Power-consumption-limiter

Description: A simple solenoid driver utilizes incandescent lamp filaments as on-indicators to limit power consumption. High magnetic reluctance in the coil of an armature-driven device, such as a solenoid or relay, requires a surge of activation current, followed by a lower DC level to maintain operation, as the surge to on-current ratio is typically 5:1. The cold filament permits a surge of coil-activation current to flow; as the filament heats up, it reduces the current to a more manageable hold value. The solenoid driver circuit features 5-V logic swings that turn the power MOSFET switch, Q1, fully on and off. Low-cost flashlight lamps, connected in parallel, manage the peak current. Since their DC current is only 50% of the peak and they operate at 60% of their rated voltage, the lamps have an operational life of 12,000 hours. Additionally, the positive temperature coefficients of the lamp filaments increase each filament's resistance. This increase in resistance mitigates current-hogging issues and provides short-circuit protection. The steady-state on-current is 700 mA, compared to 1700 mA without the lamps. A minimum supply rating of 4.6 V allows for battery operation.

The solenoid driver circuit is designed to efficiently control the activation of solenoids and relays by leveraging the properties of incandescent lamp filaments. The circuit operates by initially allowing a high surge current to flow through the solenoid coil when the device is activated. This surge current is essential for overcoming the high magnetic reluctance present in the coil, which is typical in armature-driven devices. The surge current is significantly higher than the steady-state current required to keep the solenoid engaged, typically following a ratio of 5:1.

As the incandescent filaments heat up, their resistance increases due to their positive temperature coefficient. This characteristic is advantageous as it naturally limits the amount of current flowing through the circuit after the initial surge, effectively transitioning to a lower hold current that is sufficient to keep the solenoid engaged without excessive power consumption. The use of low-cost flashlight lamps in parallel allows the circuit to handle peak currents effectively while ensuring that the average operating current remains manageable, thus prolonging the lifespan of the lamps to approximately 12,000 hours.

The circuit is activated by a 5-V logic signal that controls a power MOSFET switch, labeled Q1. When the logic signal is high, the MOSFET fully turns on, allowing current to flow through the solenoid and the lamp filaments. The design ensures that the steady-state on-current is maintained at 700 mA, which is significantly lower than the 1700 mA that would be required in the absence of the lamps.

In terms of power supply, the circuit is designed to operate with a minimum voltage of 4.6 V, making it suitable for battery operation. This flexibility allows for a variety of applications where a compact and efficient solenoid driver is required. The overall design emphasizes efficiency, longevity, and reliability, making it ideal for various automation and control applications.A simple solenoid driver uses incandescent lamp filaments as on-indicators to limit power consumption. High magnetic reluctance (opposition to flux) in the coil of an armature-driven device, such as a solenoid or relay, calls for a surge of activation current, followed hy a lower de level to remain on, since surge to on-current ratio is typically 5:1.

The cold filament allows a surge of coil-activation current to pass through; as the filament heats up, it throttles the current to a more reasonable hold value. The solenoid driver circuit offers these features: 5-V logic swings turn the power-MOSFET switch, Q1, fully on and off. 1vo low-cost flashlight lamps, in parallel, handle the peak current. Because their de current is only 50% of peak and because they operate at 60% of their rated voltage, the lamps have an operating life of 12,000 hours.

Further, the lamp filaments" positive temperature coefficients raise each filament"s resistance. This rise in resistance eliminates current-hogging problems and provides short -circuit protection. The steady-state on-current is 700 mA, vs. 1700 mA without the lamps. A 4.6-V min supply rating allows battery operation.