In this tutorial we will discuss about the design of dual polarity power supply circuit. Components, connection diagram and explanation of dual regulated power supply. The circuit is simulated in ISIS Proteus for verification and results shows shat configuration can act as negative voltage power supply circuit.
Power supplies are important part of electronic circuits. Many electronic circuits and components require negative voltage in addition to positive voltage. An example can be operational amplifiers. They require +15 and -15 for biasing. Similarly other components also require negative voltage. Providing negative voltage is always been a challenge. If a circuit requires both positive and negative voltage than providing two power supplies for a single circuit increases cost and size of electronic circuit. Due to this reason lots of useful circuits and components are regarded as impractical because of dual polarity voltage requirement. The solution to this problem is given in this article by presenting a regulated dual polarity power supply circuit. The design uses single power supply circuit to supply voltage of dual polarity. Its negative voltage power supply as well as positive voltage power supply in one circuit.
It must be noted that this article is about dual polarity power supply. Same configuration can be used to build dual voltage power supply which is explained in this article Dual voltage power supply
Components and ratings of dual regulated power supply
Following components are required for dual polarity power supply.
- SPST Switch
- Fuse 1A
- 4 Diodes 1N4007
- Transformer 220/25V
- Capacitors 2200uF, 0.33uF and 0.1uF (2 each)
- Voltage regulator IC LM7815 & LM7915
- Veropins (Optional)
1A fuse is used to provide protection against high current currents. The rating of fuse depends upon the rating of other electronic components. A center tap transformer capable of reducing 220V to 25V is need in dual polarity power supply. Diodes are used to construct bridge rectifier. Since voltage is step down to 25V, PIV (peak inverse rating) of each diode is 50V since double voltage appears across each diode in rectification process.
Circuit diagram: Positive & Negative voltage power supply circuit
Following figure shows circuit diagram for dual regulated power supply.
Transformer steps down 220V 50Hz voltage to 25V and gives it to the bridge configuration for rectification. Bridge circuit converts AC to pulsating DC. In order acquire smooth constant DC voltage, smoothing capacitor of 2200 uF is installed next to the bridge. Till this point a 25V DC unregulated voltage is achieved. To get regulated 15V supply, voltage regulator IC 7815 is used. In order to understand more about LM7815 click here.
On both sides of voltage regulator IC, bypass capacitors (0.33uF and 0.1uF) are connected to provide optimum stability and helps in correct transient response. The values of bypass capacitors are provided in voltage regulator datasheet. The output of LM7815 gives regulat
ed 15V. For negative voltage, the same configuration as for positive voltage is connected with back end of diode bridge configuration. So LM7915 along with its parallel capacitors captures negative cycle of AC supply and converts into negative DC voltage.
Voltage regulator IC can also be used to make constant current source which is explained in this article Constant current source using LM317
Simulation of Dual polarity power supply
Above explained circuit is simulated in proteus ISIS and the result is shown
It can be seen that one side porivdes +15V and second terminal provides -15V.