How can I lower the working point of a Tip31. I need to be able to use it at a slightly lower voltage.

 

A little more info, please.

What is your intended voltage?

do you have a schematic?

Can you explain what you hope to achieve with this circuit and why you feel you need a lesser voltage?

Why not use a NPN with the ratings you require?

 

I built the circuit from this website-http://www.instructables.com/id/Music-LED-Light-Box/step6/Building-the-circuit/
When I use my ipod I have to turn the volume almost all the way up before the lights start to go to the music. I added speakers to the circuit and do not want them at full volume to go with the lights. I need the transistor to allow the lower volume on my ipod to start and light up the lights. Hope this helps!

 

Did you build it EXACTLY as listed?

And are you usind a tip31? tip31a, b or c?


And read this:
http://forum.allaboutcircuits.com/blog.php?b=378

 

I used a 9V battery instead of the 12V to power 4 2.2V leds. I added two speakers to the audio of the left right wire from the audio jack - not going through the transistor. Tip31c

 

Yes, you need more a different NPN. the tip31 requires more voltage than you are providing.

Check the link on post #4. Read that for good ideas and other parts.

Each of you 2.2v leds are reducing the voltage.

4 leds at 2.2v each is 8.8v.

8.8v - 9vbattery leaves only .2v to power the transistor.

 

Hi

It is a good idea to measure some output voltages from your IPOD, so as to have an idea of what voltages to design for.

If you have a voltmeter, put music in your ipod, and using the jack hook up your voltmeter with a DC setting,

than turn the volume to minimum, and record peek voltages, just find a round off number, as there changing so fast with the music.

then set the volume for high, and write down the peek voltages, again.

Then set the volume in the middle, and write down the peek voltages.

That way your letting people know what voltages to design for.

 

Instructables are written by people who know nothing about electronics.
The circuit you linked to has no biasing for the transistor, no base current limiting, no reverse emitter-base voltage protection and no current limiting for the LEDs.

The MP3 player might blow up its output trying to drive the base-emitter junction of the transistor with nothing to limit the current.

 

Hi,

You can try this,
It works at a min. of 200mV pk.



I used 4 green LED's, and designed it for 8v. so 9v. battery will work fine for it.

The input resistance is low though, less then 700 ohms, it may work depending on what your IPOD can handle with impedances.

Also uses some current too, but its a start to get you in some direction for your project, you can add to it or deviate from it to make it suit your wants..