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Step down 12v --> 6v

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juan123

Member
Hey there! I want to step down 12volts that my motorcycle has to 6 volts so that I can power some portable speakers..How can I do this ? The speakers are rated at 6 volts but I'm guessing 7.5 would be better without hurting any components,in order to get better output, right? Well many thanks!
 

dknguyen

Well-Known Member
Most Helpful Member
How much current do you need? This has a critical role in deciding the method to use. As far as speakers go...what does "better output" mean? If you mean louder, then maybe 7.5V (if the speakers can actually tolerate that). But if you mean better quality, then no, stick with 6V.

Also, alternators are very noisy. You have to account for the surges, as well large voltage fluctuations which means more protective components.
 
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juan123

Member
ohh yeah, I forgot to say, mmm about 500milliamps to 1 amp , since this device uses 4 AAA batteries...I'm guessing one amp would be better so that the sound can be a bit louder without getting distorted... Well thanks again!
 

Hero999

Banned
Is it AC or DC?

If it's AC then you need a transformer and a rectifier.

The more common LM7805 will also probably work.

Here's the schematic, the earth/ground symbol should be connected to the negative rail.

 

AlainB

Member
Hi,

I did exactly that, reducing the voltage of the car to use a computer amplified speaker that is running at 6 volts.

I soldered 11 diodes in serie, I think it was some 1N4001, and it is reducing the voltage to around 6 or 7 volts, enough anyway for the speaker to work well.

Alain
 

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Frosty_47

New Member
Hey there! I want to step down 12volts that my motorcycle has to 6 volts so that I can power some portable speakers..How can I do this ? The speakers are rated at 6 volts but I'm guessing 7.5 would be better without hurting any components,in order to get better output, right? Well many thanks!
Use LM317 with an output NPN transistor to take the load of the regulator. It's a must because at one amp of current there will be around 6Watts of load on the regulator without the pass transistor. The regulator will go into current-limmitng mode because it will overheat. Hence without the pass transistor you will most likely get no more than 350mA of current. With pass transistor in place, you can get more than one amp output. Also the transistor will handle all the load +heat so the regulator will stay cool. Here is the circuit below:



Transitor can be any NPN with at least 2A of Collector current. And a minimal of 10Watt type.
 
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Sceadwian

Banned
I'm very surprised you get acceptable audio quality with that many diodes dropping the main voltage. The current on an amp is going to be fluctuating which will vary the current through the diodes and their forward voltage will drop causing feedback.
 

Frosty_47

New Member
Is it AC or DC?

If it's AC then you need a transformer and a rectifier.

The more common LM7805 will also probably work.

Here's the schematic, the earth/ground symbol should be connected to the negative rail.
7805 will give +5V and he needs 6.4V min (4AAA bateries as mentioned above = 6.4V on full charge).
 
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AlainB

Member
I'm very surprised you get acceptable audio quality with that many diodes dropping the main voltage. The current on an amp is going to be fluctuating which will vary the current through the diodes and their forward voltage will drop causing feedback.
I can't comment on that. I am using the speaker combine with a microphone as a hands free system for my cell phone. I keep the volume fairly low to avoid feedback through the microphone. I use it every day and It is working well for me.

Alain

Edited: On that system, I used 10 diodes, not 11.
 

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Hero999

Banned
7805 will give +5V and he needs 6.4V min (4AAA bateries as mentioned above = 6.4V on full charge).
No, if it's designed to work on four AA batteries, it should happily work down to 4V or less so 5V will be fine.
 

Hero999

Banned
I'm very surprised you get acceptable audio quality with that many diodes dropping the main voltage. The current on an amp is going to be fluctuating which will vary the current through the diodes and their forward voltage will drop causing feedback.
I doubt that would be a problem.

If the amplifier has good enough power supply rejection and a large enough capacitor connected across the supply, i.e. it's well-designed, that shouldn't happen.
 
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