Minimizing Forward Voltage Drop Across Diodes

Minimizing Forward Voltage Drop Across Diodes

Diodes are often used to prevent reverse polarity of power input leads. In battery powered applications this can present a problem, because diodes have a natural voltage drop, that lowers the available supply voltage to the circuit. For example, if you have a 6V battery which powers a 5V circuit, then there isn't much margin. A simple trick to lower the forward voltage drop is to place diodes in parallel. For example, the BAT54 is a dual diode that comes in a SOT23 package. A single diode has the following voltage drop characteristics:

If (mA) Vf (mV)
.1 240
1 320
10 400
30 500
100 800

In the case where our circuit draws 150mA, then if we use three BAT54 diodes in parallel, then the forward voltage drop goes from 1V to less than 500mV, since 6 diodes divide the current down to 25mA.

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