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Hi Folks,

having a 5V CCD cam and a two cell LIPO battery I need to reduce battery voltage.

I have read most of the topics regarding the voltage regulators.

Has anybody yet spent a thought about just using 3-4 diodes in series to reduce the voltage?

I'm wondering if it will work ...

Thx 4 your inputs

moscito

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A 2-cell Lipo will give you 8.4V when full and 6V when empty. You'll soon notice that if you adjust the diode count to have the correct drop at the start it will be too low once the battery discharges.

The 7805 regulator is as easy to use and will at least always give you the right voltage.

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Might be best to use a LDO Vreg like the old LM2940 rather than a LM7805. With the 7805, when the input voltage goes below 7V, the output voltage will be out of regulation (and on some brands it becomes very goofy).

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Thanks folks,

I have choosen the LM2940CT -5 with a VDO of .5Volts

Tomorrow I'll check what capacity I cann pull before the Vreg shuts off.

Cheers

Moscito

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I use the same regulator myself. Im not sure what you mean by capacity before it suts off ?

I find it works down to 5.5v perfectly and normally no problems even down to 5v when supplied by battery power.

It will give 1A but will need a heat sink at this level of current. I use a 100mW transmitter and camera on 2 LiPo with no heat sink.

Terry

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I use the 7805 from ST. The dropout voltage has the advantage of being a good tradeoff in the way it won't overdischarge your battery too much if you forget to disconect the battery. It will still let you the entire capacity... which anyway shouldn't be done ;)

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Sorry - the story has not ended yet ...

After buying the 2940 I tried it, but it would not regulate to 5 Volts.

I used pinout IN-GND-OUT just as the datasheet was saying.

Interestingly other samples of the same type behaved the same.

Can somebody pls veryfi his/ her pinout?

Thx in advance

Cheers

Moscito

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In/Gnd/Out is correct. If the mfg suggested caps are omitted, the Vreg may not behave correctly (may oscillate and act weird). Post a photo of your work and maybe we can see if anything odd is in the wiring.

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Hi Mr. RC-Cam,

thanks for the hint.

Well it was the missing cap.

Interestingly it would not regulate at all w/o output cap.

Hmmm. this lets me think about what's going to happen, if the cap will loose contact during cam operation. The reg will probably fry the cam then. :blink:

I finally decided to use the LT1085.

Safer operation ...

Cheers

Moscito

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Like most Vreg IC's, the LT1085 will require the stability cap too. The minimum recommended cap is a low ESR 10uF tantalum (or low ESR 50uF electroyltic). The data sheet has the details.

Despite the warnings, I have seen many folks wire up Vreg ICs without the caps recommended by the IC manufacturer. These are all situations that are ripe for trouble. I have seen some strange results, even when they Vreg appears to work without the caps. So, do not omit them.

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