Circuit Schematic Diagram Variable High Power Resistor for Power Supply Testing

May 1st, 2010

The handling capability of a power supply system is sometimes needed to be checked. It might be difficult to find high power rated variable resistor to provide variable load testing. The following circuit of variable high power resistor uses 2N3055 power transistor to provide the required function :

Circuit Schematic Diagram Variable High Power Resistor for Power Supply Testing

The schematic can replace the load resistor in power supply testing, moreover you can adjust the current by setting the potentiometer. The applicable maximum voltage for this circuit is 60V. Take note to put the circuit in a box with sufficient heat sink. Although 2N3055 is specified for maximum collector current for 15A, but practically the current is limited by maximum power dissipation of the transistor. When this resistor is not connected to a power supply output then the current consumption of the battery is maximum. This is because there is no voltage reaction coming from collector current at R2 to counter the base current flow for the whole transistor, but it would never exceed 1.9 mA. It is also good to switch off the switch SW1 if the circuit is not used. The current consumption when the circuit is in use to test a power supply system is around 0.9 mA.

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