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Cornelius

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Joined: 26/12/2008
Location: Norway
Posts: 27

Posted: 04:15pm 19 Dec 2010

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Just a quick question... :)

I have some of those lcd volt panels featured in an article at TheBackShed site, and a 5V to 9V dc-dc converter from an old nic.

I have several old nic's here, and all of them have the 'unregulated' variant of the dc-dc converter. When supplied with 5V from a 7805, i get around 11V unloaded, and the voltage doesn't drop much with those lcd panels connected; should i be worried?

Does the lcd panel handle the ~11 volts? Could i eventually add a 9V zener?

Cornelius

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Joined: 26/12/2008
Location: Norway
Posts: 27

Posted: 11:46pm 19 Dec 2010

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Uh...

I just had a look at the documentation that came with the panels, and it says '7-11VDC supply voltage'

(Found a french doc for the same panel that says 8-12VDC...)

The panel itself uses 1mA; the dc-dc converter + 7805 uses around 20mA unloaded... A shame to waste all that power though...

Edited by Cornelius 2010-12-21

kevbo
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Joined: 17/12/2010
Location: United States
Posts: 2

Posted: 05:18pm 20 Dec 2010

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Throw a couple-three diodes (1N914 or 1N4148 should be fine) in series with it.
These will drop about .65V each.

Cornelius

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Joined: 26/12/2008
Location: Norway
Posts: 27

Posted: 06:48pm 20 Dec 2010

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Yes, i thought about that after i wrote the last post.

But nothing goes as planned.

I had a CFUS0509-C and added an 78L05, and connected it to the panel. the panel showed just above half the input voltage...

Since i had swapped + and - somewhere, sometime, i put on my gear and dived deeper in my pc-junk-boxes and found another 10base2 card, and this one had an CFUS1209-C. Connected it up to the panel (now without the need of the 78L05), and it worked without a flaw.

I wanted to give the CFUS0509 another chance, and connected it to another panel... Same result as first time. Staring hard on the construction for a while, it dawned on me that the 78xx series like some caps on the input and output, so i added those and Vo�la!

Seems there are several wild frequencies there from both the 78xx and dc-dc converter that needs to be tamed.

The story ends with me using the 12-9V converter, since i can skip the 78xx. I'm going to add a diode or two in series to the Input of the CFUS1209, since the spec says max 15V in, and currently it's -10C outside where my battery bank resides, and i have a temperature compensated controller, giving 15.5V boost charge at these low temperatures.

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