Electronic Ballast

Introduction: Electronic Ballast

About: I am a retired Electronic Systems Engineer now pursuing my hobbies full time. I share what I do especially with the world wide student community.

This Compact, lightweight, high-frequency electronic ballast is designed to operate off the 230V AC mains supply at 50-60 Hz and is suitable for 36 – 40 W fluorescent tubes.

The advantages of such a ballast are:

  • Saving in Energy
  • Longevity of tube
  • Low noise
  • Operates at low voltages
  • No Flickering
  • No heat
  • Instant-Start operation
  • Minimal Weight
  • No Starter Required

This unit cost me less than $2 to build.

Step 1: Caution


This unit operates off the AC mains with a voltage of 230 Volts and voltages generated within the unit can reach 600 to 800 Volts. Extreme caution must be exercised while building, testing and using this unit.

At a minimum a VARIAC (Variable AC transformer), Isolation transformer and meters for monitoring the input voltage and current are required during initial testing of the prototype units.

It is strongly suggested that you go through the excellent Instructable "Work safely with high voltage" by kovo:


Warning & Disclaimer:

All content provided here is for informational purposes only. I make no representations as to the accuracy or completeness of any information. I will not be liable for any errors or omissions in this information. I will not be liable for any losses, injuries, or damages from the use of this information.

Step 2: Circuit and Description

The schematic of the unit conforms to that of a “Half-Bridge Resonant Converter”, and operates as follows:

The AC mains input is fed at AC1-AC2 and full-wave rectified by diodes D3, D4, D10 and D11. The rectified output is filtered by the high-voltage capacitor C5 to form the DC supply voltage to the half-bridge converter.

A mid-point DC voltage is formed by the diode-capacitor network D2, D5, D8, D12 and C2, C7.

The half-bridge transistors Q1, Q2 effectively switch the load between the collector junction of Q2 and the junction of diodes D5 and D8. High frequency filtering of mid-point DC voltage is provided by capacitors C1 and C6.

The effective load is a series combination of the base-drive toroid-transformer, resonant-inductor and florescent tube.

The series-resonant frequency is determined by the 1.3mH inductor and the series combination of capacitors C3 and C4. The circuit resonates at a nominal 60 kHz.

The toroid transformer provides the base-drive to transistors Q1 and Q2 in the correct phase so that the transistors switch on-off alternately.

Resistors R4 and R9 provide a dc-bias path for Q1 and Q2. R3 and R8 limit the base drive and resistors R5 and R10 limit the collector currents of Q1 and Q2.

To ensure start-up the voltage across C8 builds-up through R1 and R7 till it crosses the breakdown voltage of DIAC D6. A sharp pulse is fed to the base of Q2 when this occurs. D9 inhibits this triggering once the resonant-converter starts-up.

On initial start-up a very high AC voltage is impressed across the fluorescent tube terminals TL1-TL2 the tube ionizes and breaks down setting up the discharge between the terminals. Once this occurs a voltage of 80-100 volts across the tube is sufficient for generating the light output. This voltage and the current through the tube are regulated by the inductor L1.

Step 3: Waveforms

Half-bridge drive:

The half-bridge output drive drive voltage to the load at Pin 4 of the toroid transformer is a 60 kHz nominal square-wave modulated by the AC ripple voltage at 50 Hz.

Mid-point DC voltage:

The mid-point voltage of approximately 200 Volts DC with a ripple of 200 Volts at 50 Hz is seen.

Toroid drive:

The input-voltage seen by the toroid-transformer is 18 V p-p at a nominal 60 khz.

Resonant high-voltage:

The resonant-voltage at the tube terminal TL3 is 600 V p-p at 60 kHz.

Step 4: Bill of Materials

The table provides the bill of materials required for this unit.

Step 5: Wound Components 1 - Toroid Transformer:


This toroid-transformer provides the drive to transistors Q1 and Q2 in the correct phase and amplitude to create a positive-feedback system which oscillates at the resonant frequency. The transformer is wound using single-strand insulated wire with primary of 4 Turns and two secondary’s of 5 Turns each. The toroid is a ferrite core from Mahindra-Hinoday with part number T 10 X 3 and material MSB5S. The direction of winding should be exactly as shown in the images.

Step 6: Wound Components 2 - Resonant Inductor:


Is a wound inductor with air-gap using an EE core from Mahindra-Hinoday with part number EE 19X8X5 and material MSB5S. A 0.33 mm air-gap is created by pasting three layers of standard insulation tape on the three legs of the EE core. The winding is 130 Turns of 2 X #38 gauge insulated copper wire. The inductance value is 1.33 mH and resistance 1.9 Ohms.

Step 7: Printed Circuit Boards:

The images show the component placement details both by value and name.

The physical placement of components on the wired PCB is also shown.

The Choke_BOT.pdf file gives the 1:1 size of the PCB bottom on A4 size paper. This can be used to fabricate the PCB.

Step 8: Summary

This Instructable provides essential information for fabrication and operation of the Aj-Electronic Choke which is a form-fit-function equivalent of a standard wound-choke.

Address any doubts and clarifications to me at e-mail

Other projects can be downloaded from my website Home

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    Question 11 days ago on Introduction

    Sir, I would be very much grateful, if you could kindly inform the value of R2 and R6 resistors. Is it 10 ohms 1 watt or 1/2 watt?


    Answer 2 years ago

    I have tried this with only a single tube. If you connect 3 X 18W tubes in parallel firstly this comes to 54W which is beyond the 40W rating. Also, as tubes in parallel may not start simultaneously whichever comes ON first is likely to get damaged. I advise you not to try this!


    Question 3 years ago on Step 7

    How the torroid Transformer drives the transistor and how the voltage is controlled by the inductor in later stage and how the voltage increased in initial stage...pls explain me sir...


    Question 3 years ago on Step 7

    I can't understand this circuit working....can any one help me with it


    Question 3 years ago on Step 3

    Nice instructable. I am in the U.S. What changes must be made for this to operate on 120V / 60 Hz? I saw a similar question was posted, but not a reply.


    Answer 3 years ago

    With a 220V AC Supply the input circuit acts like a full-wave bridge rectifier and the voltage across C5 is approx 300V DC.
    To obtain this DC voltage with a 110V AC Supply it could be possible to replace the full-wave bridge by a voltage-doubler circuit. I have not tried this and one would need to experiment with the capacitor values for the doubler.


    Question 4 years ago

    hi. how can i modify this to use for 8W fluorescent tube?
    i have a UV 8W Tube and i need to turn it on!


    4 years ago

    I have a good tube which lights up without starter and hence without flickering. It works only with stater in other frames. The tubelight was probably not used for sometime. How does this happen? Does this consume less power.


    Reply 4 years ago

    The electronic-ballast generates the high voltage for startup using a high-frequency oscillator and so does not need the starter. However, normal ballast-chokes which are wound-inductors along with the starter create the high voltage for the tube to start up based on the principle that interrupting an inductor current suddenly creates a high voltage. Yes, the electronic ballast is more efficient.


    5 years ago

    Appreciated Ajoy Raman, i live in Colombia here the supply of energy is 120volts
    and i would like to help me to convert its ballast of 220 to 120v Thanks


    Reply 7 years ago on Introduction

    I voted for you!

    And your web site is certainly worth a read as well - for everyone with even the slightest interest in electronics!

    Have a nice day :)


    7 years ago

    ...or you can take out the electronic ballast from an old energy saving bulb...

    but nice tutorial nevertheless


    Reply 7 years ago

    That's true, but making them is a lot cooler and much more knowledge is gained this way, which is what most people come to Instructables for.