Varistors in LED Circuits

Have you heard of light-emitting diodes? You might not recognize the term light-emitting diode, but you definitely know its abbreviation—LED.

In the past, people used kerosene lamps and incandescent bulbs. Kerosene lamps provided dim, limited light that strained the eyes, while incandescent bulbs were brighter and covered a larger area. But with technological advancements, incandescent bulbs have largely been replaced by LED lights.

LED, short for Light Emitting Diode, is a semiconductor device that converts electrical energy into light energy by allowing electrons and holes to recombine and release photons.

LEDs are now widely used, especially in lighting—many modern city streetlights, for instance, are LED-based.

Advantages of LEDs

LEDs have many benefits:

High efficiency — They provide much higher brightness than incandescent bulbs while consuming far less energy.

Long lifespan — LEDs can operate for many times longer than incandescent bulbs.

Low power consumption — They reduce carbon emissions and are environmentally friendly.

Compact size — Their small form factor allows them to be used in a wide range of applications, from lighting fixtures and displays to automotive lights.

However, LEDs are sensitive to current and voltage fluctuations and have poor overvoltage tolerance. When an overvoltage occurs, LEDs can easily burn out or degrade in performance. That’s where varistors come in to protect them.

How Varistors Protect LEDs

A varistor is a nonlinear voltage-dependent resistor used for overvoltage protection. Its resistance changes with the applied voltage:

Under normal voltage, the varistor’s resistance is very high, and it conducts almost no current.

When the voltage exceeds the varistor’s rated value, its resistance drops sharply, allowing current to pass through. The varistor then absorbs the excess current and clamps the voltage within a safe range, preventing damage to the following circuit.

In LED circuits, varistors are typically installed at the input of the LED power supply to shield the LEDs from overvoltage damage. When an overvoltage event occurs, the varistor responds instantly, clamping the voltage spike and protecting the LED from burnout.

This article is provided by JYH HSU (JEC) Electronics. JEC is a research, development, production, and sales-oriented company specializing in manufacturing and selling various electronic components such as capacitors and resistors.