power supply
Tuesday, January 26th, 2010
How to set up a power supply with 2 different currents?
Suppose I have an electronic device that requires 2 different currents through 3 different circuits. One is a 12V 0.8A, the other 2 are 3.3V 2.7A.
I want to power this with a single battery pack made of multiple D Cell Alkaline Batteries.
How would you design the Power supply?
The nominal output voltage of single-use D cells is 1.5 volts. I assume the loads need not have a common ground. The current capacity is about 7.8 ampere-hr, so you need to try to equalize the current drawn from the individual batteries.
So, you need 8 of them in series for the 12 volt supply. The string can then be tapped across three of the batteries for one supply, and three other batteries for the other supply, with a 0.22 ohm resistor common to the return paths of the two supplies, connected to the middle of the four batteries, to reduce each voltage to 3.3 volts.
Later: Hi,
My first idea was wrong.
The easiest way to explain how to do it right is to move circuit two and its associated resistor In your schematic one battery to the right. Then, circuit one and two are not connected to one another. Then, replace both 0.22 ohm resistors with 0.44 ohm resistors. That should be okay.
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