Thread Content
During circuit design, it is common for field-effect transistors to overheat, and overheating indicates that they are operating incorrectly. To prevent the heat generated by the field-effect transistor from compromising the operation of the entire device, it is necessary to identify the cause of this heating before restarting it. There are mainly these situations in which field-effect transistors generate heat. I. Circuit Design: Ensure that the field-effect transistor operates in a linear mode, rather than in a switching mode. If an N-MOS is used as a switch, the gate voltage needs to be several volts higher than the supply voltage in order to achieve full conduction; the opposite is true for P-MOS. If it is not fully opened, the voltage drop becomes too large, which increases power consumption; the equivalent DC impedance is high, the voltage drop increases, and as a result U*I also increases. Losses lead to heating. II. Operating frequency: This is a common phenomenon during the debugging process, and the reduction in frequency is mainly caused by two factors. The ratio of the input voltage to the load voltage is low, resulting in high system interference. For the former, be careful not to set the load voltage too high, as although a higher load voltage results in higher efficiency. For the latter, the following approaches can be tried: 1. Set the current value to be lower. 2. Ensure clean wiring, especially along the critical sense path. 3. Choose inductors with smaller values or those that feature a closed magnetic circuit. 4. Add an RC low-pass filter; although this has some negative effects due to issues with C’s consistency and significant variations, it should be sufficient for lighting applications. Reducing the frequency in any case brings only disadvantages, no benefits at all; therefore it must be resolved. Sometimes, the frequency of field-effect transistors is too high; this is mainly due to the excessive focus on minimizing size, which leads to an increase in frequency and consequently higher losses in the field-effect transistors, resulting in more heat generation. III. Heat dissipation design: The circuit board does not have an adequate heat dissipation design; the current level is too high. The rated current value of the field-effect transistor can generally only be achieved with proper heat dissipation. Therefore, if the ID is smaller than the current, severe heating may occur, requiring sufficient auxiliary heat sinks.