Optocoupler Lifetime Extension via Periodic Switching in STO Circuits
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Optocouplers in Safe Torque Off (STO) circuits have a short lifetime due to their always-ON state, leading to reduced reliability and potential safety issues, especially in systems with high security requirements, where conventional diagnostic methods increase cost and complexity.
Innovation Solution
A control circuit with a primary side on/off control circuit and a secondary side filter, periodically switching the optocoupler's primary side on and off to extend its lifetime, and a diagnostic circuit to monitor the optocoupler's state, allowing for fault detection and operation downgrading when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the primary side of the optocoupler is kept always-ON for STO circuit operation, then the STO safety function is maintained, but the optocoupler lifetime is seriously reduced
Solution Approach 1:
The patent applies periodic action by switching the primary side of the optocoupler on and off at a frequency of 1kHz. This periodic switching extends the optocoupler lifetime by reducing continuous operation stress while the low-pass filter maintains the STO safety function by filtering the switched signal to produce a stable output.
2Duration of action of stationary object
If the primary side of the optocoupler is switched on and off to extend lifetime, then the optocoupler lifetime is improved, but the output signal contains switching frequency components that must be filtered
Solution Approach 1:
The patent introduces a low-pass filter as an intermediary component between the optocoupler and the load. This filter mediates by removing the high-frequency switching components (1kHz and above) from the optocoupler output while preserving the control signal, thus enabling lifetime extension without significantly increasing circuit complexity.
3Reliability
If an inversed optocoupler is added for online dynamic check to improve safety, then the diagnostic capability is improved, but the cost and circuit complexity increase
Solution Approach 1:
The patent makes the optocoupler primary side switching serve multiple functions: it both extends the optocoupler lifetime by reducing continuous operation and provides diagnostic capability by enabling detection of optocoupler faults. This multi-functionality eliminates the need for separate diagnostic circuits, reducing overall system complexity.
4Reliability
If a dynamic power source with transformer is added to the STO channel to improve safety, then the safety requirement is met, but the space occupation increases significantly
Solution Approach 1:
The patent extracts and removes the transformer component from the STO circuit by using the optocoupler's inherent isolation properties combined with primary side switching. This extraction eliminates the need for large magnetic components while maintaining safety requirements, significantly reducing circuit space occupation.
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 extends the optocoupler's lifetime, improves circuit reliability and safety, and reduces costs by intermittently switching the primary side, maintaining stable power supply through low-pass filtering, and enabling fault diagnosis without increasing complexity.
Implementation Method 1
a primary side (light emitting diode, LED) of the optocoupler is in an always-ON state
Implementation Method 2
a first secondary side filter circuit connected to the secondary side of the first optocoupler, and configured to filter the output of the secondary side, wherein the first secondary side filter is configured as a low pass filter having a cutoff frequency lower than an on/off frequency of the primary side
Data Source
AI summary
An optocoupler based control circuit and a method thereof are disclosed. The control circuit comprises a first control branch, which includes a first control signal input terminal configured to receive a first OFF function control signal; a first optocoupler, wherein a primary side of the first optocoupler is coupled to the first control signal input terminal, and an output of a secondary side of the first optocoupler is configured to control a first power supplied to a motor driving circuit; a first primary side on/off control circuit connected to the primary side of the first optocoupler, and configured to periodically turn on and off the coupling of the primary side to the first control signal input terminal; and a first secondary side filter circuit connected to the secondary side of the first optocoupler, and configured to filter the output of the secondary side, and configured as a low pass filter having a cutoff frequency lower than an on/off frequency of the primary side. The control circuit further comprises a diagnostic circuit configured to diagnose an operating state of the control circuit based on the output of the secondary side of the first optocoupler and the first power. The control circuit may be a Safe Torque Off (STO) circuit.