Relay Drive Circuit Using Current Mirror for Constant Drive Conditions
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Solution Overview
Problem
Relay switches driven by transistor circuits face variations in current consumption and operation timing due to changes in relay coil resistance caused by temperature changes, leading to inconsistent drive conditions.
Innovation Solution
A relay drive circuit incorporating a current mirror circuit with a first and second resistor element, where the second resistor element has a greater resistance value, and a current suppression circuit with a capacitor and resistors to maintain constant drive conditions by adjusting current flow through the relay coil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a constant drive voltage is applied to the relay coil, then the relay switch can be simply controlled, but the drive conditions vary when the relay coil resistance changes due to temperature changes
Solution Approach 1:
The patent changes the control parameter from voltage to current. By using a constant current circuit, the drive current through the relay coil is maintained constant regardless of resistance changes due to temperature. This resolves the contradiction by maintaining reliable drive conditions (improving reliability) while keeping the control mechanism simple through automatic current regulation (preserving ease of operation).
Solution Approach 2:
The patent implements a feedback mechanism where the voltage across the relay coil is detected and used to regulate the drive current. When the coil resistance increases due to temperature, the feedback circuit automatically increases the drive voltage to maintain constant current, and vice versa. This feedback loop ensures consistent drive conditions while maintaining simple control operation.
2Loss of energy
If the relay coil resistance changes due to temperature changes, then heat generation is reduced, but the operation timing and current consumption vary
Solution Approach 1:
The patent changes from voltage control to current control. By maintaining constant current through the relay coil regardless of resistance changes, the operation timing and current consumption remain consistent. The heat generation is managed through the current mirror circuit's ability to regulate current flow, ensuring reliable operation timing while controlling energy loss.
3Reliability
If a current mirror circuit is used to maintain constant current, then drive conditions become consistent, but the circuit complexity increases
Solution Approach 1:
The patent uses a current mirror circuit that copies the reference current to the relay coil drive path. The current mirror replicates the current characteristics from one branch to another, providing constant current drive without requiring complex control circuits. This copying mechanism achieves reliable drive condition consistency while keeping the circuit structure relatively simple through the use of standard current mirror topology.
4Reliability
If the second resistor element has greater resistance value, then current suppression is improved, but power consumption increases
Solution Approach 1:
The patent optimizes the resistance value of the second resistor element to achieve the right balance. By carefully selecting the resistance value, the circuit achieves effective current suppression during the off-state while minimizing power consumption during the on-state. The current mirror circuit compensates for the resistor's power consumption by regulating the overall current flow, maintaining reliability while controlling energy usage.
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 ensures constant drive conditions for the relay switch, reducing power consumption and heat generation in the steady ON state, and maintaining reliable attachment of the movable piece to the relay coil, even with variations in relay coil resistance.
Implementation Method 1
a current mirror circuit including a first semiconductor element Q1, a second semiconductor element Q2... the current mirror circuit adjusts a current flowing through a first current path from a DC power supply to the first semiconductor element Q1 according to a current flowing through a second current path from the DC power supply to the second semiconductor element Q2
Implementation Method 2
The relay switch includes, e.g., a relay switch with a relay coil and a movable piece. The relay coil operates as an electromagnet, and a current is applied to the relay coil such that the movable piece is attached to the relay coil
Data Source
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AI summary
The present invention is intended to provide constant drive conditions of a relay switch. A relay drive circuit includes a current mirror circuit, a current suppression circuit 26, and a transistor Q3. The current mirror circuit includes a transistor Q1, a first resistor element R1, a transistor Q2, and a second resistor element R2. A relay coil 18 is provided on a current supply path extending from a collector terminal of the transistor Q1 to an earth conductor. The current suppression circuit 26 includes a capacitor C1 as a current suppression element configured to suppress, after conduction between an emitter terminal and a collector terminal of the transistor Q2 has been made, the current flowing through the current suppression element itself as compared to that in such conduction.