alistairolsen
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| posted on 1/9/10 at 03:12 PM |
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Zener Diode Voltage regulators
Any electronics folk around?
Im looking at a wee project for which I need a regulated power supply.
I have a camera with a small 3.7v internal battery and I want to hardwire it to the car.
The cars battery voltage will vary between what, 8 and 15 at the outside?
I found this site
http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm
Am I correct in thinking Any resistor exceeding the power required and any zener exceeding the power required is fine, it is just the zener voltage
and resistance that matter?
Also, the resistance varies dependant upon the input voltage, if I select a resistor based on 13.2v (engine running) will it cope ok with battery
voltage with engine off?
Cheers
My Build Thread
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BenB
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| posted on 1/9/10 at 03:28 PM |
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Only issue there is that the shunt resistor resistance will need to vary depending on the current flow required (which will vary). I'd
personally be tempted to run a variable voltage regulator. Nice and simple and more reliable than a zener diode.... Don't forget if you're
running 12v down to 3.7v that's some watts you'll be kicking out so you might need a heatsink depending on the amps your camera will be
pulling.
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ChrisW
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| posted on 1/9/10 at 03:32 PM |
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I'd use a 7805 regulator - which looks like a transistor and has voltage in, voltage out and ground. It'll give 5v.
Then put 2 regular diodes in series with the load. The junctions in the diodes will drop 0.65v each (+/- 0.5v) which should leave you with 3.7v to
play with.
Chris
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02GF74
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| posted on 1/9/10 at 03:56 PM |
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that circuit is providing a defined voltage - it is not designed to supply oodles of current to act as a power supply.
so no, don't use that unless you want to damage your camera.
you need to have some idea of the current requirements of your camera.
either buy a regulared voltage swuply - these already have the cigar light plug and can have output voltage configured.
or if you insist on making your own, an LM 317 can supply up to 1.5 A for the voltage range of 1.2 - 37 V.
maplins do a kit using this device - albiet for an AC input voltage - which will work on
your car's DC but with redundant diodes.
[Edited on 1/9/10 by 02GF74]
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Liam
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| posted on 1/9/10 at 04:17 PM |
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Try this...
http://www.reuk.co.uk/Using-The-LM317T-To-Regulate-Voltage.htm
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britishtrident
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| posted on 1/9/10 at 07:28 PM |
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Don't assume because the battery is 3.7 volts the camera runs on 3.7 volts --- under load the battery will have an internal voltage drop.
It could be you could get away with a cheap off the shelf convertor.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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