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Will be clean, not soiled or stained. See all 2 brand new listings. Buy It Now. Add to cart. A weak driver circuit often slows down the switch. However, under certain circumstances, such as utilizing zero voltage switching ZVS of a resonant converter, a weak gate driver circuit slows down the switching. When this happens, one would expect the EMC performance becomes worse. The trend from through-hole packages to low-cost surface mounted device SMD applications is marked by the improvement of chip technologies.
There are cases in which through-hole packages such as TO devices were selected for high-voltage high-power DC-DC converters. There are three main reasons for doing so.
First, a through-hole package is a lot cheaper than an SMD type. Second, it makes thermal design a lot easier, as one can put heat sink directly to the devices. Third, it frees the printed circuit board area horizontally, though it does increase the height of the board. However, a through-hole package is certainly not good for EMC. In fact, it is extremely difficult to contain the noise that is associated with through-hole devices and design engineers often must deal with the consequences of selecting through-hole devices as the main converter switches.
To start with, the long lead of the package easily introduces an extra 10 nH inductance. This parasitic inductance, together with the parasitic capacitance of the device, causes over-shoot and ringing when the device is switched at a fast speed.
As can be seen in Figure 9, the over-shoot and ringing are reduced by reducing the parasitic inductance. Figure 8: Over-shoot and ringing observed from both simulation and measurement.
Figure 9: Reducing the inductance in the loop reduces the over-shoot and ringing. The fact that a TO device can be directly mounted with a heatsink could also cause EMC problems depending on the size of the heat sink, the connections, and other factors [11]. Each device that stands on the board acts like a little antenna. If the board heat sink is not bonded correctly, each device could also increase the radiation emissions.
The layout of the devices can also pose challenges. If the through-hole devices are located near the edge of the PCB as they often are for better thermal performance , they tend to radiate a lot more than when they are located in the middle of the PCB. If you think selecting through-hole devices would make your bill of materials cost look better, then think again.
The total number of the main power stage switching devices per DC-DC converter is not big. If an SMD package cannot achieve the same level of thermal performance compared with a through-hole package, one could always use two devices in parallel to share the current. Doubling the number of devices also means doubling the cost. But the fact that SMD packages have much better EMC performance could mean that one or two filter components can be omitted from the converter filter design.
For HV high-power converters, magnetic components such as common mode chokes CMC are bulky, heavy, and expensive. Adding one or two of these to the design will significantly increase the weight and the cost. To make matters worse, there is often no space to put a CMC due to the compact design of the converter.
We would like to mention the impact of temperature and deadtime because we were involved in a case where significant low-frequency noise kHz MHz was observed in the conducted emissions originating from a HV-LV DC-DC converter.
The DC link capacitor selection and design were good where expensive high-voltage, high-volume film capacitors were selected, and the DC link bus bar meant that minimum impedance between the DC link and the switches was achieved. But the fact that the noise was at low frequency and in differential-mode suggested that the DC link was not good enough.
It turned out that the deadtime of the converter was set too small. The switching devices in this case were IGBTs and tail current was not accounted for when setting up the deadtime [12]. A short deadtime can lead to shoot through of a converter. Shoot through will cause a very high, short-duration current to be drawn from the DC link.
This is most likely to happen when one of the devices has a long tail current. The tricky thing here is that tail current time is also related to temperature. In this case, the emission problem only got worse after the converter had been running for a while, which made the troubleshooting process to identify the problem a challenging task.
Such equipment should benefit from reduced warranty costs and financial risks, whilst improving uptime, competitiveness and profitability. Find your EMC Standards quickly and easily Search ». What EMC issue do you want to learn about today? Your Name.
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