TOP switch auto-restart behavior

Posted by: Markus86 on 06/30/2015

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Dear technical support team,

In a TOP266KG-based application we always short the LED of the regulating fotocoupler to provoke an overvoltage event in the end-of-line test to verify the protection circuits. In this case, the low voltage elko at the C-pin of the TOP-switch device would get the energy always from the high voltage DC-Link, so the resulting voltage waveform at the capacitor is a DC-biased sawtooth between 4,8 V and 5,8 V.

At page 5 of the datasheet is a description of the behavior of the TOP device if such an error occurs. There is written, that the internal MOSFET will only turn on again (auto-restart), after 16 periods of the capacitors charge/discharge cycles had elapsed. This principle has worked well in our prototype devices which were built up about three years ago, but in our actual device there is a start-up event in EACH cycle, that means every time the elko on pin C has charged to 5,8V! After some measurements I have soldered an ‘old’ TOP266KG (bought in February 2012) on the board and after this modification the device worked like the prototype (in compliance to the datasheet).

Thanks in advance for any hint!

Comments

Hi,

Kindly verify the behavior at high input voltage and low input voltage. If the behavior is different at high input voltage and and low input voltage with the newer part, I will be able to explain.

Regards,

Thanks for the response.

Could you give me that possible explanation please, i have to be sure, that the design works properly.

Thank you.

Hi,

In order for me to explain the behavior I will need to be sure of the observation. Are you confirming that the auto-restart time is small at low input voltage and becomes large(16 periods of C pin capacitor charge and discharge) as the input voltage is increased at least 10 volts above the line UV detection threshold?

Please confirm.

Regards,

PI-Sarek

Hello,

my Switcher is fed from a PFC preregulator, so the DC link voltage of the flyback converter is always about 390 VDC.

If your possible explanation depends only to the rail voltage of the converter, then the behavior of the switcher must have another background..

Kind regards, Markus

Hi,

Based on the information that you have provided, I do not believe that your observation fits the expected response.

Does the TOPSwitch power supply startup only after the PFc has started up or does it start before the PFC is turned ON?

Regards,

PI-Sarek

Hello,

the PFC stage is already in steady state, when this 'open-loop-failure'-test is started.

As I said already, with the TOPSwitches from February 2012 the design works well...

The only thing changed to make the circuit work is to solder out the device from 2015 and put in the 'old'

switcher IC from our R&D material..

Regards, Markus

Hi,

We request that you contact the Power Integrations sales office in your area and one of our field application engineers can review the design and also investigate the behavior that you have reported. Alternately I suggest you contact our sales office in your area and request an RMA be processed so that the issue can be investigated at our factory.

Best Regards,

PI-Sarek