How to build 12 V transformerless power supply circuit

12V transformerless power supply circuit

Introduction 

Imagine you want to power a small electronic device that requires 12 volts DC, but you only have access to the standard wall outlet power (which is typically much higher, such as 230 volts). Usually, you'd use a big, heavy part called a "transformer" to lower the voltage safely.

This article talks about a clever way to get a 12-volt DC power supply without a transformer, making the power supply smaller and lighter.
Interesting that you can build this tiny circuit at a low cost. 

Know your circuit

The circuit schematic of the transformerless power supply unit is given here. Please go through the connections and the components involved in the circuit schematic. Study the circuit and familiarise yourself with the design. 

Parts List

1N4004 Rectifier diode ..................... 2 nos. 

12V 1W Zener diode .........................2 nos.

0.22MFD 250V AC Capacitor...............1 no.

470 MFD 15V electrolytic Capacitor ....1 no. 

100 ohms 1W Resistor .....................1 no. 

Know your design

Wall outlet power is "AC" (alternating current), which means the direction keeps flipping. Most electronic devices need "DC" (direct current), where electricity flows in one constant direction. This circuit uses 2 nos of Silicon power rectifier diodes to change the AC into DC. This also helps provide more stable power.

Replacing the Transformer: Instead of a bulky step-down power transformer, this circuit uses a special capacitor C1 of value 0.22 MFD (like a tiny energy storage device) to "drop" most of the high voltage. 230 V AC is being reduced to almost 12V AC through this capacitor. Think of it like a controlled bottleneck that only allows a smaller amount of electrical pressure (voltage) to pass through.

Keeping the Voltage Steady: After the voltage is dropped and changed to DC, another special component called a "zener diode" steps in. Diodes D3 and D4 refer to this. Its job is to make sure the output voltage stays exactly at 12 volts, even if the input power fluctuates a bit.

To control the excessive flow of current, at times a limiting resistor R1 is also used in the circuit. Its main purpose is to limit the sudden rush of electricity when you first plug in the power supply, protecting other parts from getting damaged.

Important Safety Warning: Because this circuit connects directly to the high voltage from your wall outlet, it's extremely dangerous if you touch it while it's plugged in. It's vital to build it carefully and enclose it in a protective box so no one can accidentally touch the live parts. As such, no parts are to be touched with the bare hand, as it may give a heavy electrical shock. Hence, one should be careful in handling this gadget while it is in operation. This is very, very important.  

Know your construction

Since the circuit design is very simple, it can be assembled easily on any general-purpose veroboard. It is very important, as mentioned above, that the parts of the circuit should be completely isolated from exposure to the open. A proper safety enclosure, such as high quality plastic box, is necessary to cover the circuit elements from exposure. 

Hence, beginners should be careful in assembling this power supply unit for utmost safety. 

Utilities

This circuit is a compact way to get 12V DC power from an AC wall outlet without a heavy transformer. It uses capacitors to drop voltage, diodes to convert AC to DC, and zener diodes to regulate the output to 12V. As such, the cost of the unit will be much less when compared to a transformer used power supply unit. Safety is paramount! Always handle such circuits with extreme caution and ensure they are properly enclosed before use.
Learn how to assemble a dual power supply circuit by visiting this post. 

Conclusion

Beginners and hobbyists can easily assemble this power supply unit, which is lightweight and cost-effective. Please give your comments on this piece of work.