DER-237 Bias Winding Voltage

2 posts / 0 new


I am using the TOP264 and copying the DER-237 reference design. This uses a 9.6V bias winding voltage with an optocoupler to provide feedback to the CONTROL pin.

Can I use a transformer with a higher bias winding turns ratio and therefore have a bias voltage of 16V? Will this cause any problems to the CONTROL pin which has absolute maximum voltage of 9V?
I think that the bias voltage will be dropped across the optocoupler and so the CONTROL voltage will be much lower than the bias voltage. Is this correct?


Hi Calumr,

Thanks for using power integrations product.
Yes you are correct. Typically a bias voltage of 12V to 22V works well.
Please make sure that the primary sense OVP circuit will not prematurely trigger.
(AN-47 figure 20 and figure 21)

you can refer to the topswitch design guide

For optimized bias winding for low No-load requirments,
the bias should be designed approximately 8V

Hope this helps.