Collapse effect of field-effect transistors in power applications 3

3. Analysis of Collapse Mode

When the field-effect transistor enters the breakdown effect, the Drain and Source voltages will be embedded in its breakdown voltage, and the current will generate reverse operation current through parasitic diodes. The collapse phenomenon measured in a typical switch mode power supply circuit is shown in Figure 2. From the figure, it can be seen that the voltage (CH3) of Drain and Source is clamped at 1KV, and the reverse current (CH4) can be clearly observed.

The evaluation method of UIS is a very useful approach for analyzing crash phenomena. In Figure 3, the UIS safety work area can be divided into three major areas: (1) the area above the 25 ℃ line or to the right in the figure, (2) the area below the 150 ℃ line or to the left in the figure, and (3) the area between (1) and (2). Among them, (1) it can be clearly understood that the component is operating outside the rated working range, and (2) it is within the rated working range. As for the area definition of (3), we need to obtain the initial UIS joint surface temperature of this component to determine its working ability. We will provide an example later on how to calculate the temperature of this joint surface. transistor

The evaluation method of UIS is not limited to being applied to a single pulse, and can also be analyzed for the application of continuous pulses using the Super position theorem. In a continuous pulse, each pulse can be regarded as a single pulse in the UIS application. Usually, the last continuous pulse occurs when the junction surface temperature is at its highest. And this is also the most demanding situation. If we can prove that the result of the last continuous pulse of the field-effect transistor can be within the safe working area of UIS, then the pulses that have passed before must also be within the safe working area of UIS. Because the previous bonding surface temperature must be lower than the bonding surface temperature of the last continuous pulse.transistor