PWM Dimmer/Motor Speed Controller

This is yet another project born of necessity. It's a simple circuit, but does exactly what it's designed to do - dim LED lights or control the speed of 12V DC motors. The circuit uses PWM to regulate the effective or average current through the LED array, 12V incandescent lamp (such as a car headlight bulb) or DC motor. The only difference between the two modes of operation is the addition of a power diode for motor speed control, although a small diode should be used for dimmers too, in case long leads are used which will create an inductive back EMF when the MOSFET switches off.

 

Photo of Completed PWM Dimmer/Speed Control

The photo shows what a completed board looks like. Dimensions are 53 x 37mm, so it's possible to install it into quite small spaces. The parts used are readily available, and many subsitiutions are available for both the MOSFET and power diode (the latter is only needed for motor speed control). The opamps should not be substituted, because the ones used were chosen for low power and their ability to swing the output to the negative supply rail. Note that if used as a motor speed controller, there is no feedback, so motor speed will change with load. For many applications where DC motors are used, constant speed regardless of load is not needed or desirable, but it is up to you to decide if this will suit your needs.

Description

First, a description of PWM is warranted. As the pot is rotated clockwise, the input voltage changes linearly with rotation. At first, the voltage is such that the comparator output is just narrow spikes, which turn the MOSFET on for a very short period. Average current is low, so connected LEDs will be quite dim, or a motor will run (relatively) slowly. As the input voltage coming from the pot increases, the MOSFET is on for longer and longer, so increasing power to the load.

figure 1 - PWM Waveform Generation

Figure 1 shows how the PWM principle works. The red trace is the triangle wave reference voltage, and the green trace is the voltage from the pot. When the input voltage is greater than the reference voltage, the MOSFET turns on, and current flows in the load. Because the frequency is relatively high (about 600Hz), we don't see any flicker from the LEDs, but the tone is audible from a motor that's PWM controlled. The PWM signal is shown in blue. The average current through the load is determined by the ratio of on-time to off-time, and when both are equal, the average current is exactly half of that which would be drawn with DC.

Figure 2 - Dimmer/Speed Controller Schematic

The circuit is shown in Figure 2. U1 is the oscillator, and generates a triangular waveform. R4 and R5 simply set a half voltage reference, so the opamps can function around a 6V centre voltage. U2A is an amplifier, and its output is a 10V peak to peak triangle wave that is used by the comparator based on U2B. This circuit compares the voltage from the pot with the triangle wave. If the input voltage is at zero, the comparator's output remains low, and the MOSFET is off. This is the zero setting. In reality, the reference triangle waveform is from a minimum of about 1.5V to a maximum of 9.5V, so there is a small section at each end of the pot's rotation where nothing happens. 

This is normal and practical, since we want a well defined off and maximum setting. Because of this range, for lighting applications, an industry standard 0-10V DC control signal can be used to set the light level. C-BUS (as well as many other home automation systems) can provide 0-10V modules that can control the dimmer. While a 1N4004 diode is shown for D2, this is only suitable if the unit is used as a dimmer. For motor speed control, a high-current fast recovery diode is needed, such as a HFA15TB60PBF ultra-fast HEXFRED diode. There are many possibilities for the diode, so you can use whatever is readily available that has suitable ratings. The diode should be rated for at least half the full load current of the motor, and the HFA15TB60PBF suggested is good for 15A continuous, so is fine with motors drawing up to 30A.

Construction

While it's certainly possible to build the dimmer on veroboard or similar, it's rather fiddly to make and mistakes are easily made. Also, be aware that because of the current the circuit can handle, you will need to use thick wires to reinforce some of the thin tracks. This is even necessary for the PCB version. Naturally, I recommend the PCB, and this is available from ESP. The board is small - 53 x 37mm, and it carries everything, including the screw terminals. The PCB is double-sided with plated-through holes, and has solder masks on both sides. The MOSFET will need a heatsink unless you are using the dimmer for light loads only. It is necessary to insulate the MOSFET from the heatsink in most cases, since the case of the transistor is the drain (PWM output).

For use at high current and possible high temperatures, the heatsink may need to be larger than expected. Although the MOSFET should normally only dissipate about 2W or so at 10A, it will dissipate a lot more if it's allowed to get hot. Switching MOSFETs will cheerfully go into thermal runaway and self destruct if they have inadequate heatsinking. You may also use an IGBT (insulated gate bipolar transistor) - most should have the same pinouts, and they do not suffer from the same thermal runaway problem as MOSFETs. As noted above, there are many different MOSFETs (or IGBTs) and fast diodes that are usable. The IRF540 MOSFET is a good choice, and being rated 27A it has a generous safety margin. There are many others that are equally suitable - in fact any switching MOSFET rated at 10A or more, and with a maximum voltage of more than 20V is quite ok.

Testing

Connect to a suitable 12V power supply. When powering up for the first time, use a 100 ohm "safety" resisor in series with the positive supply to limit the current if you have made a mistake in the wiring. The total current drain is about 2.5mA with the pot fully off, rising to 12.5mA when fully on. Most of this current is in the LED, which is also fed from the PWM supply so you can see that everything is working without having to connect a load. Make sure that the pot is fully anti-clockwise (minimum), and apply power. You should measure no more than 0.25V across the safety resistor, rising to 1.25V with the pot at maximum. If satisfactory, remove the safety resistor and install a load. High intensity LED strip lights can draw up to ~1.5A each, and this dimmer should be able to drive up to 10 of them, depending on the capabilities of the power supply and the size of the heatsink for the MOSFET.

source: sound.westhost

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Brushless DC Motor Driver Circuit Diagram

Use of brushless DC motors (BLDCs) is on the rise. But their control usually requires rotor-position information for selecting the appropriate commutation angle. Normally, a Hall Effect sensor is used to sense rotor position. But in cost-sensitive applications, a sensor-less commutation scheme is often desirable. The circuit described here uses a DRV10866 driver IC to drive a small BLDC fan, without using any position sensors. A BLDC fan’s speed can be varied smoothly, without the usual steps associated with a normal AC fan.

Circuit and working
Fig. 1 shows the circuit of a sensor-less BLDC motor driver. The circuit is built around an NE555 (IC1), a DRV10866 (IC2) and a few other components.

Fig. 1: Circuit of brushless DC motor driver

Fig. 2: An actual-size, single-side PCB for the brushless DC motor driver

  

 Fig. 3: Component layout for the PCB

DRV10866 driver IC from Texas Instruments is used to drive a small three-phase BLDC motor (M1). The circuit is of a three-phase, sensor-less motor driver with integrated power MOSFETs having drive-current capability up to 680mA peak. DRV10866 is specifically designed for low noise and low component-count fan-motor drive applications. A 150° sensor-less back emf scheme is used to control the three-phase motor.

A 100k pull-up resistor (R2) is used at pin 1 of IC2. Pins 2, 4, 7 and 6 of IC2 are connected to common, phase A, phase B and phase C of the BLDC motor, respectively. Pin 10 of IC2 is connected to pin 7 of IC1 to get the pulse-width modulated (PWM) signal from IC1 to control the speed of the BLDC motor.

The output signal (PWM) is available at IC1’s pin 7 (DIS) and not from the usual output pin 3 of the IC. The 25kHz (approx.) PWM signal’s duty cycle can be adjusted from 5% to 95% using potentiometer VR1. The speed of the BLDC motor can be controlled by varying the duty cycle of the PWM signal. Turning VR1 counter-clockwise lowers the duty cycle which, in turn, lowers the speed of the motor, and vice versa.

Construction and testing

An actual-size, single-side PCB for the brushless DC motor driver is shown in Fig. 2 and its component layout in Fig. 3. Assemble the circuit on the recommended PCB to minimise assembly errors. IC2 should be fitted on solder side of the PCB.

After assembling the components, connect a 5V DC supply to CON1 connector. To test the circuit for proper functioning, verify correct 5V supply for the circuit at TP1 with respect to TP0. Turn VR1 clockwise or counter-clockwise to increase or decrease the speed of the motor.

Author Name: Abhijeet Rai Sourced By: EFY

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Speed Controller for Small Cooling Fans

Small cooling fans are used in some equipment for cooling semiconductor devices. The circuit given here is of a simple automatic speed controller for a 12V, 0.6W (or 1.2W) cooling fan that increases the fan’s speed when temperature rises, and vice versa.

Circuit and working
Fig. 1 shows circuit diagram of the speed controller for a small cooling fan. Resistor R1 limits the initial current for the motor and lowers the speed of rotation, if needed. The temperature control is done with one or more NTC (negative temperature coefficient) thermistors connected in series with the electrical motor. The number of thermistors depends on their power dissipation.

Usually you cannot find low-cost NTCs with enough power dissipation. Therefore four of them in parallel are used here. This way power dissipation and self-heating of the NTCs are reduced. It is better to use NTCs with tolerance of ±2%. The NTCLE100E3 are available with nominal values of 3.3-ohm to 470-kilo-ohm and have maximum power dissipation of 0.5W at +55°C.

Table I shows easily-available NTC thermistors that can be used in the circuit. The resistors R2 through R5 are equalisation and limiting resistors. These resistors are usually between 3% and 15% of the resistance of the thermistors at +25°C.


LED1 is used as power on/off indicator for the circuit. LED2 indicates the speed of rotation of the fan. If speed of the motor is high, LED2 glows brightly, and vice versa. Diode D1 is used to prevent back EMF when power supply is removed.

Connector CON1 is used for the power supply. It is better to have power supply 10 to 25% higher than the nominal working voltage of the fan to compensate for the voltage drop across the resistors and the thermistors.

Voltage drop across resistor R8 is proportional to the current in the motor. Connector CON2 is used to connect a digital voltmeter to measure the voltage drop.

Construction and testing
An actual-size, single-side PCB for the circuit is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on a PCB, enclose it in a suitable plastic box.

Fig. 1: Circuit diagram of the speed controller

Fig. 2: An actual-size PCB for the speed controller

Fig. 3: Component layout for the PCB

Fix all the four NTC thermistors (NTC1 through NTC4) at appropriate locations, within the equipment whose heat is to be dissipated, for temperature sensing. On front panel of the speed controller fix switch S1 for power on/off, LED1 for power on/off indication and LED2 for fan-speed indication. Before using the circuit, verify that voltages at various points in the circuit are as per Table II.

Sourced By: EFY Author:  Petre TZV Petrov

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Simple Pwm Motor Drive Circuit Diagram

This is the Simple Pwm Motor Drive Circuit Diagram. This circuit will drive a small dc motor over a wide range of speeds without stalling by controlling the duty cycle of the motor, rather than the supply voltage.

Simple Pwm Motor Drive Circuit Diagram

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Temperature Monitor Circuit Diagram

A simple op-amp circuit that will trigger a relay when a preset temperature is reached. Please note that there is no hysteresis in this circuit, so that if the temperature changes rapidly, then the relay may switch rapidly.

Temperature Monitor Circuit Diagram

Circuit Notes:

This circuit uses an ordinary NTC thermistor with a resistance of 47k at room temperature. A suitable part from Maplin Electronics is FX42V. The circuit is set in balance by adjusting the the 47k potentiometer. Any change in temperature will alter the balance of the circuit, the output of the op-amp will change and energize the relay. Swapping the position of the thermistor and 47k resistor makes a cold or frost alarm.

Calibration:
At room temperature (25 degrees Celsius) a 47k NTC thermistor resistance is approximately 47k. The non-inverting op-amp input will then be roughly half the supply voltage, adjusting the 47k pot should allow the relay to close or remain open. To calibrate the device, the thermistor ideally needs to be at the required operating temperature. If this is for example, a hot water tank, then the resistance will decrease, one way to do this is use a multimeter on the resistance scale, read the thermistors resistance and then set the preset so that the circuit triggers at this temperature.

Please note that if the temperature then falls, the relay will de-energize. If the environment temperatures changes rapidly, then the relay may chatter, as there is no hysteresis in this circuit.

Hysteresis, allows a small amount of "backlash" to be tolerated. With a circuit employing hysteresis, there will be no relay chatter and the circuit will trigger at a defined temperature and require a different temperature to return to the normal state. Hysteresis can be applied to the circuit using feedback, try a 1Meg resistor between op-amp output, pin 6 and the non-inverting input pin 2 to give the circuit hysteresis.

Without offset null adjustment, the output of the 741 IC will be around 2 Volts (quiescent) swinging to nearly full supply when triggered. The 4.7k and 1k resistor form a potential divder so that under quiescent conditions the transistor will be off. Quiescent or steady state means no signal, or in this case (when the temperature does not cause the output to swing to full voltage) 

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Simple Speed Control Temperature DC Fan Circuit Diagram

This is a simple speed control temperature DC fan circuit diagram. This simple circuit based on two transistors that can be used to control the speed of a 12 V DC fan depending on the temperature.A thermistor (R1) is used to sense the temperature. 

When the temperature increases the base current of Q1 (BC 547) increases which in turn decreases the collector voltage of the same transistor. Since the collector of Q1 is coupled to the base of Q2 (BD 140), the decrease in collector voltage of Q1 forward biases the Q2 more and so do the speed of the motor. Also, the brightness of the LED will be proportional to the speed of the motor.

 Simple Speed Control Temperature DC Fan Circuit Diagram

Notes.

• The R1 can be a 15K @ 20°C ,N.T.C  thermistor.
• The M1 can be a 12V,700mA fan motor.
• The capacitor C1 must be rated 25V.
• The circuit can be powered from a 12V PP3 battery or 12V DC power supply.
• Assemble the circuit on a good quality PCB or common board.

Sourced By: Streampowers

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