POWER_SWITCHING_CIRCUIT

Published:2009/7/2 3:00:00 Author:May | From:SeekIC

Circuit Notes This circuit provides on/off switching, soft starting, current monitoring, current tripping, and protection against overcurrent for a 30 Vdc power supply at normal load currents up to 2 A. The switch is turned on by an“on”command pulse; it is turned off by an“off”command pulse. An overcurrent trip can also be set on the bus side by a 6-digit binary signal, which is converted to an analog voltage and compared with the amplified voltage developed across a loadcurrent-sensing resistor. Resistor/capacitor combinations（0.027 μF, 2 kO）at the inputs of the current-sensing amplifiers act as low-pass filters: this introduces a few hundred its of delay in the response to overcurrent, thereby providing some inununity to noise. The 0.022 pF capacitors connected to the drain terminals of the PFETs provide a Miller effect, which reduces the rate of change of the drain voltage and therefore the rate of rise of current at turn-on. The soft-turn-on time depends upon the load impedance and is typically 100 to 200 ms.



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