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IGBT module heat sink selection and use principle
First, the basic principle of radiator selection
1, the basic basis of the choice of radiator
The choice of IGBT heat sink should be considered based on the dissipated power of the device, the thermal resistance of the device, the thermal resistance of the contact, and the temperature of the cooling medium.
2, the requirements of the device and the heat sink fastening force
In order for the device to have good thermal contact with the heat sink, it must have a suitable mounting force or mounting torque, the value of which is given by the device manufacturer or device standard, and should be strictly adhered to the specified range.
3, the rated cooling conditions of the radiator
Self-cooling radiator: The ambient temperature is preferably not higher than 40 °C. When installing, the radiator fins should be arranged vertically, and the upper and lower end surfaces should not be blocked, so that there is good air convection environment and passage around the radiator.
Air-cooled radiator: The inlet air temperature is controlled below 40 °C, and the inlet end wind speed is preferably 6 m/s.
Water-cooled radiator: The inlet water temperature is not higher than 35 °C. The water flow rate is determined by the total heat demand of the heat sink and the temperature difference between the inlet and outlet water.
4, the comprehensive consideration of the choice of radiator
The selection of the radiator should take into account the heat dissipation capability range, cooling method, technical parameters and structural characteristics of the radiator. One device can only meet the requirements from the technical parameters. However, it should be combined with cooling and installation. , universal interchange and economic considerations are selected.
Second, the general method of using a radiator
The user should select the heat sink according to the actual cooling conditions when the device is working, the steady and transient load conditions, and properly consider the safety factor, and consider the steady state not exceeding the maximum working junction temperature of the device.
1. According to the current waveform and conduction angle of the device operating in the circuit, determine the average current IAV when the device is working, and calculate the effective value of the current IRMS by IAV.
IRMS = F·IAV F is the waveform coefficient.
2. The IAV is determined by IRMS or 180° conduction angle, and combined with the device surge current to determine the device model. IAV = IRMS/1.57.
3. From the relationship between the maximum allowable case temperature Tc of the selected device and the main current IAV, the Tc value corresponding to the device at the operating point IAV is found. Or calculate the Tc value as follows according to the relevant parameters of the selected device.
Tc = Tjm - Rjc·PAV
Tjm is the maximum allowable maximum wage junction temperature of the device, 150 °C for ordinary rectifiers, 125 °C for common thyristors, and 115 °C for fast thyristors.
Rjc is the junction thermal resistance of the device.
PAV is the dissipated power of the device. Its calculation formula is:
PAV = 0.785 VTM·IAV +0.215VTO·IAV or
PAV = VTO·IAV + 2.47rT0·IAV
VTM is the on-state peak voltage drop of the device.
VTO is the threshold voltage of the device. When the device parameter table is not marked, it can be taken as: 0.8V for rectifier, 1.0V for common thyristor, and 1.2V for fast thyristor.
rT0 is the on-state slope resistance of the device.
4. Calculate the maximum allowable radiator table temperature TS by the following formula
TS = Tc - RCS·PAV
RCS is contact thermal resistance, spiral type device can take 1/3 Rjc, flat type device can take 1/5 Rjc
5. Calculate the thermal resistance of the heat sink by the following formula
Rsa = (Ts – Ta) / PAV
Ts is the ambient temperature and is measured at the time of the test.
6. When the working condition of the heat sink is consistent with the rated cooling condition, the heat sink with the same or lower thermal resistance value and the closest calculated value is selected from the calculated value Rsa. Inconsistent, check the relationship between the heat resistance of the radiator and the flow rate of the cooling medium.
Third, the series of radiators should be noted in the use of matters
1. When the air-cooled radiator is installed, the radiator blades should be in the direction of the cooling airflow. If the air-cooled radiator is used for self-cooling, the load capacity of the radiator should be determined according to the thermal resistance value of the heat resistance of the radiator and the wind speed in the vicinity of the zero wind speed. Igbt mode 2. The water quality of the water-cooled radiator should have certain requirements. The resistivity of the circulating water should be no less than 2.5KΏcm and the PH value should be between 6-9. Water-cooled radiators should pay special attention to water leakage, anti-clogging and anti-condensation during work.
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