Mostly we need a 5-volt power supply for micro-controllers, digital chips, op-amps, etc. So, we want a small as well as reliable 5v power supply. The article is completely about such a type of power supply. We are using LM-7805 IC to build a 5-volt power supply.
7805 is a 5V fixed three-terminal voltage regulator. The IC has internally safe operating features such as short-circuit, over-current, thermal shutdown protection which makes the IC very reliable to make a simple 5V power supply. Must see various type of voltage regulators
The first pin of 7805 IC is input, second is Ground while the third one is the Output pin.
Here is the image of LM-7805 and it’s biasing.
5-volt power supply-Circuit:
Click the image to enlarge.
Working of 5-volt power supply-Circuit:
The working of the circuit can be understood in the following steps…
A DC voltage source converts the AC for the supply voltage to the required DC and acts as a DC voltage source.
1.) Step down:
TR1 step-down transformer is used here which steps 220V AC down to 6V. 6V is AC voltage and this is RMS value. The peak value of RMS 6V is 6 x square root 2 = 8.5V.
To convert AC to DC, a Bridge rectifier is used. The bridge rectifier converts bi-directional AC into a unidirectional DC pulsating voltage which is having too many ripples and AC parts. This can’t be fed to the 7805 IC, we need to filter these ripples.
The voltage just after the bridge rectifier is smoothed by capacitor C1, this is a C filter. After smoothening, this voltage contains fewer ripples.
voltage is given to the input pin of 7805 IC. It regulates the voltage at 5V. Capacitor C3 and C4 are here for the loading effect. If a load is applied, there will be a sudden voltage change. These capacitors will oppose that change and hence will make the circuit more stable.
The circuit is simple and can be built on the PCB board or breadboard easily. For a current less than 250mA, there is no need for heat sinks with 7805 IC. But to get high current, there is a need for the heat sink to get better performance and to avoid the overheating of IC.
The output of IC can vary in the range of 4.7V-5.3V depending on the Input voltage and thermal condition of the 7805 IC.
A button can also be used to switch ON or OFF the power supply. You can put it on the AC side (in series with transformer).
Transformer 220V to 6V (step down)
C1) 470uF (25V electrolytic)
C2) 0.01uF (non-polar)
C3) 10uF (15V electrolytic)
C4) 0.01uF (non-polar)
Bridge Diodes (4 x 1N4007)
U1) LM – 7805 IC
This circuit gives a regulated 5 volt DC output which can be used to operate any 5 volts operated circuit and it can charge mobile phones also.