RE: [N8VEM-S100:4641] 8080 CPU - Heat is ON

Thanks Tom,

Only .7V drop out, very cool. I think there won't be much trouble if 7.5V drives the 7805. I've got 8.9V on the input...
I'll have to test the current draw and also I can test reducing the voltage to see if the heat issue cools off.

I'll test this after my week long break.

I've seen this regulator or the L4960 IIRC on a 12V battery circuit. It lets a 12V SLA battery run a 12V circuit with regulation.

Cheers,
Josh

Date: Sat, 19 Jul 2014 14:31:22 -0700
Subject: Re: [N8VEM-S100:4641] 8080 CPU - Heat is ON - Wet Finger Test
From: laf...@lafleur.us
To: n8vem...@googlegroups.com

Looks like the price of the L4940 has gone up... its now ~$1.57 at 10 each from Avnet...

On Sat, Jul 19, 2014 at 2:26 PM, Tom Lafleur <laf...@lafleur.us> wrote:

I have been using ST-Micro L4940 LDO (.7v drop) 1.5A, TO220 voltage regulators on my board... Much better that the 7805, runs cooler that the 7805's and at Avnet Express, its a bit under $1 each...

I have also found that Avnet Express is alway cheaper that Mouser, Jamco or Digikey for most parts....

On Sat, Jul 19, 2014 at 9:47 AM, Gary Kaufman <geka...@gmail.com> wrote:

Josh -

There's a tiny 1A switch mode voltage regulator on Ebay (Item 261355553215) and directly on the seller's site:

http://www.elabpeers.com/40v-to-5v-voltage-regulator-lm7805.html

Looks like it might be a perfect fix for the problem here. I suspect the problem isn't the 1A rating, but rather the thermal limitations of the TO-220.

I've ordered two and can report back once I receive them. I offered the seller $9.50 each / quantity 2 with the ebay "Make an offer" and it was quickly accepted.

- Gary

On 7/19/2014 11:49 AM, John Monahan wrote:

Just want to mention, people may want to consider using the 1.5A To-220 regulators rather than the old 1A 7805’s. For example a L7805CV (Jameco #924633). Indeed I seem to remember Mouser had 3A 5V’s in a TO-220 package.

There are a lot of chips for one 7805 on that board. On a V2 version Josh, you might want to consider a 3A LM232K, I know they are a real pain to get, take up much more room, but they do run much cooler. Alternatively put two To-220’s on the board. It’s probably just me, but I don’t like hot boards. Over time the fiberglass starts to deform/change color… minimally put a mica washer between the heat sink and board. Also use heat sink paste.

John

From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Crusty OMO
Sent: Saturday, July 19, 2014 5:34 AM
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:4637] 8080 CPU - Heat is ON - Wet Finger Test

Hi Guys,

Because the 7805 can get hot, I want to just issue a safety warning for everyone.

Hopefully, most of you already know this, but just in case, it's always a good idea to remind and inform the new comers.

When powering a board for the first time, be ready to check the voltages and monitor the heat of the regulator(s).
Cut power off at the sign of any trouble.

When monitoring the heat of the regulator by finger, always use a wet finger. Doesn't sound right near electricity, but hopefully you have a properly grounded power supply and chassis. The wet finger will prevent severe burns if the temperature is over 100c. When it's over 100c, a quick light tap on the surface with a wet finger will give a quick sizzle. It's like testing the temperature on your clothes iron. The best way is to use an infrared surface thermometer, but I only got one of those a few months ago. Up to now, I've always used the wet finger without incident.

Regards,
Josh Bensadon

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RE: [N8VEM-S100:4641] 8080 CPU - Heat is ON - Wet Finger Test