Push-Pull Amplifier Bias Switching to Cut Idle Current
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Solution Overview
Problem
Conventional class AB push-pull amplifying circuits waste electricity due to idle currents passing through transistors, especially when large transistors are used for load driving, leading to increased power consumption.
Innovation Solution
The amplifying circuit employs a configuration where one transistor operates in class AB mode during positive signal periods and is cutoff during negative periods, while the other transistor operates in class AB mode during negative periods and is cutoff during positive periods, minimizing idle current flow and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If class AB push-pull circuit uses bias voltage to operate transistors in active region, then output continuity is improved, but idle current increases and power consumption increases
Solution Approach 1:
The patent applies periodic action by switching transistors on and off in alternating half-cycles of the input signal. During positive half-cycles, the first transistor conducts while the second is off; during negative half-cycles, the second transistor conducts while the first is off. This periodic switching eliminates continuous idle current flow while maintaining output continuity through proper timing and overlap control.
Solution Approach 2:
The patent extracts the bias voltage application from the conventional class AB configuration. Instead of applying bias voltage to both transistors simultaneously to maintain continuous conduction, the invention removes this continuous biasing and replaces it with controlled periodic activation, thereby eliminating the source of idle current while preserving output continuity.
2Power
If large transistors are used for load driving capability, then output current capacity is improved, but idle current increases and power consumption increases
Solution Approach 1:
The patent uses periodic switching control where large transistors are activated only during their respective conduction periods (positive or negative half-cycles) and turned off during non-conduction periods. This periodic on-off operation allows large transistors to provide sufficient output current capacity when needed while eliminating continuous idle current flow that would otherwise occur in class AB operation.
Solution Approach 2:
The patent applies dynamics by transitioning from static class AB biasing to dynamic switching operation. The transistors' operating states are dynamically changed based on the input signal polarity and timing, allowing large transistors to operate at full capability during active periods while being completely off during inactive periods, thereby optimizing both current capacity and power consumption.
Data Source
AI summary
An amplifying circuit comprising an output stage circuit composed of a first and a second output transistor and operating as a class AB push-pull circuit reduces electricity consumed by an idle current. A pre-stage circuit outputs a first and a second control signal, and controls a channel current of the first and the second output transistor. In a period in which one control signal causes the corresponding output transistor to operate in class AB mode, the other control signal places the corresponding output transistor in a cutoff state.