Basic Motor PWM Speed Control With 555IC

Abstract

This project is about, controlling a fan using 555IC with PWM. PWM is controlled with a potentiometer. I drove a fan but you can use it for a DC motor. The circuit has a back-emf diode. I did this project using a prototyping board but if you want to produce the PCB, I will share the Gerber files too.

Features

• Input has a 500mA fuse for protection.
• PWM is controlled with a 10k potentiometer
• Min. duty-cycle limiting at %25
• 1.5kHz PWM frequency.
• 1A@12V input supply.
• On/Off Switch.
• Back-emf diode for the motor.
• 350mA max @ 12V fan.

I selected these features but you can change input power, minimum duty-cycle value, or frequency depending on your motor power. I will show you later.

Why I Did This Project?

Hi everyone! Today I came to you with a basic project. I made this project a simple and cheap solution for soldering fume filters. Whenever I try to solder, fumes always follow me and I don't want to breathe it anymore! And I want you guys to don't breathe those fumes too.

Circuit Material List

• 1xTLC555
• 1xIRF3710ZPBF
• 1x12V Fan
• 1x500mA fuse
• 1xOn/Off switch
• 1xDC Power Jack
• 4xSchottky or Standard Silicon Diodes
• 2x2.2uF, 1x1uF, 2x100nF, 1x10nF capacitors
• 1x10k Pot
• 1x3.3kOhm, 1x2kOhm, 1x1.2kOhm resistors
• At least 5x5cm Prototyping board
• Any adaptor plug above 500mA @12V

Mechanic Material List

If you want to make a box too, I will share the STL files.

• Circuit protection box
• Some support materials for holding the fan
• 2 sides tape
• Some screws and nuts

As you can see in the photos above, a flexible, I guess aluminum material holds the fan. I found it in an old desk lamp.

How Does This Circuit Work?

This circuit is working on the astable mode. In this way, we can simply adjust the C3 capacitor charging and discharging time with a 10k pot. D1 and D2 diodes block one side of the currents on the pot. R3 resistor is used for the limiting minimum duty-cycle value. We need to have a minimum value because the fan can't work under the 3V. So for the 12V input, the %25 duty-cycle is equal to the 3V. The C4 capacitor is not necessary but you can use it for the line regulation. The D4 diode is for back-emf protection. In this way, you can use any DC motor. The Q1 MOSFET is completely adequate. It can handle 100V and 49A!. If you want a more compact circuit, you can change it with another MOSFET that has fewer ampere value. So that, the size will be much fewer too. I used the F1 fuse because the circuit is plugged into the outlet. If any problem with the adapter, the fuse popped up and protects the circuit.

PWM Frequency Calculation

1.5kHz works like charm. But under 20kHz can cause some audible noise. 1.5kHz has some audible noise too but it doesn't bother me. If you want to increase the frequency, you can choose any frequency under the table.

With the minimum %25 Duty cycle value;

2kHz → 50nF

3kHz → 35nF

5kHz → 20nF

10kHz → 10nF

15kHz → 7nF

20kHz → 5nF

By using TLC555 and IRF3710, you can increase the frequency 52kHz. But I am not suggesting it. Because discharging time getting too long according to the frequency. If you want to calculate your own frequency value, you can use this formula;

R3 = (Dmin * RPOT)/(1-Dmin) → Dmin: Minimum duty-cycle value.
f = 1/(0,693*(R3+RPOT)*C)

MOSFET Gate Resistor Value Calculation

At first sight, it looks kinda difficult I know. But actually, it is just a simple capacitor theory. The capacitor is charged through the R1 resistor and discharged through the R1 + R2. If you add a diode parallel to the R1, it just discharged through the R2. TLC555 max. output current is 10mA. We have to choose the R1 value with respect to the 10mA.

R1 = Vo/Io → Vo is the out voltage of the 555IC and Io is the max. output current of the 555. 12V/10mA = 1.2kOhm

If we didn't use a diode parallel to the R1, the capacitor will discharge R1 + R2. The total resistance can be calculated like this;

R2 = (1-Dmax) / (-ln(Voff/Vout)*Cg*f)
Dmax: Maximum duty-cycle value
Voff: Turn off voltage of the MOSFET
Vmax: Output voltage of the 555
Cg: Gate capacitance of the MOSFET
f: Frequency

These are some graphs on the circuit. Maybe they can give some idea for working process.

I used SMD versions of some diodes and capacitors. In this way, they can allow you to use both sides of the board. DC power jack's legs are bigger than the holes. Before you start soldering, drilling the adequate size for the jack makes your job easier.

PCB GERBER FILES