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Power Integrated Switching Darlington With Speed-Up Capacitor

IP.com Disclosure Number: IPCOM000043664D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Russell, SS: AUTHOR

Abstract

It is proposed here to use a speed-up capacitor in place of the normally employed speed-up diode in power integrated switching Darlington networks. Fig. 1 shows the standard switching Darlington with speed-up diode 1, while Fig. 2 shows the speed-up diode replaced with a speed-up capacitor 3. The value of capacitor 3 will depend on the characteristics of transistor Q2 and resistor R2. Typically, capacitor 3 will have a value of between 0.05 mfd and 0.15 mfd with a voltage rating of 20 volts. The functional advantage of the capacitor over the diode is in the reduction of static "off" drive current between the base and emitter terminals when VBE is reverse biased. Since R1 is > 2 x R2, the diode increases IBOFF dramatically when VBE is negative. Capacitor 3, following the peak of IBOFF (i.e.

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Power Integrated Switching Darlington With Speed-Up Capacitor

It is proposed here to use a speed-up capacitor in place of the normally employed speed-up diode in power integrated switching Darlington networks. Fig. 1 shows the standard switching Darlington with speed-up diode 1, while Fig. 2 shows the speed-up diode replaced with a speed-up capacitor 3. The value of capacitor 3 will depend on the characteristics of transistor Q2 and resistor R2. Typically, capacitor 3 will have a value of between 0.05 mfd and 0.15 mfd with a voltage rating of 20 volts. The functional advantage of the capacitor over the diode is in the reduction of static "off" drive current between the base and emitter terminals when VBE is reverse biased. Since R1 is > 2 x R2, the diode increases IBOFF dramatically when VBE is negative. Capacitor 3, following the peak of IBOFF (i.e., following charging of capacitor 3) ceases to conduct current, thus reducing the static "off" drive current (IBOFF) by 50 to 95%.

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