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

Comments

Electronic Extended Play Circuit Diagram

This is a Electronic Extended Play Circuit Diagram. A single op amp-one of four contained in the popular LM324-is operating in a variable pulse width, free-running square wave oscillator circuit, with its timed output driving two transistors that control the on/ off cycle of the tape-drive motor. The Oscillator` s positive feedback path holds the secret to the successful operation of the variable on/ off timing signal. Electronic Extended Play Circuit Diagram The two diodes and pulse width potentiometer R8 allows the setting of the on and off time, without affecting the oscillator`s operating frequency. One diode allows only the discharge current to flow through it and the section of R8 that it`s connected to. The other diode, and its portion of R8, sets the charge time for the timing capacitor, C3. Since the recorder`s speed is controlled by the precise off/on timing of the oscillator, a simple voltage-regulator circuit (Ql, R3, and D4) is included. Connecting the spe...

Power Amplifier with voltage regulator 4 × 50 Watt TDA8588

Power Amplifier with voltage regulator 4 × 50 Watt TDA8588 The TDA8588 is a multiple voltage regulator combined with four independent audio power amplifiers configured in bridge tied load with diagnostic capability. The output voltages of all regulators except regulators 2 and 3 can be controlled via the I2C-bus. However, regulator 3 can be set to 0 V via the I2C-bus. The output voltage of regulator 2 (microcontroller supply) and the maximum output voltage of regulator 3 (mechanical digital and microcontroller supplies) can both be either 5 V or 3.3 V depending on the type number. The maximum output voltages of both regulators are fixed to avoid any risk of damaging the microcontroller that may occur during a disturbance of the I 2C-bus. The amplifier diagnostic functions give information about output offset, load, or short-circuit. Diagnostic functions are controlled via the I2C-bus. The TDA8588 is protected against short-circuit, over-temperature, open ground and open VP ...

Digital Voltmeter Circuit with ICL7107

Description. The circuit given here is of a very useful and accurate digital voltmeter with LED display using the ICL7107 from Intersil. The ICL7107 is a high performance, low power, 3.5 digit analog to digital converter. The IC includes internal circuitry for seven segment decoders, display drivers, reference voltage source and a clock. The power dissipation is less than 10mW and the display stability is very high. The working of this electronic circuit is very simple. The voltage to be measured is converted into a digital equivalent by the ADC inside the IC and then this digital equivalent is decoded to the seven segment format and then displayed. The ADC used in ICL7107 is dual slope type ADC. The process taking place inside our ADC can be stated as follows. For a fixed period of time the voltage to be measured is integrated to obtain a ramp at the output of the integrator. Then a known reference voltage of opposite polarity is applied to the input of the integrator and allowed to r...

My Circuit

Search This Blog