PWM solenoid driver and method

A driver circuit comprising:

• (a) an input terminal for receiving an actuation pulse, an output terminal for connection to a terminal of a load element, a ground terminal, a turn-on current duration adjustment terminal, and a maintain current duty cycle adjustment terminal;
• (b) a turn-on current duration circuit having a first input coupled to the input terminal and a second input coupled to the turn-on current adjustment terminal and producing a turn-on current duration control pulse in response to the actuation pulse, the duration of the turn-on current duration control pulse being determined by a signal level on the turn-on current adjustment terminal;
• (c) an oscillator producing a triangular waveform signal;
• (d) a maintain current duty cycle control circuit having a first input coupled to receive the triangular waveform signal and a second input coupled to the maintain current duty cycle adjustment terminal to produce a PWM signal, and the maintain current duty cycle control circuit including a third input coupled to the turn-on current duration adjustment terminal and logically ORing the turn-on current duration control pulse with the PWM signal to produce a switch drive signal on an output conductor;
• (e) an output transistor having a control electrode coupled to the output conductor of the maintain current duty cycle control circuit, and a current-carrying terminal coupled to the output terminal of the driver circuit;
• and
• (f) the maintain current duty cycle control circuit applying the switch drive signal to the control electrode, the switch drive signal including a turn-on current pulse turning on the output transistor for the duration of the turn-on current duration control pulse to cause a turn-on current of like duration to be established in the load element followed by a sequence of PWM maintain current pulses repetitively turning the output transistor on and off with a duty cycle determined by a voltage on the maintain duty cycle adjustment terminal until the end of the actuation pulse.

A method for operating a solenoid driver circuit including an input terminal, an output terminal for connection to a terminal of a solenoid coil, a ground terminal, a pull-in current duration adjustment terminal, and a hold-in current duty cycle adjustment terminal, the method including:

• (a) applying a solenoid actuation pulse to a pull-in current duration circuit having a first input coupled to the input terminal and a second input coupled to the pull-in current adjustment terminal;
• (b) setting a desired duration of a pull-in current duration control pulse to be produced by the pull-in current duration circuit by controlling a signal on the pull-in current adjustment terminal;
• (c) producing the pull-in current duration control pulse in response to the solenoid actuation pulse and the signal on the pull-in current adjustment terminal;
• (d) producing a triangular waveform signal;
• (e) applying the triangular waveform signal to a first input of a hold-in current duty cycle control circuit and setting a duty cycle adjustment voltage level on a second input coupled to the hold-in current duty cycle adjustment terminal and comparing the triangular waveform signal to the duty cycle adjustment voltage level to produce a PWM signal;
• (f) logically ORing the pull-in current duration control pulse with the PWM signal to produce a switch drive signal, the switch drive signal including a pull-in current pulse followed by a sequence of PWM pulses lasting until the end of the solenoid actuation pulse;
• and
• (g) applying the switch drive signal to the control electrode of an output transistor having a current-carrying terminal coupled to the solenoid coil.

A driver circuit comprising:

• (a) an input terminal for receiving an actuation pulse, an output terminal for connection to a terminal of a load element, a ground terminal, a turn-on current duration adjustment terminal, and a maintain current duty cycle adjustment terminal;
• (b) means having a first input coupled to the input terminal and a second input coupled to the turn-on current adjustment terminal for producing a turn-on current duration control pulse in response to the actuation pulse and a signal level on the turn-on current adjustment terminal, the duration of the turn-on current duration control pulse being determined by the signal level on the turn-on current adjustment terminal;
• (c) means for producing a triangular waveform signal;
• (d) duty cycle control means having a first input coupled to receive the triangular waveform signal and a second input coupled to the maintain current duty cycle adjustment terminal for producing a PWM signal in response to the triangular waveform signal and a signal level on the maintain current duty cycle adjustment terminal and logically ORing the turn-on current duration control pulse with the PWM signal to produce a switch drive signal on an output conductor, the switch drive signal including a turn-on current pulse turning on an output transistor for the duration of the turn-on current duration control pulse to cause a turn-on current of like duration to be established in the load element followed by a sequence of PWM maintain current pulses repetitively turning the output transistor on and off with a duty cycle determined by a voltage on the maintain duty cycle adjustment terminal until the end of the actuation pulse;
• and
• (e) the output transistor having a control electrode coupled to the output conductor of the maintain current duty cycle control circuit, and a current-carrying terminal coupled to the output terminal of the driver circuit.