About the basic theory of paralleling transistors and MOSFETs: Firstly, transistors have a negative exponential temperature value, that is to say, when the temperature of the transistor itself rises, the on-resistance will become smaller. Secondly, MOSFETs have a positive exponential temperature value in contrast to transistors, which means that when the temperature rises, the on-resistance will slowly increase.
Compared to transistors, MOSFETs are actually more suitable for equalizing the current in parallel power circuits. So when the current in the power supply circuit is relatively large, we generally recommend the use of parallel MOSFETs for shunt. When we choose MOSFETs to equalize the current, and in one of the way the current exceeds the other way the MOSFET current, the current of the MOSFET caused by the heat of the large MOSFETs, which will result in the on-off resistance becomes larger, reducing the lowering of the current; MOSFETs based on the difference in the current to constantly adjust, and finally realize the current balance between the two MOSFETs.
One of the things we need to note: transistors can also be connected in parallel to complete the flow of high-current goods, but then you also need to be based on the base of the series drive resistor to deal with the current balance of each parallel transistor in the middle of the problem.
Common problems of transistor parallel connection:
(1), the gate of each transistor can not be directly connected to each drive resistor in series to carry out the drive, in order to avoid oscillation.
(2), to manipulate each transistor (MOSFET) open time and close time to maintain consistency, because if not consistent, the first open the pipeline or close the pipeline will be destroyed because of excessive current penetration.
(3), and finally, we would like to be able to the source of each transistor in series with an equalizing resistor, of course, it is not necessary to do, just in case.
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Post time: Jul-05-2024
