Electronics Tips and Tricks

Guaranteed One Percent Resistors

1% resistors are often required in electronics applications, however, during manufacturing, sometimes manufactures will make a mistake by ordering a generic resistor that may be 5% or even 10% in order to save costs. A useful trick is to specify resistors that only come in 1% values. For example if you have a resistor divider that requires a ratio of 10, rather than using a 10K ohm resistor and a 100K ohm resistor, specify a 10.2K and a 102K ohm instead. This way there is no possible way to use higher tolerance resistors.

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.