Simple 5 volt regulated Power Supply Unit (PSU)

 Here is a simple positive voltage regulator (5V in this case) using only a hand full of components.

The aim was to have a modulor regulator which (with 1 or 2 component changes) would allow me to create a range of fixed voltage power supplys depending on the voltage needed with out the need for post calibration.

Now, since the circuit has been designed to be modular, I have included terminals for a output enable switch and a resistor leading to an LED terminal to show when power is enabled. Once the circit is constructed, no more soldering is required.

Specification

Voltage input:

12 – 24V AC or 7.2 – 30Vdc

Output Voltage:

5Vdc

Max current output:

1A

LED output current:

20 mA @ 5V

Circuit Diagram

Parts List

U1:

LM7805 voltage regulator

D1 – D6:

1N4001 rectifier diodes

R1:

230R resistors

C1 and C2:

100nf ceramic disc capacitor

C3:

33uf 50V electrolytic capacitor

Explaination

• D1 to D4 are configured as a full wave rectifier which ensures that no matter what the polarity of the input voltage, you will always get positive output
• U1 is a three terminal positive voltage regulator which has a fixed output voltage for a range of inputs. Input voltage is applied to pin 1, 0V to pin 2 and Vo is is on pin 3.
• D5 and D6 have been included to protect U1 against reverse voltages.
• C1 to C3 are all decoupling capacitors to help smooth the output.
• W1 and W2 are for the input voltage.
• W3 and W5 are for the output enable switch.
• W6 and W4 are for the output voltage.
• R1 is for limiting the current through the LED to approx. 20mA.
• W7 and W8 are for the LED output.

As I said earlier, this power supply was designed to be modular and to be easily to be modified. Now to do this all you need to do is look at two of the components.

• U1 – This is the heart of the power supply. The LM 78o5 voltage regulator is a part of a range of regulators all with the same pin out. to change the voltage all you have to do is replace U1 wih a regulator which gives you the required voltage. E.g. LM7808 gives 8V output, LM7812 gives 12V output. Take note that the number after the LM78.. is the voltage delivered by the regulator. Please be sure to use 2.2V over the required output voltage as you input on W1 and W2.
• R1 must be changed to conpenstate for an increase or decrease in the output voltage. The formular is

(Vout – Vled) ÷ I

Where Vout = Regulator output

Vled is the LED’s voltdrop (between 1 and 3 volts)

I = current required (I opted for 20 mA)

The circuit will now operate at a new voltage.