battery backup circuit


Posted on Feb 5, 2014

A 2 diode selector circuit if your primary voltage source is greater than the diodes turn on voltage and the input voltage of the second diode. Schottky diodes are recommended for both their low lower turn on voltage (typically 0. 4v) and high switching speed. You can use a 2 diode selector circuit if your primary voltage source is grea


battery backup circuit
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ter than the diodes turn on voltage and the input voltage of the second diode. Schottky diodes are recommended for both their low lower turn on voltage (typically 0. 4v) and high switching speed. Yes provided your voltages are all within the range the transistor can handle. I think the attached circuit would work. I`ve used something like this in a recent design and now the main and backup voltages can be equal. The transistor in the diagram is a PNP. Diodes have a voltage drop that needs to be accounted for. Another way to do it is with complementary FETs. A nice example is in the power source switching used here (the part of the schematic labeled "Power" which switches between +5v and +3v sources): Of course, the two weaknesses here are 1) these are low-power parts (intended for extremely low current device), and 2) it relies on the battery backup power source having a lower voltage than the external power source. Diodes have a voltage drop that needs to be accounted for. Another way to do it is with complementary FETs. A nice example is in the power source switching used here (the part of the schematic labeled "Power" which switches between +5v and +3v sources): Of course, the two weaknesses here are 1) these are low-power parts (intended for extremely low current device), and 2) it relies on the battery backup power source having a lower voltage than the external power source. Left out a diode. Here is a circuit I`m...




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