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Old 26th February 2009, 01:28 PM   #1
kanifee is offline kanifee  United Kingdom
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Default voltage control

Need a little help. I have a 19v charger that i need 15v form, what is the best way for me to do this?
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Old 26th February 2009, 05:28 PM   #2
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What sort of current does your application require?
If the current is low (less than 1.5A) the LM7815 regulator is probly the easiest way. Its data sheet and application notes are widespead on the www.
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Old 26th February 2009, 09:56 PM   #3
kanifee is offline kanifee  United Kingdom
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Its a laptop, i need to down the voltage form a laptop charger from 19 to 15v with 5a
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Old 26th February 2009, 11:32 PM   #4
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Ok, at 5A the linear 7815 will not work.
You could go for the LM338, which is electrically VERY simple to use, but will generate quite a lot of heat (4V drop @5A = 20Watt of heat).
(http://www.national.com/mpf/LM/LM338.html)
It will require a physically big heatsink.

Electrically a bit more complex is the LM2679 (http://www.national.com/pf/LM/LM2679.html)
which will run cool, but requires more support components.

The BEST way to do this - but it requires a knowledge of the circuit involved, would be to get into the existing charger and change the value of the resistor that sets its output voltage.
If you can open it, and see what regulator chip they use, you could maybe find its datasheet on the web and figure out how it is being operated.
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