i have an AC-DC adapter with 5volt 350mA (actually an old cellphone charger). i need to decrease it's voltage to 3volt. i tried adding a resistor in series & it worked, but it also decreased the output current very much. how can i decrease the voltage of without decreasing the current (mA)?
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\$\begingroup\$ Voltage regulators?!! \$\endgroup\$– nidhinCommented Jan 18, 2015 at 19:10
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2 Answers
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Use a voltage regulator. The LM7803 will regulate a 5V source down into a 3V one. Using resistors isn't the greatest option as the voltage actually used by your load/device will change with the current drawn by the load/device.
Additionally, the 350mA referenced on the adapter is the maximum rated current, not what will automatically come out.
What application do you need a specific voltage and current for?
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\$\begingroup\$ Most would refer to the LM7803 and similar a linear voltage regulator, rather than a DC-DC converter which in practical usage typically implies something a bit more sophisticated such as a switching regulator. \$\endgroup\$ Commented Jan 18, 2015 at 22:12
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\$\begingroup\$ You're right, I was just using the blanket categories from element14 which considers regulators a subset of DC-DC converters. \$\endgroup\$– SarrkCommented Jan 19, 2015 at 10:49
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Connect three forward biased diodes (e.g. 2N4001) in series to the output to drop the voltage with approximately 2V (3*0.65V).
Another (better) idea - open the adaptor and replace the zener.. I suppose there is such an element inside... I also suppose this is an analog AC-DC converter...
answered Jan 18, 2015 at 21:33