Battery Charger Current Observer Circuit Reduces Voltage Overshoot
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Solution Overview
Problem
Conventional battery chargers experience significant battery voltage overshoot due to the limited bandwidth of their negative feedback loops, which can lead to reduced battery charge capacity and shorter talk times in GSM cell phones, as specified by JEITA standards.
Innovation Solution
The implementation of load current observer circuitry as a feed-forward path that bypasses the slower error amplifier of the feedback loop, utilizing a high-pass R-C filter and operational amplifier to quickly adjust the duty cycle of the PWM signal or control the output transistor, thereby reducing or eliminating battery voltage overshoot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional negative feedback loop control is used in battery chargers, then the system is simple to implement, but battery voltage overshoot occurs due to limited bandwidth
Solution Approach 1:
The patent applies preliminary action by using an observer circuit to predict and compensate for voltage overshoot before it occurs. The observer circuit estimates the battery current and generates a compensation signal that is applied in advance to prevent the overshoot condition, rather than reacting after the overshoot has occurred.
Solution Approach 2:
The patent introduces an intermediary observer circuit between the existing feedback loop and the PWM controller. This observer circuit processes battery current information and generates compensation signals that modify the feedback voltage, effectively mediating between the simple feedback structure and the need for overshoot compensation without requiring complete redesign of the control system.
2Object-affected harmful factors
If float voltage is reduced to prevent voltage overshoot, then battery safety is improved, but battery charge capacity and talk time are reduced
Solution Approach 1:
The patent enhances the feedback mechanism by adding an observer circuit that continuously monitors battery current and generates compensation signals. This improved feedback system allows the charger to maintain higher float voltages without causing harmful overshoot, as the observer circuit dynamically adjusts the charging voltage based on real-time battery conditions, thereby preserving both safety and charge capacity.
3Speed
If faster response to load current changes is implemented, then battery voltage overshoot is reduced, but control circuit complexity increases
Solution Approach 1:
The patent replaces the slow mechanical/electrical feedback response with an electronic observer circuit that uses operational amplifiers and RC networks to rapidly estimate battery current and generate compensation signals. This substitution of the pure feedback mechanism with an active observer system enables much faster response to load current changes while keeping the overall circuit implementation practical.
Data Source
AI summary
According to one aspect of the present disclosure, there is provided a battery charging system. The battery charging system includes battery charging circuitry configured to provide charging current to a battery. The battery charging system further includes feedback circuitry configured to generate a feedback signal indicative of a battery charging condition, wherein the battery charging system is configured to control the battery charging current based on, at least in part, the feedback signal. The battery charging system further includes feed forward circuitry configured to adjust the feedback signal to decrease battery charging current when a decrease in battery current draw exceeds a threshold, and wherein the feed forward circuitry is configured to decrease the battery charging current faster than the feedback circuitry.