"John Popelish" wrote in message
...
Tfort wrote:

On Mon, 02 Feb 2004 00:52:18 GMT, Uwe Langmesser
wrote:

I need a 12-14 V power supply for my new 2m tranceiver. ...
Uwe

look at this...

http://www.rason.org/Projects/powsupply/powsupply.htm

Tracy

It can be easily improved. Eliminate the two .1 ohm emitter resistors
and connect one emitter to R6 and one to R7.

Good inputs, John. Yea. That is strange.

Then replace R4 with a
pair of resistors, one going to R6 and one to R7, to average the
voltage from them to reproduce the current limit signal.

I'd say this is ok. Don't know how important. Haven't done a 723
regulator in a long time...

You will
have to double the value so that two in parallel have the same total
effect. This change will not only eliminate two 10 watt resistors,
but will improve the current sharing between Q2 and Q3....
John Popelish

Remember. Cap input filters like this draw high peak current at the
peak of the sinewave when the caps get charged. It is not a sinewave
current waveform. Make sure that you have enough filter cap (& diode
capability) so that at the lowest point of the ripple on the filter caps you
still have voltage on the series pass transistors (the 3055's) which is
"enough" Here are some rough numbers, but should be close.
To figure how much drop you'll have with given caps or how much cap you
need to get a given drop you can use the formula I=C dV/dt where I is the
DC current (in amps), dVis the drop (in volts) you have room for over dt
which is about 7 miliseconds. Solve for C or V as appropriate.
The minimum cap voltage is somethign like 13.8 PLUS the drop across the
0.15s PLUS 2 volts for the darlington connected 3055's base and some left
over for collector voltage on the driver 3055. If I have it right that is:
13.8 + (7.5 x 0.15) + 2 (transistors 2 x Vbe) +2 (minimum driver Vcb) and
this is at low line voltage.

I get around 13.8 + 1.2 + 2 + 2 = 19V. Oh yea, the transformer has to have
2V more to allow for the bridge diodes also. SO at 30-35 peak amps the xfmr
needs to have 21 volts peak, if I did it right -- that's around 15V RMS
(there is flatening of the peaks due to the peak current).


FYI:
On one I built, I wound a few extra turns on the transformer and added some
diodes to provide the driver collector voltage. This was a 5V 30A supply
and I was trying to minimize loss. When TTL was in vogue...

--
Steve N, K,9;d, c. i My email has no u's.