Variable Voltage Power Supply Using The LM317T


Variable power supply

The power supply section is always an inevitable part of every electronic circuit, the whole working of an electronic circuit must be started from this section.
Mostly power supply section are been in various types, here we are explained about a simple and cost-efficient circuit.

And we are introducing a very common regulator IC called lm317, this particular ICs are used to build variable power supply circuits and fixed power supply circuits, today we try to build a variable power supply circuit.

LM317

LM317 ICs are mainly used for variable voltage regulators, LM317 IC has three pins First pin indicates the adjustments, second pin for output and third pin for input supply, these pins can be adjustable to set a variable or fixed voltage basis.

Working

 This circuit only has three parts
1.   Rectifier section
2.   Filter section
3.   Regulator section

 For this circuit, we are using 15v step down transformer 15-0 (transformer current rating must be lower than 1.5 amperes because maximum current affordable for Lm317 is only 1.5amps)
Supply mains provided 220 volt AC to transformer then our step down transformer limits it into 15 volt AC, secondary of the transformer provide 15 volt AC to next section for the rectification process, for that 15vAC supply voltage injected towards a full-wave rectifier and then it will convert into corresponding DC supply.

Generally we use diodes at the rectifier section but we had a second option that is bridge IC, it is a better option than diodes because complicity of the circuit must be reduced due to IC.

The generated DC include more AC content, these unwanted noises are called ripple factor, here we can use a special circuit called filter circuit for the removal of AC content at this rectified DC output, and also filter circuits are in different types, here we are using capacitor filter circuit for filtration process because it is cost-efficient and minimum component usage.

Capacitor filter works behind a simple operation that is an electrolytic capacitor, this particular capacitor blocks alternating variations at the signal and charge direct current content at the output signal as a result we can reduce ripples at the rectified output.

Now the last section is the regulator section, here we use LM317 regulator IC for this, the first pin of this IC is the main part for this voltage adjusting process, but in this IC input we have to provide 40 volt supply sadly we only have a 15-volt transformer, so we use a 15-volt transformer.

 As if we provide 40 volt supply we had a 1.2 volt to 37-volt output, and the second pin indicates the output pin, then the third pin is our output pin.


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