阅读说明：本技术 一种电流控制电路 (Current control circuit ) 是由 张从峰 杨宏 于 2020-04-22 设计创作，主要内容包括：一种电流控制电路,电流检测电阻的一端连接到开关管,电流检测电阻的另一端连接到电感,开关管导通的时候,开关管、电流检测电阻、电感流过相同的电流,开关管关断的时候,开关管流过的电流为0,电流检测电阻、电感流过相同的电流；电流检测电阻上得到的电压信号进入峰值电流控制器,与峰值电流给定信号比较,当所述电流检测电阻上得到的电压信号达到峰值电流给定信号时,峰值电流控制器输出关断信号,使得开关管关断；电流检测电阻上得到的电压信号进入到平均电流控制器,平均电流控制器输出峰值电流给定信号。用一个电流检测电阻,就可以同时实现对输出电流和开关管峰值电流的控制。(A current control circuit, one end of a current detection resistor is connected to a switching tube, the other end of the current detection resistor is connected to an inductor, when the switching tube is conducted, the same current flows through the switching tube, the current detection resistor and the inductor, when the switching tube is turned off, the current flowing through the switching tube is 0, and the same current flows through the current detection resistor and the inductor; the voltage signal obtained from the current detection resistor enters a peak current controller, is compared with a peak current given signal, and when the voltage signal obtained from the current detection resistor reaches the peak current given signal, the peak current controller outputs a turn-off signal to turn off the switching tube; the voltage signal obtained from the current detection resistor enters the average current controller, and the average current controller outputs a peak current given signal. The control of the output current and the peak current of the switching tube can be realized simultaneously by using one current detection resistor.)

1. A current control circuit is characterized in that one end of a current detection resistor is connected to a switching tube, the other end of the current detection resistor is connected to an inductor, and when the switching tube is conducted, the same current flows through the switching tube, the current detection resistor and the inductor; when the switch tube is turned off, the current flowing through the switch tube is 0, and the same current flows through the current detection resistor and the inductor.

2. A current control circuit as claimed in claim 1, wherein the voltage signal obtained at the current sensing resistor is fed to the peak current controller, and compared with the peak current set signal, when the voltage signal obtained at the current sensing resistor reaches the peak current set signal, the peak current controller outputs a turn-off signal to turn off the switching tube.

3. A current control circuit as claimed in claim 1 or 2, wherein the voltage signal obtained at the current sensing resistor is fed to the average current controller; and after the voltage signal obtained on the current detection resistor is subjected to low-pass filtering and amplification, an error signal obtained by subtracting the average current given signal enters an error regulator, and the output of the error regulator is the peak current given signal.

4. A current control circuit as claimed in claim 1 or 2, wherein when the voltage signal developed across the current sensing resistor falls to 0, the peak current controller outputs a turn-on signal to turn on the switching tube.

Technical Field

The invention relates to the field of DC-DC converters, in particular to a current control circuit.

Background

In power management of DC-DC power supplies, current sensing is used to perform two basic circuit functions. The first is to measure the magnitude of the current flowing in the circuit, and compare it with a given current value, thereby obtaining information on the increase or decrease of a control signal such as a pulse width; the second is to measure whether the current flowing in the circuit has reached a limit value, and if so, to trigger a protection command, which shuts down the device if necessary.

There are various methods for current detection, and a resistance measurement method, a current transformer measurement method, and a hall effect element measurement method, which are commonly used in power supplies, have advantages and disadvantages, respectively.

The current measurement by using a resistor is a direct method, a current detection resistor and the current to be measured are arranged in a circuit, a small part of electric energy is converted into heat by the current flowing through the resistor, and a voltage signal is generated in the energy conversion process. The method has the advantages of simplicity, easiness in use, good linearity, high cost performance, stable temperature coefficient and the defects of large power loss, weak signals and no electric isolation function.

The method of current transformer measurement requires the use of a varying current, such as an alternating current, transient or switched current, to generate a varying magnetic field magnetically coupled to the secondary winding, and the secondary measurement voltage can be scaled according to the turns ratio between the primary and secondary windings. The method has the advantages of isolation from line voltage, small power loss and higher price than a resistance measurement method.

The Hall effect element method has the advantages that the method can measure large current, can realize the electrical isolation function and has small power loss; the method has the disadvantages of needing to compensate for nonlinear temperature drift, having limited bandwidth, being susceptible to external magnetic fields, being sensitive to ESD and having high cost.

The characteristics of the current transformer are between those of the resistor and the hall element, and the current transformer is the most used current detection method. The common use of DC-DC converters is pulse DC mutual inductors, which work in a unidirectional magnetization mode similar to a forward converter. When the primary current flows, the magnetic field in the magnetic core is gradually increased; when the primary switch tube is turned off, the primary current becomes 0, and the secondary magnetic reset circuit starts to work, so that the magnetic core is reset to the residual magnetic induction intensity Br.

The inductor in a DC-DC converter operates in three states: current continuous state, current discontinuous state, current critical continuous state. In the critical continuous state of the current, the average value of the inductive current is half of the peak value of the inductive current; in the current continuous state, the average value of the inductive current is larger than half of the peak value of the inductive current; in the current interruption state, the average value of the inductor current is less than half of the peak value of the inductor current.

The DC-DC converter is generally divided into two output modes of a constant voltage output and a constant current output. In a constant voltage output mode, obtaining output feedback voltage by detecting output voltage, entering an output voltage regulator, comparing the output feedback voltage with output given voltage to obtain error voltage, entering a pulse width modulator, and outputting a PWM signal; in a constant current output mode, output current feedback voltage is obtained by detecting output current, the output current feedback voltage enters an output current regulator, the output current regulator is compared with an output given current signal, error voltage is obtained, the error voltage enters a pulse width modulator, and a PWM signal is output.

In general, in order to limit the current of the switching tube, the current of the switching tube needs to be detected; thus, for a DC-DC converter operating in constant current output mode, two current detectors are usually required, one for detecting the output current and one for detecting the current of the switching tube.

Disclosure of Invention

The invention provides a current control circuit.

One end of the current detection resistor is connected to the switching tube, the other end of the current detection resistor is connected to the inductor, and when the switching tube is conducted, the same current flows through the switching tube, the current detection resistor and the inductor; when the switch tube is turned off, the current flowing through the switch tube is 0, and the same current flows through the current detection resistor and the inductor.

And when the voltage signal obtained from the current detection resistor reaches the peak current given signal, the peak current controller outputs a turn-off signal to turn off the switching tube.

Voltage signals obtained from the current detection resistor enter an average current controller; and after the voltage signal obtained on the current detection resistor is subjected to low-pass filtering and amplification, an error signal obtained by subtracting the average current given signal enters an error regulator, and the output of the error regulator is the peak current given signal.

When the voltage signal obtained on the current detection resistor is reduced to 0, the peak current controller outputs a switching-on signal to switch on the switching tube.

The current detection resistor is equal to the average current of the inductor, and if the average current of the inductor is equal to the output current of the DC-DC converter, the control of the output current and the peak current of the switching tube can be realized simultaneously by only one current detection resistor.

Drawings

Fig. 1 is a circuit schematic of a current control circuit.

Detailed Description

Embodiments of the present invention are described in detail below with reference to the accompanying drawings.