Interference interference on the switching power supply solutions
Time:2013-03-21
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EMI interference on the switching power supply solutions for general interference from external radiation, lightning, or network jitter, and other related component of the power switch devices such as rectifier diodes, high frequency transformer, power switch and other interference from the external environment switching power supply is the main source of EMI interference expression. First: The radiation transmission channel interference
(1) switching power supply, can constitute a source of radiation interference components and wires are the antenna can be assumed to use electric dipole and magnetic dipole theory analysis; diodes, capacitors, power switch can be assumed to be electric dipole, induction coil can be assumed to be magnetic dipole;
(2) no shield, the electric dipole, magnetic dipole, the resulting electromagnetic wave transmission channel for the air (which can be assumed to be free space);
(3) shield, the shield into account the gaps and holes, in accordance with the leakage field of mathematical model analysis and processing. Second: the transmission channel is conducted interference
(1) capacitive coupling
(2) inductive coupling
(3) resistance coupling
a. resistance generated by the public power transmission coupling resistance
b. public ground conductive coupling impedance of the resistance
c. public transmission line coupling impedance of the resistance
The following are sources of EMI interference suppression schemes related to:
1. High-frequency transformer shielding
High-frequency transformer to prevent leakage magnetic interference on the surrounding circuitry, shielding can be used to bring high-frequency transformer of the leakage magnetic field shielding. Shielded with copper foil production generally, around a week in the external transformer and grounding, shielding leakage magnetic field with a relative is a short loop, thus inhibiting the leakage of magnetic leakage field larger.
High frequency transformer, core and winding between the relative displacement occurs between, leading to produce high-frequency transformer noise at work (whistle, vibration). Vortex flowmeter in order to prevent the noise, the need for transformers to reinforce measures:
(1) the core with epoxy resin (such as EE, EI core) for the three adhesive contact surface, inhibiting the production of relative displacement;
(2) The "glass beads" (Glass beads) adhesive bonded core, better.
EMI suppression in terms of switching power supply separate from 9 major measures:
(1) reasonable PCB Design
(2) the reasonable application of varistors to reduce the surge voltage
(3) reduce the dv / dt and di / dt (lower peak and slow down its slope)
(4) The damping network to suppress overshoot
(5) using rational design of power line filters
(6) with soft recovery characteristics of the diode to reduce the high frequency EMI
(7) active power factor correction, and other harmonic correction technique
(8) effective shielding measures
(9) reasonable ground handling
