Hi,

I want to make a small isolated DC-DC supply around 200mW, taking 12VDC on the input side and giving me +/-6V @ 10mA on the output. The isolation level does not have to be very high, e.g. 24VAC is fine.

It has to be low cost.

This is qhat I have come up with so far (TransformerDrive.jpg):

A microcontroller, or maybe a 555 timer creates a PWM signal PWM_ISO.

The transistor and pullup resistor boost it to a 0-12V square wave.

The capacitor C701 turns this into 6VAC for the transformer primary.

Will this way of driving the primary will work? I could use a centre-tapped transformer and drive two halves anti-phase, but I expect that will be more expensive.

What parameter of the transformer would determine the size of the capacitor?

IS this likely to create EMI problems? (i.e. primary winding and capacitor oscillating?)

Attached Images

transformerdriver.jpg (60.0 KB, 165 views)

 

i think the secondary side is ok, but prefer to make the primary driving a push pull with 547/557 combo