Temperature Controlled Fan Circuit for Audio Amplifiers

Amplifiers create heat when they are in use and this heat can hurt how well they work and how long they last.

To solve this problem, a special Temperature Controlled Fan Circuit for Audio Amplifiers has been made to keep the temperature just right.

This circuit turns on the fan only when the amplifier gets too hot.

It is really smart because it does not turn on the fan when the volume is low, which means less heat is made so the fan stays off and saves energy.

The circuit is built using parts like an LM311 comparator, a 2N2222 transistor, an NTC thermistor and a 12V relay which all work together to run the fan.

To make this circuit work properly you need to use a 12V DC power supply.

Circuit Working:

Parts List:

In the above circuit diagram the R2 NTC thermistor works with resistor R1 to form a voltage divider circuit.

This circuit produces a voltage that changes with temperature and sends it to the inverting input which is pin 3 of the LM311 comparator.

At the same time the non inverting input at pin 2 receives a steady reference voltage from resistor VR1.

As the temperature rises the thermistors resistance decreases causing the voltage at pin 3 to drop.

If this voltage goes below the reference voltage at pin 2 the output at pin 7 of the LM311 switches to a LOW state.

This change turns on the 2N2222 transistor Q1, which then activates the 12V relay to start the 12V fan and cool down the amplifier.

A diode called D1 is placed across the relay coil to prevent any voltage spikes.

To show that the fan is running an LED1 lights up with the help of resistor R4 when the fan is on.

Formulas with Calculations:

The below mentioned formulas with calculations are required for Temperature Controlled Fan Circuit for Audio Amplifiers:

Voltage Divider for Thermistor & Resistor R1:

V_NTC = (R2 / (R1 + R2)) * V_supply

Comparator Operation:

When V_NTC drops below the reference voltage set by VR1, the comparator output switches states activating the transistor.

Relay Activation:

Base current of transistor:

I_B = (V_output – V_BE) / R3

Collector current for the relay:

I_C = V_relay / R_relay

Fan Power Calculation:

P = V * I

If the fan draws 200mA at 12V:

P = 12V * 0.2A = 2.4W

How to Build:

To build a Temperature Controlled Fan Circuit for Audio Amplifiers following steps are required to follow:

• Assemble all the components as mentioned in the above circuit diagram
• Connect pin 1 of IC1 LM311 to GND of the circuit
• Connect pin 2 of IC1 to center leg of VR1 preset the upper leg of VR1 connect to positive supply terminal and lower leg to GND of the circuit.
• Connect pin 3 of IC1 between resistor R1 and resistor R2.
• Connect pin 4 of IC1 to GND of the circuit.
• Connect pin 5 of IC1 to pin 6 of IC1
• Connect pin 7 of IC1 to base of transistor Q1 through resistor R3
• Connect pin 8 of IC1 to positive terminal of +12V DC
• Connect the collector of transistor Q1 to positive terminal through diode D1
• Connect the emitter of transistor Q1 to GND of the circuit
• Connect the Coils of 12V relay one to positive supply and other other coil to collector of transistor Q1
• Connect the N/O of the relay to positive terminal and COMMAN pin of relay connect to one end of 12V Fan and other end of fan connect to GND.
• Connect resistor R4 one end between COMMAN pin of relay and 12V fan and other end of resistor R4 connect to anode of LED1 and cathode of LED1 connect to GND.

Conclusion:

This Temperature Controlled Fan Circuit for Audio Amplifiers helps keep amplifiers cool without needing any manual help.

It uses an NTC thermistor and an LM311 comparator to turn on the fan only when it is really needed saving energy and stopping things from getting too hot.

This setup is perfect for audio amplifiers and other electronics that cannot handle too much heat.

References:

Datasheet IC LM311