DC power supply from AC source

A power supply converting AC line voltage to DC power must perform the following functions at high efficiency and at low cost. The advantage of this kind of power supply over batteries is that this power supply is low cost and also long lasting. We have to perform the following functions to convert AC power to DC power:

1. Voltage transformation
2. Rectification
3. Filtering
4. Regulation

Voltage transformation:

Supply the correct AC voltage level. We use a transformer here which converts the 220 V to the appropriate level of voltage.

The lower voltage is according to the specification of the transformer and specification of the transformer is decided from the requirements of the system.  There are main three specifications about the transformer:

1. Output voltage
2. Output current
3. Centre node or no center node

Rectification:

Convert the incoming AC line voltage to DC PULSATING voltage. This is done by using bridge rectifier because bridge rectifier is better than other rectifiers.

Filtering:  

This is used to smoothen the ripple of the rectified voltage. We use capacitor to do this.

Regulation:

Control the output voltage level to a constant value irrespective of line, load and temperature changes. This function is performed by following IC series as shown:

Constant positive voltage regulators:  These are the regulators which are able to produce positive and constant voltage. Some of them are given below:

S. no.	Name of regulator	Output voltage
1	LM 7805	5v
2	LM 7810	10v
3	LM 7812	12v
4	LM 7815	15v

These regulators are used according to the required voltage need. Given below is the usage of regulators.

 Constant negative voltage regulators: These are also the constant output voltage regulator but there output is negative in polarity. These regulators are also employed according to voltage requirements. Some of them are given below along with their outputs:

S. no	Name of regulator	Output voltage
1	LM7905	-5v
2	LM7910	-10v
3	LM7912	-12v
4	LM7915	-15v

 Variable voltage regulators: These are the regulator whose output voltage can be varied according to the desired need. These regulators again of two types i.e.:-

• Positive
• Negative

The output of these regulators can be varied by varying the resistance of the variable resistance which is connected to the adjustable pin of the regulators.

• LM317 (it is positive regulator)
• LM 337(it is negative regulator)

Regulation:

Control the output voltage level to a constant value irrespective of line, load and temperature changes. This function is performed by following IC series as shown:

Constant positive voltage regulators:  These are the regulators which are able to produce positive and constant voltage. Some of them are given below:

S. no.	Name of regulator	Output voltage
1	LM 7805	5v
2	LM 7810	10v
3	LM 7812	12v
4	LM 7815	15v

These regulators are used according to the required voltage need. Given below is the usage of regulators.

 Constant negative voltage regulators: These are also the constant output voltage regulator but there output is negative in polarity. These regulators are also employed according to voltage requirements. Some of them are given below along with their outputs:

S. no	Name of regulator	Output voltage
1	LM7905	-5v
2	LM7910	-10v
3	LM7912	-12v
4	LM7915	-15v

 Variable voltage regulators: These are the regulator whose output voltage can be varied according to the desired need. These regulators again of two types i.e.:-

• Positive
• Negative

The output of these regulators can be varied by varying the resistance of the variable resistance which is connected to the adjustable pin of the regulators.

• LM317 (it is positive regulator)
• LM 337(it is negative regulator)