40 watt Electronic Ballast Circuit

Simple electronic fluorescent ballast circuits are difficult to find and build. A simple homemade electronic 40 watt ballast circuit is neatly explained in this article. The PCB layout of the proposed electronic fluorescent ballast is also provided along with the torroid and the buffer choke winding details.
Even the promising and the most talked about LED technology is perhaps unable to produce lights equal to the modern electronic fluorescent ballasts lights. The circuit of one such electronic tube light is discussed here, with efficiency better than LED lights.
So what’s the exact advantage of using electronic fluorescent ballast compared to the age old electrical ballast? To understand the differences correctly it is important to know how ordinary electrical ballasts work.
Electrical ballast is nothing but a simple high current, mains voltage inductor made by winding number of turns of copper wire over laminated iron core. Basically, as we all know a fluorescent tube requires a high initial current thrust to ignite and make the electrons flow connect in between its end filaments. Once this conduction is connected the current consumption to sustain this conduction and the illumination becomes minimal. Electrical ballasts are used just to “kick” this initial current and then control the supply of the current by offering increased impedance once the ignition is completed.
A starter makes it sure that the initial “kicks” are applied through intermittent contacts, during which the copper winding’s stored energy is used to produce the required high currents. The starter stops functioning once the tube gets ignited and now since the ballast is routed via the tube, starts getting a continuous flow of AC through it and due to its natural attributes offers high impedance, controlling the current and helping sustain optimal glow.
However, due to variation in voltages and lack of an ideal calculation, electrical ballasts can become quite inefficient, dissipating and wasting a lot of energy through heat. If you actually measure you will find that a 40 watt electrical choke fixture may consume as high as 70 watts of power, almost double the required amount. Also, the initial flickers involved cannot be appreciated.
Electronic ballasts on the other hand are just the opposite as far as efficiency is concerned. The one which I built consumed just 0.13 Amps of current @ 230volts and produced light intensity that looked much brighter than normal. The have been using this circuit since last 3 years without no problems whatsoever (though I had to replace the tube once as it blackened at the ends and started producing lesser light.)
The current reading itself proves how efficient the circuit is, the power consumption being just around 30 watts and an output light equivalent to 50 watts.
Its working principle of the proposed electronic flourescent ballast is rather straightforward. The AC signal is first rectified and filtered using a bridge/capacitor configuration. The next comprises a simple two transistor cross-coupled oscillator stage. The rectified DC is applied to this stage which immediately starts oscillating at the required high frequency. The oscillations are typically square wave which is appropriately buffered via an inductor before it is finally used to ignite and illuminate the connected tube. The diagram shows a 110 V version which can be easily modified into 230 volt model through simple alterations.
 

The following illustrations clearly explains how to build a homemade electronic 40 watt electronic fluorescent ballast circuit at home using ordinary parts.

 

R1,R2,R5=330K MFR 1%
R3,R4,R6,R7=47 Ohm, CFR 5%
R8=2.2 Ohms, 2watts
C1,C2=0.0047/400V PPC
C3,C4=0.033/400V PPC
C5=4.7uF/400V Electrolytic
D1=Diac DB3
D2……D7=1N4007
D10,D13=B159
D8,D9,D11,D12=1N4148
T1,T2=13005 Motorola Heatsink is required for T1 and T2.

◙  alterations can be done to use directly in 230V:

√  Change C3, C4 = 0.0047uF/1KV, use MOV at the input after a 22 Ohm/1watt resistor.

◙  To reduce from 40w to 20 or 22w ballast:

√   reducing the value of C3, C4 to 0.0022uF

 

◙  The choke inductor is not critical, neither is the torroid, however the torroid wire type and turns are critical. The torroid core is T13 or similar and the wire is single core insulated type, the core should be very thin can't say about the exact gauge.
The choke utilizes E-cores, any small type will do, with as many turn as possible using enameled copper wire, gauge can be 25 to 30 SWG.