Transformers are indispensable in the field of electronics. But the need for a bulky and expensive component like a transformer can be eliminated in circuits of low current drain. One such circuit which gives both polarity (positive and negative) zener regulated output voltages is shown in the following transformerless symmetrical power supply circuit diagram.
Circuit Diagram of Transformerless Symmetrical Power Supply
This project can be designed using a few basic components. The circuit diagram of this project is shown below.
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Explanation of Transformerless Symmetrical Power Supply
The desired output voltage can be obtained by using appro- priate zener diode. If only one kind of voltage is needed, the other half need not be used.
The circuit is capable of providing up to 25 mA of load current. The output voltage is stable even if the line voltage varies from 195 to 270 volts. However, the power dissipation in the series dropping resistance increases with the rise in line voltage and increase in load current. It is better to use such circuits in applications of low current drains only.
Warning: An important point to note in this circuit is that the supply is not isolated from the mains supply and hence, extreme care should be taken while using the supply to minimize the chance of an electric shock.
The following table gives the values of components to be used for different voltages:
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