Method and controller for controlling output current of switch electric power

Abstract

The invention discloses a method for controlling the output current of a switching power supply and a controller for realizing the method, belonging to the switching power supply field. The method comprises the following steps: the output voltage of the switching power supply or an equivalent signal thereof is sampled at the primary side of a transformer, the scaling signal of the output voltage is obtained, meanwhile, the current or an equivalent signal of a primary coil is sampled, the square processing is carried out after the scaling signal of current of the primary coil, and a current square signal to be compared is obtained; the scaling signal of the output voltage is compared with the current square signal to be compared to obtain a current enabling control signal, if the current square signal to be compared is less than or equal to the scaling signal of the output voltage, the current enabling control signal enables the power switch not to be turned off, otherwise, the power switch is turned off through the current enabling control signal. The controller comprises a multiplier or squaring circuit for performing square processing to the current of the primary coil, and a comparator for performing comparison. The invention has the advantages of simple structure and low cost.

Description

technical field [0001] The invention belongs to the field of switching power supplies, in particular to a method for controlling the output current of a switching power supply and a controller for realizing the method. Background technique [0002] With the improvement of switching power supply efficiency, the reduction of volume and cost, switching power supply is more and more widely used in electronic products. In practical applications, it is not only necessary to control the output voltage of the switching power supply, but also often requires controlling the output current of the switching power supply, such as controlling a constant output current to drive LEDs. [0003] At present, in the application of flyback switching power supply (flyback AC-DC converter), there are two common control methods for constant output current. The most common method is to use the feedback signal of the output current on the secondary side of the transformer (the secondary side of the ...

AI Technical Summary

Problems solved by technology

[0015] Due to the influence of operating temperature, operating power and other conditions, the primary coil current I P The value of is difficult to keep constant, and when mass production, due to the influence of the manufacturing process, there are inconsistencies in the discrete components of the system (such as sense resistors), so that the primary coil current I P It is difficult to keep consistent, which requires an increase in the compensation circuit for the primary coil current I P Compensate to make it consistent

Therefore, the frequency of the modulation system is controlled using the feedback signal of the output voltage, and at the same time the primary coil current I P The method of keeping constant makes the control circuit complex and increases the cost of chips and systems

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