5 Watt LED Driver Circuit (SMPS)

This article explains how to construct a power supply that uses a wall plug to directly power brilliant LEDs.

Though it is specifically designed for white LEDs it can also function with blue, green, red, yellow and even ultraviolet (UV) lights.

What is a 5 Watt LED Driver Circuit:

A 5 watt light emitting diode LED is powered by a 5 watt LED driver circuit which is designed to supply a regulated and constant current or voltage.

For LEDs to function smoothly and constantly an appropriate current or voltage is necessary and a specially designed LED driver helps to maintain the required electrical properties.

A self oscillating flyback converter that provides efficient LED operation straight from the mains can be seen in the schematic diagram of a 5 Watt LED driver circuit below.

Circuit Working:

Parts List:

The primary winding T1 serves as the power switch for the power supply which functions as a flyback self oscillating converter.

To do this a KSC5027 transistor are used.

The shunt resistor Rx senses the LED current in this current mode setup.

Also, the auxiliary winding acts as a feedback system.

Resistor Calculation:

The formula as follows is used to calculate the shunt resistor value Rx:

Rx = 0.65V / I

where,

• The required LED current is marked by I.

Higher brightness and a longer LED lifespan are made possible by adjusting the LED current.

Transformer Construction:

The transformer Tr1 is wound on an EE core with a middle column measuring 4.5 x 4.5 mm sourced from an old ATX PC supply.

The primary winding consists of 180 turns with a wire diameter of 0.2 mm and the secondary winding comprises 6 turns of triple wire with a diameter of 0.5 mm.

The winding sequence involves the first half of the primary followed by the secondary and then the remaining half of the primary.

If required a ready made transformer designed for 5V switching power supplies is used with the auxiliary winding left unused.

Adding Voltage Feedback:

To demonstrates the integration of voltage feedback into the power supply one should ensure longevity in the case that an LED shuts down or discontinues.

The systems overall dependability is improved by this addition.

Power Supply Frequency

The power supplies frequency of operation is around 80 kHz which improves its efficiency for LED applications.

How to Build:

Constructing a 5 Watt LED Driver Circuit operating directly from 220V mains voltage are mentioned below:

• Wind the primary winding with 180 turns of wire with a diameter of 0.2 mm.
• Wind the secondary winding with 6 turns of triple wire with a diameter of 0.5 mm.
• Wind the first half of the primary 90 turns followed by the secondary and then the remaining half of the primary.
• Install the transistor eg KSC5027 to perform the power switch function.
• Calculate the shunt resistor value using the formula R = 0.65 VIR = I0.65V​.
• Connect the shunt resistor Rx to sense the LED current.
• Integrate the Schottky diode as the rectifier due to its higher efficiency.
• Place capacitors and resistors according to the schematic
• Ensure the correct values and orientations.
• Connect the LED to the output ensuring correct polarity.

Testing:

• A variable power source is used to slowly increase the circuits power.
• Keep an eye on LED brightness and measure output current and voltage..

Warning: Safety Precautions:

Making clear that all circuits are directly connected with the fatal mains voltage aims to make this switching power supply unsafe for beginners.

Capacitors can maintain dangerous voltages even after being disconnected if the LED diode is not isolated from the mains.

Each task is done at ones own risk and the writer hereby denies any responsibility for any property or health damage.

This power supply should be built and operated with extreme attention for safety standards.

References

1 W to 5 W LED Driver