Imagine a heatsink like a mini radiator for your electronics, it keeps things cool.
A heatsink temperature protection circuit is like a safety guard for this mini radiator.
It has a special sensor that checks the temperature of the heatsink.
If things get too hot, like when you have a fever the circuit steps in.
It can either turn off the power to the electronics or turn on a fan to cool things down.
This prevents the electronics from getting damaged by the heat.
Circuit Working:
Parts List:
| Category | Part Description | Quantity | Notes |
|---|---|---|---|
| Resistors | 10k | 2 | 1/4 watt |
| 1k | 2 | 1/4 watt | |
| Preset 1M | 1 | ||
| Capacitors | Ceramic 0.01µF | 1 | |
| Semiconductors | IC 555 | 1 | |
| Thermistor NTC 4.7k | 1 | ||
| Transistor BC547 | 1 | ||
| Diode 1N4007 | 1 | ||
| Other Components | Reset push button | 1 | |
| Buzzer | 1 | ||
| Relay 12V | 1 |
Protect your power transistors from damage caused by excess heat with this circuit.
It automatically cuts off power to the transistor when it detects a high heatsink temperature and reconnects power once the temperature returns to normal.
The circuit utilizes an NTC thermistor as a heat sensor and includes audible warning and reset features.
The circuit employs the 555 IC as a temperature-controlled switch.
Its trigger pin 2 connects to a potential divider comprising VR and the NTC thermistor setting the voltage level at pin 2 based on the thermistors resistance and the VR1 setting.
The NTC thermistor has high resistance at normal temperatures which decreases as the temperature rises.
The ICs threshold pin 6 resets the IC when necessary detecting a higher voltage than pin 2 to trigger a reset and set the output low.
Power is supplied to the circuit board through the normally connected NC contacts of the relay ensuring power availability when the relay is not energized.
VR1 sets the thermistors resistance to maintain a high trigger pin 2 voltage at normal temperature.
As the temperature increases inside the amplifier cabinet, the thermistors resistance decreases allowing it to conduct.
This lowers the trigger pin 2 voltage, setting the output high and causing T1 to conduct energizing the relay and activating the buzzer.
This action breaks the power supply to the circuit board.
The relay de energizes automatically once the temperature returns to normal.
Place the thermistor near the transistors heatsink and adjust VR1 to set the relays activation temperature.
Formulas:
Below formula is to calculate NTC for Heatsink Temperature Protection:
The resistance temperature R-T connection of the NTC is more accurately represented by the Steinhart Hart equation, although it requires more intricate computations.
Usually, high precision applications make use of it.
The beta coefficient is a more straightforward method of expressing the sensitivity of the NTC by stating the percentage change in resistance for each degree Celsius of temperature change.
It is frequently shown as follows:
Beta = (ΔR / Rref) * (100°C) / ΔT
- Beta is the negative sign of the NTCs beta coefficient (e.g. -3.5%°C) denotes a reduction in resistance with temperature.
- ΔR is the resistance change (R – Rref)
- Rref is the reference resistance, which the datasheet typically states at 25°C
- ΔT is the temperature change (°C)
Applying the Coefficient of Beta
By using the beta coefficient, you may determine the NTCs resistance at a given temperature by comparing it to its reference resistance. How to do it is as follows:
- Determine the target temperature T.
- Determine the temperature difference ΔT between the standard temperature, which is typically 25°C: ΔT is equal to T minus 25°C.
- Divide the result by 100 after multiplying the beta coefficient (Beta) by the temperature difference (ΔT): (Beta * ΔT) / 100
- The % change in resistance with respect to Rref is shown by this number.
- To obtain the estimated resistance at temperature T, add (or subtract, depending on the sign of Beta) this percentage change to the reference resistance (Rref): R = [(Beta * ΔT) / 100] ± Rref * Rref
Note:
It should be noted that the beta coefficient is an estimate and could not be entirely accurate for the whole working range of the NTC.
The best place to look for precise R-T curves or tables for the NTC thermistor you are using is the manufacturers datasheet.
How to Build:
To build a Simple Heatsink Temperature Protection Circuit below mentioned are the steps:
- Connect the NTC thermistor and VR1 to create a potential divider connected to pin 2 of the 555 IC
- Connect pin 6 of the 555 IC to a reference voltage to enable resetting the IC when needed.
- Connect pin 7 of the 555 IC to pin 6.
- Connect pin 5 of the 555 IC to pin 8.
- Connect pin 4 of the 555 IC to pin 8 through a resistor.
- Connect pin 1 of the 555 IC to ground.
- Connect pin 3 of the 555 IC to the base of the transistor T1.
- Connect the emitter of the transistor T1 to ground.
- Connect the collector of the transistor T1 to one terminal of the relay coil and the other terminal of the relay coil to VCC.
- Connect the normally connected NC contacts of the relay to the power supply for the circuit board.
- Connect a diode across the relay coil to protect the transistor from voltage spikes when the relay de energizes.
- Connect the buzzer in parallel with the 12V relay to sound the alarm when the relay energizes.
Note:
Please note that this is a basic schematic and additional components may be required depending on the specific requirements of your circuit and the components you are using.
Also, ensure that the power supply and all components are rated appropriately for the circuits requirements.
Conclusion:
To conclude, a Heatsink Temperature Protection Circuit is a crucial component in electronic devices safeguarding against damage caused by overheating.
By monitoring temperatures and triggering actions to mitigate excessive heat these circuits ensure the safe and reliable operation of electronic components.