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Self Protected Totem Pole Driver

IP.com Disclosure Number: IPCOM000085215D
Original Publication Date: 1976-Mar-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Malaviya, SD: AUTHOR

Abstract

A self-protected totem pole bipolar driver includes circuitry for preventing damage to output devices by limiting the maximum currents therein.

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Self Protected Totem Pole Driver

A self-protected totem pole bipolar driver includes circuitry for preventing damage to output devices by limiting the maximum currents therein.

Referring to the drawing, true and complement of the input signal are applied to the bases of transistors Q1, Q3 and Q2, Q4 while the output is taken from the juncture of the emitter of Q1 and collector of Q2.

Small series resistors R3, R4 in the emitter circuits of transistors Q3 and Q4 maintain the currents therein small (e.g., 10%) as compared with the currents in the output devices Q1, Q2. Alternatively, the emitters of Q1, Q2 may be made much larger than the emitters of Q3, Q4.

As the base-to-emitter voltage of transistor Q1 increases, the current in Q3 also increases, till, depending upon the values of resistors R1 and R3, the Schottky barrier diode SD1 begins to conduct and diverts the excess base drive of Q1 to the output line via Q3 and R3. The current in Q1 is thus limited to a safe value.

The circuit designer has a good control over the threshold at which the current in Q1 begins to limit itself because of resistors R1 and R3, whose values can be adjusted to suit the design. Note the added utility that the current of the current-limiting device Q3 also contributes to the total output current of the driver.

A similar role is played by diode SD2 and transistor Q4 in limiting the current in the lower output device Q2.

The resistor R2 can be returned to either the same positive supp...