My PSU Project

[uMinded]

I just finished watching the PSU build videos and let me say THANK YOU!! I have had most of my components laying around and have been trying to figure out how to limit the wattage dropped by my series pass transistor when drawing high currents and low voltages.

In my design I have a 160VA 2x40VAC torroid transformer so as to get dual 0-30V/2A design. However when set at 5V and 1A the transistor will be dropping 25W which is a LOT of heat to try and handle in a small package. I had never thought of using a DC-DC converter to track my output voltage before. The closest I came up with was a relay to switch the center tap of a transformer so it would be 0-15V and 15-30V but that still left me with ~10W to handle.

In the uSupply design you are using a DC-DC boost regulator where I will require a buck regulator. I am however having a horrible time trying to find one that meets my requirements on digikey's search. I was hoping somebody had used a brand before and knew of a chip I can use.

DC-DC Buck
High switching freq, >750kHz preferable
40+ VDC input
3A current
MUST have a control pin, Similar to the MIC2253 for tracking.

I will also require a smaller less robust chip to bring the 5V LDO out of the melting zone. A LM3805 at 250mA on a 40VDC supply would drop ~8W, if I can get a cheap low frequency DC-DC buck converter I wont need to mount my LDO on anything at all.

DC-DC Buck
Any switching freq
40+ VDC input
6-12VDC output
250mA current