I'm researching designs for a simple bipolar output switching power supply and came across the design below in a ST datasheet for the MC34063A. Dual-output MC34063 SMPS

However, there isn't enough information in the datasheet for me to implement this design and I couldn't find any SMPS topologies in other resources that looked to be equivalent. I was hoping someone would recognize the topology so that I could find more information on it.

On a related note, are there any other/better designs using the MC34063A (since I have a bunch on hand) for producing +/-7V @ 100mA from a 3V input? Thanks!


Looks like a variant of a flyback converter based around a center-tapped transformer. (Here's an example from another site.) Some things that identify it as a flyback are:

  1. The switch is connected directly to the transformer. This indicates an isolated/off-line converter.
  2. There's no freewheeling diode on the input side of the transformer (or any freewheeling diode at all, for that matter). That says it's a flyback.
  3. There are multiple output voltages, which is common for a flyback. This is done by having multiple windings on the transformer.

If the drawing were more detailed, it would show opposite-polarity dots on the two sides of the transformer, which would be another giveaway.

If you build this circuit, you will probably want to buy a transformer designed for flyback converters.

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  • \$\begingroup\$ Thanks, I guess the full bridge rectifier was throwing me off. Do you have any suggestions for resources that would help me pick the proper components for this circuit? \$\endgroup\$ – tarheels Apr 10 '15 at 15:43
  • \$\begingroup\$ Unfortunately, I do not. I don't have any experience building isolated converters. Other companies also make MC34063s (with possibly more helpful datasheets), but I didn't find any others that had this circuit. It sounds like you're looking for something simple, and I wouldn't call flyback converters simple. I think separate boost and buck-boost stages would work better. It would be easier to find reference circuits, and unlike this circuit both voltages would be properly regulated. \$\endgroup\$ – Adam Haun Apr 10 '15 at 18:13

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