By eectech | 01 June 2018 | 0 Comments
Guidelines for the selection of heat sinks for power semiconductor devices
A basic principle of radiator selection
1 Selection of heat sinks
The main basis for selecting the heatsink is the internal thermal resistance of the power semiconductor device (the sum of the thermal resistance of the junction and the thermal contact resistance) and the dissipated power, followed by the maximum operating junction temperature and the cooling medium temperature of the device.
2 Determine the principle of tightening force (torque)
Tightening force (torque) is a good installation force or installation torque after the heat sink is assembled with the device.
The fastening force (torque) is an indispensable and important parameter for connecting the device and the heat sink. Correctly determining and using it plays an important role in ensuring long-term stable operation and reliability of the device.
The tightening force (torque) is a rated value with a certain tolerance range and should be strictly adhered to during assembly. The tightening force (torque) is given by the device manufacturer or device standard, or by the characteristic curve of the fastening force (torque) and related parameters. When the device factory does not provide the fastening force, the contact area of the device shell and the heat sink can be 1.3-1.6kN/cm2.
In order to improve the contact between the heat sink and the device, increase the effective contact area, and improve the heat dissipation effect, a thin layer of conductive and thermally conductive material such as grease may be coated between the heat sink and the device.
3 Radiator rated cooling conditions
Self-cooling radiator: The ambient air temperature is not higher than 40°C, and the natural convection air velocity is not more than 0.5m/s.
Air-cooled radiator: The inlet air temperature is not higher than 40°C, and the inlet wind speed is 6m/s.
Water-cooled radiator: The inlet water temperature is not higher than 35°C and the water flow is 4L/min.
4 General principles for selecting a radiator
First, according to the stability and transient operation of the device in the circuit, a certain margin should be taken into consideration to select the device parameters, and then the required heat sink should be selected according to the device parameters.
5 Comprehensive consideration of optional radiator
The selected radiator should correctly identify the type and meaning of the radiator, insulation, and fasteners, and understand the range, cooling method, technical parameters, and structural features of each series of radiators. A device can only meet two or three types of heat sinks based on the thermal resistance parameters, but it should be combined with cooling, installation, universal interchangeability, and economic considerations to select an optimal heat sink.
Second, the general method of selection of radiator
The heat sink of the device in the complete machine should be based on the actual cooling conditions (cooling medium temperature and flow rate) and steady and transient load conditions when the device is operating in the complete machine, with due consideration of the margin required for the safety factor, according to the steady state. Do not exceed the maximum working junction temperature to select.
1 According to the current waveform and conduction angle of the device working in the circuit, the average current IAV of the device during operation is determined, and the IRMS of the current is calculated by IAV.
IRMS=F•IAV F is the form factor.
2 By IRMS or 180° conduction angle IAV, and considering the device parameters such as device inrush current, determine the device model.
3 From the relationship between the maximum allowable case temperature TC of the required device and the main current IAV, the TC value corresponding to the IAV value of the working point is found. Or calculate the TC value as follows by the relevant parameters of the desired device.
TC=Tjm-RjcPAV
Tjm is the maximum allowable operating junction temperature for the device, typically 150°C for rectifiers, 125°C for common thyristors, and 115°C for fast thyristors.
Rjc is the device's junction thermal resistance.
PAV is the power dissipated by the device. Its calculation formula is:
PAV=0.785VTM•IAV + 0.215VTO•IAV or
PAV=VTO•IAV1 + 2.47 rT•I2AV
VTM is the device's on-state peak voltage drop.
VTO is the device threshold voltage. When the device parameters are not marked, it is desirable: 0.8V rectifier, 1.0V ordinary thyristor, and 1.2V fast thyristor.
rT is the on-state slope resistance of the device.
4 Calculate the maximum allowable radiator table temperature TS from the following equation
TS=TC-R?CS•PAV
RCS is thermal contact resistance, 1/3Rjc for bolt-shaped devices, and 1/5 Rjc for flat-plate devices.
5 Calculate the thermal resistance of the heatsink by the following formula Rsa
Rsa=(Ta—TS)/PAV
Ta is the ambient temperature, which is 40°C for cold or air cooling and 35°C for water cooling.
6 When the working condition of the radiator is the same as the rated cooling condition, the selected radiator can be obtained from the calculated value Rsa and the radiator data table. If the radiator does not match, the radiator thermal resistance and the cooling medium (air or water) must be checked. ) The curve of the flow rate or flow rate is obtained.
Three series radiators should pay attention to matters needing attention
1 When installing from a cold radiator, the radiator blades should be parallel to the natural convection direction of the hot and cold air vertically above and below.
When the air-cooled radiator is installed, the radiator blades should follow the direction of the cooling airflow. If it is used for self-cooling, the load capacity of the radiator must be determined based on the thermal resistance value of the heat resistance of the heat sink and the wind speed curve around zero wind speed.
2 The water quality of water-cooled radiators should have certain requirements. The resistivity of circulating water should not be lower than 2.5kW, and the PH value should be between 6-9.
Water-cooled radiators should pay special attention to preventing leakage, preventing clogging and preventing condensation when working.
1 Selection of heat sinks
The main basis for selecting the heatsink is the internal thermal resistance of the power semiconductor device (the sum of the thermal resistance of the junction and the thermal contact resistance) and the dissipated power, followed by the maximum operating junction temperature and the cooling medium temperature of the device.
2 Determine the principle of tightening force (torque)
Tightening force (torque) is a good installation force or installation torque after the heat sink is assembled with the device.
The fastening force (torque) is an indispensable and important parameter for connecting the device and the heat sink. Correctly determining and using it plays an important role in ensuring long-term stable operation and reliability of the device.
The tightening force (torque) is a rated value with a certain tolerance range and should be strictly adhered to during assembly. The tightening force (torque) is given by the device manufacturer or device standard, or by the characteristic curve of the fastening force (torque) and related parameters. When the device factory does not provide the fastening force, the contact area of the device shell and the heat sink can be 1.3-1.6kN/cm2.
In order to improve the contact between the heat sink and the device, increase the effective contact area, and improve the heat dissipation effect, a thin layer of conductive and thermally conductive material such as grease may be coated between the heat sink and the device.
3 Radiator rated cooling conditions
Self-cooling radiator: The ambient air temperature is not higher than 40°C, and the natural convection air velocity is not more than 0.5m/s.
Air-cooled radiator: The inlet air temperature is not higher than 40°C, and the inlet wind speed is 6m/s.
Water-cooled radiator: The inlet water temperature is not higher than 35°C and the water flow is 4L/min.
4 General principles for selecting a radiator
First, according to the stability and transient operation of the device in the circuit, a certain margin should be taken into consideration to select the device parameters, and then the required heat sink should be selected according to the device parameters.
5 Comprehensive consideration of optional radiator
The selected radiator should correctly identify the type and meaning of the radiator, insulation, and fasteners, and understand the range, cooling method, technical parameters, and structural features of each series of radiators. A device can only meet two or three types of heat sinks based on the thermal resistance parameters, but it should be combined with cooling, installation, universal interchangeability, and economic considerations to select an optimal heat sink.
Second, the general method of selection of radiator
The heat sink of the device in the complete machine should be based on the actual cooling conditions (cooling medium temperature and flow rate) and steady and transient load conditions when the device is operating in the complete machine, with due consideration of the margin required for the safety factor, according to the steady state. Do not exceed the maximum working junction temperature to select.
1 According to the current waveform and conduction angle of the device working in the circuit, the average current IAV of the device during operation is determined, and the IRMS of the current is calculated by IAV.
IRMS=F•IAV F is the form factor.
2 By IRMS or 180° conduction angle IAV, and considering the device parameters such as device inrush current, determine the device model.
3 From the relationship between the maximum allowable case temperature TC of the required device and the main current IAV, the TC value corresponding to the IAV value of the working point is found. Or calculate the TC value as follows by the relevant parameters of the desired device.
TC=Tjm-RjcPAV
Tjm is the maximum allowable operating junction temperature for the device, typically 150°C for rectifiers, 125°C for common thyristors, and 115°C for fast thyristors.
Rjc is the device's junction thermal resistance.
PAV is the power dissipated by the device. Its calculation formula is:
PAV=0.785VTM•IAV + 0.215VTO•IAV or
PAV=VTO•IAV1 + 2.47 rT•I2AV
VTM is the device's on-state peak voltage drop.
VTO is the device threshold voltage. When the device parameters are not marked, it is desirable: 0.8V rectifier, 1.0V ordinary thyristor, and 1.2V fast thyristor.
rT is the on-state slope resistance of the device.
4 Calculate the maximum allowable radiator table temperature TS from the following equation
TS=TC-R?CS•PAV
RCS is thermal contact resistance, 1/3Rjc for bolt-shaped devices, and 1/5 Rjc for flat-plate devices.
5 Calculate the thermal resistance of the heatsink by the following formula Rsa
Rsa=(Ta—TS)/PAV
Ta is the ambient temperature, which is 40°C for cold or air cooling and 35°C for water cooling.
6 When the working condition of the radiator is the same as the rated cooling condition, the selected radiator can be obtained from the calculated value Rsa and the radiator data table. If the radiator does not match, the radiator thermal resistance and the cooling medium (air or water) must be checked. ) The curve of the flow rate or flow rate is obtained.
Three series radiators should pay attention to matters needing attention
1 When installing from a cold radiator, the radiator blades should be parallel to the natural convection direction of the hot and cold air vertically above and below.
When the air-cooled radiator is installed, the radiator blades should follow the direction of the cooling airflow. If it is used for self-cooling, the load capacity of the radiator must be determined based on the thermal resistance value of the heat resistance of the heat sink and the wind speed curve around zero wind speed.
2 The water quality of water-cooled radiators should have certain requirements. The resistivity of circulating water should not be lower than 2.5kW, and the PH value should be between 6-9.
Water-cooled radiators should pay special attention to preventing leakage, preventing clogging and preventing condensation when working.
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