Message 27367 in TECHNI.WW
From: G8MNY
Date: Thu, 06 Aug 26 08:34:00 Z
Newsgroups: TECHNI.WW
Subject: A Common UA723 PSU
Message-ID: <1266_GB7CIP>
Path: N2MH4|VE3KPG|VE3CGR|OK2PEN|GB7CIP
R:260806/0839Z 34937@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260806/0839Z 28086@VE3KPG.#ECON.ON.CAN.NOAM BPQ6.0.25
R:260806/0838Z 89847@VE3CGR.#SCON.ON.CAN.NOAM LinBPQ6.0.25
R:260806/0838Z 30003@OK2PEN.SP.BRA.SOAM [Sao Jose dos Campos] $:1266_GB7CIP
R:260806/0834Z @:GB7CIP.#32.GBR.EURO #:1266 [Caterham Surrey GBR] $:1266_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Apr 09)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This is a common design used by several makers both 13V & 27V models etc.
AC
The mains is wired straight to the conventional transformer either 17V @ 6A or
30V 3A, for these 2 types.
No Resistor Capacitor Diode Transistor Fuse ICs
1 1K 2200uF 40V 8A TIP31 6A uA723
2 2200uF 40V 8A 2N3055 6A
3 4K7 100uF 40V 8A
4 1K 0.1uF 16V 8A
5 680R 1nF 1N4001
6 8K2
7 100R 1N4001
8 33R 8A
9 4k7 Preset
10 6K8 1N4001
11 0R33
13 1N4147
No Resistor Capacitor Diode Transistor Fuse ICs CR
1 2K2 1000uF 63V 8A TIP31 3A uA723 TAB SCR
2 2K2 1000uF 63V 8A 2N3055 3A
3 3K9 47uF 63V 8A PNP
4 1K 0.1uF 16V 8A NPN
5 680R 1nF 1N4001
6 15K
7 100R 47uF 40V
8 6K2 8A
9 4K7 Preset 47uF 30V Zener
10 3K3 1N4001
11 0R68 36V Zener
12 1K
13 1K 1N4147
14 1K
15 1K
17 100R
HOW THEY WORKS
The 4 rectifiers D1-4 charge up C1/2. D5 puts voltage onto the IC (via 36V reg
D11/T4 on 27V model). The attenuated R8/R9/R10 output voltage on pin 4 is
compared to the internal 7V reference pin 6, fed back into pin 5, & drive on
pin 10 turns on T1 & heatsinked T2. Output current is the voltage across R11 &
the control loop goes into current limit mode when this is greater than the DC
set up across R5 by R6.
Diode D7 ensures the output voltage is not higher than the input, Diode D8
protects the circuit from reverse current.
On the higher voltage model also has crowbar where if a 30V is exceeded T3 is
turned on firing the SCR to short the PSU.
PSU FAILINGS
There is a high overhead needed in this design of about 3V! This is partly
overcome by making the 2nd power rail D5/C3 for the IC that holds up from the
peaks when the main high current one badly sags due to the small smoothing Cs.
Volts
This results in quite a lot of heat at full output.
The Ua723 is prone to having the current input opamp damaged due to direct
connection to the current sample resistor R11. Series R of 1K on pin 3 is
recommended, if you find this failure when there is no current limit working.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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