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#### Aluminum Heat Sink & Profile Manufacturing

address：No. 51 Luming Road Heavy River Management District - Qing Town Dongguan City

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Telephone：+86 13827205356

mailbox：cnc@cncstamping.com

# Design the heat sink of the power amplifier

Design of heat sink and power calculation example of low frequency power amplifier The power operational amplifier PA02 (product of APEX) is used as a low frequency power amplifier. The device is an 8-pin TO-3 metal case package. The working conditions of the device are as follows: The working voltage VS is 18V; The load impedance RL is 4, the operating frequency can reach 5kHz under DC conditions, the ambient temperature is set to 40℃, and natural cooling is adopted.

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Design of heat sink and power calculation example of low frequency power amplifier

The power operational amplifier PA02 (product of APEX) is used as a low frequency power amplifier. The device is an 8-pin TO-3 metal case package. The working conditions of the device are as follows: The working voltage VS is 18V; The load impedance RL is 4, the operating frequency can reach 5kHz under DC conditions, the ambient temperature is set to 40℃, and natural cooling is adopted.
Check the PA02 device data to know: The typical value of quiescent current IQ is 27mA, and the maximum value is 40mA; The R JC (from die to case) of the device is typically 2.4°C/W and the maximum value is 2.6°C/W.
The power consumption of the device is PD:
PD=PDQ+PDOUT
Where PDQ is the power consumption of the internal circuit of the device, and PDOUT is the power consumption of the output power. PDQ=IQ(VS+|-VS|), PDOUT=V^{2}_{S}/4RL, substitute the above formula
PD=IQ(VS+|-VS|)+V^{2}_{S}/4RL=37mA(36V)+18V2/4 4=21.6W
In the formula, the quiescent current is 37mA.
Radiator thermal resistance R SA calculation: R SA≤({T_{J}-T_{A}}\over {P_{D}})-(R_{ JC}+R_{ CS}})

To leave a margin: TJ is set to 125°C, TA is set to 40°C, R JC is the maximum value (R JC=2.6°C/W), and R CS is set to 0.2°C/W (PA02 is directly installed on the radiator with thermal grease in the middle). Substituting the above data into the formula, R SA≤ {125℃-40℃} \over {21.6W}-(2.6℃/W+0.2℃/W) ≤1.135℃/WHSO4 thermal resistance in natural convection is 0.95℃/W , Can meet the heat dissipation requirements.

Precautions
1. The maximum power consumption value in the electronic device data cannot be used in the calculation, but the calculation should be based on the actual conditions; The maximum junction temperature in the data is generally 150°C, 125°C is left in the design, and the ambient temperature cannot be 25°C (the actual temperature in summer and the case should be considered).
2. The installation of the radiator should consider the direction conducive to heat dissipation, and open a heat dissipation hole in the corresponding position on the chassis or casing (to make cold air enter from the bottom and hot air to escape from the top).
3. If the shell of the electronic device is an electrode, the mounting surface is not insulated (not insulated from the internal circuit). Mica gaskets must be used for insulation during installation to prevent short circuits.

4. The pins of the electronic device must pass through the heat sink, and drill holes must be made on the heat sink. To prevent the pin from colliding with the hole wall, a PTFE sleeve should be put on.

5. In addition, different models of radiators have different thermal resistances under different heat dissipation conditions, which can be modified during design. That is, in practical applications, it can be calculated by referring to the thermal resistance of these radiators, and a radiator composed of profiles with similar structural shapes (cross-sectional area, perimeter) can be used as a substitute.

6. In the above calculation, some parameters are set, which may be different from the actual value, and the size of the substitute model is not exactly the same. Therefore, simulation tests should be performed to verify whether the radiator selection is appropriate during mass production, and mass production can only be done after making some corrections if necessary. (Such as the length of the aluminum profile or changing the model of the profile, etc.)

IDT heat data
Considering the power consumption of microelectronic devices, thermal energy management is essential for the best performance of any electronic product. The operating temperature of microelectronic devices determines the speed and reliability of the product. IDT is actively committed to strengthening the research and development of its products and packaging to achieve the best speed and reliability. However, product performance is often affected by implementation. Therefore, careful handling of various factors that affect the operating temperature will help give full play to the production. The most important factors that affect the operating temperature of electronic devices include work: rate consumption, air temperature, packaging structure, and cooling devices. These factors together determine the working temperature of the product. The following is the equation currently used to calculate the operating temperature:

QJA = (TJ-TA)/PQJC = (TJ-TC)/PQCA = (TC-TA)/PQJA = QJC + QCATJ = TA + P [QJA]
TC = TA + P [QCA]
QJA = package thermal resistance from die to ambient air (degrees per watt)
QJC = package thermal resistance from die to package shell (Celsius per watt)
QCA = package thermal resistance from package shell to ambient air (per watt degrees Celsius)
TJ = average die temperature (Celsius)
TC = Package case temperature (Celsius)
TA = ambient air temperature (degrees Celsius)
P = power (watts)
The above equation is the current method of determining package temperature.