Temperature Controlled Fan Circuit for Audio Amplifiers

Amplifiers make heat when working.

Too much of heat make it work bad and can die soon.

This Temperature Controlled Fan Circuit for Audio Amplifiers keep amplifier cool.

Fan starts only when amplifier is hot.

If volume is low and less heat then fan stays OFF and saves power.

The circuit is made with LM311 comparator IC, 2N2222 transistor, NTC thermistor and 12V relay.

It need 12V DC power to run.

Circuit Working:

Parts List:

R2 NTC thermistor and R1 make voltage divider.

This give voltage that change with heat to pin 3 (inverting) of LM311.

Pin 2 (non-inverting) get fixed voltage from VR1.

When temperature goes up the thermistor resistance goes down and voltage at pin 3 drops.

If pin 3 voltage is lower than pin 2 then LM311 IC output pin 7 goes LOW.

This turns ON the Q1 transistor and Q1 turns ON 12V relay and relay start 12V fan to cool the amplifier.

D1 diode protect relay from spikes and LED1 with R4 show fan is ON.

Formulas with Calculations:

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

V divider with thermistor R2 and R1 formula:

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

Comparator:

If V_NTC < V_ref set by VR1 comparator flips and turns transistor ON.

Relay transistor base:

I_B = (V_output – V_BE) / R3

Relay coil current collector:

I_C = V_relay / R_relay

Fan power:

P = V * I

Example: 12V x 0.2A = 2.4W

How to Build:

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

• Assemble parts like in circuit diagram.
• Pin 1 of LM311 IC goes to GND
• Pin 2 goes to middle of VR1 and top of VR1 connects to +12V and bottom pin goes to GND
• Pin 3 connects between R1 and R2
• Pin 4 connects to GND
• Pin 5 connects to pin 6
• Pin 7 goes to base of Q1 through R3
• Pin 8 goes to +12V
• Q1 collector connects to +12V through D1
• Q1 emitter connects to GND
• Relay coil one side connects to +12V and other side connects to Q1 collector
• Relay N/O connects to +12V, COM connects to one side of 12V fan and other side of fan connects to GND
• R4 one side connects between COM and fan and other side goes to LED1 anode and LED1 cathode goes to GND

Conclusion:

This Temperature Controlled Fan Circuit for Audio Amplifiers keeps amplifier cool automatically.

It uses NTC and LM311 IC to start fan only when hot.

The circuit saves energy and stops overheating.

It is good for amplifies and other heat sensitive gear.

References:

Datasheet IC LM311