R:190628/0921Z
31762@N3HYM.MD.USA.NOAM BPQ6.0.18
R:190628/0928Z @:GB7CIP.#32.GBR.EURO #:10235 [Caterham Surrey GBR]
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. ┌───────────┐
│ ┌─────┐ │ Current limiting
│ │\ │ │ Over voltage Crowbar @ 14.5V
│ │ \ │ │
│ └─────┘ │
│ │
│ o o │
└┬┬──────┬┬─┘
INPUT CIRCUIT
The mains transformer's 2 secondaries feed a bridge rectifier & then to the capacitor bank. (the bridge can fail on heavy use)
__ ___________________
L─o-o──o\─┐||( \__ / │+ │ │+ +20V
3A )||(_ / Single === │+ ===
)|| _X Bridge │ === │3x
)||( \_Rectifier │ │ │6m8
N─────────┘||(__/ \ \__│___│___│________-Ve (0V)
E──┐ 2x 17V 10A \ \
\ └┤>├─┬┤>├─180─┬───┬───┬─+24V
\AC │ │+ _│_ │u1
└─┤├─┘ === /_\'=== ON PCB
+ │ │24V│
└───┴───┴─0V
CONTROL CIRCUIT
+20V┬─────────┬────┬──────────┬──────┐
│ │/ │ │/ │/ 2x
┌─┬───)───┬───┤TIP120│ ┌───┼───┬──┤ 2N3055
│ │ │ │ │\e │/ │ │\e │ │\e PASS
│ │ │ _│_ └──┤ ├─┤├──┤ └┤├──┤TRANSISTORS
│ │ _│_ \_/ │\e │ │ R
│ │ /_\ │ Driver └────┤ ┌─1k┴──R───┴────────────────(Amp)─┬─>+13.8V
│ │ │ ├───────────────)─)───────────────────2k2──┐ │
│ │ ├───)────┬──────────)─)─────┬───────────┬──────)──┬──┬──┤
│ │ │ │ │ │ │ │ _│_ _│_ │u1│ │
+24V │ │ │ │ │ ┌SETI──)─┘ │ \_/ =\_/ │ === │
├─┐ │ │ │ │ │ │/e │ ┌5k1─┤ │ red│ │ │ _│_
2│3│8│1│ │ │ └─┤PNP u1│ │ ┌──┴───┐8 ├──────┤ 1K │ /_\
┌┴─┴─┴─┴┐ 18k │ │\ === ├─┤MC3423├─┐ SCR_│_ │ │ │ │
│ LM376 │ │ \│ │ │ │2└┬─┬─┬┬┘ │ \_/ _│_ │ │ │
└┬─┬─┬─┬┘ SET NPN├─┬2k2┬┴──┐ │ │ 1│8│4││3 │ /│ =\_/ │ │ │
4│5│7│6└┬─>V e/│ │ │+ │ │ 1k ├─┘+├┘ +├100┤ │ Green│ │ │ │
│===└┤├┘ │ │ === === 10K │ │ │ === === ===│ 2k2 │ │ │
│ │u1 2K2 │ u1│ │10u│ │ │ │10u│10u│ u1│ │ │ │ │ │
──┴─┴───────┴───┴───┴───┴───┴───┴──┴──┴───┴───┴───┴─┴──────┴──┴──┴──┴─>0V
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 & 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), & 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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* Origin: HAMRADIO telnet lu9dce.dynu.com (21:5/101)