PWM Load Open Circuit Detection via Voltage Threshold Analysis
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Solution Overview
Problem
Existing load control systems using pulse width modulation (PWM) face challenges in detecting open load conditions, which can lead to motor failures and system failures in applications like electronic stability programs (ESP) and anti-skid braking (ABS) systems, due to degradation or faults in motors.
Innovation Solution
The system employs a PWM signal to selectively turn on or off a switch, measuring the voltage change at the load's end after a predefined delay to determine if it's less than a threshold, indicating an open load condition, or measuring the time it takes for the voltage to reach a threshold, allowing for accurate detection of open loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If PWM signal is used to control the load, then the load control precision is improved, but the difficulty of detecting open load condition increases
Solution Approach 1:
The system performs preliminary action by turning off the PWM signal before detecting open load conditions. The controller stops generating PWM signals to the load driver, allowing the load to enter a known state where voltage measurements can accurately indicate open load conditions without interference from active PWM control.
Solution Approach 2:
The system uses voltage measurement at the load driver output as an intermediary indicator to detect open load conditions. Instead of directly detecting the mechanical or electrical open load state, the system measures the voltage level at the driver output, which serves as a mediator that reflects the load status through the electrical characteristics of the circuit.
2Speed
If voltage measurement is performed immediately after PWM switch-off, then the detection speed is improved, but the measurement precision deteriorates due to transient voltage effects
Solution Approach 1:
The system introduces a predefined delay period after turning off the PWM signal before performing voltage measurement. This preliminary waiting period allows transient voltage effects to settle, ensuring that the subsequent measurement reflects the true open load condition rather than transient switching effects.
Solution Approach 2:
The system employs periodic action by using a predefined delay period in the detection sequence. The detection process is structured as a periodic cycle: PWM off → delay → measure voltage → determine open load condition. This periodic structure ensures consistent measurement timing that avoids transient effects while maintaining detection speed.
Data Source
AI summary
Methods and apparatuses for detecting an open load condition for a load. The load is coupled to a power source at a high side and to a ground at a low side through at least one switch, the load has a first end and a second end, a first voltage at the first end is kept constant. A switch is controlled by a PWM signal. After the switch is turned off by the PWM signal, the voltage associated with the second end of the load is measured. In one embodiment, a change of the second voltage during a predefined delay is compared with a predefined voltage threshold. In another embodiment, the time it takes for the change of the second voltage to reach a predefined voltage threshold is compared with a predefined time threshold.