Regulated Power Supply
A regulated power supply can convert unregulated an ac (alternating electric current or voltage) to a constant dc (direct electric current or voltage). A regulated power supply is used to ensure that the output remains constant even if the input changes. A regulated DC power supply is also called as a linear power supply, it is an embedded circuit and consists of various blocks. The regulated power supply will accept an ac input and give a constant dc output. Figure below shows the block diagram of a typical regulated dc power supply.
The basic building blocks of a regulated dc power supply are as follows:
1. A step down transformer
2. A rectifier
3. A DC filter
4. A regulator
Operation of Regulated Power Supply:
Step Down Transformer:
A step down transformer will step down the voltage from the ac mains to the required voltage level. The turn’s ratio of the transformer is so adjusted such as to obtain the required voltage value. The output of the transformer is given as an input to the rectifier circuit.
Rectifier is an electronic circuit consisting of diodes which carries out the rectification process. Rectification is the process of converting an alternating voltage or electric current into corresponding direct (dc) quantity. The input to a rectifier is ac whereas its output is unidirectional pulsating dc. Usually a full wave rectifier or a bridge rectifier is used to rectify both the half cycles of the ac supply (full wave rectification).
The rectified voltage from the rectifier is a pulsating dc voltage having very high ripple content. But this is not we want, we want a pure ripple free dc waveform. Hence a filter is used. Different types of filters are used such as capacitor filter, LC filter, Choke input filter, π type filter.
This is the last block in a regulated DC power supply. The output voltage or electric current will change or fluctuate when there is change in the input from ac mains or due to change in load current at the output of the regulated power supply or due to other factors like temperature changes. This problem can be eliminated by using a regulator. A regulator will maintain the output constant even when changes at the input or any other changes occur. Transistor series regulator, Fixed and variable IC regulators or a zener diode operated in the zener region can be used depending on their applications. IC’s like 78XX and 79XX are used to obtained fixed values of voltages at the output. With IC’s like LM 317 and 723 etc we can adjust the output voltage to a required constant value.
Figure below shows the complete circuit of a regulated +5V DC power supply using transformer, bridge rectifier, filter (smoothing) and a fixed +5 V voltage regulator.
Here we can use IC 7803(for 3V),7809(for 9 V),7812(for 12V) etc.
Application of Regulated Power Supply
Regulated power supply is the main component of electrical,electronics and as well as automation equipment. Mobile phone charger, oscillator, amplifier needs the regulated power supply.