Detection of plunger movement in DC solenoids through current sense technique

In a system for operating a solenoid, a circuit to detect complete movement of a plunger of a solenoid, comprising:

• a device for measuring current through the solenoid and generating a first current signal;
• an active peak detector circuit receiving the first current signal for detecting a peak thereof and generating a peak detection signal;
• a level shifter circuit coupled in parallel with the active peak detector and receiving the first current signal, the level shifter circuit adding a threshold voltage to the first current signal to generate a level shifted signal;
• and
• a comparator comparing the peak detection signal with the level shifted signal, whereby if the level shifted signal matches the peak detection signal, complete movement of the solenoid is detected.

A control circuit for operating a solenoid comprising:

• a circuit for applying a voltage across a solenoid coil and measuring current through the coil to generate a first signal;
• a detector circuit detecting a peak in the current through the coil represented by the first signal;
• a circuit for detecting a valley in the first signal;
• an adder circuit for adding a predetermined threshold to the first signal;
• a comparator comparing output of the adder circuit to the peak signal to detect movement of the plunger of the solenoid.