Smoothing Capacitor Values

Hi, Michael. The specs say you should have a cap at the input of the regulator if the power source is more than a couple of inches away, For being fed from a battery, 10uF should be plenty. For the output, a small cap helps for high frequency stability, and to keep the noise voltage within spec. You can either use another 10uF electrolytic, or an 0.1uF ceramic or film would be fine, too.

When you lay it out, tie the GND pin of the regulator and the - pins of the electrolytics within an inch of each other if you can.

Good luck Chris

Thanks again Chris

Michael

No smoothing cap is needed because your input supply is DC already.

You will however need some small caps to ensure stability located close to the regulator. See the manufacturer's data sheet for recommended values.

Graham

That regulator doesn't have a high enough input voltage spec to survive automotive supply voltage transients.

Graham

"Eeysore"

What bollocks.

........ Phil

(I'm

If you're still there, Mike, Graham has a good point. An automotive environment has high voltage transients of over +60VDC, which will eventually fry your regulator.

For greater reliability, you might want to add a 24V Transzorb (Maplin N95CA part number 1.5KE24A, =A30.46 ea. in stock) and a 1 ohm junkbox power resistor to your circuit like this (view in fixed font or M$ Notepad):

| _____ | B+ ___ | | | o----|___|-o-----o----|78S05|---o-------o | 1R | | |_____| | + | | +| | +| | D1| --- | --- | /-/ C--- | C--- 5VDC | ^ | | | | | | | | | | | | | - | o----------o-----o-------o------o-------o | GND (created by AACircuit v1.28.6 beta 04/19/05

If a spike occurs on B+, the transzorb will act like a zener and clip the transient to a maximum voltage of around +24V. It's made to absorb brief, high energy spikes like this, and isn't too expensive for what you get. A quick scan didn't show any 1 ohm resistors at Maplin, but you'll probably have one (anything between 0.47 ohms and 2 ohms will do) in your junkbox. The 1 ohm resistor will limit the current during the spike, and keep the Transzorb from smoking. Actually, the resistor will also drop some of the voltage, which might mean you can use a smaller heat sink, too.

This will make your automotive circuit a lot more reliable.

Cheers Chris

Google for "automobile electronics load dump".

is off the first link. There are many others.

There were a lot of burnt electronics in many vehicles -- in the 1960s, as the newfangled solid state electronics were being rolled out into cars. Everyone learned the hard way about load dump transients, which will frequently happen if the battery connection is intermittent.

Usually some inductance is placed at the power input to automotive electronics, and there are various methods used to clip the amplitude of transients, many of them built into the boards in odd places. The junkbox resistor/Transzorb method is clunky, but it works.

Either that, or if you'd like to use tubes in your car radio, they're very happy with voltage transients. ;-)

Chris

Yup I'm still here....havn't quite gathered up the courage to finally submit my order :-)

The circuit won't be connected up to a car though.....(although it will be connected to a car battery)

What w rating should the resistor be in that circuit? As big as possible I'm guessing.....

I guess better safe than sorry is the key phrase here....

Cheers,

Michael

"Michael" wrote in message news:lVPTg.56475$ snipped-for-privacy@fe2.news.blueyonder.co.uk...

Don't know if it makes a difference......but the ROV is the underwater type.....

Example:

Michael

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or

mit

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Hi, Mike. Load dump is a problem associated with alternators (and to a lesser extent, with battery chargers). If you're just running it off straight battery power (and there's zero chance that it will be powered when the battery is being charged) you won't need transient protection.

If you decide you still need transient protection for your power supply, the value of series resistor just depends on the current requirement. P =3D (I ^ 2) * R. If you have a wirewound 1 ohm resistor in your junkbox, it will probably be 5 watts or more, which should be just fine for any current you might require (the 78S05 is good for 2 amps max, which would mean 4 watts max).

Good luck with your project, and feel free post back if you have any other questions.

Cheers Chris

Mike... linear regulators are not efficient... Look for a 12V to 5V DC to DC converter at Jameco or Digikey.. they can be 90% effcient! Batteries will thank you.

if that was the case, there would be a lot of burnt electronics in many vehicles.

No, it isn't, because there are spikes in an automotive electrical system that go well above + 35 volts. If your weren't such a loser, you would have checked the facts BEFORE you dumped your usual load of crap. There are standards for automotive electrical and electronics hardware, including "Load Dump".

Go back to molesting toasters, Phyllis, and leave the real electronics to the men.

Delco used a "Spark plate" which was a piece of thin double sided PCB material in their car radios, as well. It was soldered to the case on one side, and used as a tie point in the DC input and filtering.

"Michael A. Terrell "Eeysore"

F****NG MORON !

Go back to molesting little kids in Vietnam - like real US soldiers.

....... Phil

Only in your small mind. There is a lot of stray inductance and capacitance in the wiring harness. Do you really expect anyone to believe that the arc when a starter solenoid opens doesn't impress a number of large spikes on the rest of the electrical system? Your glaring ignorance is showing, toaster molester.

About damn time that you admitted it, Phyllis.

First of all, i never served in Vietnam. Its you that got caught in those sexual acts, and real soldiers don't molest anyone, f***ot.

The photos from Abu Ghraib would seem to indicate otherwise.

"Michael A. Terrell"

" Eyesore "

" Actually, I was sent to Alaska INSTEAD of Vietnam. Two months after I arrived the base I was supposed to go to in Vietnam was overrun, and the entire staff was killed. "

Be one less TOTALLY INSANE Septic Tank Cunt polluting the earth.

Most reg ICs have a similar input voltage limit to the one in question anyhow - so Eyesore has to say what ** HE ** meant by his asinine remark.

NOT SOME CRIMINAL, LYING PSYCHO CUNT LIKE YOU !!!

F*CK OFF - ASSHOLE !!!!!!!!

........ Phil