A Frequency Shaking Control System of Primary Side Feedback AC-DC Switching Power Supply

Abstract

The invention discloses a jitter frequency control system of an original-side feedback AC-DC switching power supply. The jitter frequency control system comprises a control chip, a transformer and an NMOS (N-channel Metal Oxide Semiconductor) tube, wherein the control chip further comprises a frequency jitter unit which is connected with a constant-current frequency control unit in the control chip; the frequency jitter unit is provided with a jitter frequency control current generation circuit; the jitter frequency control current generation circuit comprises an oscillator, a frequency divider, a plurality of groups of current sources and switches; and the constant-current frequency control unit comprises a charging current source, a discharging current source, a first switch, a second switch, a phase inverter, a capacitor and a comparator. According to the jitter frequency control system of the original-side feedback AC-DC switching power supply, proper frequency jitter is introduced to the control chip and the work frequency of the jitter frequency control system jitters periodically within a certain range, so that the electromagnetic interference energy is dispersed in the frequency section within the whole jitter frequency range but not focused on some frequency point; and therefore, the jitter frequency control system has low electromagnetic interference, and the constant-current characteristics of the jitter frequency control system are not influenced by the frequency jitter.

Description

technical field [0001] The invention relates to the technical field of switching power supplies, in particular to a frequency shaking control system for primary-side feedback AC-DC switching power supplies. Background technique [0002] The primary-side feedback AC-DC control technology is a new type of AC-DC control technology developed in the last 10 years. Compared with the traditional secondary-side feedback switching power supply structure, its biggest advantage is that it eliminates the need for isolation chips and isolation A group of components that work together on a chip, which saves space on the circuit board, reduces cost and increases system reliability. The primary-side feedback DC power supply has a large market share in applications with high cost pressure such as mobile phone chargers, and applications with high volume requirements such as LED drive power supplies. [0003] attached figure 1 A structural block diagram of a primary-side feedback AC-DC power...

AI Technical Summary

Problems solved by technology

[0005] When the system works in constant current mode, when the input voltage and output voltage are fixed, for the same system parameters, the secondary conduction time Tons=(Ips×Ls) / (Vout+Vz)=Ipp×(NS / NP )×Ls / (Vout+Vz)=(Vcs / R3)×(NS / NP)×Ls / (Vout+Vz), since Vcs is the current limiting threshold inside the chip, it is a fixed value, and other parameters are also fixed value, so the secondary conduction time Tons is a fixed value, so the period T=K×Tons is a fixed value, that is, when the system works in constant current mode, its operating frequency is fixed, so the energy of EMI is concentrated in this The operating frequency and its Nth harmonics make the EMI very large, and it is difficult to meet the EMI requirements of the charger and LED drive system

Images