what size resistor to reduce 4.5v to 3v?

Discussion in 'Misc Electronics' started by BIGSteve, Jan 26, 2005.

1. BIGSteveGuest

got an old portable cd player needs 3vdc got a 4.5vdc car adapter need
to make the 2 work together. So how do i reduce the 4.5v to 3v can i
use a resistor? what size?
thanks

2. Jerry G.Guest

Resistors in the proper configuration can work as a voltage divider. The
voltage across the load is depended on the applied voltage, current, the
value of the resistance in series, and also the load resistance.

A simple series resistor, or a divider circuit is not accurate, unless the
current pull from the load is very constant, and precise. To run your CD
player you should get the proper regulated 3 VDC supply.

If your CD player uses less than 1 amp, you can put two of 1N4007 rectifier
diodes in series with the plus side of the voltage feed going to the player.
The cathode sides (side with the silver ring) of the diodes must face the
player's plus input. Each of these diodes will make a loss of about 0.68 to
0.72 Volts. This should get the 4.5 Volts down to be close enough. There
will not be very much added instability, because the voltage drop through
these diodes is very stable and constant.

--

Jerry G.
=====

got an old portable cd player needs 3vdc got a 4.5vdc car adapter need
to make the 2 work together. So how do i reduce the 4.5v to 3v can i
use a resistor? what size?
thanks

3. CWattersGuest

A single resistor is unlikely to work because the current drawn by the cd
player isn't constant.

You could probably use a "low drop out 3V regulator" and some capacitors but
it might be worth looking for a cell phone adaptor that produces 3V. The
voltage isn't usually written on the box - look for a label on the actual

4. JamieGuest

i would say that you could experiment with using 2 or 3 silicone diodes
in series. each one will drop the voltage aprox. to 0.5..0.6 voltage.
it mite be better to simply place a safe load on the end of the string
and then measuring it with a DVM (volt meter) to verify that its close
before connecting to the CD unit.