EMI Solutions for DC/DC Converters
Electromagnetic interference is a problem that every design engineer has to confront. There are various mechanisms that can cause electromagnetic noise in electronic circuits and devices. A typical example is when a switching power supply is used in an automotive application.
Since power supply is essentially a circuit that provides only direct current, it should be unlikely to become a cause or pathway for electromagnetic noise. However, because of the way switching power supply operates, it actually becomes a cause for EMI issues during radiated and conducted emission performance.
This cause can be due to the following reasons:
- Even though the voltage seems stable, its electric current may contain a large amount of high-frequency current flowing to electric circuit
- Since the power line is a shared wire in the circuit, noise is circulated and can affect the entire circuit
- The grounding in particular is often shared throughout the equipment and provides a common voltage and sometimes it is challenging to separate this.
- Since it is the energy source for the equipment, the noise energy also becomes significant
Typical examples where the power supply causes noise are contact noise and switching power supply. The contact noise is a type of noise that occurs at a point of contact when the source current is turned on /off with a switch (it is particularly strong when turned off), which has the same meaning as the switching surge. Since a very high voltage occurs and the flow of transient but high-frequency current spreads radio waves, it can cause a circuit failure or can lead malfunction of the surrounding electronic devices.
Switching power supply is a circuit that changes voltage and frequency and it is this fast switching that can generate high-frequency energy which causes noise interference when it leaks to the outside world. This is an example Murata can offer as a solution to mitigate the potential EMI issues as shown in the presentation.
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But do not assume maximum interference occurs at maximum load. Some time ago I worked with a Class 4 Argon Ion Laser and the interference went up substantially when the laser power was reduced. Probably different regulations then, but worth considering in any design.
Even test for failure conditions such as with no load.