Capacitive Battery Voltage Detection Circuit
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Solution Overview
Problem
Existing battery voltage detection circuits require high voltage endurance operational amplifiers, leading to increased costs due to the need for high-accuracy ADCs and special processing for resistors with large resistance values and low voltage dependency, which complicates the detection of battery voltages in series connections.
Innovation Solution
A battery voltage detection circuit utilizing capacitors instead of resistors for differential amplification, with operational and comparator offsets to reduce the voltage applied to the operational amplifier and comparator, allowing for accurate voltage detection without the need for high voltage endurance, thereby reducing costs and improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gain of the operational amplifier is increased to reduce the output voltage to 3.3V or less, then the voltage output to the ADC is reduced, but a highly-accurate ADC is necessary to accurately detect the battery voltages, resulting in increase in costs
Solution Approach 1:
The patent changes the fundamental parameter from resistive voltage division to capacitive voltage division. By using capacitors C1 and C2 instead of resistors R3 and R4, the circuit achieves voltage scaling through capacitance ratios rather than resistance ratios. This allows the operational amplifier to operate at lower voltages while maintaining the ability to accurately detect battery voltages through precise capacitance matching, eliminating the need for highly-accurate ADCs.
Solution Approach 2:
The patent substitutes the traditional resistive voltage division mechanism with a capacitive voltage division mechanism. The resistors R3 and R4 that created the voltage scaling issue are replaced by capacitors C1 and C2 in the feedback path of the operational amplifier. This substitution fundamentally changes how the voltage is scaled and allows for accurate measurement without requiring high-precision ADCs or high-voltage-endurance components.
2Reliability
If resistors with large resistance values are used to restrain discharge from the batteries, then the discharge current is reduced, but the resistors are required to have less voltage dependency in resistance values, thus when producing an integrated circuit including such resistors, a special processing is necessary, resulting in increase in costs
Solution Approach 1:
The patent replaces resistors with capacitors in the voltage detection circuit. By using capacitors C1 and C2 instead of resistors R3 and R4, the circuit eliminates the need for high-value resistors with low voltage dependency. Capacitors can be manufactured with standard tolerances in integrated circuits without special processing, significantly reducing manufacturing complexity and cost while maintaining reliable discharge current control.
Solution Approach 2:
The patent changes the component type from resistive elements to capacitive elements. This parameter change fundamentally alters the circuit's voltage-dependent behavior. Capacitors exhibit minimal voltage dependency compared to resistors, especially high-value resistors required for low discharge current. This substitution allows standard manufacturing processes to be used without special high-precision resistor fabrication techniques.
3Device complexity
If the gain of the operational amplifier is set to about 0.26 to eliminate the need for high voltage endurance, then the voltage VOUT input to the ADC is reduced, but a highly-accurate ADC is necessary, resulting in increase in costs
Solution Approach 1:
The patent changes the gain mechanism from resistance ratio to capacitance ratio. By using capacitors C1 and C2 in the feedback path, the gain is determined by the ratio C1/C2 rather than R4/R3. This allows the operational amplifier to operate at lower voltages (eliminating high voltage endurance requirements) while maintaining accurate voltage detection through precise capacitance ratios that can be achieved with standard components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables accurate battery voltage detection with reduced costs by eliminating the need for high voltage endurance in operational amplifiers and using a single power source for reference voltages, enhancing detection precision and reducing noise interference.
Implementation Method 1
a second capacitor (C2) having one end connected to an output terminal of the operational amplifier (20) and the other end connected to the other input terminal of the operational amplifier (20)
Implementation Method 2
a constant current circuit (47) configured to output a constant current causing electric charge accumulated in the second capacitor (C2) to be discharged at a predetermined speed
Data Source
AI summary
A battery-voltage detection circuit comprising: a first-capacitor; an operational-amplifier; a second-capacitor; a voltage-application-circuit to sequentially apply one and the other-battery-terminal-voltages to the other-first-capacitor-end; a discharge circuit to allow the second-capacitor to discharge before the other-battery-terminal-voltage is applied to the other-first-capacitor-end; a constant current circuit to output a constant-current causing predetermined-speed-discharge of electric charge accumulated in the second-capacitor in response to a discharge-start-signal input after voltage is applied to the other-first-capacitor-end; a comparator; and a measurement-circuit to measure a time-period from a time when the discharge-start-signal is input until a time when an comparator-output-signal changes to one logic level as a time-period corresponding to a battery-voltage, at least one of the operational-amplifier and the comparator being provided with an offset so that the comparator-output-signal changes to the one logic level when voltage applied to the other operational-amplifier input terminal is at a predetermined level lower than a reference-voltage level.