Browse Prior Art Database

Bidirectional Parasitic PNP Transistor

IP.com Disclosure Number: IPCOM000086493D
Original Publication Date: 1976-Sep-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Chang, HC: AUTHOR

Abstract

A transistor is substituted for a pair of diodes in a floating voltage driver circuit so that an isolation diffusion acts as the emitter of the transistor when current is sourced from the driver circuit, a P+ base diffusion acts as the emitter of the transistor when current is sourced from the driver circuit and a P+ base diffusion acts as the emitter of the transistor when current is sinked by the circuit.

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Bidirectional Parasitic PNP Transistor

A transistor is substituted for a pair of diodes in a floating voltage driver circuit so that an isolation diffusion acts as the emitter of the transistor when current is sourced from the driver circuit, a P+ base diffusion acts as the emitter of the transistor when current is sourced from the driver circuit and a P+ base diffusion acts as the emitter of the transistor when current is sinked by the circuit.

The driver module operates in a floating system. All voltages are referenced to VL, which is switched between ground and a high positive voltage of about 100 volts. During the first phase of operation, VU is about 50 volts above VL. Depending upon VIN to the high voltage drivers, the VOUT will be either near zero or 50 volts with respect to VL. During this phase of operation, diodes D1 and D2, or the proposed replacement TX, should act as open circuits and not affect circuit operation. Transistors T1 and T3 are connected in a conventional driver configuration.

During the second phase of operation, VU is open-circuited, VIN is at a one level and VL is alternating between ground and a higher voltage. When VL is in an upward transition, current is being pulled out of the driver. When VL is in a downward transient, current is being pushed into the driver.

Circuit operation for existing design: During sourcing of current from the driver, diode D1 acts as a conducting path between VL and VOUT. During current sinking, diode D2 and transistor T2 conduct between VOUT an...