What kind of power supply does car audio equipment use?

Skraggy_uk · 04-09-2003, 09:11 AM

Just thinking about Car headunits, Amps etc.

They use standard electronics parts just like 12v PSUs, so they must use some kind of regulation.

What about maybe gutting an Amp and seeing what kind of powerboard it uses, and maybe use that to regulate the power to a DC-DC 55/60w PSU board?

hijinks21 · 04-09-2003, 09:22 AM

problem is getting like the +12v +5v etc out of it.

Skraggy_uk · 04-09-2003, 09:26 AM

Quote:

Originally posted by hijinks21
problem is getting like the +12v +5v etc out of it.

All you need is the plus 12v. use that to feed a clean 12v supply to the Casetronic/Morex 26**R case single board DC-DC PSUs

Scafremon · 04-09-2003, 10:53 AM

I was going to pose this same question this morning!

Late model cars have so much electronics in them already that my thinking is that either each device has some sort of regulator, or more likely there is a main voltage regulator that feeds a constant 12v to all the devices.

Skraggy_uk · 04-09-2003, 11:01 AM

Quote:

Originally posted by Scafremon
I was going to pose this same question this morning!

Late model cars have so much electronics in them already that my thinking is that either each device has some sort of regulator, or more likely there is a main voltage regulator that feeds a constant 12v to all the devices.

Must be something consideroing all the computer based factory audio stuff that is fitted these days.

mp3hombre · 04-09-2003, 06:44 PM

Most HU use unregulated 12 volts, hi power amps use a dc-dc switching power supply which converts the 12 volts to 15 and -15 volts or 35 and -35 volts, etc. This voltages are also unregulated.

Telek · 04-10-2003, 04:06 PM

Right, almost all components in a car are rated to work over a large power range, from 8-16V or whatever, without requiring regulation. There isn't going to be much in the way of high-power regulation, and even if there was, you're never going to be able to just "borrow" 5-7A off of some device, as no device is going to regulate power to have 5-7A in excess of what it itself requires to operate.

Nice idea though

Skraggy_uk · 04-10-2003, 04:16 PM

Oh well, another plan down the drain. Was thinking, as an amp is quite a high current item, a small amp, with blown components, but good power control, might be useful as a source of parts rather than tapping from the power source. I guess not now though.

Scafremon · 04-10-2003, 04:17 PM

If true...bummer.

Even though I am almost complete on my car PC (just need power supply and LCD), I probably won't hook anything up until I can be confident that I am not going to fry my components due to voltage fluctuations. I've seen quite a few posts on the forum stating how simple it is to build your own regulator, using an LM1084IT, a heatsink, some capacitors, etc. But having never soldered anything in my life, and having no experience with electronics, this simple project is a bit daunting.

It would sure be nice if someone could create a shopping list, and photo-DIY of how to do this. Then I could probably see how simple it really is.

Telek · 04-10-2003, 04:26 PM

Scafremon:

Well, it's actually not that simple.

The LM1084IT is a linear regulator: meaning (a) it is only step-down and (b) it burns off all excess voltage.

This basically means that it is not very efficient, and it can only give you +12V out when the car is running.

And, for example, if you are using 3A output at 12V, and you are feeding in 14.5V then you're burning off 2.5 * 3A = 7.5W of heat.

If only being able to use while your car is on is not a problem, and you don't care about the efficiency, then it is really really easy to set up a circuit using that regulator.

If you want something that will always give you a +12V output, then you need to either use a boost regulator to give you somewhere around 16V, and then a buck regulator to give you your +12V stable output, or use an LM2587T-12 with a transformer. Neither of these are that difficult to do if you can get the parts, however you can't get much current out of this method. Yeah, getting the regulated +12V out is the most difficult part of the power supply.

Skraggy:

Well it was a good idea, it's just too bad that things don't really work that way

Scafremon · 04-10-2003, 04:47 PM

Thanks Telec for that description.

At this point, I'd be willing to limit myself to only using the PC when the car is on. As for heat, that doesn't sound like too much heat, even if I wanted about 7A of load.

I'm ready to build one..... where do I start

Telek · 04-10-2003, 08:22 PM

First off, here is the datasheet

Now, here is the schematic that you will need:

You can get at least 5A out of that depending on the size of your heatsink and if it is force air cooled or just convection cooled. Although the "limit" is 5A, this is protected by a thermal overload circuit, so if you cool it well then you might be able to get more than 5A. However I would not suggest pushing it much past that.
If you need more than 5A, then just use two of these in parallel.

This regulator does not protect against reverse polarity. I do believe that it does protect against undervoltage, and it does protect against (thermal) overload, in both cases by shutting down.

The output will typically be around 12.00 +/- 0.05V however the absolute maximums for output are +/- 0.240V

You're going to want the LM1084IT-12 in the TO-220 package, and an appropriate heatsink to attach it to. If the heatsink is grounded (don't) then you'll need an isolator as well, otherwise just attaching it directly should work fine.

I think that the size of the capacitors is not all that important, i.e. I'm pretty certain that you can use 100uF caps in their place, for example. Tantalum capacitors are very small (between 0.12 and 0.3in long) which is why they are recommended, however you should be able to use any regular 10-100uF capacitors.