4 Sep
2007
4 Sep
'07
12:18 p.m.
On 4 Sep 2007 at 3:12, J Blaser wrote:
That's the strange thing to me. The two
secondaries from the transformer (one
for the 24V line, and the other for the 10V line [which sources the regulated
5V output]) are 'proper' at 27.8V and 11.2V, respectively. What I don't
understand is how a 24V line can suddenly produce 42V! It's like something
is 'pumping' the circuit, and I admit I have never studied how such things work.
Your measurement of the AC output (27.8 volts) is the RMS value of
the voltage. In an unloaded rectifier-capacitor setup, the capacitor
will charge to the *peak* value of the AC voltage. 42 vdc is "close
enough".
Notice that there's no regulator on the +24 PSU line--just a simple
full-wave rectifier formed by D1 and D2 and C1 as a filter cap.
There's a 10K bleeder on the line, but that accounts for only 2 ma of
current draw at 24 volts on a supply that's rated for 1000 times that
current.
Put a load on it, say 12-24 ohms or even two automovtive lamps hooked
in series and watch the voltage drop.
Cheers,
Chuck