General Purpose Power Supply by L146 or IC 723


General Purpose Power Supply

Project Description

This power supply is designed for general purpose use. Advantages of the circuit are first the voltage can be adjusted from 0V to greater and second it does not require a double sided secondary winding transformer.

For high voltage outputs you can use L146 or alternatively if you need lower voltage outputs you can use IC 723.  Although output current limit is variable, it will be fixed after adjusted. In the table,  suitable component values are listed for three different cases (max. outputs: 30V, 40V and 60V). In the schematic 40V/0.8A example is shown.

Vout Iout
R1
R4, R5 R9
Tr1
C1/C5
IC1
Tr2
Tr3
0-25-30V 1.3A
0.47Ohm
33k
2k7
24V/2A
40V
723
BD242
2N3035
0-40V  0.8A
0.82Ohm
47k
5k6
33V/1.5A
63V
L146
BD242A
2N3035
0-60V
0.6A
1.2Ohm
68k
19k
48V/1A
80V
L146
BD242B
2N3442

The reason why L146 is used in the schematic is higherslew rate than the IC 723.

Regulation voltage for both integrated circuit is at least 2V. R3, R4, R5 and R6 resistors prevent this limitation and keep the output voltage at 0 level with the help of P2 potentiometer. If the input voltage is less than required, this resistors provides sufficient potential between 4 and 5 numbered pins.

When the necessary output voltage is less than the tolerance of the regulator’s minimum value, than potential at 4 and 5 are less. This situation causes the IC balance the output voltage by using 9 numbered pin.

However 9 numbered pin is grounded through R7 and D2, it limits the voltage increase.  But current increases too and R7 limits it to 6mA. Current entering to 11 numbered pin and passing through 9 numbered pin causes voltage drop on P1. So Tr3 is got conduction by Tr2.

Middle pin of P1 potentiometer is connected to the base of T1, so  it is possible to control the current limitation. When the voltage drop on R1 exceeds 0.6V , Tr1 and P1 are omitted so Tr3 switches off.

At without current limitation mode,  voltage drop on P1 is constant at 1.2V.  Some of this voltage is used to operate T1 without reaching 0.6V value on R1.  This is possible because, base voltage of T1 is derived from voltage drop on R1 and divided voltage on the middle pin of P1. By this explained way, output current can be adjusted from 0 to its maximum value.

Note that 723 responses up to 36V. L146 must be used with a transformer higher than 24V supply. A L146 can response  up to 80V safely but seconder winding of the transformer must capable to supply 48V. 

On the other hand, you must choose the capacitor and semiconductor values with respect to which mode you will use. Don’t forget that a 2N3055 can be used for maximum 60V so for 80V you must use 40411 or 2N3442 or any other equivalent. Table shows the suitable values.


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