> > > > Actually, no. That honour goes to the PSU in a Zenith MDA monitor > > which as I said 'combines the efficiency of a linear with the reliability > > of a switcher'. The design (if you can call it that) of this PSU is to > > rectify the mains, feed it into a free-running chopper circuit, then > > a transformer. The output of that is half-wave (!) rectified giving > > about 18V DC. Note the chopper free-runs, so there is no regulation > > applied at this point. That 18V is then fed to a discrete-transistor > > linear regulator. > > > > And that's not the end of the 'curious' design. As you know, a linear > > regualtor compares the output voltage of the supply with a > > > reference votlage. That reference voltage is typically produced by > > a zener diode. Not in this monitor. It uses the drop across the > > power-on LED. Which means it is important to use a green LED. > > Another colour, with a different Vf, and the PSU output is wrong. >
> I would love to have a copy of that schematic for an Engineering Wall of > Shame. Seriously, that is the strangest supply design I've ever heard. I don't know if it was ever published [1], but I should have a reverse-engineered version somewhere. When I unpack it (after the move...) I will see about getting it scanned. It really is a crazy design. [1] There was the standard 'safety component' warning telling you only to use the parts specified in the service manual on the back cover. But I was totally unable to obtain said service manual. -tony
