What is an Electronic Ballast?
An electronic ballast (or electrical ballast) is a device which controls the starting voltage and the operating currents of lighting devices.
It does this through the principle of electrical gas discharge. An electronic ballast will convert power frequency to a very high frequency to initialize the gas discharge process in Fluorescent Lamps – by controlling voltage across the lamp and current through the lamp.
Use of Electronics Ballast
There are some advantages to use electronic ballast instead of electromagnetic ballast.
- It operates in low supply voltage. It produces high frequency to give very high output voltage initially to start up the discharge process.
- It creates very low noise during operation.
- It does not create any stroboscopic effect or RF interference.
- As it works with very high frequency, it helps to start the lamp operation instantaneously.
- It does not require any starter that is use in electromagnetic ballast.
- It never creates flickering.
- No start up vibration occurs.
- Its weight is very minimal.
- Ballast loss is very less. Hence energy saving is possible.
- It increases the life of the Lamp.
- Due to operation at higher frequency, discharge process in fluorescent lamp is at higher rate. Hence quality of light is increased.
Working Principle of an Electronic Ballast
Electronic ballast takes supply at 50 – 60 Hz. It first converts AC voltage into DC voltage. After that, filtration of this DC voltage is done by using capacitor configuration. Now filtered DC voltage is fed to the high frequency oscillation stage where oscillation is typically square wave and frequency range is from 20 kHz to 80 kHz.
Hence output current is with very high frequency. A small amount of inductance is provided to be associated with high rate of change of current on high frequency to generate high valued . Generally more than 400 V is required to strike the gas discharge process in fluorescent tube light. When switch is ON, initial voltage across the lamp becomes 1000 V around due to high valued , hence gas discharge takes place instantaneously.
Once the discharge process is started, the voltage across lamp is decreased below 230V up to 125V and then this electronic ballast allows limited current to flow through this lamp. This control of voltage and current is done by control unit of the electronic ballast. In running condition of fluorescent lamp electronic ballast acts as a dimmer to limit current and voltage.
Basic Circuitry of an Electronic Ballast
In present days, electronic ballast design is so robust and somewhat complicated to work very smoothly with high leveled controlling ability. The basic components used in the Electronic Ballast are listed below.
- EMI filter: Blocks any electromagnetic Interference
- Rectifier: Converts AC power to DC power
- PFC: It does Power Factor Correction
- Half-Bridge Resonant Output: Converts DC to square waved voltage with high frequency (20 kHz to 80 kHz).
- Control Circuit: Controls voltage and current across and through the lamp respectively.