joule thief help

[rahulm]

hiiiiiiiiiiii.....i hav seen videos of joule thief......n i have made one from the site evil mad scientist...the basic joule thief circuit with transistor 3904 ,1 k resistor, 1 white led, ...n its working well...
i hav few questions,
1. i hav heard tht this circuit doubles the output voltage n current. but when i check in my circuit it comes the same as input voltage...n current is decreased.....???
2. how many led i can connect with this basic circuit....parallel or in series????
3. i hav seen in many video they connect a supercap in circuit ....can u plzzz tell me wht is the benefit of connecting a supercap? n how & where to connect supercap in circuit??
4. plzzz suggest me how to improve this basic circuit for more led approx 10 led??
5. in many videos i hav seen tht they provide high input like 3v and gets tremendous output voltage (in some videos approx 200v ) how they can do it....in this basic circuit how i can do this...??
is this circuit allow me to do tht???plzzz tell me how to do it???
and plzzz also tell me little bit abt inductors n its windings.....can more winding produce more voltage n current?????
plzzz help mee...

 

[Hero999]

You're better getting the one LED working first.

Try swapping the connections to one of the coils.

The circuit doesn't double both the voltage and current, that would be perpetual motion which is impossible, the truth is, it boosts the voltage but the current is reduced.

A supercapacitor won't power the circuit for very long, you're better off sticking with an AA cell.

 

[rahulm]

to hero

thts wht i m saying hero in my case the voltage remain same as input voltage....
but in circuit there is no problem wht so ever.....my led glows nice n really bright.....
i have tried to connect 7 led parallel n it works.....but its not as bright as much.....
i hav made another coil this time i have done around 10-11 turns.....with this coil led glows more brighter but the voltage remains same.....plzz tell me why i m not getting high voltage...
i m familliar with basic electronic actually more then basic......plzzz let me explain it...
plzzzz let me knw how to improve this circuit.....

 

[audioguru]

The output of a Joule thief is pulses that cannot be measured properly with a meter. Your meter measures the average voltage not the peak voltage of the pulses. The peak voltage of the pulses is the forward voltage drop of the LED.

 

[rahulm]

The output of a Joule thief is pulses that cannot be measured properly with a meter. Your meter measures the average voltage not the peak voltage of the pulses. The peak voltage of the pulses is the forward voltage drop of the LED.

kkkk.....i measured voltage across anode n cathode of led n then collector n emitter of transistor.....n wht abt improving the circuit??

 

[Hero999]

You need to use an oscilloscope to measure the voltage accurately.

You might also receive more help if you use English rather than text speak.

To get more power you need to use a larger core.

Have you tried connecting the LEDs in series?

 

[rahulm]

You need to use an oscilloscope to measure the voltage accurately.

You might also receive more help if you use English rather than text speak.

To get more power you need to use a larger core.

Have you tried connecting the LEDs in series?

no i have not tried led in series....i have wind the core with telephone wire....is this the reason for low voltage??
is this type of english will do ???

 

[Hero999]

You English a little better now.

How did you measure the voltage? Was it with a meter? Audioguru has already told you that it won't give an accurate reading because it's high frequency and the meter will only be designed to work with 50/60Hz, so if the meter says it's low, that's why.

 

[rahulm]

You English a little better now.

How did you measure the voltage? Was it with a meter? Audioguru has already told you that it won't give an accurate reading because it's high frequency and the meter will only be designed to work with 50/60Hz, so if the meter says it's low, that's why.

thanx i will try to improve now on.....

i have measured with multimeter...and it is a cheap chinese meter i have bought it for general use ....so maybe audioguru is right....but i dont have oscilloscope...
u told me to swap the coil connection...i will try that...and can i wind the core above one layer of winding??? for more power ....
or should i have to add other components like capacitors or diodes for high voltage?

 

[Hero999]

Don't exchange the connections.

You said the output voltage was low, which lead me to believe it wasn't working which is why I recommend swapping the connections to one of the coils.

Now I know it's working, I recommend you shouldn't exchange the connections because it will stop it working because it was right in the first place.

 

[rahulm]

hey dude.....i have got the problem and it is a silly one from my side.....i have put multimeter in VDC mode and i am taking reading in this mode when i put in VAC then it is giving me correct reading ...i am getting 2v frm input of 1.2v with my old coil and also i have changed my old coil with new and larger one with more turns on it....with new coil i am getting 2.2v from 1.2v also with this new coil i can connect 2 AA batteries means 2.4v input and i am getting 4.5v output...
is this happens because of new coil ?? because it has more winding??plzzz reply my this query??
also i have connected 10 leds parallel with this circuit and it works......its really amazing ....
now i understood that its all depends on the turns of the coil ..now i am planning to make larger one..to get more voltage...anyways thanx for your help dude....
i had not got this thing in my mind that it changes DC into pulsating AC thats why i got wrong readings...

 

[Hero999]

You're not listening.

For the third and final time, the meter will not give you the correct reading becaese the frequency is too high and the wave shape is not sinusoidal.

Doubling the input voltage will not double the output voltage because the LED connected across the output will always clamp the voltage at about 3.5V, all that will happen is the current will increase which might burn out the LED. Connecting two batteries in series should enable you to power more LEDs connected in series though, which is what you want.

 

[rahulm]

no hero i think you got me wrong .....yes my meter might be still giving me faulty reading because of its low freq...but when i am getting the same voltage as my input voltage that time my meter was in VDC mode after that i have changed it to VAC mode...then i got 2v from 1.2v input which is still wrong because of low freq......i got 2v from single AA battery....
and after all this i changed my old coil with new one.....with new coil i can double the input voltage....from old coil i was unable to do so....

 

[Hero999]

I'm not arguing with you!

The voltage will be equal to the forward voltage of the LED which will be about 3.5V peak

 

[rahulm]

hey hero dont take it seriously man....i am just a hobbiest and a newbie...i dont know much technical things as much you know .....also i am not arguing with you ....i have asked you because you have the knowledge about it......
you can correct me whereever i am wrong......

 

[rahulm]

okkk you mean whenever led glows fully bright or at peak the voltage across led should be 3.5v .....it means that my joule thief circuit producing voltage more then 3.5v???

 

[Hero999]

Yes that's it, you've got it.

To see this you need to look at the waveform on an oscilloscope.

 

[rahulm]

Yes that's it, you've got it.

To see this you need to look at the waveform on an oscilloscope.

okkkk....anyways what improvements can i do in this circuit?

 

[Hero999]

The truth is there's not much you can do to improve it.

The circuit is very quick and dirty way of powering an from a single AA cell.

If you want to power 10 then I suggest you use four or more AA batteries in series, use a larger core such as a ferrite core from the converter inside an old CFL ballast and power the LEDs as two strings of five in parallel.

 

[rahulm]

The circuit is very quick and dirty way of powering an from a single AA cell.

If you want to power 10 then I suggest you use four or more AA batteries in series, use a larger core such as a ferrite core from the converter inside an old CFL ballast and power the LEDs as two strings of five in parallel.

okkkk but as i told early that i was able to glow 7 led in parallel from this circuit...so from single AA battery it wont light as long ???