TOP254EN stop running
Hello,
I have designed a dc-dc converter for 90-260V input to 5V regulated and 24V.
My problem is that sometimes, at 260V the switch stop working and can't do an autostart. I have to kill the line voltage, wait till the DC voltage is gone and the he is able to start again.
It happend mostly under full load (each at 0.5A) and sometimes in idle run.
Sometimes this happens even when there is 250V, then at 265V he ran throught.
When I removed the resistor RK13, this phenomenon does not appear. But the voltage across this resistor never exceeds 100mV, which means a current of about 20µA in the Voltage Monitor Pin.
So I think the OV-protection shuts my switch down?
Mfg
Comments
Thanks for your quick reply.
to 2: The Bias voltage never exceeds 12.5V.
to 3: At first, reducing the line voltage does not work, but after removing the capacitor CK13 the device starts up by reducing it.
to 1: I tried but the problem stays on.
Now there happens something new. I have a LED on each output to see if there is voltage.
I adjust the line voltage on 260V. The power supply works a while (few minutes), then the LEDs start blinking. ON for a moment, OFF for about 3.5 seconds In the OFF-phase, I can see the 4.8V-5.8V ripple voltage for about 30 cycles on the control pin. Then the 5V rise for a short time but then it is over again.
Like in the picture enclosed(blue: 5V output, red: control pin voltage).
When I observed this behavior, I could notice that the ON-time varies, once longer, once shorter.
When I lower the voltage on e.g. 257V it works, but after a while the same as above happen. The same after reducing then to 255V.
But when the LEDs are blinking, and I remove only the load on the 5V output, from the next ON-State it works fine. Until I load the 5V again.
Mfg,
The secondary diode (DS2) for the 5V output has a PIV rating of 20V. I would recommend probing the voltage across this diode and make sure the PIV value is not exceeded. For this diode, at 250V(DC) input and 5V(DC) output, the ratio of secondary turns to primary turns should be less than 0.06 to avoid hitting the PIV voltage. Check to see if this solves your problem!
I have just solved the problem.
DS3 is a schottky-diode, but it should be a Z-diode. Now everything works :)
Mfg,
I would recommend the following:
1. Instead of connecting the cathode of DS3 between DU1 and RK10, connect it after CE7 so that some sort of low-pass filtering exists and check if the problem persists.
2. Monitor the voltage across the bias winding (junction of DU1,RK10,DS3); is this voltage hitting the over-voltage limit?
3. Once the device enters the latch-up state, reduce the line-voltage and check if the device starts up again without having to power-cycle.