voltage distrbuter

[Faisal__saf]

hy all of my unseen friends,..
I have a power supply of 12 volts.. and i need 1.5 or 3 volts
so i connected 8 resistors in series and took the outputs from all the connections, so the 1st resistor from the ground will give 1.5.the 2nd will give 3volts & like this all will give.....
but i dont know why I am not able to glow a 3 volt bulp any thing even after i tried about 6or7 times

 

[Scubasteve]

You are making a voltage divider when you chain all of those resistors together, which isn't suitable to power anything significant.

This technique is used to generated references and low current voltages easily, not to step down voltages.

You should consider using a voltage regulator, but you will not get significant current out of it without burning out the regulator. You have a very large voltage drop of 9V, with only 100mA load, you will be converting nearly 1w into heat. Assuming that you will not have a heatsink, your package will probably rise to 60-70degrees from ambient(to220 package).

Steve

 

[Faisal__saf]

hy steve
thanku for that but could u help me again plz
can u write me a method of that experiment
i dont have any idea for that :?

thanx again
Faisal

 

[Scubasteve]

There is no real mystery here, it just requires the voltage regulator device. If you could ask for a "3V Voltage Regulator" and get one, find the datasheet for it, there is no problem putting it together.

One pin will go to your input voltage (12V), one will go to ground, and one will be your 3V regulated output. You should use capacitors on both input and output, this will help the regulator work better. This can be assembled quite easily on a breadboard.

Make sure your regulator can handle the 12V input. All of the necessary information is in the datasheet.

Steve

P.S.- You might consider a zener diode for this also, which might be a little bit better in your situation. Do a search on www.google.com and you will see circuits and etc for this device.