Charging Circuit Reverse Current Detection Without Series Resistors
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Solution Overview
Problem
Existing charging circuits face issues with erroneous disconnection detection and reverse current generation when using unstable power sources like solar cells, due to the reliance on resistors for reverse current detection, which leads to power loss and inaccurate voltage detection.
Innovation Solution
A charging circuit design that eliminates the need for resistors by using a power path control unit with switches and voltage comparators to detect voltage differences and current flow between the external power supply and battery terminals, ensuring reliable disconnection detection without erroneous results even with unstable power sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resistor is connected in series to detect reverse current, then reverse current detection is enabled, but power loss is generated and detection accuracy deteriorates under no-load conditions
Solution Approach 1:
The patent extracts the reverse current detection function from the series resistor configuration and relocates it to the negative terminal of the battery through a dedicated detection circuit. This eliminates the need for a series resistor, thereby removing the associated power loss while maintaining detection capability through voltage comparison at the battery negative terminal.
Solution Approach 2:
The patent introduces a detection circuit as an intermediary component that monitors voltage at the battery negative terminal without requiring current flow through a series resistor. This intermediary detection mechanism enables reverse current detection while avoiding the power loss inherent in resistor-based methods.
2Device complexity
If voltage drop across a series resistor is used for detection, then reverse current detection is simple, but erroneous detection occurs under no system load conditions
Solution Approach 1:
The patent extracts the detection point from the series resistor voltage drop method and relocates it to the battery negative terminal. This extraction allows detection to occur independently of system load conditions, eliminating erroneous detection while maintaining circuit simplicity.
Solution Approach 2:
The patent uses voltage comparison at the battery negative terminal as a copy or alternative measurement point that reflects reverse current conditions without being affected by system load variations. This copied detection method provides reliable indication of reverse current flow independent of the main power path load conditions.
3Ease of operation
If input voltage is compared with a predetermined value to detect reverse current, then detection is straightforward, but incorrect detection occurs with unstable power supplies like solar cells
Solution Approach 1:
The patent introduces a reference voltage generation circuit as an intermediary that creates a dynamic threshold based on the input voltage itself. This intermediary reference voltage adapts to unstable power supply conditions, allowing the comparison circuit to maintain accurate reverse current detection despite variations in the external power supply voltage.
Solution Approach 2:
The patent dynamically changes the reference voltage parameter based on the input voltage level. Instead of using a fixed predetermined voltage value, the reference voltage is generated as a proportion or function of the input voltage, allowing the detection threshold to adapt automatically to unstable power supply conditions while maintaining detection simplicity.
Data Source
AI summary
A charging circuit includes a power path control unit which switches a first switch connected between a system connection terminal and a battery connection terminal on while not charging, and switches the first switch on and a second switch connected between an external power supply input terminal and the system connection terminal on while charging so as to supply power to a system and charge a battery. A voltage difference between the external power supply input terminal and the battery connection terminal is detected, a current flowing between the external power supply input terminal and the system connection terminal is detected, and it is determined that an external power supply is disconnected based on the detection results of the voltage differences and the current.