Universal Power Supply Circuit Diagram DIY

Introduction

Universal power supply circuits are versatile circuits that can be used to provide a stable and regulated output voltage for a wide range of electronic devices. In this article, we will explore a DIY universal power supply circuit diagram using the L200 IC and BC547B transistors. Additionally, we will discuss the functionalities and key characteristics of the L200 IC, BC547B transistors, 1N5404, and 1N4148 diodes.

The universal power supply circuit diagram shown below has two output ranges; one from 2.7 V to 12 V, and the other from 10 V to 24 V. The output is short circuit protected. Current limiting is adjustable. These two features are mainly incorporated for preventing accidental damages to the power supply as well as circuits that get power from this supply.

Universal Power Supply Circuit Diagram

This project can be designed using a few basic components. The circuit diagram of this project is shown below.

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Components List of Universal Power Supply Circuit Diagram

Following is the list of all components used in this project:

Capacitors:

C1 = 2200 μF/25 V
C2 = 2200 μF/40 V
C3 = 220 nF
C4 = 1 μF/35 V, Tant.

Resisters:

R1 = 15 ΚΩ
R2 = 680 Ω
R3 = 150 ΚΩ
R4 = 1.2 ΚΩ
R5 = 220 Ω
R6 = 2.2 ΚΩ
R7 = 220 Ω
R8 = 2.7 ΚΩ
R9 = 33 Ω
R10 = 680 Ω
R11 = 180 Ω
R12 = 0.47 S2, 1 W
R13 = 220 Ω

IC & Transistors:

IC1 = L200
T1, T2, T3 = BC547B

Diodes:

D1, D2, D3, D4 = 1N5404
D6, D7, D9 = 1N4148 or 1N4002
D5 = LED Red
D8 = LED, Green

Miscellaneous:

X1 = 12-0-12 V/1.2 A
S1 = DPST main switch
P1 = 4.7 km2, Linear
P2 = 470 2, Linear
D2 = SPDT Switch, 2A rating
F1 = 250 mA fuse with holder

Circuit Explanation of Universal Power Supply Circuit Diagram

The most important part of the power supply is the integrated voltage regulator L200. It looks similar to a power transistor with five terminals. The number of terminals obviously means that there is much more in it (refer its datasheet for other details). The voltage regulation takes place as long it is ensured that the control pin (pin 4) gets 2.7 V. The current limiting sets in when the voltage between the output pin (pin 5) and the current limiting input pin (pin 2) exceeds the value of 0.46 V. These are inherent electrical properties of the L200 and cannot be altered.

The output voltage has been divided in two ranges, to avoid heavy losses and overheating at low voltages.

If suppose the input voltage is 28 V and we need an output voltage of 5 V, then somehow the regulator must “destroy” these extra 23 volts. This will result in loss of power as well as overheating of the regulator IC. If we have an input of 14 V and the output is 5 V, then the regulator has to reduce the input only by 9 V. By dividing the output into two different ranges the efficiency has been increased and heating reduced.

The switching over from one range to another is done by switch S2. In the lower range diodes D1 and D3 form a full-wave rectifier with the center-tapped transformer. In the higher range the bridge rectifier action doubles up the end-to-end voltage of the secondary winding. This doubles the d.c. voltage input to the regulator circuit.

Potentiometer P1 and resistors R4… R9 set the output voltage. Potentiometer P2, transistor T3 and associated circuits set the current limit. Transistors T1, T2 and the red LED D5 give the indication of the current limiting action.

Potentiometer P1 and resistors R4 to R9 form a voltage divider network. The junction of R4 and R8 or R8 and R6 (depending on the range) is connected to the control input. The regulator adjusts the output voltage in such a way that voltage at the control input remains constant at 2.7 V. The output voltage thus depends on the setting of the potentiometer P1.

The setting of current limiting is somewhat difficult to understand. It becomes effective when the voltage difference between pins 2 and 5 of the regulator increases beyond 0.45 V.

The voltage present here is equal to the voltage drop over R12 plus the voltage at the sliding contact of potentiometer V2. The constant current source formed using T3 provides for the fact that the value of output voltage does not affect the current limiting function. As the voltage drop across R12 depends upon the current drawn by the load and the voltage at pin 2 is derived from a constant current source, the setting of current limiting is independent of the voltage at the output. The green LED D8 has a dual function. It severs for switching control as well as for control of the constant current source T3.

Transistors T1 and T2 and the red LED D5 are used for fault indication, when output current reaches the limit value that is set for it. In normal condition, the voltage on pin 4 is 2.7 V, which is greater than the threshold voltage of D6, D7 and the base-emitter junction of T2. Thus, T2 is always conducting. This causes the base of T1 to remain at zero volts and it is always off. LED D5 also remains off. But as soon as the voltage on pin 4 reaches about 2 V, which is less than the required voltage to keep T2 on, T2 is turned off and T1 then starts conducting. Red LED D5 glows, indicating fault condition.

Diodes D10 and D11 serve as the protection for the circuit.

Testing the Power Supply

If the power supply is assembled correctly, the circuit must function correctly after it is switched on. Both the voltage ranges can be confirmed with a multimeter.

Whenever the regulator switches off due to overload, the power supply from mains must be switched off for some time and then restarted.

If the circuit does not function as expected, it can be tested stage-by-stage with a multimeter. First of all, the interconnections must be checked. The diode and capacitor polarities must be correct. Pin orientation of the IC and transistors must be carefully checked.

It must also be ensured that the cooling fin of the IC is not short circuited with any other pin or with any other component. It must be connected only to the minus pole of the power supply.

Before starting further measurements on the circuit, point C must be disconnected from the pole of switch S2a. By doing this, we have isolated the regulator part of the circuit from the rectifier. Both LEDs will now glow when the power is switched on.

The following values should be measured:

Voltage at each transformer winding: 12V a.c.
Voltage over both windings together: 24 V a.c.
Voltage over C1 (Point B to earth): 18 V d.c. ¤ Voltage ever C2 (Point A to earth): 36 V d.c.
Voltage over both LEDs: 2 V

If all these are correct, it means that the transformer and rectifier part of the circuit is correct. As the next step, connection between P2 and R13 is desoldered. Now if a multimeter set to 100 mA is inserted between point B and collector of T3, it should indicate a current of 13 mA approximately.

The desoldered connection can now be restored and the following voltages should be measured:

Pin 4 of IC1 and the earth: 2.7 V d.c. independent of the potentiometer setting. Reduces only when current limiting sets in.
Voltage between D6 and D7: 1.2 V d.c.
Voltage between base of T3 and earth : 3 V d.c.
Voltage between emitter of T3 and earth: 2.5 V d.c. independent of potentiometer setting.
Voltage over D9 : Approximately 0.8 V d.c.

Any wrong indication during the test procedure indicates that the particular component is either wrongly connected or it is defective.

Conclusion of Universal Power Supply Circuit Diagram

In conclusion, the universal power supply circuit diagram using the L200 IC and BC547B transistors provides a reliable and efficient solution for generating a stable and regulated output voltage. The L200 IC offers excellent voltage regulation and current limiting capabilities, making it an ideal choice for such applications. On the other hand, the BC547B transistors act as switching devices, enhancing the overall functionality of the circuit. The 1N5404 and 1N4148 diodes play crucial roles in rectifying and protecting the circuit from voltage spikes and reverse currents, respectively. By understanding the functionalities and characteristics of these components, electronics enthusiasts can successfully build and customize universal power supply circuits to meet their specific requirements.

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