Insight - How Electronic Ballast works

Electronic ballasts are gradually replacing conventional magnetic ballasts (commonly known as choke) from the fluorescent tubes. They have higher efficiency as compared to magnetic ballasts and provide a flicker free start up to the tube. Also it does not produce the ‘hum’ sound which is very annoying with the magnetic ballast. There are two primary functions of the electronic ballast:

1. To provide the initial high voltage required to ionize the gas, thereby setting up an arc between the two electrodes.

2. To limit the current through the tube once it has started up. If the current is not controlled it may result in voltage spike thereby damaging the lamp.

The other functions include ignition, warm-up, constant power control, power factor correction, and protection against all lamp and ballast fault conditions.

Fig. 1: Image Showing A Typical Electronic Ballast

Electronic ballast as shown in the above image uses semiconductor components and operates at 20 KHz-80KHz unlike the magnetic ballast which operates at 50 -60 Hz. At high frequency the lamp requires less input power, thereby increasing the efficiency.

Fig. 2: Electronic Ballast’s Printed Circuit Board

The PCB that holds all the components of the ballast is shown in the above image. This PCB is enveloped in a rectangular plastic case.

Electronic Ballast Components

Fig. 3: Electronic Components of Ballast’s PCB

Electronic ballast uses electronic components that are shown in the above image. The components used are diodes, capacitors, high frequency transistors, inductor, transformer and resistances.

Electronic Ballast's Printed Circuit Board

Fig. 4: Electronic Ballast PCB Capacitors

When power supply enters in to the ballast circuit, it first goes through an EMI filtration to block the ballast generated noise. Capacitors shown in the above image are used for the same.

Rectifier & Inverter

Fig. 5: Image Showing Positioning of Diodes In An Electronic Ballast

Four diodes are positioned in the circuit to make a full wave rectifier. It converts AC mains voltage to a full wave rectified voltage.

Fig. 6: Closer Look At Inverter In Electronic Ballast’s PCB

An inverter which uses high frequency transistors convert the low frequency DC to high frequency AC (alternating square wave) of the order of 20KHz- 80KHz. The other components of the circuit are used for functions like power factor correction, harmonics filtering etc.

Use of Transformer

Fig. 7: Image Showing Positioning of A Transformer In PCB Circuit of Ballast

A transformer is used at the end of the circuit. The output to the lamp is fed through this transformer. Another advantage of the high frequency is the small size of the transformer. The size of a transformer is inversely proportional to frequency and hence higher the frequency smaller is the size of transformer thereby reducing the weight of the electronic ballast to almost 1/5 th of the magnetic ballast.