Today, operating parameter monitoring has become an integral part of power modules. In power modules, temperature sensors have become more or less standard, and even current sensors are being used more and more widely. In fact, the integrated sensor is a more cost-effective solution than an external sensor solution, which gives the user additional protection while reducing the size of the module. current sensor If a power module is equipped with a current sensor, its signal is mainly used as output current control (eg in drive applications) and can also serve to protect the device. The need for motor control determines the characteristics of the current sensor. In many cases, faults (including temperature drift) must be less than 1 ... 2%. The requirements for temperature (-40°C to 125°C) and low current consumption are set by the power module itself. The device protection function sets the overcurrent capability (the maximum short-circuit current is 5 times the rated current) and the upper cut-off frequency (> 100kHz). For medium- and low-power devices, using current shunts is a precise and cost-effective solution. The current limit is about 30A to 40A. The disadvantage is that there is extra power loss, and if the shunt is used to measure the emitter current, it will lose isolation and there will be interference in the IGBT gate signal. Electrically isolated sensors are generally used for high performance and high power semiconductor modules. Pure Hall effect sensors without compensation current have poor performance in terms of error and temperature stability. Sensors can be used in user-specified modules because the requirements in these modules are clearly defined. Sensors with high linearity and low temperature drift operate with compensation currents. This current cancels the magnetic field that measures the current in the sensor core. The compensation current amplifier's control signal is provided by a Hall effect, magnetic field, or magnetoresistive probe. For intelligent power modules (IPMs) such as SEMIKRON's SKiiP system, the use of high-precision sensors is the most suitable due to the high performance requirements of the final application. In the final application, the sensor is integrated directly into the module's housing and surrounds the main terminal to save space (Figure 1). The evaluation circuit for signal monitoring and conversion is part of the driver circuit. The specially designed ASIC chip ensures high integration and high reliability, which is difficult to achieve in the solution using external sensors. Inside the IPM, the current monitoring circuit is directly connected to the driver circuit. It can detect an external short circuit in the shortest time, and can turn off the power semiconductor in 2 ~ 3μs. In the future, this characteristic will become more and more important, because the new generation IGBT allows only short circuit time of 6 μs compared with the short circuit time of the past IGBT allowed 10 μs. The current sensor at the AC terminal of the voltage source inverter circuit cannot detect the short circuit in the inverter bridge. Here, by monitoring VCE(sat), the slope resistance of the semiconductor in an open state is used for protection purposes. This method is adequate for short-circuit protection but is not suitable for current measurements. Figure 1: SKiiP power module with integrated current sensor at AC terminal There are several temperature sensors available for device protection. These sensors have negative temperature coefficient (NTC) or positive temperature coefficient (PTC). The most used standard industrial module is the NTC sensor. SEMIKRON uses its own silicon sensor SKCS, which is characterized by PTC characteristics, high linearity, and small errors. With suitable monitoring circuitry, IPMs such as SKiiP provide an analog output signal for temperature measurement and protection with a failure rate below 5°C. The location of the sensor within the module greatly influences its temperature protection capability. In fact, the position of the sensor in this respect is more important than the error of the sensor. This is especially true if the hardware trip level is set by a driver or control circuit. Figure 2: Case Study of Different Temperature Sensor Locations in Power Modules; Model and Temperature Simulation A study was conducted on the effects of sensors at different locations. A model of the power module is shown in Figure 2. The module does not have a copper backplane and is mounted on an air-cooled aluminum heat sink. The thermal coupling of different sensors is different, from sensors A) directly on the same copper layer to the power semiconductors, to sensors B) and C) in different locations within the module, to sensors D) placed next to the module on the heat sink. Due to different thermal couplings, each sensor has a different junction (j) to sensor (r) thermal resistance Rth(jr). The trip level for over-temperature protection can be set for each sensor at quasi-static conditions. For example, if Tj cannot exceed 140°C, the "overheat shutdown" trip level of the case system will be from 120°C (sensor A), 110°C (sensor B), 100°C (sensor C) to 70°C (sensor D) does not equal. The better the coupling between the source and the sensor, the lower the influence of the cooling system. This is a big advantage of integrated solutions. However, for other cooling conditions (heat sink material and base thickness, cooling medium, thermal grease thickness), the trip level has to be set to a new value. This makes it difficult for IPM manufacturers to set the overheat trip level to a suitable value for any given application. For this purpose, the sensor signal should be monitored by an external host controller and, if required, the thermal protection level should match the cooling system. To show the effect of the cooling system, the thickness of the thermal grease layer increased from 50 μm to 100 μm. Since sensor A has the best thermal coupling with power semiconductors, it can be seen that the impact on Rth(jr) is the lowest and its value only increases by 3%. The Rth(jr) values ​​for sensors B and C increase by 7...8%. The cooling system has the greatest influence on the Rth(jr) of sensor D, which increases by more than 25%. Another issue is whether the temperature sensor can protect the power semiconductor in a short time overload. Each sensor has a delay in reacting to a rise in junction temperature, which is related to the position of the sensor. This characteristic is described by the thermal impedance Zth(jr). Its performance is inconsistent with expectations (see Figure 3). A comparison of Zth(jr) and junction-to-heat sink thermal impedance Zth(js) (directly under the chip) shows that after one second the system's junction-to-sink heat resistance has reached a steady state condition, and the system's junction-sensor It takes 100 seconds to reach steady state. The reason for this is the thermal diffusion inside the heat sink. Figure 3: Thermal impedance of junction (j) to different position sensor (rX) and heat sink For each power semiconductor, the maximum value of the static power consumption Ptot is specified. For the example of an overload transition from 50% Ptot to 200% Ptot, the semiconductor will overheat after some time. Sensor A will reach its 120°C open circuit level after 0.19 s, providing reliable device protection and maintaining the junction temperature at approximately 150°C. The junction temperature of devices protected by sensors B and C will be in a critical range of 160 °C to 170 °C; in these cases, the sensor needs 0.3...0.4 s to reach the trip level. Depending on the characteristics of the device, this may mean that the limits specified in the data sheet have been exceeded. The response time of sensor D is longer than 1 second and therefore cannot protect the device. For very high overloads and low start-up temperatures, the temperature sensor does not provide any suitable protection. An overview of the advantages and disadvantages of different temperature sensor locations is given in Table 1. Because of the isolation, sensors located in position B are now the preferred solution. If the driver is protected in the future and the signal is transformed on the secondary side of the driver, it may mean that sensor position A may be a better solution. If there is a short-term overload, there will be a gap in device protection. The current sensor's trip value is set to a higher value to allow short-term overloads, such as when the motor is starting. Long-term operation at this current level will cause the device to overheat. In most cases, the response time of the temperature protection element is too long to detect this overheating. One possible way to fill this gap is to use software shutdown of the current and temperature signals. The inverter controller calculates the junction temperature based on the sensor's temperature and electrical operating conditions. The junction temperature at tp can be calculated from the following equation: P0 is the power consumption at t=0s and Pover is the power consumption at overload. Here, the thermal impedance Zth(jr) is as described in the data sheet, and the analog temperature signal Tr is also required. Table 1: Comparison of temperature sensors at different locations for protection of power semiconductors. to sum up The integrated sensors in the IPM protect power modules like the SKiiP in a wide range of operating conditions. Equipped with a suitable evaluation circuit, it can provide high-quality information for process control as a synergy effect. This can save space, cost and development time. With an external observer, the combination of available sensor signals can fill in the gaps in a particular protection in an application.