- Ordinary DC Power supply
- What is the need for a Regulated Power supply
- Working of the Regulated Power supply
Introduction to Power Supply
We all know that many electronic circuits using tubes or transistors requires a DC power supply. We cannot use DC batteries everywhere because DC batteries are costly and require replacement once discharged. So in such scenarios, we need to make use of electronic circuits which can convert ac supply into dc power supply using a rectifier-filter system, these kinds of electronic circuits are called as DC power supply.
Rectifier-filter circuit contains an ordinary dc power supply. The output of ordinary dc power supply remains steady as long as ac mains voltage or load is contrast. But in many electronics circuits it very important to keep the contact DC power supply irrespective of variant ac mains supply. There is a high possibility of circuit damage if the DC power supply is not constant. To avoid this situation, we can make use of voltage regulating devices which can keep the DC voltage at a constant level. So this combination of Voltage regulating devices with the ordinary dc power supply is called as Regulated DC power supply. Regulated DC power supply is an electrical device which produces the constant DC power supply irrespective of variant ac mains supply.
Ordinary DC Power Supply
Below circuit shows ordinary or unregulated power supply. This circuit contains a rectifier and a filter circuit. The output of a rectifier is pulsating dc because of the presence of pulsating ac component. The filter circuit is used to remove these pulsations of AC component to produce a steady dc output.
[caption id="attachment_1768" align="aligncenter" width="543"]
Unregulated DC power supply[/caption]Limitations of Ordinary DC power supply
- DC output voltage is directly proportional to the AC input voltage. If AC voltage is increased, the output will increase in the same proportion, thus we won't get constant dc output voltage.
- DC output voltage decreases as the load current increases because of voltage drop in transformer windings, filter and rectifier circuit.
What is the need for a Regulated Power supply?
We have already covered the limitations of an ordinary power supply. In an ordinary power supply, the voltage regulation is poor i.e. d.c. output voltage changes considerably with load current. Moreover, output voltage also changes due to variations in the input a.c. voltage. Thus there is a need of regulated power supply.
Working of the Regulated Power supply
The general block diagram of regulated power supply is shown below:
[caption id="attachment_1769" align="aligncenter" width="688"]
Regulated Power Supply Block Diagram[/caption]
Construction and working of regulated power supply
1. AC supply and transformer:
A power supply is used to provide the required amount of power at specific voltage from a primary source which can be ac mains or a battery. A transformer changes the ac mains (line) voltage to a required value and it is used to step the voltage up or down. In a transistor radio it may be a step-down transformer and in a CRT it may be a step-up transformer. Transformer provides isolation from the power line. It should be used even when any change in voltage is not necessary.
2. Rectifier:
- Full wave bridge rectifier circuit diagram
A rectifier converts ac into dc. It may be a half-wave rectifier, a full-wave rectifier using a transformer with centre-tapped secondary winding or a bridge rectifier. But the output of a rectifier may be fluctuating.
3. Filter:
- LC filter
A filter circuit is used for smoothing out the ac variations from the rectified voltage. There are four types of filters: 1) Capacitor filter, 2) Inductor filter, 3) L-C filter and 4) R-C filter.
4. Voltage regulator:
A voltage regulator is necessary to maintain a constant output dc voltage by providing line regulation and load regulation. For this purpose, we can user A Zener-regulator, transistorized regulator or three terminal IC regulator. A switched mode power supply (SMPS) is used to provide large load current with negligible power dissipation in the series pass transistor.
We recommend you to please watch below lecture for a complete understanding of Regulated Power Supply:
https://www.youtube.com/watch?v=x2wqwqUhMdE
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