Electronic – Help with designing negative part of Dual-Sided SMPS

buckpower supplyswitch-mode-power-supply

For a project of mine, I'm trying to make a dual-sided SMPS that has independently variable positive and negative supply rails, current limiting, short circuit protection, etc etc…

My current plan of attack would to use a center-tapped transformer to convert wall power to about +/- 40VAC. I can easily rectify both and get about +/-28VDC. For the positive side supply I can easily use a voltage-controlled buck regulator.

My issue is that i don't know how to step down negative voltage for the minus side! i feel like a topology similar to a buck should work, but I'm not sure how to keep the transistors operating in the right modes.

I am considering using a buck-boost to get the negative output, but the controls for it are a lot higher 🙁

My question is basically, how could i create the variable, regulated negative voltage supply?

thanks

Best Answer

In principle, you can make inverted buck converter; however, this will be difficult in real life since suitable parts are rare. You may want to try a different approach; generate negative output from the same positive input using inverting or Cuk converter topology. Read Jim Willams' "Switching Regulators for Poets" -> http://cds.linear.com/docs/en/application-note/an25fa.pdf if you desire more elegant solution.