Push-Pull Amplifier Current Replication for Accurate Overcurrent Detection
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Solution Overview
Problem
Existing push-pull amplifier circuits face errors in current detection due to bias currents, leading to inaccuracies in overcurrent detection between the detected current and the actual output current.
Innovation Solution
The amplifier circuit design includes a current replication circuit that subtracts one detection current from another, mirroring currents across resistors to eliminate errors caused by bias currents, ensuring a small difference between the output current and detection current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a push-pull amplifier circuit detects overcurrent by simply detecting current flowing into one of the transistors, then the detection circuit is simple, but an error corresponding to the bias current occurs between the detected current and the actual output current
Solution Approach 1:
The patent segments the current detection function into two separate detection paths: one for detecting the current through the first transistor (including bias current) and another for detecting the current through the second transistor (including bias current). By separating these detection functions and subsequently subtracting the detected currents, the circuit achieves accurate output current measurement while maintaining reasonable circuit complexity.
Solution Approach 2:
The patent creates a copied detection path that mirrors the other transistor's current detection. The first detection circuit copies the detection function to detect the second transistor's current, and the second detection circuit copies the detection function to detect the first transistor's current. This copying approach enables accurate differential measurement to eliminate bias current errors.
2Device complexity
If bias current is included in the detection path, then the detection circuit is simple, but the detected current includes error corresponding to the bias current
Solution Approach 1:
The patent applies the counterweight principle by introducing a compensatory detection path that mirrors the bias current effect. The first detection circuit detects the second transistor's current (which includes bias current), and this detected value is subtracted from the direct detection of the first transistor's current. This counterbalancing approach cancels out the bias current error, improving overcurrent detection reliability without significantly increasing circuit complexity.
3Ease of operation
If current detection is performed through one transistor only, then the detection process is simple, but the difference between detected current and actual output current includes bias current error
Solution Approach 1:
The patent implements a feedback mechanism where the detection circuits continuously monitor the currents through both transistors, and the subtraction operation provides feedback about the actual output current. The first detection circuit provides feedback on the second transistor's current, and the second detection circuit provides feedback on the first transistor's current, enabling accurate real-time measurement of the output current while maintaining operational simplicity.
Data Source
AI summary
An amplifier circuit includes, a first transistor and a first resistor connected in series between a power supply voltage and an output terminal. A second transistor and a second resistor are connected in series between the output terminal and a ground reference voltage. There is a first operational amplifier and a second operational amplifier. A first detection current corresponding to a voltage drop across first resistor is generated. A second detection current corresponding to a voltage drop across the second resistor is generated. A first replication circuit subtracts the second detection current from the first detection current. A third resistor conducts the current obtained by subtracting the second detection current from the first detection current.