Stepper motors are really popular in automation, robotics and CNC machines because they can control movements very accurately.
The Transistor Based Stepper Motor Drive Circuit is a simple way to run a unipolar stepper motor using logic gates and transistors.
This circuit uses four 2N2222 transistors to control the motors windings and it has two NOT gates and one XOR gate to understand the two bit control signals needed to activate the four windings.
The whole setup includes logic integrated circuits like the 7404 and 7486 along with transistors and diodes, all working together to manage the pulse sequence that makes the motor work.
A 5V power supply powers the logic ICs, while the motor is powered by a separate 24V DC supply.
Circuit Working:
Parts List:
| Component | Specification | Quantity |
|---|---|---|
| Resistors | 1k 1/4 watt | 4 |
| ICs | 7404 | 1 |
| 7486 | 1 | |
| Transistors | 2N2222 | 4 |
| Diodes | 1N4007 | 4 |
| 24V stepper motor | 1 |
In the above circuit diagram the stepper motor works by carefully turning on its coils in a specific order.
In this design, there is a four step method to activate the motor coils connections named A+, A-, B+, and B- which helps the motor spin.
The control signals called d0 and d1 are really important because they decide the order of the electrical pulses.
The first chip IC1 7404 NOT gate flips the input signals to create the needed drive signals.
At the same time IC2 7486 XOR gate helps create the right stepping pattern for the motor.
The transistors Q1 to Q4 2N2222 act like switches to control the current going through the motors coils.
There are diodes D1 to D4 1N4007 that protect the transistors from any back EMF produced by the motor.
Resistors R1 to R4 1kΩ are used to limit the current going to the transistors.
By switching the control pins d0 and d1 the outputs from IC1 and IC2 give the motor the right pulse sequence allowing it to turn smoothly and accurately.
Formulas with Calculations:
Below mentioned are the formulas with calculations for Transistor Based Stepper Motor Drive Circuit:
Base Current Calculation for Transistors:
The base current (IB) for each transistor is given by:
I_B = (V_in – V_BE) / R_B
where,
- V_in is the logic high voltage for 5V
- V_BE is the base emitter voltage for 2N2222 transistor which is 0.7V
- R_B is the base resistor which is 1k
Substituting values:
I_B = (5V – 0.7V) / 1000Ω
I_B = 4.3V / 1000Ω
I_B = 4.3mA
Collector Current Calculation:
The collector current IC is determined by the transistors current gain (β):
I_C = β × I_B
For 2N2222 transistor assuming β = 100:
I_C = 100 × 4.3mA
I_C = 430mA
This is the maximum current the transistor can drive through the stepper motor coil.
Power Dissipation in Resistors:
The power dissipated in the base resistor (PR) is given by:
P_R = I_B² × R_B
Substituting values:
P_R = (4.3mA)² × 1000Ω
P_R = 18.49µW × 1000
P_R = 18.49mW
Thus, a standard 1/4W resistor is sufficient.
Stepper Motor Voltage and Current Requirements:
The voltage supplied to the stepper motor (Vmotor) should be compatible with the transistors collector emitter voltage (VCE).
V_motor = V_CC – V_CE_sat
For 2N2222, V_CE_sat = 0.2V when conducting fully.
If V_CC = 24V
V_motor = 24V – 0.2V
V_motor = 23.8V
This ensures proper stepper motor operation.
How to Build:
To build a Transistor Based Stepper Motor Drive Circuit following steps are required for connections of the circuit:
- Gather all the components as mentioned in the above circuit diagram.
- Connect pin 1 of IC1 7404 to base of transistor Q3 through resistor R3
- Connect pin 2 of IC1 to transistor Q1 through resistor R1
- Connect pin 3 of IC1 to transistor Q4 through resistor R4
- Connect pin 3 of IC1 to pin 1 of IC2 7486
- Connect pin 4 of IC1 to transistor Q2 through resistor R2
- Connect pin 1 of IC1 to pin 3 of IC2
- Connect pin 1 of IC2 to control logic pin d0
- Connect pin 2 of IC2 to control logic pin d1
- Connect pin 7 of IC1 and IC2 to GND of the circuit
- Connect pin 14 of IC1 and IC2 to +5V positive terminal
- Connect all emitters of transistor Q1 to Q4 to GND of the circuit
- Connect anode of diodes D1 to D4 from collector of transistor Q1 to Q4 and cathode of diodes connect to positive supply of +24V terminal
- Connect collector of Q1 transistor to A+ of 24V stepper motor
- Connect collector of Q2 transistor to A- of 24V stepper motor
- Connect collector of Q3 transistor to B+ of 24V stepper motor
- Connect collector of Q4 transistor to B- of 24V stepper motor
Conclusion:
This Transistor Based Stepper Motor Drive Circuit is an easy and efficient way to manage a unipolar stepper motor with the help of logic gates and transistors.
It is great for beginners in electronics and robotics who are looking to learn about how to drive stepper motors.
You can change the logic sequence to make the circuit work with different types of stepper motor setups.