CD player power adapter from car cigarete lighter socket

[grrr_arrghh]

Hi.

I am going to build a power supply for my portable cd player, so i can power it from my car cigarette lighter. The voltage (including fluctuations) don't matter to much, as I will be using a regulator.

1) Usually, with a reg, i would just put a 10uF cap from +v to ground on either side of the reg. Is this enough, when taking power from a car ciggarette lighter, or are there more precautions needed?

2) Also, my cd player is normally powered by 2 AA batteries (1.5v), but it says on the back that an external power supply must be 6v DC... Any ideas why this might be (it doesn't matter, i'm just interested)?

3) If I wanted to power more than one player, could I just build two regulators and connect them both to the cigarete lighter socket?

4) I would probably use the case as a heat sink for the regulators (not that very much current will be drawn), but if I had more than one regulator, would it matter if they were all heat sinked on the same case?

Thanks

Tim

 

[Painandsuffering]

ok...

I understand you wanna make this yourself and all but it would be cheaper to go to a radioshack or something and just buy an adaptor than to build it yourself.

 

[evandude]

I doubt it. since you only need a regulator, a couple capacitors, an enclosure, and a couple of connectors, the parts will be very cheap... if you want some more protection you could put a zener diode reverse-biased across the inputs from the cigarette lighter socket... something rated a little over the normal voltage level of the socket, to help catch big voltage spikes.

 

[grrr_arrghh]

the cheepest i can find them is about £10!! as evandude says, I don't need many parts...

I may add the zener, just to give me piece of mind (you meen something like 13v zener?)

thanks for the input

Tim

 

[tansis]

The addition a of a diode such as 1n4001 for example
across the regulator can smooth out small ripples in the supply
and improve the stabilty of the output of the supply to the cd player.

[apologies for posting picture sideways am in a hurry]

 

[evandude]

yeah, 13v should be fine. any zener between the normal voltage level of the socket, and the maximum input voltage of the regulator would work. most voltage regulators have reasonably high maximum input voltages to begin with, so spikes of 20 or so volts shouldn't be a problem anyway, but cars can have some nasty spikes sometimes; I don't have a lot of firsthand experience with it but i've heard that spikes of 100v or more are not unheard of. so the zener, and the capacitors, should be a huge help. you might consider putting some bigger than usual capacitors on there just in case. they're cheap enough.

 

[grrr_arrghh]

ah, thanks everyone (i only posted the quesiton this afternoon, I didn't expect answers so soon...)

tansis, sideways is fine...! what sort of value is the resistor?

cheers evandude, that really puts my mind at rest, knowing that i have accounted for any spikes (it was because i'd heard of these spikes that I was asking the questions in the first place)

Thanks again everyone.

Tim

 

[grrr_arrghh]

I have gained a couple more questions...

There arn't that many 6v regulators around, but I found one: L7806CV. According to the data sheet, this is in a T0-220 (Type-A) style case. A standard T0-220 heat sink would be fine yeah? (theres nothing special about 'type-a' is there?)

Having said this, do I really need to heat sink it? Max current is 1.5A, and I don't think I would get close to this (I will try and find out the current that the player draws)

If I did have to sink it, I would preferably heat sink it on the case, but if I had more than one regulator, could I sink them on the same case, or would that cause problems?

Also, (sorry to go on about heat sinking), do I need thermal grease or anything?

If I know the current required (for the sake of argument 600mA), can I work out the current that will be drawn by the regulator? Will it be the same, will it change depending on the input voltage?

Thanks

Tim

 

[tansis]

True 7806 regulators are not that common, one solution is to use a more available device like the 7805 and fool it to produce six volts by creating a virtual / artificial value for the zero volt rail with a resistor divider.

I have changed the resistor from the previous drawing to diode you will notice, this is stop the feedback diode and regulator from trying to stabilise the entire vehicles electrical system, often you will hear of automotive electronics refered to as 12vdc... well it varies somewhat!
with the engine running ,eighteen volts is not uncommon.

Bolting the heatsink to the case is a normal way of doing things, provided its a metal case! also it it worth the extra expense of an insulating / mounting kit ,the device heatsink / mounting tab is often connected to the semiconducter substrate and is best isolated for safety reasons, that and should the case short out other wires where it is mounted your electronics will be safe. Thermal grease is a nice finishing touch but claims for this gunk are much overated, and modern kits are comprised of a soft washer designed for dry use, overclockers of course will swear blind that copper or silver loaded paste works better, but the minor benifts are swamped by the extra cost.

 

[Exo]

Keep in mind that the 7805's internal SC protection won't work if you give it a virtual ground ...

 

[grrr_arrghh]

i found a 1A 7806 for less than a 0.5A 7805, so I might as well use the 7806. This aside, what is 'SC Protection'?

 

[Exo]

short circuit protection ...

 

[grrr_arrghh]

ahh, that sounds handy...
I was gonna have a fuse for to guard against shorts, but if it has SC protection built in...

I think I'm all out of questions now.

For building and beyond.

Cheers guys, much appreciated.

Tim

 

[grrr_arrghh]

me again...

in the diag posted by Tansis, what sort the rating does the zener need to be?. The max current will be about 1A, and the expected voltage will be about 12-20v. Presuably I don't need a zener rated at 20Watts!?!?

 

[Exo]

No, the zener is in parallel with the supply, not in series, so the current doesn't go trough it...
I've used a 2W zener in my previous car without problems

 

[Exo]

ahh, that sounds handy...
I was gonna have a fuse for to guard against shorts, but if it has SC protection built in...

You might still want to put a fuse in front of the 7805, in case the 7805 itselfs gets damaged, the internal protection only guards the circuit behind it

 

[grrr_arrghh]

No, the zener is in parallel with the supply, not in series, so the current doesn't go trough it...

thats what I thought, but I wasn't sure

You might still want to put a fuse in front of the 7805, in case the 7805 itselfs gets damaged, the internal protection only guards the circuit behind it

hmm, good idea. I'll have to wait until i've built it so I can measure the current it draws though...

Thanks alot guys, I don't know what i'd do without you.

Tim

 

[ante]

Tim,

The voltage in the socket will rise to 13.8 or more when the alternator charges the battery so the Zener will conduct and get destroyed. You should use a 16 V or higher Zener or just omit it. To protect the regulator put an extra cap in front of it paralleled with the electrolytic and as close as possible to the regulator, use 0.22uF. You should not exceed 1.5W without a heatsink on this type of regulator so the maximum current without heatsink is something like 150 to 200mA in this case. You don’t need any insulation for the mounting just remember that there will be (ground) negative in the box. If you are using a 7805 a way to rise the output voltage is to put some diodes in series with the ground connection (cathodes pointing to ground) and you will rise the voltage 0.6V or so extra per diode.

Ante :roll:

 

[grrr_arrghh]

The voltage in the socket will rise to 13.8 or more when the alternator charges the battery so the Zener will conduct and get destroyed

oh. So tansis was wrong...?

To protect the regulator put an extra cap in front of it paralleled with the electrolytic and as close as possible to the regulator, use 0.22uF

ceramic? non electrolytic?

You should not exceed 1.5W without a heatsink

is that even if I use the case as a heat sink?

and insulation thingys cost about £0.10, so it doesn't make much difference.

also, I'm going to use a 7806, so don't worry about the virtual ground thing.

I thought I had it all sorted!!

Tim :?

 

[ante]

Tim,

The electric system in a car can reach as high as 14.2Volts when the alternator is charging. I am not saying that someone was wrong just by thinking (12V). The extra cap can be any poly non-polarized types just remember short leads.

Ante :roll: