Five solutions to buck circuit electromagnetic interference

Do you know that when a switching power supply is working, it will generate electromagnetic radiation?

If the radiation is too large, the system will not be able to work stably.

Is there any way to reduce the electromagnetic interference generated by the switching power supply?

Today we will look at five solutions to Buck circuit electromagnetic interference found online.

1. Shorten the switch current loop

When Q1 is turned on, the current flows from CIN->Q1->L1->COUT. When Q1 is closed, the current loop is L1->COUT->D1.

Regardless of whether Q1 is turned on or off, the current flowing through L1 and COUT is a continuous current , and the current flowing through CIN, Q1, and D1 is a switching current . The switching current will generate a glitch voltage on the parasitic inductance and radiate electromagnetic waves to the outside.

 When di/dt remains unchanged (V=L*di/dt), the parasitic parameters of the switching circuit loop can be reduced by shortening the current loop of CIN, Q1, and D1, effectively reducing the electromagnetic radiation generated by the system.

2. Reduce the current change rate

When the conditions remain unchanged, the amount of current change is unchanged, so the value of di/dt can only be reduced by extending the current change time .

The diode has a relatively slow switching speed and can be used to reduce the rate of change of the D1 loop current.

13. Suppress high frequency noise

Schottky itself has parasitic capacitance and parasitic inductance in the loop. When the switch current flows through D1, the parasitic inductance and capacitance will produce ringing. If the oscillation frequency exceeds 30MHz, it will enter the radiation test frequency band. At this time, we can filter out high-frequency signals by connecting magnetic beads in series at D1 to reduce the external electromagnetic radiation energy of high-frequency signals.

 But it should be noted here that the series connection of the magnetic beads will produce a large negative spike voltage.

4. Add RC snubber circuit

Connecting an RC absorption circuit in parallel between the chip SW and GND can absorb the glitch voltage generated by parasitic parameters, change the resonant frequency, and suppress electromagnetic radiation.

Usually they can be used in combination, with a magnetic bead in series with D1 and an RC circuit added , the suppression effect will be better. The magnetic bead is generally selected with an AC impedance of 60-80R. The smaller the impedance, the smaller the loss. The RC resistance value is selected to be around 10R, and the capacitance is within 1nF.

 5. Add common mode inductor

Generally speaking, the power cord at the output end is relatively long and may become an antenna that emits electromagnetic waves. We can filter out the common-mode signal and suppress excessive radiation by connecting a common-mode inductor in series at the system output end.

 However, please note that common-mode inductors are not suitable for small-volume, low-cost solutions.

Above we can use 5 solutions to BUCK circuit electromagnetic interference. Well, this is the end of this issue. Thank you for reading!