit reduction with line voltage feature. This is detailed in figure 23 of the TopSwitch-HX datasheet. You can use this configuration in conjunction with the standard V-pin configuration to give you UV/OV and line sensing/feed forward.
The external current limit reduction with line-voltage feature should help limit the maximum output power at high-line while still keeping low-line operation as you intended. You might have to experiment with some different values of resisters but the starting values in the datasheet should get you pretty close.
If you require an extremely precise output current limit, you'll need to create some additional current sensing circuitry on the secondary side of your power supply. This will likely require an additional optocoupler.
-The Traveler