Dec 22, 2011

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.

Homemade Electronic Fluorescent Ballast

Just a decade ago electronic ballasts were relatively new and due to frequent failures and high costs were not generally preferred by everyone. But with passing time the device went through some serious improvements and the results were encouraging as they started becoming more reliable and long lasting. The modern electronic ballasts are more efficient and fail proof.

So what’s the exact advantage of using electronic flourescent 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.




PCB Component Layout

40 watt Electronic Ballast Component Layout
WARNING: PLEASE INCLUDE A MOV AND A THERMISTER AT THE SUPPLY INPUT, OTHERWISE THE CIRCUIT WILL BECOME UNPREDICTABLE AND MIGHT BLOW-OFF AT ANY MOMENT.




ALSO, MOUNT THE TRANSISTORS OVER SEPARATE, 4*1 INCH HEATSINKS, FOR BETTER EFFICIENCY AND LONGER LIFE.

PCB Track Layout
40 watt Electronic Ballast PCB track side
Torroid Inductor

40 watt Electronic Ballast torroid inductor wiring
Choke Inductor

40 watt Electronic Ballast EMI choke
Parts List
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.


140 comments:

  1. Hi,
    Can you please explain how the alterations can be done to use directly in 230 V.

    Thanks in advance.

    Hussain

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

      Delete
  2. hi there
    if u upload the schematic and also tell about the value of choke inductor and torroid inductor
    regards

    ReplyDelete
    Replies
    1. Hi,

      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.

      Delete
    2. Hi...
      i did everything as you stated. only thing am stuck with is..with the choke & torroid coil. can you please specify much more details or mention some equivalent parts avail in the market.

      TIA

      Delete
    3. Hi...bro...
      if you can send me any clear pic of PCB diagram or layout diagram....i can post the clear schematic diagram for you & everyone else..this will also helps me too...
      waiting for your esteemed reply....
      TIA

      Delete
    4. Bro, everything is shown quite clearly in the article above, if you are having difficulty understanding, you can specify those... I'll clarify them immediately.

      If possible I'll try to produce a clearer PCB diagram.

      Delete
  3. Bundle of thanks for reply
    one other thing if upload the clear schematic of the design it will be easy as it is power circuit so it is risky without it.There are some areas which is not very clear.
    regards

    ReplyDelete
    Replies
    1. Hi,

      You are welcome!

      Actually I don't have the schematic, I modified the above circuit from a ready-made 110V version, and drawing a fresh schematic now will be difficult for me. The PCB layout is clearly given so if you can make the PCB, everything else becomes absolutely easy.

      I have used this design and it has proved very reliable to me so far.

      Regards.

      Delete
  4. can we use this type of circuit to drive white LEDs?
    I've made mains LED driver with 0.22uF/400V capaciotr, but using it with a general(lower quality square wave) inverter duirng power cuts causing decreased light in LEDs and a more load to the inverter than required!
    So, how can we use an electronic choke/CFL ballast circuit which can easily drive many white LEDs powering from a general inverter?

    ReplyDelete
    Replies
    1. I don't think you can use the above circuit for driving LEDs, use 2.2uF/400V, for making the LEDs brighter in your earlier circuit.

      Delete
  5. how to reduce from 40w to 20 or 22w ballast?

    thanks..

    ReplyDelete
    Replies
    1. By reducing the value of C3, C4 to 0.0022uF

      Delete
  6. good day sir,

    how can we convert the circuit to 20W? 220V?

    ReplyDelete
    Replies
    1. You can replace C3, C4 with 0.0022uF caps and see what happens.

      Delete
    2. Hi. I want this to run only from 12 or 24volts dc. Can you help please I want to power a 42 or 57 watt cfl lamp. Osram dulux te plus

      Delete
  7. i have heard that this process will less the life time of tube light is it true?

    ReplyDelete
    Replies
    1. Yes, the tube blackens at the ends after 2 years of use, so you may have to replace it after every couple of years.

      Delete
  8. ok swagatham do you have circut for dc ballast ?

    ReplyDelete
    Replies
    1. I have never looked for it so I haven't designed any, but there are plenty of such circuits present online, you can easily find them.

      Delete
  9. hi boss
    i have found a 8 watt flourcent inverter circuit here http://tacashi.tripod.com/elctrncs/inverter/inverter.htm ..can i use the same for 8 watt ready made led bulb which avaliable in market

    ReplyDelete
    Replies
    1. Hi Sandy,

      How does the LED bulb operate, it should be operating from an AC mains outlet I guess? Then what's the need of using an inverter?

      Delete
  10. to run with batter when power fails

    ReplyDelete
    Replies
    1. OK, it may light up but it is not recommended because the voltage from the inverter will be very high and might damage the LED lamp, try using a 100 Ohm 3 watt resistor in series first, then gradually modify the value of the resistor for best results.

      Delete
  11. ok swagatham thanku

    is it ok if that inverter produce exact 230v

    ReplyDelete
    Replies
    1. Welcome Sandy...

      Yes at 230v it will be fine.

      Delete
  12. Youvaraj

    Using this inductor what gauge? ang how many turns?

    ReplyDelete
  13. Hai sir:

    Tell using this circuit inductor gauge what? and how many turns?

    ReplyDelete
  14. Dear Swagatham, first of all thanks ! I was looking for this circuit for quite some time . Now to the question I need this to drive a 56wPLL what tweaks would I have to make ?
    Thanks in advance,
    Jithin

    ReplyDelete
    Replies
    1. Dear Jithin,

      I don't think a 56w tube would work here, because even with a 40 watt tube the transistors become considerably hot, so a 56watt might not fit here.

      Regards.

      Delete
  15. how to convert 40 W into 24 W? please reply fast

    ReplyDelete
    Replies
    1. Sorry actually it's C3, C4 that needs to be made as 0.0068uF

      Delete
  16. hello sir this is ajay and i want to ask that what is the function of torroidal...and should we replace it with anything else

    ReplyDelete
    Replies
    1. Hello Ajay,

      The torroid is the most important part of the ballast and cannot be modified in any way....the one shown in the diagram is the only option you can go for.

      Delete
  17. Hello Swagatam !!

    In description value of R8 is mentioned as 2.2 ohm and in you comment for VAC you have mention R8 = 22 ohm !! which is correct value ? 22 ohm or 2.2 ohm ??

    ReplyDelete
    Replies
    1. You may use any value between 2.2 and 22 Ohms, it's kept for arresting the initial surge current, so any low value resistor will do the job.

      Delete
  18. Hi swagatam,, im searching over the net but i saw your blog.. i know this is not your topic here but will you mind teach me how to wire in series the (4)10watts flourescent bulb and using only (1) 40watts ballast?? Thanks in advance...

    ReplyDelete
    Replies
    1. Hi TheMan,

      Do you mean 4 nos 10 watt fluorescent Tubes??

      Delete
    2. No,, Swagatam.. is it posible on ordinary 40w electrical ballast on 4 10watts flouscent tubes?
      i already tried with parallel connection on the pin of tubes but the problem is only 1 tubes will light.. i hope you can give me some ideas my needs,, also im soory for my noob questions.. ;)

      Delete
    3. Putting their pins in parallel is fine, however since their firing levels may be different therefore the one with the lowest value is igniting first.

      Try adding a 50 Ohms resistor in series with each tube light and see what happens.

      Delete
    4. ok,, thanks for your reply bro... i`ll try it and will update you tomorrow...

      Delete
  19. Update @Swagatam,,, negative bro.. even if i put 50 ohms in series with each tubes but its same, only 1 tube will light...

    ReplyDelete
    Replies
    1. No ideas Bro, since it's not an electronic device cannot figure out the remedy.

      Delete
  20. OK,, thanks anyway for helping and replying me Bro.. ur such a good guy, God Bless you..

    ReplyDelete
    Replies
    1. The pleasure is all mine...God bless you too!

      Delete
  21. Can you please provide a schematic diagram?

    ReplyDelete
  22. hi.... Swagatam.. This is rahul here, First I like to tell u thanks... can i use any alternate to torroid inductor because it is not available in my city.. i tried above ckt using inductor coil but it is not glowing...

    ReplyDelete
    Replies
    1. Hi, Rahul, welcome to my site!

      You can try a different diameter torroid but it shouldn't be too big.

      Only torroid inductor will work here, other forms will not work.

      Delete
    2. Thank you Bro... i will try it, one more thing where the negative end of both the diodes D2, D3, connected specially D2..

      Delete
    3. Thanks Bro, Yes the connection is not shown by mistake, it is joined with the straight track that's running just under it

      Delete
    4. Thank you......

      Delete
  23. Hi,
    have a good day

    can you please provide me the calculation of the C3, C4 change for different watt.

    regards
    robi

    ReplyDelete
    Replies
    1. Hi,

      C3, C4 should be changed to 0.0047uF/400V for 220V inputs, I am not sure how to modify it for different watts tubes....

      Delete
    2. swagata can you please tell me how to calculate the value of capacitor required in elecronic circuit. I would be thankfull for a small circuit demo

      Delete
    3. it will depend on a particular circuit application, it might differ from circuit to circuit....there's no general or specific formula or method of implementing it.

      Delete
  24. Hi,
    when i search for the making of electronic choke i visited your site.everything in your site is useful. But i could not find the circuit diagram .Can you please send me the circuit diagram?

    ReplyDelete
    Replies
    1. Hi,

      I have provided the PCB and the component layout, i think it's enough for building the circuit, because PCB would be anyway required for this project.

      making the circuit diagram would be difficult for me due to lack of time.

      Delete
  25. Thanks Swagatam..... Sorry for the late reply. I'm from the physics background so i asked u about the circuit diagram.I'm not having any idea in PCB layout. Thats y......Any way thanks for your reply....

    ReplyDelete
  26. I have a unusual question. What changes to this circuit would be needed to a drive a single 96 inch 100Watt UVA/UVB fluorescent tube? I've noticed that this circuit is very similar to the SunQuest Electronic Ballast in a lot of tanning beds we have today.
    Thanks.

    ReplyDelete
  27. hai myself githin

    Iam interested to know details about ur design, i got the concept but i want to know the design parameters.

    could u please tell me.
    1) which freg the oscillator works
    2) need of chock and the value
    3) need of Torrid Inductor
    4) how can i calculating the watts
    ( u discussed earlier changing the capacitor value need calculation method)

    i hope u will guide me my mail address vgithin@gmail.com contact no 09345772248.
    need ur contact details

    ReplyDelete
    Replies
    1. Hi Githin,

      I copied this from a ready made sample, so I don't know much about the calculations.

      The choke can be any type of coil wound over any type of ferrite core...use maximum possible number of turns, example you can try with 200 turns of 30 swg wire.

      I have explained the torroid detail in the article.

      Delete
  28. Hi I have fitted nev pcb but when I connect d power atoumaticaly t1 ant t2 gone.what can I do plz help me

    ReplyDelete
    Replies
    1. Initially please connect a 60 watt bulb in series to confirm the results first.... if the tube illuminates would confirm your circuit and then we can proceed with further improvements like adding thermister, MOV etc.

      please also note that D2 cathode is connected to the track which is passing just under it

      Delete
  29. PLEASE GIVE CLEAR CIRCUIT DIAGRAM

    ReplyDelete
  30. sir please send choke circuit for the 40W tublight and also clear pcb layout.
    thank you

    ReplyDelete
  31. Sir can you please explain the full circuit working and please give the circuit diagram

    ReplyDelete
  32. Bro how can i drive 40w fused(1 end/ 2 end)Tube light by electronic ballast like as electrical ballast? Although i have tried it by shorting the fused end of the light but it do blink when power on then it run.Sometime in the mid of running of light it start blinking then get stable.In this way i reuse that fused light some day but my ballast burst out.So what is the safe solution of it?

    ReplyDelete
    Replies
    1. Bro, the one that is shown in the above article can be used for the same purpose, I have already tried it and it worked for me

      Delete
  33. Bro how long i can reuse the fused tube light in this way(shorting fused end) safely without bursting my electronic ballast?

    ReplyDelete
    Replies
    1. bro, shorting the tube ends will never affect a good quality ballast in anyway, so you can expect a normal operation from it even with the ends shorted

      Delete
  34. bro today im again try to reuse fuse tube lite also CFL as per ur instruction(shorting lite ends) but when i give power then lite start blinking with some time then it run.Is this normal condition or i continue this way will my ballast or CFL burst?

    ReplyDelete
    Replies
    1. bro connecting or shorting the two pins of the tube is not required.

      simply take out single wires from the corresponding sides of the ballast and connect them to any one pin on either side of the tube

      Delete
  35. Bro make i clear it first.U said i have to take only 2 cables from each pairs of cable from out put section of the ballast.then i have to connect that 2 cables individually with any one pin on either side of the tube.is This configuration is allowed for 2 end fused tube or 1 end fused tube?if possible pls make it clear with diagram.

    ReplyDelete
    Replies
    1. yes this wiring method will work for fused tubes.

      Delete
  36. in that pcb track layout, where is the line that does not touch a point touches...?
    thank you

    ReplyDelete
    Replies
    1. at the bottom center edge of the PCB, you will find three pads closely placed.
      the rightmost pad needs to be linked with the track passing just below it.

      Delete
    2. sir,
      i dont get you..
      i asked you that, there is a track which does not touches any pad.I asked you to which pad that track should be linked.?
      thank you

      Delete
    3. sir, can u please correct the track layout and post....
      please please...

      Delete
    4. it's linked to the central large copper containing 6 pads

      Delete
  37. i want to manufacture choke can u guide me

    ReplyDelete
  38. Can u guide me to manufacture a ftl electronic choke

    ReplyDelete
  39. how to manufacture a electronic choke

    ReplyDelete
    Replies
    1. you will need to invest minimum 10 lacs initially and wait for 6 months for the first payment to arrive without stopping the production.

      you can try the following circuit, it will work with ftls also:

      http://homemadecircuitsandschematics.blogspot.in/2014/04/single-chip-electronic-ballast-circuit.html

      Delete
  40. Hi,

    For Electronics Ballast,how we can decide the number of turns for E type inductor an torroid.And how we can calculate it.

    ReplyDelete
    Replies
    1. I have no idea about it, it will depend on the given manufactures specifications.

      Delete
  41. please provide me some idea to use irf840 in place of 13005 in this circuit

    ReplyDelete
    Replies
    1. mosfet will not work properly in place of a BJT in a ballast circuit...because the components are specifically selected for a BJT operation and not for a mosfet.

      Delete
  42. well not in this circuit but how to connect mosfet with this type of circuit? i mean how to provide gate voltage with zener when supply is 240v dc

    ReplyDelete
    Replies
    1. here's one example you may refer to:

      http://4.bp.blogspot.com/-q2OdIb3tOWQ/UvcbVFrEzKI/AAAAAAAAGRo/ROKukGqYUx4/s1600/surge+suppressed+led+driver+circuit.png

      Delete
  43. Hi,
    Can you please explain how the alterations can be done to use directly in 230 V 50hz Supply.With Corrected printed pcb.Please help me.


    Thanks in advance.

    ReplyDelete
    Replies
    1. Hi, the circuit is designed for 220v AC, and the PCB is also correct except one small error which I have explained in one of the above comments

      Delete
  44. sir,
    which date you posted the comment pl tell me.Tell me the specification of coil inductor,terriod and Mov.

    ReplyDelete
    Replies
    1. suresh, see the comment replies from Akarsh above

      Delete
  45. finally i able to make 40w cfl design using mosfets,they are more efficient and more reliable than transistor.i made 3 of them and they are working great.

    ReplyDelete
  46. please publish a circuit of electronics starter for 40 watt fluorescent tube light with magnetic ballast.

    ReplyDelete
    Replies
    1. OK I'll try to design and publish it soon....do keep in touch

      Delete
  47. To all the people asking for values and such, you should try LTSpice or another analog electronics simulator. It even has power analysis if you're trying to figure out how much wattage is going to be dissipated by the transistors, for example. Sadly, it does require some knowledge of how to make a schematic and figure out their 'unique' interface. Luckily, tons of good tutorials with pictures, though!

    I haven't seen if they simulate a fluorescent bulb, but you can add devices with custom behaviors/curves. Even without that, these programs are wonderful for learning electronics and well worth the effort to learn!

    ReplyDelete
  48. can i do it on pcb ie pro-ject board GLno.12 i am a wireman and most of my client call me to replace electronic ballast tube light. but by reading you 40watt electronic ballast i feel i should try to repair all broken ballast it will hwlp my clent in some way. other they have to bring new one from the market.

    ReplyDelete
    Replies
    1. I won't recommend the above circuit since the technology is quite old and not very reliable, today there are IC based much improved circuits which are very reliable and long lasting, you could try one of those circuits...here's one article that may help you regarding the subject:

      http://www.irf.com/technical-info/appnotes/an-995a.pdf

      Delete
  49. hi sir i want to make a robot that can implement the Swach Bharat Abhiyan for school science exhibition .
    for this i had planned to make three robo cars - first will work like a vaccum cleaner which took light weight things like paper and leaves to clean ,second will clean the splits on road or anywhere ,third will took off heavy things .but sir i have one problem with third robot.if anything comes in front of it ,it will took off that object but suppose there is a valuable object like a money purse than it will also took it .sir what can i do so that my robot took off only the waste things not any valuable things.

    ReplyDelete
    Replies
    1. Hi Ritish,

      that's not feasible, you cannot make a vacuum cleaner understand the difference between a valuable material from a scrap material....but this can be handled by a human being at the other end who could segregate the materials appropriately...,...but I don't think you will get too many valuable things on road.... 99% will be scrap and garbage.

      Delete
  50. sir i think for taking off light weight objects like paper or leaves a hi speed C.P.U fan is sufficient with a net in front of it to stop collision between paper and fan.

    ReplyDelete
  51. Sir ..i require 11-18 watts electric ballast..can i proceed this same procedure

    ReplyDelete
    Replies
    1. You can try the following circuit instead:

      http://www.homemade-circuits.com/2014/04/single-chip-electronic-ballast-circuit.html

      Delete
  52. hello sir , i have one more problem regarding to my project swatch bharat abhiyan robot that described before , sir i thought that i will use solar pannel as a source of energy but how to run three dc motor and a c.p.u fan using a solar pannel . if i use batteries then the heavy weight will create problem .if i use ac current then the wire and the plug point will create problem .sir please advice me what to do .

    ReplyDelete
    Replies
    1. hello Ritish,

      batteries will not create any problems, your trolley will easily run on the road with the CPU fan operating along with the batteries.....

      use good quality motors for the wheels.

      for more info you can read the following article:

      http://www.homemade-circuits.com/2015/04/remote-controlled-trolley-circuit.html

      Delete
  53. sir, i have made a robot that implement swatch bharat abhiyan . in project i have a problem that is "what source of energy i should use 1)solar energy but it cannot run 3 dc motors and 1 c.p.u fan 2)batteries but the weight will create problem 3)a.c. current but the plug point and the wires will create problem .so sir please kindly advice me .
    thank you for your kind advice

    ReplyDelete
    Replies
    1. use batteries, sealed SMF type 12V 25AH,, and build the trolley as suggested in the previous comment.

      Delete
  54. sorry for your disturbance ,sir i have one more problem regarding my project . my trolley run in a straight path so sir what can i do so that it can change its path automatically

    ReplyDelete
    Replies
    1. how do you prefer it to take the turns? depending on what?

      Delete
    2. it should take turn after certain time intervals

      Delete
    3. how will it know the obstacles and the turns of the road??

      Delete
  55. no sir it should take turn after certain time interval

    ReplyDelete
    Replies
    1. you will need a relay timer circuit for that but adjusting the turning angle will be complicated...or you can make it through a remote control design that will be more sensible and manageable

      Delete
  56. How can I get the ready made PCB card & spares part, kindly provide the link or address.
    Also, Can you please provide a schematic diagram?

    ReplyDelete
    Replies
    1. I am sorry, PCB is not available ready made for this project

      Delete
  57. Hello Mr. Swagatam Majumdar,
    Thank you very much for all the information you posted on your website. It's very interesting and informative.
    I am sorry if this question is sort of off topic but you know alot about electronics and I can't seem to find the answer.
    I have been making portable insect traps that I use with a 12 volt Gel cell battery and a 40 watt fluorescent UV light bulb (u shaped type bulb).
    I have been buying simple DC ballasts from China that are rated to be used for fluorescent bulbs that are 10-40 watts. The ballasts work, however, they don't seem to reach their full brightness. When I measure the current, it only measure 1.2 amps with a 40 watt bulb. This seems much too low and I assume it should be 3.3 amps. So I'm assuming that this ballast is really only a 20 watt DC ballast and I am using the wrong ballast.
    I have ordered some other 40 watt DC ballasts to test them.
    My question is:
    1. If a DC ballast is rated at 40 watts and you use a 40 watt lamp, should the current be 3.3 amps? If it is lower, does that mean you are not getting the full wattage of the lamp?
    2. I have read that it's ok to use a 20 watt bulb on a 40 watt ballast. It may shorten the life of the bulb somewhat but it will run ok. If you use a 20 watt bulb on a 40 watt ballast, will the current drop to 1.7 amps or will it remain at 3.3 amps because the ballast is 40 watts?
    I am sorry if these questions or off topic. Unfortunately, i do not have the skills to build my own ballast and must purchase them but it is often difficult to find quality DC ballasts.
    Thank you

    ReplyDelete
    Replies
    1. Thank you Consumer Watchdog,

      if the operating voltage is 12V then yes it should 40/12 = 3.33 amps
      if it's lower then simply multiply it with 12 to get the effective wattage output from the ballast.
      technically a 20 watt load can be operated with a 40 watt source if the voltage is compatible with the load, because if the voltage is as per the load spec then current will not matter or affect the load in any manner.
      the current consumed by the 20 watt load will be 1.7amp

      Delete
    2. Thank you so much for your fast reply and informative answer. It is very much appreciated.
      best regards,

      Delete
    3. Thank you so much for your helpful response. I'm sorry but I have one other question regarding the 20 watt lamp with the 40 watt ballast.
      If I connect the 20 watt bulb to the 40 watt ballast and the current measured is high, say for example 2.5 amps, does that mean the bulb is being overdriven? i talked to a company that sells dc ballasts and he told me that there cheaper dc ballasts will over drive the 20 watt bulb connected to a 40 watt ballast and it will shorten the life of the lamp. However, they have more expensive dc ballasts that will adjust the current to match the bulb and they will not overdrive the 20 watt bulb and it will instead be only 1.7 amps as it should be.
      Does this sound correct to you?
      Thank you again.

      Delete
    4. Technically the current cannot become high, however since we are dealing with high frequency circuits, compatibility could be a critical factor and things could get unpredictable so if you see more current being consumed than the specified range then definitely the load is being overdriven and could get adversely affected in the long run.

      Delete
  58. Thank you for your fast and helpful replies.
    Best regards.

    ReplyDelete
  59. Hi Swagatam,
    I'm looking for a 12V inverter circuit to power 2 T8 fluorescent lamps of 36W each. The circuit mas include a battery charger to work with a 12V SLA battery. Do you have anything like this?

    Thanks.
    Best Regards.
    Nélio

    ReplyDelete
    Replies
    1. Hi Nelio,

      for the inverter you can try the following circuit:

      http://www.homemade-circuits.com/2012/07/simplest-and-best-100-watt-inverter.html

      and for the charger the following design can be used:

      http://www.homemade-circuits.com/2012/02/how-to-build-automatic-6-volt-12-volt.html

      Delete
  60. Thank you Swagatam.
    Best Regards.
    N.A.

    ReplyDelete
  61. Dear sir, Please help me .In my home 2 tube light Electronic choke had burned after I have checked it i realized transister 13005ED and Cap 682J was burned but it is very rare to find kindly provide equivalent TRANSISTOR and cap

    Thanks

    ReplyDelete
    Replies
    1. Dear Raj, the transistor MJE13005 is very popular and should be available in almost parts of the world...moreover there's no easier alternative to this part.

      the cap 682J can e replaced with 0.0068uF/250V

      Delete

Swagatam Majumdar
Swagatam MajumdarHi Friends, Welcome to my site, a place where you will discover a massive collection of electronic circuit ideas, mostly requested by the dedicated readers and exclusively designed by me for their customized application needs. I have posted more than 1100 circuit designs in this site, if you have a personalized circuit requirement you may feel free to request it through the comment box, if it seems feasible to me then surely you may find it published here with your credentials attached in the post, thanks and please keep reading



 
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