Message 27135 in TECH.WW
From: G8MNY
Date: Sun, 02 Aug 26 22:13:00 Z
Newsgroups: TECH.WW
Subject: BNOS 12A 13.8V PSU
Message-ID: <948_GB7CIP>
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From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Dec 12)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I have repaired some these, the 12A (15A meter) & 30A model are similar.
INPUT CIRCUIT
The mains transformer's 2 secondaries feed a bridge rectifier and then to the
capacitor bank. (the bridge can fail on heavy use)
__ ___________________
CONTROL CIRCUIT
Volt Control Current Limit Over Voltage Crowbar
VOLTAGE CONTROL
The voltage control IC LM376 runs on a voltage doubled supply of 24V. It
compares it's internal reference with the preset SET V and drives the TIP120
darlington to drive the 2 heat sinked pass transistors to maintain the output
voltage.
CURRENT LIMITING
The 2 pass transistors have current equalising emitter resistors (R), and when
one of these is over the base emitter voltage of the PNP, that turns on a NPN
to override the LM376 drive, to limit the current.
OVER VOLTAGE PROTECTION
IC MC3423 is a triggered over voltage IC that fires the crowbar SCR to short
the output if it is too high. Danger here is when charging batteries if the
trip should go causing a fire. So use a fuse with battery!
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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