DC Power Supply
Battery operated walkmans, radios and other electronic devices need their batteries to be changed very often. We get tired replacing old batteries and purchasing a new one from shops. Alkaline batteries are some what more expensive than ever.In our project we are going to build an electronic device that will be an alternative to the battery. Yes, we are going to build a regulated power supply from AC mains. Just connect input to AC mains and the output to the line of the battery of your device and relax. Listen to your walkmans and radios without bothering to replacing batteries. You can use this Power Supply to charge your rechargeable batteries. Thus no more replacement. Just recharge and reuse.
A regulated DC voltage source is obtained from a AC voltage source is easily by
rectification. AC voltage is of 230V r.m.s. is easily available. This voltage is
step downed by a transformer. Then rectified by diodes. If a center taped
transformer is used only two diode is sufficient for full wave-rectification. If
transformer is not a center taped bridge rectifier is used. After rectification
the voltage is DC but contains high ripple. A LC or RC filter is used at the
output to filter the high ripple voltage. Now this voltage can be used for DC
supply. But this DC source is not regulated means if the input AC voltage
changes output also changes. To get a regulated output zener diode regulation
and Voltage Regulator may be used.
Voltage regulators come in integrated circuits in a variety of ranges. Regulators are of four types
1. Fixed output voltage regulators: positive or negative output voltage
2. Adjustable output voltage regulators: positive or negative output voltage
3. Switching regulators
4. Special regulators
We use 7806 to 7812 for positive fixed Regulated power supply.
Parts List for DC Power Supply
T1- Center Taped
Transformer 230/12V 1A max
D1, D2 - IN4007 1A max
R1- 100kohm, 1/2. watt resistor
Load- 100kohm, 1/2. watt resistor
C1-2200uF 25 V DC electrolytic capacitor
C2- 1uF 25 V DC electrolytic capacitor
C3- 220nF 25 V DC paper capacitor
U1- Regulator 7812, Plastic
Testing:- The circuit shown in the fig. is for 12V DC supply. You can make 3-12 V range supply DC source by replacing the regulator. Also you need to replace the transformer. But you can get variable range of voltage from a single transformer, if you use multiple winding in secondary. This type of transformer is easily available in market and cost little more. Thus you can make 3-12 V supply from one transformer.
Application:- Use the circuit to play your walkman or radio. You don't need any battery. You can also charge rechargeable batteries. To use it as a charger use higher rating transformer and suitable regulator with high current rating.