23 Jul
2012
23 Jul
'12
1:22 p.m.
You're right, it is an emitter follower with a full-wave rectifier. The ripple is
quite bad, I figure it at 3.5%. I'll have to hunt down an appropriate capacitor.
Sent from my iPad
On 2012-07-23, at 3:27 PM, ard at p850ug1.demon.co.uk (Tony Duell) wrote:
I checked out the power supply. It's basically a common-base amplifier
with a 5.6v Zener diode. It doesn't have a full-wave bridge rectifier.
Are you sure? Most such regualtor circuits are emitter followers with the
base held at a suitable voltage by the zener.
What is the input rectifier? Half wave? Or a pair of diodes and a
centre-tapped transfofmer secondary winding (which is a full-wave
circuit)?
Theres a 4,000uf electrolytic capacitor for
filtering the input to the
transistor. Given the design, I'd expect it to be pretty sensitive to
problems with that capacitor. If I have a suitable part, I think I will
I don't see why. If the ripple is sufficiuently low that the zener stays
conducting all the time, then the output voltage will be stable. A 7805
won;t do better than that.
replace the transistor and the diode with a
proper 7805 regulator.
Check the output for ripple. If necessary, replace that capacitor. But
dont change the design if you don't have to.
-tony