Lee Solenoid Valve Drive Circuit Schematics

Solenoids of all different sizes are used in most electro-mechanical systems. Because solenoids are so prolific, there are also many different ways to drive them. These methods include several off the shelf options such as PWM chips, mechanical relays, and alternate circuit designs. The Lee Company has developed circuit schematics that can be used to drive many of the solenoid operated valves and pumps on this website. Listed below are a few specific circuit schematics which may serve as general guidelines and can be reproduced or modified by the end user to meet specific application requirements. For questions about which circuit is best suited for your application, contact a Lee Company Sales Engineer.

Basic Transistor / Fast Response

(Lee Drawing LFIX1002200A)

This circuit schematic demonstrates the simplest form of solenoid drive circuitry and may be used to actuate most solenoid operated valves and pumps on this website. The circuit requires an input voltage (Vcc) to actuate the solenoid as well as a control signal input (from a controller, function generator, or timing circuit), which switches a transistor. This, in turn, allows the drive current to energize the solenoid. A diode is placed in parallel with the solenoid to protect the transistor from the inductive voltage spike which occurs as the solenoid de-energizes. A significant voltage drop between the power supply and solenoid may occur if there is unexpected resistance, such as long lead wires or other electrical components. Therefore, be sure to verify that the solenoid is receiving its rated actuation voltage by measuring directly across the solenoid's pins. Depending on your application requirements, this circuit may be configured for two different operating modes:

  1. Basic Driver – In the simplest operating mode, this most basic solenoid drive schematic does not require the 51V Zener diode.
  2. Fast Response Driver – A 51V Zener diode placed in series with a flyback protection diode improves the latch-out response (time to close) of the solenoid when power is removed.

Basic Transistor Circuit Schematic


Circuit Schematic for reference only. Refer to drawing LFIX1002200A which includes additional notes and operating instructions.

Spike & Hold

(Lee Drawing LFIX1002250A)

This circuit can be used as either an enhanced response time driver or as a low power consumption driver. The circuit initially supplies a brief actuation voltage (V1, “Spike” Voltage), for a period of time (ts), then switches to a lower voltage (V2, “Hold” Voltage), to keep the solenoid in an energized state for an extended time. The duration of the spike (ts) is determined by a resistor and capacitor (R1 and C1 indicated on LFIX1002250A, Note 4), connected to a 555 timer chip. Typically, the spike duration is slightly longer than the response time of the solenoid. A control signal input is required (from a controller, function generator, or timing circuit), to actuate the solenoid. The solenoid will remain actuated for as long as the control signal is applied. A significant voltage drop between the power supply and solenoid may occur if there is unexpected resistance, such as long lead wires or other electrical components. Therefore, be sure to verify that the solenoid is receiving its rated actuation voltage by measuring directly across the solenoid's pins. When measuring the signal between the solenoid pins with an oscilloscope, ensure that a differential probe is used.

Depending on whether you require lower power or faster response, this driver may be configured for two different operating modes:

  1. Fast response spike & hold driver – Solenoid response time can be improved for both actuation (time to open), and latch-out (time to close), of the solenoid by applying an “over-drive” voltage greater than the rated actuation voltage to V1, and adding a 51V Zener Diode (D4, indicated on LFIX1002250A, Note 5.1). After quickly actuating the solenoid, the driver switches to a lower holding voltage applied at V2 to reduce resistive heating and avoid damage to the solenoid. A 51V Zener diode placed in series with a flyback protection diode improves the latch-out response (time to close) of the solenoid when power is removed.
  2. Low power consumption driver – Overall power consumption can be significantly reduced (typically 75-90%), by applying the rated solenoid voltage to V1, and a lower hold voltage to V2. For most solenoids the hold voltage is half of the rated actuation voltage, unless otherwise indicated on the inspection drawing. For more specific recommendations regarding the voltage or spike duration for your particular application or part number, please contact a Lee Company Sales Engineer.

Spike & Hold Circuit Schematic


Circuit Schematic for reference only. Refer to drawing LFIX1002250A which includes additional notes and operating instructions.

Latching Solenoid

(Lee Drawing LFIX1002350A)

The primary advantage of a latching solenoid valve is that power is not required to maintain the valve’s flow state (either open or closed) between actuations. That is, a de-energized latching valve will hold its current flow state. Because of this magnetically latched feature, latching solenoid valves have polarized leads which require a different type of drive circuitry. The flow state of the solenoid is determined by a negative or positive voltage pulse, so a circuit capable of bi-directional current flow is required. The recommended LFIX1002350A schematic includes an H-bridge chip which reverses the direction of current flow, allowing for effective latching solenoid valve switching. A significant voltage drop between the power supply and solenoid may occur if there is unexpected resistance, such as long lead wires or other electrical components. Therefore, be sure to verify that the solenoid is receiving its rated actuation voltage by measuring directly across the solenoid's pins.

This schematic requires the rated input voltage to actuate the solenoid as well as switching commands provided by a micro-controller (MCU), or other programmable logic controller (PLC). Switching commands should be provided as a 5 Vdc “HIGH” or “LOW” signal, of which four are required. Two pins are required to enable the H-bridge chip, and two others are required to trigger either a positive or negative pulse to the solenoid. A description of each pin is included below, along with a state diagram. Information about solenoid pin assignments and the porting arrangements can be found on the inspection drawing for each latching solenoid valve.

MCU Pin Assignments (Waveform Graph)

  • IN1 – HIGH provides a +5 Vdc pulse. The pulse length (time) should be slightly longer than response time of the solenoid.
  • IN2 – HIGH provides a -5 Vdc pulse. The pulse length (time) should be slightly longer than response time of the solenoid.
  • D1 - Enables NXP33886 (H-Bridge Chip), should be HIGH when actuating (in either direction).
  • D2 - Enables NXP33886 (H-Bridge Chip), should be LOW when actuating (in either direction).

Latching Valve Circuit Schematic

Waveform Graph


Circuit Schematic for reference only. Refer to drawing LFIX1002350A which includes additional notes and operating instructions.

<< Engineering Data