Simple circuit controls the rate of voltage change acrossa capacitor or another load

摘要

The circuit in this Design Idea lets you set a well-controlled voltage rate of change, often expressed as the differential dV/dt (instantaneous rate of voltage change over time in volts per second). You can vary the sensitivity with a potentiometer. Set the dV/dt from 1V/200 nsec to 1V/3 msec.The input voltage can range from a few volts to 30V. Higher-voltage transistors can be used to increase the upper voltage limit. The circuit precharges a capacitor with a slow and controllable dV/dt to avoid a large inrush current during power-up. You can also use the circuit to create a high dV/dt for sus-ceptibility testing on other circuits.The circuit uses a P-channel MOSFET, Qj, to control the rate of change of the output voltage (Figure 1). You drive the MOSFET with a constant-current source comprising Q4 and Rcs, which feeds gate-to-source resistor Ros.