High-power diode thyristor knowledge serial-thermal characteristics

Power diode thyristors are widely used in AC/DC converters, UPS, AC static switches, SVC and electrolytic hydrogen, etc. However, most engineers do not understand such bipolar devices as well as IGBTs. For this reason, we organized 6 Article serial, including forward characteristics, dynamic characteristics, control characteristics, protection, loss and thermal characteristics.

High-power diode thyristor knowledge serial-thermal characteristics

Power diode thyristors are widely used in AC/DC converters, UPS, AC static switches, SVC and electrolytic hydrogen, etc. However, most engineers do not understand such bipolar devices as well as IGBTs. For this reason, we organized 6 Article serial, including forward characteristics, dynamic characteristics, control characteristics, protection, loss and thermal characteristics. The content is extracted from Infineon’s “Bipolar semiconductor Technology Information”.

4. Thermal properties

In order to maintain the heat balance, it is necessary to remove the power loss in the semiconductor that is converted into heat. To this end, we provide radiators with clear cooling properties. Describe the thermal equivalent circuit through an analog electrical circuit, as shown in Figure 32.

High-power diode thyristor knowledge serial-thermal characteristics
Figure 32. Thermal equivalent circuit of diode and thyristor

Rth JC=Junction-case steady-state thermal resistance

Rth CH=case-heat sink steady-state thermal resistance

Rth HA = steady-state thermal resistance of the radiator

aC single side cooling

bC double-sided cooling

4.1 Temperature

4.1.1 Junction temperature Tvj, Tvj max

For all basic electrical properties, junction temperature is the most important reference. It represents the average space temperature in the semiconductor system, so it is more accurately called the equivalent junction temperature or virtual junction temperature.

The maximum allowable junction temperature Tvj max is very important to the function and reliability of the device. If Tvj max is exceeded, the semiconductor performance may undergo irreversible changes and may be damaged.

4.1.2 Case temperature TC

Tc is the highest temperature in the contact area of ​​the plate-type thyristor or diode shell or the substrate of the PowerBLOCK module.

4.1.3 Radiator temperature TH

TH refers to the temperature reached by the radiator through heat exchange between the semiconductor and the radiator through the contact area of ​​the radiator and the surrounding cooling medium.

The heat sink provided by Infineon has been tested and specified with the components installed. Therefore, the given heat sink data includes the thermal resistance RthCH between the device and the heat sink. This value can be ignored in the calculation.

4.1.4 Cooling medium temperature TA

Ta is the temperature of the cooling medium before it enters the radiator. For air cooling, determine this temperature on the air inlet side of the radiator. For liquid cooling, determine this temperature at the radiator coolant inlet.

4.1.5 Shell temperature range Tcop

Tcop is the case temperature range that can make the power semiconductor work.

4.1.6 Storage temperature range Tstg

Tstg is the temperature range within which the power semiconductor can be stored without charge. The maximum allowable storage temperature has nothing to do with the maximum allowable junction temperature without time limit. According to DIN IEC 60747-1, the maximum allowable storage temperature for epoxy flat-Panel devices and PowerBLOCK modules is Tstg=150°C, and the time limit is 672h.

4.2 Thermal resistance

4.2.1 Internal thermal resistance RthJC

RthJC is the ratio of the difference between the junction temperature Tvj and the case temperature TC to the total power dissipation Ptot:

High-power diode thyristor knowledge serial-thermal characteristics

This value depends on the internal design of the device and the waveform and frequency of the on-state current.

Due to the parallel connection of thermal resistance, the thermal resistance of double-sided cooling is lower than that of single-sided cooling (see Figure 32).

The thermal resistance depends on the type and shape of the semiconductor, so it will not be 100% measured, but it can be determined in the initial type approval test.

4.2.2 Heat transfer resistance RthCH

RthCH is the ratio of the temperature difference TC-TH between the contact area of ​​the device and the heat sink to the total power dissipation Ptot:

High-power diode thyristor knowledge serial-thermal characteristics

The specified value is only valid when the device is correctly installed (see Chapter 8)

4.2.3 Radiator thermal resistance RthCA

RthCA is the ratio of the difference between the case temperature TC and the cooling medium temperature TA to the total power dissipation Ptot:

High-power diode thyristor knowledge serial-thermal characteristics

4.2.4 Total thermal resistance RthJA

RthJA is the ratio of the difference between the equivalent junction temperature Tvj and the cooling medium temperature TA to the total power dissipation Ptot:

High-power diode thyristor knowledge serial-thermal characteristics

4.2.5 Transient internal thermal resistance ZthJC

ZthJC describes the gradual change of component thermal resistance over time. In the data sheet, ZthJC is specified with a constant DC, and another is specified with a pulse current. In addition, part of the thermal resistance Rthn and time constant tn are compiled in the table as an analytical function.

High-power diode thyristor knowledge serial-thermal characteristics

4.2.6 Transient thermal resistance of heat sink ZthCA

ZthCA describes the gradual change of the thermal resistance of the heat sink over time. ZthCA is defined in a separate data sheet. In addition, the RthCAn and tn values ​​of the thermal resistance analytical function are listed in the table. Heat sinks usually do not have a generally defined transient thermal resistance. On the one hand, the transient thermal resistance depends on the contact area between the power semiconductor and the heat sink. On the other hand, the cooling method (natural cooling/forced cooling) and the flow of the cooling medium also have a great influence.

For natural cooling and oil cooling, the flow of the cooling medium is caused by the convection of air or oil. Power dissipation limits convection, so the actual power dissipation is determined for natural cooling and oil cooling. Attention must be paid to the correct orientation and location of the radiator.

For forced cooling and water cooling, the flow rate of the cooling medium is specified.

The short-term temperature change caused by the pulse current has nothing to do with these parameters. They are balanced by the large heat capacity of the radiator.

The heat sink provided by Infineon has been tested and specified with the components installed. These given heat sink data include the heat transfer resistance RthCH between the device and the heat sink. Therefore, this value does not have to be considered.

4.2.7 Total transient thermal resistance ZthJA

ZthJA describes the gradual change in total thermal resistance over time. Calculate the short-time load junction temperature based on the transient total thermal resistance. ZthJA is the sum of the following two items:

High-power diode thyristor knowledge serial-thermal characteristics

4.3 Cooling

4.3.1 Natural air cooling

In the natural air cooling (air convection cooling) process, the power loss is discharged through the natural convection of the air. The current-carrying capacity of power semiconductors is usually determined under the condition of ambient temperature TA=45°C.

4.3.2 Forced air cooling

In the forced air cooling process, the cooling air is forced through the radiator blades by the fan. The current-carrying capacity of power semiconductors is usually determined under the condition of ambient temperature TA=35°C.

4.3.3 Water cooling

In the water cooling process, the power loss is discharged through the water. The current-carrying capacity of power semiconductors is usually determined under the condition of inlet water temperature TA=25°C.

4.3.4 Water cooling

In the oil cooling process, the power loss is discharged through the oil. The current-carrying capacity of power semiconductors is usually determined under the condition of inlet oil temperature TA=70°C.

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