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Recent content by Ian1954

  1. Ian1954

    Power supply

    A piece of encapsulate is blown out leaving a hole in the device. The hole appears where I would think the internal power MOSFET is positioned. The failures, when they occurred, were instant on applying power. It certainly has the characteristic of a transient overvoltage causing avalanching of...
  2. Ian1954

    Power supply

    There isn't any added inductance. The supply is direct from the 3 phase supply. A simple 3 phase bridge to provide the DC and 20uF of smoothing capacitance. It could be resonance with the line inductance but the problem occurs so infrequently that I don't think that's the case. I have switched...
  3. Ian1954

    Power supply

    It could well be the external circuit causing the distress to the TOP268. I have scoped it. The drain to source waveform looks good. Very little overshoot. Maximum voltage is 420volts to the transient peak, 400volts is the DC bus plus the reflected secondary voltage. Only 20volts due to leakage...
  4. Ian1954

    Power supply

    The failed part is the TOP268. I've not used this part before. Never had a problem like this with other supplies I've designed. The fault occurs rarely. I've switched it on and off many times with no problem. The circuit can be found on the Power Integrations web-site...
  5. Ian1954

    Power supply

    I have designed a power supply using a TOP268 controller from Power Integrations. The supply generally works fine but has blown up 3 times during switch on. Has anyone had a similar experience and if so did you find the cause of the problem?
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