12V DC to 1.5V DC needed

Resistor and NiMHi cell perhaps ? Only 1.2v, and not terribly kind to the battery, but simple, cheap and should work ok

Arfa

Depends on the needed current. The lm317 is a simple regulator you set the voltage with a couple of resistors. Here is another one.

Hello, Arfa! You wrote on Fri, 14 Jul 2006 22:05:09 GMT:

??>> Could anyone please suggest a fairly simple circuit to convert the 12V ??>> DC of a motor car down to 1.5V DC needed by my MP3 Player ? Any help ??>> appreciated. ??>>

??>> With best regards, 3T39. E-mail: snipped-for-privacy@hotmail.com ??>>

AD> Resistor and NiMHi cell perhaps ? Only 1.2v, and not terribly kind to AD> the battery, but simple, cheap and should work ok

Hhmm, A bit brutal Arfa, I see what you mean but I was hoping for a tad more sophistication :^) but thanks anyway.

With best regards, 3T39. E-mail: snipped-for-privacy@hotmail.com

"3T39" wrote in news:44b81477$0$5221$ snipped-for-privacy@news.zen.co.uk:

A simple circuit will do it: a linear voltage regulator, a couple of resistors, a capacitor, a diode.

For further info, try sci.electronics.basics

Jim Land wrote in news:Xns9800B8C3B9BC5RrrrFfffTttt4396hotm@216.168.3.44:

Wait! You don't need to build your own circuit. You can *buy* a device that does exactly what you want.

Cheap adaptor on ebay ?

Graham

On Fri, 14 Jul 2006 23:02:06 +0100, "3T39" put finger to keyboard and composed:

Get an old mobile phone car adapter and modify the output for 1.5V. A lot of the switchmode types use an MC34063 IC which should be able to go down as low as 1.25V by changing one or both feedback resistors. Use a zener diode to crowbar the output in case of overvoltage.

- Franc Zabkar

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Please remove one 'i' from my address when replying by email.

That seems a bit like overkill.

Getting the needed voltage is really easy, given the low voltage and the likely low current consumption of the device. (A dropping resistor and a 1.5V zener would do it, though likely the forward voltage drop of 2 silicon diodes would provide the "zener" and easier to find to boot.)

But since he wants to run it off a car battery, it gets complicated. You really need to ensure that no voltage spikes are going to get itno the MP3 player from the +12v line on the car.

I suspect your suggestion would work well, under the assumption that they would have done good filtering on that car adaptor. But it's overkill in terms of current capacity, and it seems odd to start fiddling with a switching supply to get a miniscule current at 1.5V. If someone does that, they might as well just leave the adaptor as is, and drop the output via a resistor and zener, leaving the adaptor to take care of the voltage spikes.

The easiest solution would be to get an A battery, and run the MP3 player off that. Those had enough current capacity that it would likely be a long time before it needed replacing (and the thumbscrews on the terminal make the replacing easy). But I have no clue where one can buy A batteries these days, or even if they are still being made.

So one could use a D cell, and just live with the occasional replacement, which is bound to be far less frequent than the AAA inside the MP3 player.

Michael

"3T39" wrote in news:44b81477$0$5221$ snipped-for-privacy@news.zen.co.uk:

You may find it cheaper and easier to go with rechargable batteries. I've found most AA NiMH batteries do a good job, and my charger will charge any number of them I put in. (Great for a device that uses three batteries.)

(Just throwing this out as an alternative. There's plenty of other good suggestions already posted.)

Puckdropper

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Wise is the man who attempts to answer his question before asking it.

To email me directly, send a message to puckdropper (at) fastmail.fm

Agreed, but you did say that you wanted it simple. All of the solutions offered further down, which make use of a linear regulator, such as the LM317, are very inefficient in terms of heat produced. My thinking with using the NiMH cell, was that the series resistor could be dimensioned to give a very light trickle charge to the cell, of only a few mA. This sort of scheme is common in cordless phones, for instance, and doesn't seem to do the battery packs too much harm - you generally get 2 - 3 years reasonable service from them. The current to run the MP3 player would then be provided basically by the cell. When the player was out of use, the cell would continue to be gently charged, ready for your next journey. Simple and reasonably efficient ?? There is an added advantage in that the cell provides a fairly low impedance, so will tend to absorb any transients on the line from the vehicle's electrical system. To be sure, you could always 'complicate' the circuit, by adding a C of say 0.1uF across the cell. Between that, and the relatively high value of the charging resistor, just about all spikes should be slugged to the point of no consequence.

Arfa

Hello, Arfa! You wrote on Sat, 15 Jul 2006 11:51:39 GMT:

??>>>> Could anyone please suggest a fairly simple circuit to convert the ??>> 12V ??>>>> DC of a motor car down to 1.5V DC needed by my MP3 Player ? Any help ??>>>> appreciated. ??>>>>

??>>>> With best regards, 3T39. E-mail: snipped-for-privacy@hotmail.com ??>>>>

AD>>> Resistor and NiMHi cell perhaps ? Only 1.2v, and not terribly kind to AD>>> the battery, but simple, cheap and should work ok ??>>

??>> Hhmm, A bit brutal Arfa, I see what you mean but I was hoping for a ??>> tad more sophistication :^) but thanks anyway. ??>>

??>> With best regards, 3T39. E-mail: snipped-for-privacy@hotmail.com

AD> Agreed, but you did say that you wanted it simple. All of the solutions AD> offered further down, which make use of a linear regulator, such as the AD> LM317, are very inefficient in terms of heat produced. My thinking with AD> using the NiMH cell, was that the series resistor could be dimensioned AD> to give a very light trickle charge to the cell, of only a few mA. This AD> sort of scheme is common in cordless phones, for instance, and doesn't AD> seem to do the battery packs too much harm - you generally get 2 - 3 AD> years reasonable service from them. The current to run the MP3 player AD> would then be provided basically by the cell. When the player was out AD> of use, the cell would continue to be gently charged, ready for your AD> next journey. Simple and reasonably efficient ?? There is an added AD> advantage in that the cell provides a fairly low impedance, so will AD> tend to absorb any transients on the line from the vehicle's electrical AD> system. To be sure, you could always 'complicate' the circuit, by AD> adding a C of say 0.1uF across the cell. Between that, and the AD> relatively high value of the charging resistor, just about all spikes AD> should be slugged to the point of no consequence.

Yes I did say simple Arfa, and I understand what you say. You're quite right about it, and I'm thinking now I might give this a try, I thought around

800R 0.25W what do you think? Can I mention your name if I set the car on fire? :^)

Also I'd like to thank everyone who took the time to write down your thoughts on this Much appreciated !

With best regards, 3T39. E-mail: snipped-for-privacy@hotmail.com