Regarding module power supplies, their ultra-high power density has been praised by designers. However, while achieving ultra-high power, the shortcomings of poor heat dissipation are also exposed. Although designers can improve some specific designs, they are not suitable for every design.
This article will use the example as a benchmark to analyze the module power dissipation problem in a design. The module in this paper adopts 100W, Vin24VVout5V, adopts single-tube forward circuit, uses UC3843B chip control, does not use active clamp and synchronous rectification, and the working frequency is 300KHZ.
After running, it is found that it can't actually work at 100W for a long time. If long-term work will cause the MOSFET or the secondary diode to be thermally broken down, what kind of method should it be used to make it work below 100W for a long time?
The following two methods have been tested:
1. Add MOSFET: Using multiple MOSFETs in parallel and changing the drive, the 3843B can't drive multiple MOSFETs, but the effect is not good, not only increases the cost, but also solves the problem. Moreover, multiple MOSFETs cannot be turned on at the same time, there will always be a first time, so there will always be a MOSFET breakdown.
2. Add secondary diodes and use multiple parallels. The effect is similar to that of scheme 1, which is not ideal.
Let's talk about the solution. Generally speaking, the heat dissipation performance of the device is related to the thermal conductivity of the insulating material, the pressing force, the thermal conductivity of the shell, the area, and the airflow conditions outside the shell, which can be improved from these points.
Some people may have thought of synchronous rectification technology, but even with the use of synchronous rectification technology, the efficiency is not likely to increase. The design has reached 90% efficiency, most of which is 89%. The efficiency of synchronous rectification will not be much higher, so there is still a lot of loss, and heat dissipation is still a problem.
Or, from the perspective of driving waveforms, if the driving capability is insufficient, it is considered to add a push-pull driving circuit. Or you can reduce the frequency of the power supply to reduce switching losses. Another point is the leakage inductance of the transformer. If the leakage inductance is large, then the power lost will be a lot, and the heat will not be small. The power supply is overheated, which is easy to cause thermal breakdown (unrecoverable). 100W does not add a heat sink, and heat dissipation is definitely a big problem.
This article from a variety of perspectives, a comprehensive analysis of the heat dissipation of the module power supply, through the introduction of examples to facilitate everyone to understand. I hope that everyone can find the answer they want in the analysis given in this article.
Dongguan Jili Electronic Technology Co., Ltd. , https://www.ocasheet.com