Low Temperature Operation for TOP258

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We have a multi-voltage design using a TOP258. Rated for 30 VA but usually lightly loaded to less than 10 VA. I did not do this design so I could use some help.

One 5 volt secondary voltage is regulated with feedback to the TOP258 via optocoupler and tl431. There are 4 other windings or stacked windings that generate secondary voltages.

It is well behaved at most temperatures between 0 and 50C, But we have been doing some low temperature startup tests (-40C) and it has a tendency to swing the regulated secondary widely. So much so that it is damaging some ICs that are rated for maximum of 6 volts.

Anyone have ideas on how to tame this secondary during low temp startup? I was thinking of a 6 volt zener clamp to ground.

thanks, Mike

Hi,
First of all, the 6 voltage zener will for sure to help to protect the ICs from damage because of the high voltage generated. Just kindly remind to check the temperature coefficient for the zener too when selecting the zener.
For the over voltage during the start up, is it a over voltage shot during the start up or it is high output voltage in steady status under the cold temperature? Generally under very cold temperature, the behavior of the external components will be changed as well. For example the Electrolytic capacitor value will be lower, the CTR of the opto-coupler will be changed too. This may change the performance of the control loop, that may end up with the over shoot during the startup.
Hope this is helpful for you.