Driver Circuit Anomaly Detection for PWM Signal Fixation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing driver circuits for loads in bridged transformer less configurations can cause speaker damage due to continuous DC current flow when PWM signals are fixed, despite over-current prevention circuits, as even small DC currents can be detrimental.
Innovation Solution
Incorporating a detection circuit that monitors changes in PWM signals, a counter to track signal anomalies, and an anomaly detection circuit to generate a signal that turns off the drive current when a predetermined count is reached, preventing damage by identifying and addressing anomalies in PWM signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If PWM signals are fixed and output stage transistors are fixed to an on state, then the driver circuit can operate continuously, but DC current flows to the speaker causing potential damage
Solution Approach 1:
The detection circuit performs preliminary monitoring of PWM signal changes before DC current can cause damage. By detecting signal fixation early and triggering the anomaly detection circuit, the system takes preventive action to turn off transistors before harmful DC current accumulates sufficient duration to damage the speaker.
Solution Approach 2:
The system implements feedback through the detection circuit that continuously monitors PWM signal states and provides feedback to the anomaly detection circuit. When the counter detects a predetermined number of unchanged signal states, feedback is sent to turn off the output stage transistors, thereby eliminating the harmful DC current condition.
2Reliability
If an over-current prevention circuit is used to prevent large currents, then short circuit protection is improved, but small DC currents continue to flow causing speaker damage
Solution Approach 1:
The protection function is segmented into two independent circuits: the over-current prevention circuit for large current protection, and the new detection circuit with anomaly detection for DC current detection. This segmentation allows each circuit to specialize in detecting and preventing specific types of current hazards, with the detection circuit monitoring PWM signal states to identify DC current conditions that the over-current circuit would miss.
Solution Approach 2:
The detection circuit acts as an intermediary between the PWM signal source and the output stage transistors. It monitors signal integrity and intermediates the control flow by triggering the anomaly detection circuit when signal fixation is detected, thereby preventing DC current from reaching the speaker without interfering with the normal operation of the over-current prevention circuit.
3Reliability
If PWM signals are monitored continuously, then anomaly detection reliability is improved, but device complexity increases
Solution Approach 1:
Instead of continuously complex monitoring, the system uses partial action by counting a predetermined number of consecutive unchanged PWM signal states. This approach achieves reliable anomaly detection without requiring continuous complex analysis, using a simple counter mechanism that triggers only when sufficient evidence of signal fixation accumulates.
Solution Approach 2:
The detection circuit utilizes the existing PWM signal itself as the monitoring source, requiring no external sensors or additional signal generation. The counter circuit self-services by automatically counting signal state changes and autonomously triggering the anomaly detection when the predetermined count is reached, eliminating the need for external monitoring equipment.
Data Source
AI summary
A pair of PWM signals having mutually opposite or identical phases is applied to both terminals of a load to drive the load. An anomaly detection circuit detects a state of change in the pair of PWM signals (PWM+ and PWM−), performs counting operation when at least one PWM signal stops changing, and outputs an anomaly detection signal when the count value becomes a predetermined value.