High-Power 30A DC Motor Speed Control Circuit PWM LM358 CD4093

The power of the DC Motor speed control circuit can work between 30 amps and 12…32 volts. Speed control is done with PWM technique. It has “Reversible” reverse, straight control feature. Circuit LM358, CD4093, and IRF2804 speed control based on mosfets can be made with a 5k potentiometer or a joystick called “hall effect throttle”.

12-32V 30A motor speed control soft start circuit, relay switching motor direction PWM speed control circuit

30A Motor Speed Control Circuit

According to the DC Motor Speed ​​Controller High Power, materials that are easy to build can be found between 12-32V and 30A . It features soft start, relay switching of motor direction and PWM speed control.

The DC Motor Speed ​​Controller uses a pair of high power Mosfets connected in parallel to drive the motor and relay circuitry to make the motor reversible. It can operate from 12-32V batteries at currents up to 30A. The logic control of the reversing circuit means that it can only change direction when the motor is stopped.

The unit consists of two parts. The first is basic speed control with two parallel Mosfets and a dual op amplifier to provide pulse width modulation (PWM). The second section adds the relay circuit and logic control. If you don’t need motor direction reversal, you can just do the PWM control stage of the circuit

Speed control can be achieved via a built-in trimpot, an external 5k potentiometer, or a motorcycle throttle based on a Hall Effect sensor. This could be ideal for a wheelchair controller or electric bike.

Motor Speed Control Oscilloscope Images

Figure 1: Shows the basic control operation. The triangle wave from the oscillator is compared to a 3.5V reference (pink line) and when it exceeds this reference, a corresponding motor driver pulse (blue line) is produced.

Figure 2: Shows operation at higher speed settings. The triangular waveform now exceeds the reference voltage for a greater portion of the time and therefore the pulses fed to the motor are much wider.

Circuit description

First, let’s focus on the IC1 (LM358 dual op amp) and the 5k potentiometer. The op amp IC1a and its associated components include a triangle wave oscillator. Its frequency is around 300Hz and output amplitude is around 1V peak to peak. The average DC level of this triangular waveform can be raised or lowered depending on the setting of the 5k speed control potentiometer.

This output waveform is connected to the non-inverting input of IC1b, pin 5. IC1b is connected as a comparator and compares the triangular waveform with the 3.5V fixed reference on pin 6. The triangular waveform on pin 5 exceeds the 3.5V reference voltage on pin 6, the output on pin 7 will go high and this will turn on the two power Mosfets (IRF2804), Q6 and Q7.

This means the Mosfets are pulsing when the triangular waveform peaks above 3.5V. Advancing speed control increases the duty cycle of the pulses.

Circuit operation is illustrated in the Oscilloscope measurements in Figure 1 and Figure 2. In all cases, the green line indicates the triangular waveform, while the pink line indicates the 3.5V reference, which is stable. As you can see, every time a part of the triangular waveform intersects with and is above the pink line, there is a pulse to the Mosfet gates as shown in the blue line. The voltage across the motor between the positive supply line and the Mosfet drains is indicated by the yellow line.

Source: http://www.siliconchip.com.au/cms/A_112070/article.html 30A Motor Speed PWM Control schematic pcb files Alternative link: