Vreg recommendations

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bravo685
Posts: 13
Joined: Mon Nov 28, 2011 12:41 pm

Vreg recommendations

Post by bravo685 » Tue Mar 06, 2012 8:18 am

I have begun building the GPIO board and have a question about the vreg.

The instructions say the vreg doesn't need a separate heat sink unless your powering off-board accessories. I plan on supplying a MAP sensor 5v and 0v, any recommendations for a heat sink - thickness etc..?

I searched this forum but it doesn't look like anyone has made an comments about this.

Bernard Fife
Posts: 1696
Joined: Fri Apr 04, 2008 1:28 pm

Re: Vreg recommendations

Post by Bernard Fife » Tue Mar 06, 2012 9:23 am

bravo685,

Typically, MAP sensors draw very little current (typically around 7 milliamps), so they alone aren't enough to require you to use a heat sink on the regulator. If you were trying to power a 5V solenoid pulling 200 milliamps, for example, the heat sink might be needed.

If a heat sink was required, if I made it myself I would use 1/8" (3mm) thick aluminum, or I would purchase a heat sink from an electronics shop made for TO-220 devices (like 294-1107-ND from Digi-Key, many more here: http://dkc3.digikey.com/PDF/CA2011/P2591.pdf)

Lance.
"Never wrestle with pigs. You both get dirty and the pig likes it." - George Bernard Shaw

bravo685
Posts: 13
Joined: Mon Nov 28, 2011 12:41 pm

Re: Vreg recommendations

Post by bravo685 » Wed Mar 07, 2012 10:19 am

Lance,

What is the maximum input voltage for the GPIO?

Bernard Fife
Posts: 1696
Joined: Fri Apr 04, 2008 1:28 pm

Re: Vreg recommendations

Post by Bernard Fife » Wed Mar 07, 2012 11:31 am

bravo685,

You should avoid 12V supply voltages over 18 Volts. The hardware is rated to a few volts more, but you will want to have some margin for spikes, waves, temperature considerations, etc.

There are two items to protect the power supply from over-voltages:
- the metal oxide varistor (P7315-ND at Digi-Key) is a 22 Volt surge suppressor that can short significant voltage spikes to ground (http://industrial.panasonic.com/www-dat ... 000PE1.pdf)
- D5 is a 24V Zener diode will short voltages above 24V to ground for a short time (until it burns up) if the spikes are reasonably slow. D5 also has a 10% tolerance on it, so it could actually be as low as 21.6 Volts.

The regulator (LM2937ET-5.0-ND) is rated to 26V continuous, and up to 60V for less than 1/10th of a second.

Lance.
"Never wrestle with pigs. You both get dirty and the pig likes it." - George Bernard Shaw

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