Power Supply Current Mirror for Near-Zero Voltage Current Limiting
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Solution Overview
Problem
Power supply circuits face challenges in accurately detecting and limiting output current when the output voltage approaches 0 volts, leading to inadequate current detection and limitation.
Innovation Solution
The proposed power supply circuit incorporates a current mirror circuit with operational amplifiers and resistors to detect and control output current, including an offset adjustment circuit to correct input offsets, ensuring appropriate current limitation even at low output voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional current detection circuit using an operational amplifier is used, then the current limit circuit can limit the output current under normal operating conditions, but the current detection becomes inaccurate when the output voltage decreases to near 0 volts
Solution Approach 1:
The patent introduces an intermediary circuit that converts the difficult-to-detect low voltage current signal into a more detectable form. Specifically, when the output voltage is near 0V, the circuit uses an alternative detection path through resistors and operational amplifiers that can accurately measure the current by detecting voltage drops across known resistance values, rather than directly measuring the near-zero output voltage.
Solution Approach 2:
The patent changes the detection parameter from direct output voltage measurement to indirect measurement through voltage drops across detection resistors. By measuring the voltage drop across a known resistor value using an operational amplifier, the circuit can accurately determine the current even when the overall output voltage is near zero, effectively changing the measurement parameter to one that remains detectable under low-voltage conditions.
2Adaptability or versatility
If the output voltage is near 0 volts, then the power supply circuit can operate at low voltage levels, but the conventional current detection circuit cannot appropriately detect the output current
Solution Approach 1:
The patent segments the current detection function into multiple paths: one for normal voltage operation and another for low voltage operation. The circuit divides the detection task among different components (detection resistors, operational amplifiers, and switching elements) that are activated based on the output voltage level, allowing accurate current detection across the full voltage range including near-zero conditions.
Solution Approach 2:
The patent uses intermediary detection resistors and operational amplifiers that create a detectable voltage signal even when the main output voltage is near zero. These intermediaries convert the hard-to-detect low-voltage current into a measurable signal through precise resistance-based voltage division and amplification.
Data Source
AI summary
A power supply circuit in an embodiment includes a series circuit of a first resistor and a second transistor, the series circuit being connected in parallel to a first transistor between an input terminal and an output terminal, a third transistor configured to output an electric current corresponding to an electric current flowing to the first resistor, a third resistor configured to generate a voltage corresponding to the electric current, and a second operational amplifier configured to output a signal corresponding to a voltage difference between the voltage and a reference voltage to a gate of the first transistor and a gate of the second transistor.