I need to convert 12vdc to 9vdc the simplest way possable, the 9vd load is only 10mA and is constant, is there a quick way to do this? possably a resistor any help is greatly appreaciate
thanks bobb
Help, 12vdc to 9vdc
Aug 19, 2005
5 Replies
The voltage drop accross a resistor is given by V=IR.
Rearrange that to give R=V/I
Plug in the numbers..
R= (12-9)/0.01 R= 300 Ohms.
But allways check the power rating...
The power (W) burnt in the resistor is given by: W=IV W=0.01 * 3 =0.03W. which is tiny so a 0.125W (=1/8th Watt) resistor will do fine.
...but perhaps you had best tell us what the 9V will be used for just in case? You might need a capacitor as well!
relsr wrote this in :
Constant load? Yes, then a resistor is the simplest solution. You want
3V drop over the resistor, and have 10mA: 3V/10mA=300ohm should do it. You can also use a 7809, which is a simple IC with 3 legs: In, out and refference (which you connect to - on the source). I think a 7809 will work with 10mA, although not sure. A 7809 costs ~1$, and works even if load differs.
MVH,
Vidar
www.bitsex.net
300 ohm resistor ?
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
In article , snipped-for-privacy@cablespeed-dot-com.no-spam.invalid opined thusly:
About 5 or 6 diodes in series, forward biased, will do the trick and the voltage won't vary with the current draw (much).
dave wrote this in :
Then a 7809 will likely be cheaper, and with better accuracy.
MVH,
Vidar
www.bitsex.net
Join the Discussion
Have something to add? Share your thoughts — no account required.
Didn't find your answer?
Ask the community — no account required