● A simple variable power supply circuit and charger are described here. It is useful when power supply is available or when there is no power supply.
● This circuit can be used to test electronic projects on your workbench.
● It can be used to charge your cell phone battery.
● Can be used as an emergency light .
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Fig. 1: Variable power supply circuit prototype on breadboard
In this circuit you can obtain outputs by turning the different switches (S3, S4 and S5) according to your need. Activate switch S3 if you want a variable power supply as output. For variable power supply, we use LM317 variable voltage regulator, which is a 3-terminal adjustable positive voltage regulator. It will provide an output voltage in the range of 1.2V to 37V. To obtain different voltages, adjust the variable resistor to see the output on the multimeter and set the required voltage. The power supply range varies from 1.5V to 12V.
With the help of this circuit, you can charge your lithium-ion battery by pushing switch S5 which is mainly used in your mobile phones. Here the zener diode provides constant voltage of 3.3V to charge the lithium-ion battery. Resistor R13 is used to limit the charging current.
To use the S4 emergency light switch. If you want to increase the intensity of the light, you can use reflectors.
This circuit can be powered with an AC source or with the help of a battery, so we provide two switches S1 and S2. Turn switch S1 to AC power and S2 to battery. You can also use a solar panel in place of the AC source and store charge in rechargeable batteries. This will not only save your electricity bill but also help you in case of a power failure.
Circuit diagrams
| Circuit diagram-variable power supply-charger-emergency light |  |
Project Components
- Capacitor
- LED
- Resistor
