TOOP227Y - HIGH VOLTAGE ON DRAIN
Hi all,
In order to test TOP227Y I mounted the Stand By Power Switch ilustrated on Figure 7 from TOP227Y datasheet. To avoid damage I inputed an external voltage of 15VDC and an adjustable voltage to TOP227Y control pin - Vc. When Vc was about 5,6V TOP227Y began oscillating. Om the other hand, my scope registered pulses on drain in the order of 134V (~40V RMS). So I realized that for 160VDC this will be greater than 700VDC (TOP227Y limit). I was using a TRANSFORMER I´ve got from an old power supply based on TOP220Y. The limit of 700V is RMS? Or this high voltage would damage it?
Comments
In Figure 7 there is no zener restricting input voltage. See figure attached.
Yes, you are right, I was looking at schem on page seven which has a 200 volt zener primary clamp. If you are seeing such a high voltage with 47K type RCD primary clamp then there must be something wrong with how you have hooked up transformer. It sounds like you are not getting flyback on secondary winding to be clamped by output. Check to see what kind of output voltage you have. There could be open circuit or phasingis incorrect. If you do not have proper hook-up of transformer then all the energy in transformer will go into primary clamp as you are now seeing.
Everything is running fine now. The key point was that the transformer´s output voltage was too low in such a way that PC817A diode was not beeing polarized (Vout << Vz). Now Drain voltage was oscillating all the time and control voltage is constant. A few days ago Vc has a sawtooth and drain was oscillating, stopping oscillating and oscillating back - i.e., autorestarting).
Every time I connect an external 160Vdc power supply to the SMPS circuit (from Datasheet) the external power supply burns (Fuse and Line filter). The TOP circuit is not affected. What could be happening? The transformer used in my application I got from a PC power supply. I do not know its parameters (like inductance, etc). On the other hand if I used an external power supply of 60Vdc, everything works fine. I think that the current driven by this transformer is big due to its inductance (high). Could you please help me?
During tests I used a fixed dc voltage bench power supply lmited o 60Vdc. When I built the input rectifier (that gives abaout 162Vdc) the fuse blown up. I am using a transformer I´ve got from an ATX PC PSU. In reality I do not know its parameters. Could you please help me identifying the cause to this problem?
The zener clamp shown on the schematic figure you refer to will resrtict the drain voltage to be 200 volts above the input voltage.