tegwin
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| posted on 27/3/07 at 10:23 AM |
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Making a stable 8V power supply from a car outlet?
I want to be able to plug my video camera into my cars power outlet so I dont have to worry about the batteries in the camera going flat whilst im
filming...
The cars power outlet ranges from 12-14V...
The camera needs 7.9v (8v)
Is there a simple circuit that I can nock up that will give a smooth stable 8V supply?
The current drain is going to be tiny!
Any thoughts?
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nitram38
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| posted on 27/3/07 at 10:25 AM |
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Buy a multi voltage unit from maplins. They are only about £8 to buy.
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iank
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| posted on 27/3/07 at 10:33 AM |
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quote:
Originally posted by tegwin
I want to be able to plug my video camera into my cars power outlet so I dont have to worry about the batteries in the camera going flat whilst im
filming...
The cars power outlet ranges from 12-14V...
The camera needs 7.9v (8v)
Is there a simple circuit that I can nock up that will give a smooth stable 8V supply?
The current drain is going to be tiny!
Any thoughts?
Yes, a LM317T and a couple of resistors and caps. All parts available from maplins, would cost £1.50 tops built on veroboard.
Let me know if you need a circuit drawn up.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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RazMan
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| posted on 27/3/07 at 10:34 AM |
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If you want to hard wire something then a small DC-DC converter should do the trick. Maplins to the rescue
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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tegwin
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| posted on 27/3/07 at 10:42 AM |
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Chears IANK. A schematic would be handy.
I dont supose I can use an LM1458 or an OPA2134PA instead can I?....I already have boxes of those, so would be handy to use them up!
Chears.
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iank
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| posted on 27/3/07 at 10:52 AM |
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quote:
Originally posted by tegwin
Chears IANK. A schematic would be handy.
I dont supose I can use an LM1458 or an OPA2134PA instead can I?....I already have boxes of those, so would be handy to use them up!
Chears.
OK, will put one up tonight. Those chips you mention are op-amps, the LM317T is three leg adjustable voltage supply (69p from Maplin  )
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Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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Winston Todge
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| posted on 27/3/07 at 11:42 AM |
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An LM7808 reduces component count and would only require a couple of capacitors for bypass and response. But doesn't strictly need these
either...
 
Rescued attachment 8VReg.png
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MikeRJ
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| posted on 27/3/07 at 01:36 PM |
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quote:
Originally posted by iank
Yes, a LM317T and a couple of resistors and caps. All parts available from maplins, would cost £1.50 tops built on veroboard.
Let me know if you need a circuit drawn up.
Don't forget a diode connected between the input and output pins (reversed biased with regulator powered).
This saves the regulator in the event of the regulators input going to 0v (i.e. ignition off with ignition controll cig lighter) if there is any
capacitance on the output (e.g. inside the camera). Often missed out, but considerably improves the reliability for the few pence that a 1N400x
rectifier costs.
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tks
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| posted on 27/3/07 at 03:34 PM |
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yeah
Just sample a 7808 from TI
and add the diode on the input in forward bias
add a couple of caps for a smooth voltage and you are done..
Tks
The above comments are always meant to be from the above persons perspective.
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iank
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| posted on 27/3/07 at 03:57 PM |
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quote:
Originally posted by tks
Just sample a 7808 from TI
and add the diode on the input in forward bias
add a couple of caps for a smooth voltage and you are done..
Tks
Well yes, but try getting one if you aren't a company that looks like a prospect to some sales droid 
I've always found I had to sit through 20mins of nonsense to get any freebies even when I worked for major electronics companies who bought
thousands of components.
While a 7808 means 2 fewer resistors the lack of availability over the counter at an national electronics shop makes it much more awkward to make.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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iank
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| posted on 27/3/07 at 08:27 PM |
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OK, I think this is correct, but obviously measure the voltage before blowing up any expensive electronics kit. Using a multi-turn trim pot (or E96
range resistors) would allow fine tuning of the output voltage.
In theory you don't need any fuses as the power reg is short circuit protected, but I'd get the input from a convenient fuse anyway.
 
8v power reg
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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tks
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| posted on 27/3/07 at 08:37 PM |
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cant see any reason wy you would put that diode in it..
infact the car will pull from the caps from your device..
i would add a input diode for minimum
atleast it disables the car from pulling from the device and from the input cap..
Tks
The above comments are always meant to be from the above persons perspective.
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iank
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| posted on 27/3/07 at 08:54 PM |
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quote:
Originally posted by tks
cant see any reason wy you would put that diode in it..
infact the car will pull from the caps from your device..
i would add a input diode for minimum
atleast it disables the car from pulling from the device and from the input cap..
Tks
Read MikeRJ's post for the diode. If you do an internet search you will see it's common practice to prevent the regulator being damaged
by the output staying up longer than the input.
What function would in input diode have?
The caps wouldn't power a car for very long so I'm not sure what you mean by pulling power from them.
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Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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