PNP Output Circuit With Dynamic Base Current for Fast Turn-Off
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Solution Overview
Problem
The existing output circuits with PNP transistors face a long turn-off time due to large base accumulated charge, which hinders high-speed communication by slowing down the transition from the ON state to the OFF state, thereby reducing communication speed with external devices.
Innovation Solution
The output circuit employs a PNP first transistor with a first current source that reduces the base current to a predetermined value after the transistor is turned on but before it is turned off, along with additional components like a switch, second current source, and second transistor to rapidly discharge the base accumulated charge, thereby shortening the turn-off time. This configuration reduces the number of components and miniaturizes the circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the base current is maintained at a high level during the ON state of the PNP transistor, then the transistor can be reliably turned on and maintain stable conduction, but the base accumulated charge amount increases, causing the turn-off time to become long
Solution Approach 1:
The patent applies dynamics by making the base current variable rather than constant. A control circuit dynamically adjusts the base current in three stages: initially applying a high base current to ensure reliable turn-on, then reducing it to a lower level during the ON state to limit charge accumulation, and finally applying a reverse current to accelerate turn-off. This dynamic current control resolves the contradiction between maintaining stable conduction and minimizing turn-off time.
Solution Approach 2:
The patent implements periodic action through time-segmented base current control. The base current is applied in distinct phases: a first period with high current for turn-on, a second period with reduced current for stable conduction, and a third period with reverse current for turn-off. This periodic control strategy allows the transistor to maintain reliability during conduction while minimizing the accumulated charge that would otherwise extend the turn-off time.
2Productivity
If additional circuit elements are added to reduce base accumulated charge and shorten turn-off time, then the communication speed can be improved, but the number of components increases and the circuit becomes more complex
Solution Approach 1:
The patent applies universality by designing a control circuit that performs multiple functions: it regulates base current during the ON state to limit charge accumulation, generates reverse current for accelerated turn-off, and coordinates timing sequences. By consolidating these functions into a single integrated control circuit rather than separate components, the patent improves communication speed while minimizing the increase in overall circuit complexity.
Solution Approach 2:
The patent merges the functions of base current regulation, reverse current generation, and timing control into a single integrated control circuit. This consolidation achieves the dual goals of shortening turn-off time through active charge management and limiting the increase in component count, thereby improving productivity without proportionally increasing device complexity.
Data Source
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AI summary
A turn-off time of a transistor is shorten. An output circuit (100) outputs communication signals and communicates with an external device (ED), and includes: a PNP first transistor (10), which is capable of outputting a collector current as the communication signals; and a first current source (20), which is capable of changing a base current of the first transistor (10), and which reduces the base current to a predetermined current value after the first transistor (10) is turned on and before the first transistor (10) is turned off.