Optically Isolated MOSFET Latching Relay With Capacitor Refresh
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Solution Overview
Problem
Conventional latching relays, whether mechanical or solid-state, face issues such as susceptibility to damage and undesirable operating characteristics, with solid-state relays requiring a separate supply to remain latched and exhibiting non-linear operating characteristics.
Innovation Solution
A discrete packaged power semiconductor latching relay using optocoupler circuits for isolation and MOSFET transistors for linear operation, with a local supply node and capacitor to maintain the on state without external power consumption, and a refresh mode to maintain voltage levels, allowing control by a microcontroller to switch the load on and off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solid-state relays use SCRs to switch and maintain on state, then the relay can maintain latched state, but the operating characteristics become non-linear and undesirable
Solution Approach 1:
The patent changes the fundamental operating parameters by replacing SCR-based switching with MOSFET-based switching. The MOSFETs operate in their linear region rather than saturation region, providing linear operating characteristics while maintaining the latched state through capacitor-based energy storage and optocoupler control mechanisms.
Solution Approach 2:
The patent substitutes the mechanical/electromagnetic SCR switching mechanism with a solid-state MOSFET switching mechanism controlled by optocouplers. This replacement eliminates the non-linear characteristics of SCRs while maintaining reliable latched state maintenance through optical isolation and capacitor energy storage.
2Reliability
If conventional solid-state relays require separate supply to remain latched, then the relay can maintain on state, but the device complexity and power requirements increase
Solution Approach 1:
The patent merges the latched state maintenance function with the existing power supply by using the load power itself to charge and maintain the capacitor. This eliminates the need for a separate supply voltage, reducing device complexity while maintaining reliable latched operation through the capacitor's energy storage capability.
Solution Approach 2:
The relay circuit serves itself by using the load power to recharge the capacitor that maintains the latched state. The optocoupler and transistor circuitry automatically manage the capacitor charging and discharging cycles without requiring external control or additional power supplies, achieving self-maintaining latched operation.
3Reliability
If optocoupler circuits are used for isolation, then ground isolation is achieved, but the device complexity increases
Solution Approach 1:
The patent introduces optocouplers as intermediary devices between the control circuit and the power switching circuit. These optocouplers provide galvanic isolation by transferring control signals optically rather than electrically, achieving ground isolation while keeping the overall circuit complexity manageable through the use of standard isolated component modules.
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 provides a reliable, energy-efficient, and linearly operating latching relay that can be controlled by a microcontroller, maintaining the load on state without external power consumption and ensuring the relay remains functional by managing voltage levels through a refresh mode.
Implementation Method 1
The photodiode is enabled causing the latch circuit to switch digital logic levels output by the latch circuit
Implementation Method 2
The local supply node is supplied by the capacitor. When the latching relay is latched in the on state, the local supply node supplies the latching relay circuitry to maintain the on state without consuming energy from the load side
Implementation Method 3
The latching relay includes MOSFET transistors which exhibit more desirable linear operating characteristics as compared to SCRs
Data Source
AI summary
A latching relay includes a supply terminal, a load terminal, first and second coupling circuits, a latch circuit, first and second transistors, and a local supply node coupled to a capacitor. In one example, the supply terminal is coupled to a supply node and the load terminal is coupled to the load. The first and second transistors control the conductivity of a drive transistor coupled to the load. A microcontroller controls the latching relay to switch the load on and off. To enable the load, the microcontroller sinks current from the supply terminal and through the first coupling circuit. While the load is enabled, the capacitor is discharged. The latching relay is operable in a refresh mode in which current is pulsed through the first coupling circuit causing capacitor to be re-charged from the supply terminal. To disable the load, the microcontroller sinks current through the second coupling circuit.