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Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1667

Posted: 04:01pm 21 Aug 2016

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Hi @Grogster,

Noticed IC2 (LM3940) was running rather warm last night.

Was only powering the 5" display.

Is it worth grabbing a heat sink for under it?

Something like Altronics H0630?

While I'm ordering a bit of stuff....

Thanks

Phil.

Grogster

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Joined: 31/12/2012
Location: New Zealand
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Posted: 04:29pm 21 Aug 2016

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What's the total current consumption?

Lower the backlight current by dropping the brightness.

The 5" LCD should not have any problems with the 3940 getting hot, but it will get quite hot on a 7" LCD.

Adding a heatsink won't hurt if you want to do that. Heat is an electronics killer as I always say, but the circuit is designed to use the PCB copper ground-plane as a small heatsink, and normally, you should not need additional heatsinking for the 5" display - unless it is unusually thirsty over the test units we used while prototyping this board.

That is possible, as they change the design on those LCD modules as I see in another thread!

Edited by Grogster 2016-08-23

Smoke makes things work. When the smoke gets out, it stops!

WhiteWizzard
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Joined: 05/04/2013
Location: United Kingdom
Posts: 2948

Posted: 10:20am 22 Aug 2016

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I have seen a wide variation of current consumption on TFTs.

You cannot assume that a 7" draws more than a 5" when buying bits from eBay. Also, I have seen as low as 225mA on BACKLIGHT 100, and as high as 985mA. Not to mention the 'quality' of viewing angle!

This is why I am finding it hard to recommend a link to a TFT as there is great variation out there. The manufacturer I prefer to use for quality TFTs has a different pinout to that used on the E100

If the vReg is getting warm with the 'set-up' you are using then I would recommend a heatsink (or at least a nut & bolt to help spread head through the copper ground plane). As Grogster says; it won't hurt adding one.

On an early prototype of a MM+, I noticed the PIC getting warmer than expected. I added a RaspberryPi heatsink to the PIC and this was probably overkill!!

Bottom line - if a component is getting 'warm' then adding a heatsink won't do any harm!

WW
Edited by WhiteWizzard 2016-08-23

Grogster

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Posted: 03:29pm 22 Aug 2016

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Agreed. The 3940 is good for up to 1-amp of load, and it does have all the usual thermal shutdown protection etc, but in an ideal world, you don't want that protection to ever kick in, as it is usually a last-gasp attempt by the regulator to save itself.

If the TOTAL current consumption of the ENTIRE BOARD with LCD running too is more then 600mA or so, you should probably fit some kind of heatsinking to the regulator. I have found it was not necessary in my tests, and also Geoff reported that there were not any heat issues with the regulator when he was testing out his board, so as WW says about eBay LCD's.......(which is not me putting them down, but variations between manufacturers, you know)

Also, you can save quite dramatic current by simply lowering the LCD backlight to 50% or so, and in most cases, this does not really affect the readability of the display. Usually, I find that lowering the backlight down to 25% or so is actually BETTER in my case, as then the display does not look washed-out with too much white backlight. This is inside though. Point being that if you drop the backlight even to 50%, you will halve the current consumption of the backlight, the regulator will cool down and you won't even need to fit a heatsink.

Smoke makes things work. When the smoke gets out, it stops!

Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1667

Posted: 11:33am 24 Aug 2016

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WhiteWizzard said I have seen a wide variation of current consumption on TFTs.

You cannot assume that a 7" draws more than a 5" when buying bits from eBay. Also, I have seen as low as 225mA on BACKLIGHT 100, and as high as 985mA. Not to mention the 'quality' of viewing angle!

Measure it yesterday, 490mA all up, 225 is a huge difference.

Would say the viewing angle is not fantastic on the ones I have.
Probably go some voltage loss on the one on solderless breadboard;
Not much point in dropping it below 100%
Doubt it's getting a full 3.3V. (Edit, the one on breadboard, not the E100).

Cheers.
Edited by Phil23 2016-08-29

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