# reduce 6vdc to 4.5vdc

Discussion in 'Electronic Basics' started by Ken, Oct 8, 2004.

1. ### KenGuest

Hi all,

Been doing some research through the archives and have seen where I'm
probably going to be using a regulartor, however, does anybody have any
truly simple circuit diagrams for this type of thing?

Trying to reduce a car charger from 6v DC to 4.5v DC for to use as a PDA
charger.

Thanks,
Ken

2. ### Lord GarthGuest

Ken, you might open it up and look for the info on the chip. Often, the
output
can be changed simply but it depends upon the design.

3. ### John PopelishGuest

If you can get to not oscillate, a low drop out adjustable regulator
should work. I have often had to use a 1 uf film cap in series with a
1 ohm resistor output to ground to do this. Perhaps an LM2931CT.

http://cache.national.com/ds/LM/LM2931.pdf

4. ### anonymousGuest

Im prob wrong but I thought that cars put out 12V DC. You're probably
referring to a device that plugs into a car lighter socket? Ah.

5. ### anonymousGuest

Trying to reduce a car charger from 6v DC to 4.5v DC for to use as a PDA
(cut myself off)

how much current would you need?

If you could get more than 6 V from the car you could drive a voltage
regulator like a 7809 and then use a voltage divider to get the resultant
4.5.

6. ### BanGuest

The cheapest would be to put 2 diodes 1N4001...7 in series between the power
supply and your PDA, they reduce the voltage by 1.3...1.5V depending on the
current and temperature.

7. ### Rob PaisleyGuest

Question.

What sort of "car charger" are you talking about; A charger for a 6
volt lead-acid automobile battery or one for a NiCad battery from a

Rob.

8. ### KenGuest

Hi all,

Thanks for all the replies.

The car charger is a cigarette lighter charger for a magnavox cd player that
puts out 6v DC. My pda takes 4.5~5v DC.

My EXTREMELY limited knowledge of component level work is why I'm looking
for some "simplistic" methods of making this happen.

Thanks,
Ken

9. ### KenGuest

Thanks, I'll give this a whirl. Going to check and see if Radio Shack
sells them.

Thanks again,
Ken

10. ### ClarenceGuest

Without knowing what the circuit is in the charger you may be in for a nasty
surprise. If the unit is current regulated with a voltage clamp at 6 Volts,
with all the schemes using diodes as the battery is charged the output of the
charger will tend to rise to 6 volts. As the current through the diode drops
this voltage WILL BE APPLIED to the battery. The over voltage MAY have reduce
battery life, or battery heating. (Heat will also reduce life, but getting hot
has other problems for the battery, like overcharge.) BE VERY CAREFUL and
test the circuit carefully.

11. ### JamieGuest

you want to be careful with that, most likely you have more than 6 volts
from the charger on the Peaks.
any ways to make it simply for you, use lets say 3 diodes silicone
2 or more amp diodes in series with the cathode(line side) heading to
the PDA and the anode(non line side) coming from the + side of the
charger..! also one should have like a 12 volt car auto tail light
incandescent lamp in series as a current sink.
i know its kind of back yard electronics but i think it's more of what
you understand and can handle.

[charger + out]-->>--[incandescent lamp]--[-diode >| ]--[ diode ->|
]-->> PDA + input.

12. ### Lord GarthGuest

Silicone? New technology I suppose...

13. ### KenGuest

Hi all,

Here's a macro photo of the board and I've added the numbers from the sides
of the (caps; at least I'm guessing they're caps).

http://www.helpconsulting.net/images/cigarettecharger.jpg

Thanks for all the help! I went to RS and picked up a couple of IN4005's
and put them in series on the unit and the voltage still read 5v on the
digital multimeter.

Regards,
Ken

14. ### KenGuest

update! The diodes are working correctly at this point.

I tested them with a meter and they were still reading 5v, however, after
speaking with my brother who is an electronic (board leve) technician, he
stated that there needed to be some type of draw on the system, thus once I
actually plugged in the PDA it started charging properly instead of the
safety kicking in and shutting down the system.

Thanks all!!

Ken

15. ### Rich GriseGuest

It sounds simplistic, but your existing "charger" is probably not designed
to act like an ordinary DC supply - it might have some kind of charging
algorithm built in. A proper adapter is less than ten bucks.

Cheers!
Rich

16. ### Rich GriseGuest

He's plugging it into the lighter socket. Just a 317 at 4.5V, running
right off the car's 12V should work, but a RS 4.5V lighter adapter
would be cheaper and WAY less PITA.

Cheers!
Rich