Buffer Circuit Stabilizing Complementary SEPP Transistors

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Solution Overview

Problem

The complementary single-ended push-pull (SEPP) circuit used in semiconductor switching elements experiences instability due to excessive reverse voltages during turn-on and turn-off operations, which affects switching speed control.

Innovation Solution

A buffer circuit is designed with NPN and PNP transistors, along with specific resistor and load element configurations to prevent reverse voltages between the transistors' bases and emitters, allowing for stable operation by controlling charging and discharging currents and reducing reverse voltage magnitudes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a complementary SEPP circuit is used to control switching speeds of turn-on and turn-off operations, then individual control of switching speeds is achieved, but reverse voltages cause unstable operation

Engineering Contradiction:

Improveswitching speed controlVSAvoidcircuit stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

Diodes are introduced as intermediary elements connected between the bases and emitters of the NPN and PNP transistors. These diodes clamp the reverse voltages to safe levels, preventing damage to the transistors while allowing the complementary SEPP circuit to maintain its switching speed control functionality. The diodes act as voltage limiters that protect the circuit without interfering with the primary control function.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The diodes are pre-configured in the circuit to provide protective clamping action before reverse voltages can cause instability or damage. By having the protective elements in place beforehand, the circuit is cushioned against voltage spikes during switching operations, ensuring stable operation from the outset.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Reliability

If reverse voltage protection is added to the complementary SEPP circuit, then circuit stability is improved, but device complexity increases

Engineering Contradiction:

Improvecircuit stabilityVSAvoidcircuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The diodes serve as simple intermediary protection elements that add minimal complexity to the circuit. Each diode is connected in a straightforward manner between the base and emitter of its respective transistor, providing protection without requiring complex control logic or additional active components.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The diodes are simple, inexpensive passive components that provide reliable protection. They are robust elements that can withstand the harsh switching environment without requiring complex protection or replacement mechanisms, adding minimal cost and complexity to the overall circuit design.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Data Source

PatentUS10340909B2Buffer circuit and semiconductor device

Publication Date: 2019.07.02 MITSUBISHI ELECTRIC CORP

AI summary

Provided is a technique for a stably operable complementary single ended push pull (SEPP) circuit. A buffer circuit includes the following: an NPN transistor and a PNP transistor that constitute a complementary SEPP circuit; a first resistor; a second resistor; a first load element having one end connected to a gate of a semiconductor switching element and another end connected to a base of the NPN transistor; and a second load element having one end connected to the gate of the semiconductor switching element and another end connected to a base of the PNP transistor.