AN1541 Second. the leveloped across Re results in a similar division ross Shorting and VBE of the NPN transistor ill be less likely to attain a VBe high enough to device on and cause a latch-up situation The two situations described work together to protect the device from catastrophic failure. The protection period is specified with the device ratings, allowing circuit designers VOLTAGE RM(rec) the time needed to detect a fault and shut off the device The introduction of the series resistance Re also results in additional power loss in the device by slightly elevating the forward drop of the device. However, the magnitude of short circuit current is large enough to require a very low Re value The additional conduction loss of the device due to the presence of Re is not excessive when comparing a short circuit rated iGBT to a non-short circuit rated device Anti-Parallel Diode When using IGBTs for motor control, designers have to place a diode in anti-parallel across the device in order to handle the regenerative or inductive currents of the motor. As Figure 7. Waveforms Associated with discussed earlier. due to structural differences the igbt does Anti-Parallel Diode Turn-off not have a parasitic diode like that found in a MOSFET. Designers found that the diode within the MOSFET was, in fact, a parasitic, i.e., not optimized i n the design process, and its performance was poor for use as a current recovery device APPLICATION OF IGBTs: due to slow switching speed. To overcome the lack of PULSE WIDTH MODULATED INDUCTION performance, an optimized anti-parallel diode was used MOTOR DRIVE APPLICATION across the MOSFET source-to-drain. Placing a packaged diode external to the MOSFET itself created performance operated, pulse-width modul problems due to the switching delays resulting from the motor drives are an application well suited for IGBTs. In this parasitics introduced by the packages. The optimal setup is to application, as shown in Figure 8, IGBTs are used as the have the diode copackaged with the device. A specific line of power switch to PWM the voltage supplied to a motor to control its speed GBTs has been created by Motorola to address this issue These devices work very well in applications where energy is Depending on the application, the igBT may be required to recovered to the source and are favored by motor control operate from a full-wave rectified line. This can require devices to have six hundred volt ratings for 230 VAC line voltage inputs, and twelve hundred volt ratings for 575 VAC Like the switching device itself, the anti-parallel diode volt line inputs. IGBTs that block high voltage offer fast should exhibit low leakage current, low forward voltage dro and fast switching speed. As shown in Figure 7, the diode switching and low conduction losses, and allow for the design forward drop multiplied by the average current it passes is the of efficient, high frequency drives of this type Devices used in total conduction loss produced. In addition, large reverse motor drive applications must be robust and capable of recovery currents can escalate switching losses. A detailed withstanding faults long enough for a protection scheme to be activated Short circuit rated devices offer safe reliable motor planation of reverse Appendix. A secondary effect caused by large reverse drive operation recovery currents is generated EMI at both the switching CONCLUSION frequency and the frequency of the resulting ringing aveform. This EMI requires additional filtering to be The IGBT is a one of several options for designers to choose designed into the circuit By copackaging parts, the parasitic from for power control in switching applications. The features inductances that contribute to the ringing are greatly reduced Also, copackaged products can be used in designs to reduce ease of drive and relatively fast switching speeds makes it a power dissipation and increase design efficiency technology of choice for moderate speed, high voltage applications. New generations of devices will reduce the on-resistance, increase speed and include levels of integration that simplify protection schemes and device drive requirements. The reliability and performance advantages of IGB Ts are value added traits that offer circuit designers energy efficient options at reduced costs MOTOROLA

6 MOTOROLA Second, the voltage developed across Re results in a similar division of voltage across Rshorting and VBE of the NPN transistor. The NPN will be less likely to attain a VBE high enough to turn the device on and cause a latch–up situation. The two situations described work together to protect the device from catastrophic failure. The protection period is specified with the device ratings, allowing circuit designers the time needed to detect a fault and shut off the device. The introduction of the series resistance Re also results in additional power loss in the device by slightly elevating the forward drop of the device. However, the magnitude of short circuit current is large enough to require a very low Re value. The additional conduction loss of the device due to the presence of Re is not excessive when comparing a short circuit rated IGBT to a non–short circuit rated device. Anti–Parallel Diode When using IGBT’s for motor control, designers have to place a diode in anti–parallel across the device in order to handle the regenerative or inductive currents of the motor. As discussed earlier, due to structural differences the IGBT does not have a parasitic diode like that found in a MOSFET. Designers found that the diode within the MOSFET was, in fact, a parasitic, i.e., not optimized in the design process, and its performance was poor for use as a current recovery device due to slow switching speed. To overcome the lack of performance, an optimized anti–parallel diode was used across the MOSFET source–to–drain. Placing a packaged diode external to the MOSFET itself created performance problems due to the switching delays resulting from the parasitics introduced by the packages. The optimal setup is to have the diode copackaged with the device. A specific line of IGBTs has been created by Motorola to address this issue. These devices work very well in applications where energy is recovered to the source and are favored by motor control designers. Like the switching device itself, the anti–parallel diode should exhibit low leakage current, low forward voltage drop and fast switching speed. As shown in Figure 7, the diode forward drop multiplied by the average current it passes is the total conduction loss produced. In addition, large reverse recovery currents can escalate switching losses. A detailed explanation of reverse recovery can be found in the Appendix. A secondary effect caused by large reverse recovery currents is generated EMI at both the switching frequency and the frequency of the resulting ringing waveform. This EMI requires additional filtering to be designed into the circuit. By copackaging parts, the parasitic inductances that contribute to the ringing are greatly reduced. Also, copackaged products can be used in designs to reduce power dissipation and increase design efficiency. Figure 7. Waveforms Associated with Anti–Parallel Diode Turn–off IRM(rec) TIME TIME TIME POWER VOLTAGE CURRENT IIGBT IDIODE Vf APPLICATION OF IGBTs: PULSE WIDTH MODULATED INDUCTION MOTOR DRIVE APPLICATION Line–operated, pulse–width modulated, variable–speed motor drives are an application well suited for IGBTs. In this application, as shown in Figure 8, IGBTs are used as the power switch to PWM the voltage supplied to a motor to control its speed. Depending on the application, the IGBT may be required to operate from a full–wave rectified line. This can require devices to have six hundred volt ratings for 230 VAC line voltage inputs, and twelve hundred volt ratings for 575 VAC volt line inputs. IGBTs that block high voltage offer fast switching and low conduction losses, and allow for the design of efficient, high frequency drives of this type. Devices used in motor drive applications must be robust and capable of withstanding faults long enough for a protection scheme to be activated. Short circuit rated devices offer safe, reliable motor drive operation. CONCLUSION The IGBT is a one of several options for designers to choose from for power control in switching applications. The features of the IGBT such as high voltage capability, low on–resistance, ease of drive and relatively fast switching speeds makes it a technology of choice for moderate speed, high voltage applications. New generations of devices will reduce the on–resistance, increase speed and include levels of integration that simplify protection schemes and device drive requirements. The reliability and performance advantages of IGBTs are value added traits that offer circuit designers energy efficient options at reduced costs.