Simple 220V SMPS Circuit using One Transistor

This article shows how to build a simple power supply circuit that plugs into the wall outlet 220V and uses only one transistor MJE13005.

It does not need any fancy chips or extra parts to control the power.

Instead of those parts it uses a special diode and a winding on the transformer to indirectly control the voltage output.

This keeps the voltage from getting too high.

What is a 220V SMPS Circuit:

A 220V SMPS Switched Mode Power Supply circuit is designed to convert a 220V AC alternating current input voltage into a stable DC direct current output voltage.

SMPS circuits are widely used in various electronic devices such as computers, LED drivers and other electronic equipment to provide a regulated and efficient power supply.

Circuit Working:

Parts List:

Transformer Winding Details:

Use a small EE ferrite core transformer with a central pillar having a cross section of 4.5 x 4.5 mm and an air gap of 0.4 mm.

This core can be sourced from the auxiliary transformer of an ATX power supply.

Wind 1st primary winding with 200 turns of a 0.12 mm diameter wire.

Wind the first half of the primary with 100 turns followed by a thick layer of insulation.

After 100 turns in the same direction finish the second half of the primary 1st by adding the third secondary winding, another heavy layer of insulation and the auxiliary winding which has a second thinner layer of insulation.

Formula for transformer winding:

In a 220V SMPS circuit the primary winding Np of a transformer is calculated as follows:

N_p = ( V_in(nom) x 10⁸ ) / ( 4 x f x B_max x A_e )

where:

• Vin(nom) is the standard input voltage from 220V RMS which should also take peak voltage into mind.
• The standard range for SMPS circuits is 50kHz to 200kHz where f is the switching frequency in Hz.
• Bmax or the transformer cores maximum flux density in gauss which is usually between the range of 1200 and 2000 gauss.
• Ae which can be found in the datasheet of the transformer core of ones choice is the effective cross sectional area of the core in cm².

Transistor and Diode Placement:

Connect the transistor T1 to the primary winding and ensure proper insulation.

Place the zener diode to regulate the base current of T1.

For small voltages like 6V or less use a schottky diode or otherwise use a fast diode for higher voltages.

Capacitor Installation:

With the focus on polarity connect capacitors in line with the circuit design.

If one wants to indirectly decide the output voltage than C2 is essential for voltage control.

Resistor Connection:

Make sure one uses the right resistor values when adding resistors to the circuit as instructed.

Insulation Layers:

To maintain safety and avoid short circuits use insulating layers in between windings.

Output Voltage Adjustment:

By adjusting the number of turns in the third secondary winding one can change the output voltage.

While calculating the correct output voltage keep in mind the voltage loss across diode D1.

Testing:

Check for connectivity and correct wiring with a multimeter.

Use power safely by keeping an eye on the output voltage and be sure it is at the correct level.

Heat Sink Addition Optional:

To successfully release heat while looking for a greater power output connect a heat sink to the transistor T1.

Transistor Selection:

If transistor MJE13005 is not available one can select a transistor for T1 that has Uce = 450V or more and Ucb = 800V.

Transistors options include KSC5027, 2SC3150, 2SC3457, 2SC2979, 2SC2866 or BUT11AF which are economically available.

Output Voltage Adjustment:

By changing the number of turns in the third secondary winding by around 1.17 turns/V one can change the output voltage.

While calculating the necessary output voltage keep note of the voltage loss across diode D1.

Diode Selection:

For small voltages approximately 6V or less replace diode D1 with a schottky diode rated at 40V or higher.

Caution and Warning:

Beginners are not advised to use this switching supply circuit because of involvement of deadly mains voltage.

Extreme care is needed since poor design could cause mains voltage to reach the output.

Even when a capacitor is unplugged from the mains it may still hold harmful voltages.

All activities related to this project are undertaken at the individuals own risk and the writer is not responsible for any harm to health or property.

Conclusion:

By following the above methods the users can create a unique and efficient self oscillating circuit.

Simple 220V SMPS Circuit using One Transistor with adjustable output voltage avoids the complexities of integrated circuits and optocouplers.

References:

MJE13005 Datasheet