What size resistor to reduce 4.5v to 3 v

[BIGSteve]

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
also what size to go from 12vdc to 6vdc

 

[mc]

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
also what size to go from 12vdc to 6vdc

Resistors don't work that way. The voltage reduction through a resistor
depends on the amount of current flowing, which varies depending on whether
the motor is running, how loud the output is, etc. Your problem can't be
solved with just a resistor.

 

[Byron A Jeff]

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.

Use a voltage regulator.

can i use a resistor? what size?

No. Resistors don't work because the current isn't constant. So as
the current through the resistors change, so will the voltage drop.

thanks
also what size to go from 12vdc to 6vdc

Same issue.

Use a voltage regulator.

BAJ

 

[mike]

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
also what size to go from 12vdc to 6vdc

All the players I have use two AA cells but use 4.5V in the ac adapter
hole. Check with the vendor. Maybe you don't have a problem.
Also, be careful to use the correct size plug. I ruined a socket
by plugging in an adapter plug that was imperceptibly too big.
mike

--
Return address is VALID.
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
http://nm7u.tripod.com/homepage/te.html
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
http://www.geocities.com/SiliconValley/Monitor/4710/

 

[Gareth Magennis]

You can add 2 or 3 diodes in series. This will give you about 0.6 volts
drop accross each one, reducing the 4.5 volts to 3.3volts or 2.7 volts.


Gareth.

 

[aurgathor]

With non-constant load, you could use some
combination of diodes. Si diodes will drop
about 0.6 - 0.9V, Schottky diodes 0.3 - 0.5V,
Ge diodes 0.3 - 0.4V, LEDs 1.7V - 3.5V.
These are *ballpark figures*, so in rare cases
the drop could be outside of the above ranges.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

With non-constant load, you could use some
combination of diodes. Si diodes will drop
about 0.6 - 0.9V, Schottky diodes 0.3 - 0.5V,
Ge diodes 0.3 - 0.4V, LEDs 1.7V - 3.5V.
These are *ballpark figures*, so in rare cases
the drop could be outside of the above ranges.

Those drops are about right, but depend on the current. The Si diodes
such as 1N4148 can't handle the several hundred milliamps that the
player will need. The diodes should be two 1N4002 rectifiers, which can
handle 1 amp, and will drop about .8V each at several hundred mA. A
schottky rectifier that will work is the 1N5817.

Ge diodes that will handle that much current are no longer available.
LEDs would only handle 30 mA, and would burn out if a few hundred mA
went thru them.

 

[aurgathor]

I know the voltage drop is somewhat dependent on the
current, and obviously, usually the smaller the diode, the
less current it can handle. And I guess I should've
mentioned that.

As for LEDs, some can handle more than you'd expect.
I have a 486 based linux router, and to quiet down its
PS fan, I hooked up 4 LEDs in a 2 by 2 config serially.
The fan actually worked fine with only 2 series LEDs,
but I decided to double them up to halve the current.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

I know the voltage drop is somewhat dependent on the
current, and obviously, usually the smaller the diode, the
less current it can handle. And I guess I should've
mentioned that.

As for LEDs, some can handle more than you'd expect.
I have a 486 based linux router, and to quiet down its
PS fan, I hooked up 4 LEDs in a 2 by 2 config serially.
The fan actually worked fine with only 2 series LEDs,
but I decided to double them up to halve the current.

in message news:[email protected]...

Yeah, I should have said that LEDs in the 5mm package can only handle
about 100mW, which is about 50mA at 2V for red, and 30mA at 3.3V for
green, blue, white, etc. But there are bigger ones, such as the
Piranhas, 8mm, 10mm, and UFOs (search for them on Ebay), and of course
the Luxeon Star, which can handle 350mA for the 1W version, and a lot
more for the 5W version.

The 1N91 is a relatively heavy duty Ge rectifier no longer made by GE,
but you can use the junction of a Ge power transistor for a diode, just
connect the base to collector and use the emitter to collector junction.
It should handle several amps. But even Ge power transistors are
getting expensive and hard to get. Mouser wants $16.30 for the NTE104,
with very little discount for quantity.

 

[kiener656]

with:u=rxi you can simply find out,how big your resistor has to be

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

ment.com...

with:u=rxi you can simply find out,how big your resistor has to be

Not "simply" if the load is not a steady current (which it isn't). Duh.