The H-bridge is a good idea. I am glad that this is generating some thinking. But I wonder, if the proper voltage and current can be achieved, what are the other drawbacks that were mentioned. I know that the heat will be considerable, even more so if Darlington power transistors are used. Depending on the required output current, base drive may be significant for a power bipolar base unless it has a fairly high beta. Most power bipolars do not; one reason to use Darlington. Complementary n-channel and p-channel power FETS might also be a solution for the output amp. ----- Original Message ----- From: "peter green" To: "Microcontroller discussion list - Public." Sent: Thursday, August 07, 2008 3:14 PM Subject: Re: [EE] affordable full range 20+4 ATX power supply thatmay workon120V DC? > >> No, you get about 42V AC with a 60V DC offset. There are other drawbacks >> too, but this idea is too rediculous to go any further with. >> > What you can do is to use a H bridge. When one side pulls up the other > pulls down. That way there is no DC offset and the peak voltage in both > directions is the same as the DC voltage (so the peak-peak voltage is > twice the DC voltage) > > You can either use a plain squarewave or better use what is known of as > a "modified sinewave". You drive positive for 1/4 cycle, then you don't > drive at all for 1/4 cycle then you drive negative for 1/4 cycle than > you don't drive at all for the remaining 1/4 cycle. That way you get the > same peak/rms ratio as a sinewave without having the problems of an > analog output stage. > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist