Tri-State H-Bridge using CD4093B CMOS circuit.
Fig. 1

Tri-State H-Bridge using CD4093B CMOS Circuit


Here we look at an improved tri-state H-bridge. This a big improvement over earlier variations.

The goal is circuit theory. To connect to basic microcontrollers operating at 3.3V-5V to a flexible higher voltage circuit.

The voltage range of the circuit based on a CD4093B and an IRF4905 (Q4, Q6) and IRFZ44N (Q5, Q7) MOSFETs ~3-15-volts.

The Schmitt trigger inputs of the CD4093B quad, 2-input NAND gate assures more stable switching. This replaces the CD4011B from earlier circuits.

Q1, Q2, and Q3 are 2N7000 N-channel MOSFETs in a TO-92 package. With their associated 10K pull up resistors provide an easy voltage interface between the microcontroller and CD4093B switching the power MOSFETs Q4-Q7.

This replaced the SN7407 TTL integrated circuit from earlier designs. This also eliminated the use of opto-couplers.

Connections "A" and "B" with "EN" connect directly to the microcontroller or Raspberry Pi IO pins.

Make sure to connect the ground to the microcontroller ground. Connect "*" to the microcontroller 3.3V or 5V power buss.

When "EN" is HIGH motor direction is determined by inputs "A" and "B". The can be connected together and programmed for forward and reverse only. "EN" acts as motor ON-OFF.

As a final note the "EN" connection my require a 1K resistor to ground. This assures the motor is turned off if the IO pin to the Raspberry Pi, etc. isn't LOW during boot up.


EN Input A Input B AOUT BOUT OUT MODE
HIGH HIGH LOW 12V 12V STOP
HIGH HIGH HIGH 12V 0V FWD
HIGH LOW HIGH 0V 0V BRK
HIGH LOW LOW 0V 12V REV
LOW X X HiZ HiZ OFF

CD4093B internal and pin connections.
Fig. 2

CD4093B Quad 2-Input NAND Schmitt Trigger is shown in Fig. 2. Voltage range 3-15-volts. While low power the current sink or source output is low. But this no problem driving MOSFET transistors.

The Schmitt trigger input assures better circuit performance in H-bridge circuits. There is better noise response.

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