Agilent 5991-4543EN IGBT Sense Emitter Current Measurement Using the B1505A - Application Note c20141027 [ free download

File name 5991-4543EN IGBT Sense Emitter Current Measurement Using the Agilent B1505A - Application Note c2014

Keysight Technologies IGBT Sense Emitter Current Measurement Using the Keysight B1505A Application Note Introduction Insulated gate bipolar transistors (IGBTs) have become the key energy-saving devices for use in switch- ing applications such as switching convertors and invertors. However, IGBTs used in circuits that drive inductive loads (such as induction motors or igniters) risk damage due to excessive currents caused by a motor jamming or a short in the igniter circuit. To detect overcurrents and prevent damage, some IGBTs have a second emitter terminal known as a sense emitter. The ratio of sense emitter current to emitter current is very small (one part to several thousand or several tens of thousands). The sense emitter current is monitored using a shunt resistor; the voltage across the shunt resistor in-turn feeds into an overcurrent protection circuit. When the overcurrent detector circuit senses the voltage exceeding a speciied limit, it turns off the IGBT (Figure 1). Power devices such as IGBTs consist of tens of thousands of small cells con- nected in parallel, and the sense emitter uses some of these cells. Since the C individual IGBT cells vary in size and characteristics, the senseemitter current to emitter current ratio also varies. In addition, the sense emitter current to emitter current ratio depends on the emitter current level. This is due to the G effects of both the voltage across the shunt resistor and the residual resis- tances inherent in each device. Overcurrent SE E For these reasons, it is necessary to measure the sense emitter to emitter current ratio under actual use conditions to determine the correct overcurrent Detector limit. Rs The Keysight Technologies, Inc. B1505A Power Device Analyzer/Curve Tracer has a wide measurement rage (1500 A/10 kV), making it a powerful tool to characterize IGBTs. It also has a modular architecture that allows you to have multiple measurement channels, which enables the simultaneous measure- ment of both the sense emitter current and the emitter current. FIGURE 1. Overcurrent protection using sense emitter 2 The basic measurement resource of the B1505A is the SMU (Source Measure Unit). It integrates four measurement functions (voltage sourcing, current sourcing, current measurement and voltage measurement) into a single module. An SMU can function as a voltage meter by putting it into force current/measure voltage mode with a zero current output. Similarly, it can act as a current meter by putting it into force voltage/measure current mode with a