Electronic Balast

In principle, fluorescent lamp controller (often referred to as electronic ballast) is comprised of components that provide high currents with frequencies above 18KHz. Commonly used frequency is 20kHz frequency up to 60KHz.
This application has several advantages, namely:
a. Increase the conversion ratio of electric power to the light produced.
b. No detection of blink of the eye because kedipannya occur at very high frequencies which can not be followed by the speed of the eye.
c. Lightweight electronic ballasts.

But the benefits are redeemed with circuit complexity compared with conventional ballasts. In the electronic ballast, there are 3 different types of commonly used are:
a. Flyback inverter
b. Resonant Current source circuit
c. Voltage source series resonant 

Flyback Inverter
This type is not very popular because of the high voltage transients approach which impacted directly by the use of high voltage circuit voltage as well as the use of components for high-voltage transistor.
In addition, the flyback circuit will decrease the efficiency of the transistor due to losses during switching. The main disadvantage of the flyback inverter will generate a square voltage and current triangular. Voltage waveforms such as this is not good enough for fluorescent lamps. In order for this circuit to produce sinusoidal signals it is necessary to add components inductors and capacitors.

Current Source Resonant circuit
For the series using this technique requires an additional component called a feed choke inductor. This component should also use high voltage transistors. Therefore, this electronic ballast circuit requires a higher cost. Transistor components used must have the characteristics of breakdown voltage (VBR must be greater than 784 volts and must be able to drain the collector current of 1 to 2A.

Voltage Source Series Resonant
The circuit is the most widely used by various electronic ballast industry today.
AC voltage as supply voltage is rectified with bridge use traditional DR and will fill the bank kapasistor C1. C1 will be a source of DC voltage to fluorescent tube lights. Then, an input filter is formed to prevent the circuit from voltage transients from the supply voltage grid and weaken the various sources of noise, EMI (Electro Magnetic Interferrence) generated by the high frequency of fluorescent lamp tubes. Input filter is formed by a series of inductors and capacitors. Block circuit diagram can be seen in Figure bellow.

Input of this filter should have a good specification because it must to prevent the interference of radio waves so that in America it must have the input filter FCC certificate.
The resulting resonance frequency can be determined using the equation:

When the circuit is turned on, the fluorescent tubes will have a very large impedance so that the C4 as if the series with L and C3 to obtain the above equation.
The resulting resonance has a voltage large enough to ionize the gas inside the fluorescent lamp tube. This condition will cause the condition strating that suddenly so as to shorten the life of filaments because filaments not get warm enough to emit electrons. This condition is determined by the circumstances osilatornya.
At the time of starting up there is also a very large peak flows, amounting to 4 times steady state current. Therefore, transistors must be selected that have a collector current characteristics of 4 x steady flow of about 2.75A. About a steady flow of size 0.75A. So that Q1 and Q2 must be capable of passing a current of 2.75A.
When fluorescent tube has been fully ionized by the impedance will drop to just hundreds of ohms so it will remove the charge on C4. These conditions will shift the resonance frequency to a value determined by C3 and L. The energy that is used is now smaller as well as the voltage between the electrodes, the electrodes become too small. This condition is an end to the startup of this fluorescent lamp.
Below is a sample application for electronic ballasts using power transistors BUL45.
Noteworthy in terms of controlling the electronic ballasts are the parameters of power transistors that are used that can guarantee the steady state of the fluorescent lamp.