This Homemade Power supply is useful for the Electronics hobbyists and service persons to test and troubleshoot the circuits. It gives six stage well regulated output power with a current of 800 mA. Its construction is “Open type” as it is home made. You can make it like a professional power supply by fixing inside a box with connectors for tapping the output.
1. Voltage Regulator – LM7818 – 1
2. Voltage Regulator – LM7815 – 1
3. Voltage Regulator – LM7812 – 1
4. Voltage Regulator – LM7809 – 1
5. Voltage Regulator – LM7805 – 1
6. 1000 uF 63 V Electrolytic capacitor – 1
7. 470 uF 63 V Electrolytic capacitor – 1
8. 0-18, 1 Amps Step down transformer – 1
9. Bridge rectifier module – 1
10. 7pin Rotary switch – 1
11. DC voltmeter ( 0-100V ) – 1
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The power supply gives 18V, 15V, 12V, 9V, 5V regulated output voltages and 22V Unregulated output. Voltage regulator ICs 78 XX series are used to get the desired output voltage. These are Positive regulators that regulate the output voltage based on its value. For example 7812 gives 12 volt output. Even though the Voltage regulator handles 1 Amps current, generally its output current will be around 800 mA if the input is 1 Amps or higher. Each voltage regulator needs minimum 2 volt extra input voltage than its value for proper working. For example, for a 7812 voltage regulator, we have to give 14V in the input. Voltage regulator IC is a three pin device and the pins are In, Ground and Out from the facing side. It needs a Heat sink to dissipate heat, if the input current is higher than 500 mA.
Constructing the circuit is simple. All the regulator ICs are connected in series in the descending order of their value. Connection is in the order 7818-7815-7812-7809-7805. From the transformer, around 22 volt will be available after rectification and smoothing. This 22V passes into 7818 and it gives 18V output which passes into 7815. It then gives 15V output which passes into 7812. The 12V output from 7812 passes into 7809 which gives 9V output. This 9V passes into 7805 and it gives 5V output. The output voltage from each section is tapped from the output of each IC. For example, 18V from the output of 7818. Like this , we get 5 output voltages. A Rotary switch is used for selecting the desired output voltage. The outputs from the Regulator ICs are connected to the 5 input pins of the Rotary switch. The output pin of the Rotary switch is common and it gives particular output voltage when we rotate the rotary switch. 22V Unregulated voltage is tapped from the output of the Smoothing capacitor C1.A Digital DC voltmeter is connected at the output to see the output voltage. Small DC volt meter is available now for Rs. 70 and you can procure it from e bay or other online stores.
An Ampere Meter also added.It is charging a 12 V 4.5 Ah Lead Acid Battery with 680 mA current
Since the power supply is homemade type, no casing was used. A Plywood plank was used to fix the components. Transformer is directly screwed into the plank. All the Regulator ICs are fixed on the common Heat sink which can be a large aluminium sheet. Heat sink compound was applied on the metal side of the regulator before fixing to make firm contact with the heat sink.
When the rotary switch is turned, corresponding output voltage will be available at the common output terminal. At the same time, the output voltage will be displayed in the Digital volt meter. This Power supply can be used to charge various types of batteries that need high current. If you need only less current, use either 0-18, 200 mA or 500mA transformer.