Control circuit and control method of vehicle-mounted charger DC-DC system

Abstract

The invention discloses a control circuit and a control method of a vehicle-mounted charger DC-DC system. The control method comprises the following steps: using a light-load comparator, a line loss compensation comparator and a peak current limit comparator, connecting negative input ends of the three comparators with an output signal of an error amplifier inside the DC-DC system, and connecting the positive input ends with voltages with different values, which are formed on serially-connected polysilicon resistors by positive temperature coefficient current output by a positive temperature coefficient current generating module; outputting light-load high-efficiency mode, line loss voltage compensation and peak current limit control signals at an output end. Through the control method, output current can be monitored, light-load high-efficiency mode, line loss compensation and peak current limit threshold values are determined, and the threshold values do not change along with the temperature; the control circuit is simple in functional principle and easy in process realization, can reduce the cost of a chip, is high in reliability, and is applicable to other DC-DC systems needing such functions.

Description

technical field [0001] The invention relates to a DC-DC system applied to a car charger, and realizes light-load high-efficiency, line The technology of loss voltage compensation and peak current limit control belongs to the technical field of DC-DC converter. Background technique [0002] With the vigorous development of portable electronic products, DC-DC converters have been widely used in electronic products, the market prospect is very broad, and the requirements for their performance are getting higher and higher, such as input and output voltage range, output maximum current , power conversion efficiency, operating frequency and power volume. [0003] On-board charger is a relatively new application field of DC-DC. This kind of DC-DC belongs to the BUCK type voltage converter, which has a high voltage application range and requires high light-load conversion efficiency. The cable of the battery is long, and there will be a large voltage loss when outputting a large ...

AI Technical Summary

Problems solved by technology

Second, in the constant current charging stage, the system may continuously output a charging current of 1A-3A for different types of loads

while in figure 1 It can be seen that there is a line resistance of about Rcable=150mΩ between the DC-DC output terminal and the actual load. If the output current is 2A, the voltage drop on this resistance will reach 300mV, which will affect the charged system. Safety is affected, so the car charger DC-DC needs to add line voltage loss compensation function

Third, if the system output is mistakenly short-circuited to ground, it will cause a large current in the inductor. Therefore, it is necessary to add a peak current limiting function to prevent damage to the chip due to large current conduction.

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