Power Section of an Electronic Load

The power section in this electronic load will be a N-channel power MOSFET. This design uses an IRF250, manufactured by International Rectifier . If a substitute part is used, pick a MOSFET that has the power, drain-to-source voltage, and current rating required for your range, and try to minimize drain-to-source on resistance (RDSon). The schematic of the power MOSFET and drive circuitry is shown in Fig. 5.1. 

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The connections for the output power supply under test are shown in Fig. 5.1 as + Load and - Load. The load current passes through the 

MOSFET (Ql). R4 is a gate resistor used to limit the current in the gate and to avoid any self-oscillations of the MOSFET because of noise. Components R7 and Cl provide compensation for the control loop. 

The SPICE transient model for this circuit is shown in Fig. 5.2. Note the additional 10 mf2 resistor (R14) that exists in the SPICE model but 

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