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In another thread the attached schematic was suggested to monitor voltage of a car battery.
Am I right in saying that, If I am not monitoring the voltage but merely wants to run my pic from the battery,
then I only need the portion included in the red box?
What would be appropriate components/values for Z1, D1, D2?
For Z1, what is best, a 18V transorb or a zener?
For D1, D2, is a 1n4007 good enough?
Thanking you in anticipation!
Last edited by passion1; - 6th March 2008 at 13:35.
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The only thing I would add to the first circuit and it may not be necessary, just a habit of mine, is a 4700uf on the 5 volt side.
Dave
Always wear safety glasses while programming.
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Dave
Thank you for the suggestion.
Is the purpose of the 4700uf on the 5 volt side to smooth out voltage spikes?
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Yes and no.
You should not have spikes coming from the LM7805. Spike being something more than 5V. You can pick up some high frequency noise and the 4700 will help with that.
The other thing a larger cap will do is help on brown outs. Depending on your app, it may not be a concern.
Dave
Always wear safety glasses while programming.
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That, and probably a bit of a temporary power source for when you turn on your headlights and kill main power down to a couple of volts for a split second. It's not much, but it would probably save your PIC from losing it's mind.Originally Posted by passion1
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Hi,
See picture.
Best regards,
Luciano
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Luciano
Wow! Thank you for a very comprehensive power supply design!
Can/should I still add the 4700uf to your circuit as well, as suggested by Dave and Skimask,
or does your circuit already provide a bit of a temporary power source for when one turn on the headlights?
Last edited by passion1; - 7th March 2008 at 05:46.
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Skimask
Thank you for the explanation!
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Hi,
All depends from where you get the 13.8V.
Ignition key switch? Car battery direct?
Are you using the brown-out detection of the microcontroller?
How much current is drawn by your circuit?
Headlights are not a problem unless your car is like a Christmas tree. (Rooflights).
See picture below. (Starter/battery voltage).
Best regards,
Luciano
(Click to enlarge the picture).
Last edited by Luciano; - 7th March 2008 at 12:06.
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Luciano
Thank you for the graph!
I will be using the ignition key switch to activate the circuit.
My circuit will be driving a load of up to 30A via a mosfet.
In this case, can/should I still add the 4700uf to your circuit as well?
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