Power Supplys and Zener Diodes

[Impious 1,476]

Alright all you smart folk, here's what I am wanting:

http://www.partsexpress.com/pe/showdetl.cf...tnumber=180-960

I want to be able to run that directly off of my car's electrical system. You can see from the description that it runs off of 6VDC from the included power supply.

So, what would be needed is a power supply to convert the 12VDC from my electrical system to 6VDC. I've also had something about Zener Diodes mentioned to me....but I'm not really sure what those are all about.

Anybody want to give me a quick run down of the best way to go, and how each is accomplished (i.e. what a simple yet effective PS design would consist of, what Zener diodes do and if they would be an effective and simple fix in my situation, approximate cost, etc).

Thanks

[Acidburn 10]

couldnt you just put a resistor inline with the power wire to bring down the voltage from 12V to 6V?

just use ohm's law to figure out the size or something

i dunno, just my thoughts

[ANeonRider 3]

couldnt you just put a resistor inline with the power wire to bring down the voltage from 12V to 6V?

just use ohm's law to figure out the size or something

i dunno, just my thoughts

<{POST_SNAPBACK}>

Nope.

I'll post the voltage regulator design asap. Can you find me the current draw?

You will need a LM7806 3-pin regulator forsure, other parts depend on the current draw.

Edited November 7, 2005 by ANeonRider

[///M5 2,833]

________

/\ \

| <

| R1 >

<

---------

Vin \ /\

< |

| R2 > Vout

| < |

\/ | \/

__________________

Vout = I*R2 = (R2* Vin)/ (R1+R2)

Uh that got butchered in editing, try again with a picture

Edited November 8, 2005 by ///M5

[Impious 1,476]

couldnt you just put a resistor inline with the power wire to bring down the voltage from 12V to 6V?

just use ohm's law to figure out the size or something

i dunno, just my thoughts

Nope.

I'll post the voltage regulator design asap. Can you find me the current draw?

You will need a LM7806 3-pin regulator forsure, other parts depend on the current draw.

According to PE tech support, both the unit and included PS say 250mA on them.

PS: PE tech support rocks. They didn't have that in the notes, so he ran back and pulled one off the shelf to check for me. Two thumbs up

[Supa_c 1]

Get 4D batteries...duh

[///M5 2,833]

Alright, here it is with the math filled in. You just need three resistors and they are all the same so it should be cheap. Unless of course you should be basing this on 13.5volts....I am not sure on that.

[Impious 1,476]

Unless of course you should be basing this on 13.5volts....I am not sure on that.

Well, that was sort of one of my questions. Since the voltage will swing from ~13.8V (car on) to 12V (car off), I'd assume that would complicate the design some.

[///M5 2,833]

couldnt you just put a resistor inline with the power wire to bring down the voltage from 12V to 6V?

just use ohm's law to figure out the size or something

i dunno, just my thoughts

Nope.

I'll post the voltage regulator design asap. Can you find me the current draw?

You will need a LM7806 3-pin regulator forsure, other parts depend on the current draw.

Not one, but 3 and indeed an ohm's law solution. Am I missing something? Your way does sound sexy.

[///M5 2,833]

Unless of course you should be basing this on 13.5volts....I am not sure on that.

Well, that was sort of one of my questions. Since the voltage will swing from ~13.8V - 12V, I'd assume that would complicate the design some.

Aha, I bet the regulator that Neon speaks about.

[ANeonRider 3]

Voltage divider will work, but will not regulate the voltage, which is needed in such as appliaction. Voltage dividers really are only applicaple to divide down the voltage into something workable for another circuit to handle (in what ever application it is being used for).

In this case, here is the circuit that would work just fine. If it gets warm at all, you may have to add a small heat sink to the voltage regulator. In this case, a piece of aluminum would work great.

[thch 0]

definatly use the regulation. make sure you have the cap "Co", many regulators seem to have either stability or noise issues if its not there.

LM317 is also an option, or LM7805. in both cases you need to have 2 extra resistors to fool them into giving you 6V instead of 1.2V or 5V respectively.

250mA is a lot of idle current. I advise using a relay or some switched source. a TIP31 NPN transistor would be a cheap alternative to a relay. +12V attaches to the collector pin, the base attaches to a 300-1000 ohm resistor which then attaches to the remote wire*. the emitter lead attaches to Vin of the regulator.

* - this resistor is there because this type of circuit really isn't the best choise of switching capacitive loads. if the circuit oscillates it will probably block cell phones inside the car, and the noise will likely get past the regulator... the resistor is there to keep the circuit from oscillating.

[thch 0]

here is a full schematic. values chosen to fit what you'd find at radioshack.

note that the metal cased TO220 will have a metal tab at 12V. don't let it touch anything. if you can find a plastic case transistor for 250mA, it will also work. likely the 2n3906 and 2n3904 will work for the npn and pnp transistors, but they are just on the edge with 200mA ratings instead of 250mA ratings. the devices will be saturated, so i don't think they'd burn up or anything.

[djjdnap 78]

yea.

diode bridge

cap 2200uf

cap ?

lm317

potentiometer

2 diodes

cap

and a resistor and ur all set.

lol

[ANeonRider 3]

Do not need a diode bridge unless you are converting ac to dc.

[Impious 1,476]

Well, thanks guys.

We'll see what comes of it. Deciding between attempting it myself, or having a respected member of another forum build one for me for $20.

I'm leaning towards the latter.