22 Aug
2015
22 Aug
'15
5:45 p.m.
I figured as much. And, with a 10K ohm bleeder resistor that I added on
the output (another added safety feature), the voltage dropped down to
5.2 and change - within spec.
JRJ
On 8/22/2015 6:19 PM, Dave G4UGM wrote:
Also, I now know why the +5 V is high. It has a UA 7805 3 terminal
regulator
serving as a voltage reference for a TIP-3055 so
the supply can provide
more
current. That 7805 has a forward biased diode
between the center terminal
and ground, thus raising the output voltage by right around 0.5v. I
expect I
will leave it alone.
When used as series pass transistor the TIP-3055 will usually drop 0.6v
across the emitter under any significant load. Adding a silicon diode in the
7805 base is the normal fix...
http://www.bristolwatch.com/ele/basic_power_supplies.htm
The same design is used for the +24V, which comes out at 24.2V.
So, odds are that this supply could drive two floppy drives.
JRJ
JRJ