CN104882856A - High-precision over-current detection circuit - Google Patents

Abstract

The invention discloses a high-precision overcurrent detection circuit, which is characterized in that it includes a signal amplifying circuit, a comparator circuit and a switch control circuit; the signal amplifying circuit includes an operational amplifier U1, a MOSFET tube Q2 and a resistor R2; The comparator circuit includes an operational amplifier U2 and a resistor R3; the switch control circuit includes a triode Q3 and a resistor R4; the non-inverting input terminal of the operational amplifier U1 is connected to the output end of the current detection resistor R1; the gate of the MOSFET Q2 The pole is connected to the output terminal of the op-amp U1; the drain of the MOSFET Q2 is connected to the non-inverting input of the op-amp U1; the non-inverting input of the op-amp U2 is connected to the source of the MOSFET Q2; the inverse of the op-amp U2 The phase input terminal is connected to the reference voltage; the collector of the transistor Q3 is connected to the oscillator port of the PWM controller. The over-current detection circuit proposed by the invention has high current detection accuracy, fast over-current protection response speed, and can flexibly adjust the current-limiting parameter of the working current.

Description

A high-precision overcurrent detection circuit

technical field

The invention relates to the field of switching power supplies, in particular to a high-precision overcurrent detection circuit.

Background technique

With the development of power electronics technology, DC/DC switching power supplies have gradually replaced linear power supplies in industrial equipment, communication equipment, power equipment and other fields, and have been widely used. The power tube of the switching power supply works in the state of high-frequency on and off, chopping the input DC voltage into a pulse voltage, and the controller stabilizes the output voltage by adjusting the duty cycle of the PWM pulse signal. Compared with linear power supplies, switching power supplies have the advantages of high conversion efficiency, small size, and light weight.

In the design of switching power supply, protection circuits such as overcurrent and overvoltage must be considered, so that the actual working parameters of the circuit match the design parameters. When the circuit fails, such as a short circuit or an open circuit at the output terminal, a protection circuit is required to stop the operation of the switching power supply to protect the power devices inside the power supply. If the design of the protection circuit is not good, the circuit failure will cause the switching power supply to burn out, damage the equipment connected to the output end of the power supply, and even cause dangerous phenomena such as electric shock or fire. Therefore, the design of the protection circuit is very important, which directly affects the reliability of the power supply.

Commonly used over-current protection circuit shown in Figure 1. The primary power MOSFET Q1 of the switching power supply is connected in series with the current limiting resistor R1. When the power supply is working, the primary working current of the power supply is detected by the voltage across the current limiting resistor. Once the terminal voltage of the resistor R1 exceeds a set value, the driving transistor Q2 is turned on. The collector of transistor Q2 is connected to the oscillator port of the PWM power management chip, and when Q2 is turned on, the oscillator port is pulled down to turn off the output of the power supply. The structure of the protection circuit is simple, but the accuracy of overcurrent detection is low. The accuracy of current detection is affected by factors such as resistance accuracy and transistor base threshold voltage, and the current limit value is fixed and cannot be adjusted. How to improve the detection accuracy of the overcurrent protection circuit while taking into account the adjustable current limiting parameters, this patented technology is based on this background.

Contents of the invention

The purpose of the present invention is to design a high-precision overcurrent detection circuit.

In order to achieve the above purpose, an embodiment of the present invention provides a high-precision overcurrent detection circuit, including a signal amplification circuit, a comparator circuit and a switch control circuit, wherein:

The signal amplifying circuit includes an operational amplifier U1, a MOSFET tube Q2 and a resistor R2.

The comparator circuit includes an operational amplifier U2 and a resistor R3.

The switch control circuit includes a transistor Q3 and a resistor R4.

Further, the non-inverting input terminal of the operational amplifier U1 is connected to one end of the resistor R2; the inverting input terminal of the operational amplifier U1 is grounded.

Further, the gate of the MOSFET Q2 is connected to the output terminal of the operational amplifier U1; the drain of the MOSFET Q2 is connected to the non-inverting input terminal of the operational amplifier U1; the source of the MOSFET Q2 is connected to one end of the resistor R3.

Further, the non-inverting input terminal of the operational amplifier U2 is connected to the source of the MOSFET Q2; the inverting input terminal of the operational amplifier U2 is connected to the reference voltage.

Further, the base of the transistor Q3 is connected to one end of the resistor R4; the other end of the resistor R4 is connected to the output end of the operational amplifier U2; the collector of the transistor Q3 is connected to the oscillator port of the PWM controller.

Further, the MOSFET Q2 is an N-channel MOSFET.

Further, the transistor Q3 is an NPN transistor.

The embodiment of the present invention provides a high-precision overcurrent detection circuit. The circuit realizes the high-precision detection of the operating current value, and at the same time, the current limiting value of the operating current of the power supply can be adjusted conveniently by changing the reference voltage value. Compared with the prior art, the overcurrent protection circuit has high detection precision and faster response speed, and can realize flexible adjustment of the maximum value of the current limit.

Description of drawings

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of an overcurrent protection circuit in the prior art;

FIG. 2 is a schematic diagram of the high-precision overcurrent detection circuit of the present invention.

Detailed ways

The method of the present invention will be further described in detail below in conjunction with the accompanying drawings.

FIG. 2 is a schematic diagram of a high-precision overcurrent detection circuit provided by an embodiment of the present invention. As shown in the figure, the embodiment of the present invention provides a high-precision overcurrent detection circuit, including a signal amplification circuit, a comparator circuit and a switch control circuit, wherein:

The signal amplifying circuit includes an operational amplifier U1, a MOSFET tube Q2 and a resistor R2.

The comparator circuit includes an operational amplifier U2 and a resistor R3.

The switch control circuit includes a transistor Q3 and a resistor R4.

Further, the non-inverting input terminal of the operational amplifier U1 is connected to one end of the resistor R2; the inverting input terminal of the operational amplifier U1 is grounded.

Further, the gate of the MOSFET Q2 is connected to the output terminal of the operational amplifier U1; the drain of the MOSFET Q2 is connected to the non-inverting input terminal of the operational amplifier U1; the source of the MOSFET Q2 is connected to one end of the resistor R3.

Further, the non-inverting input terminal of the operational amplifier U2 is connected to the source of the MOSFET Q2; the inverting input terminal of the operational amplifier U2 is connected to the reference voltage.

Further, the base of the transistor Q3 is connected to one end of the resistor R4; the other end of the resistor R4 is connected to the output end of the operational amplifier U2; the collector of the transistor Q3 is connected to the oscillator port of the PWM controller.

Further, the MOSFET Q2 is an N-channel MOSFET.

Further, the transistor Q3 is an NPN transistor.

The overcurrent detection circuit in the embodiment of the present invention is composed of a signal amplification circuit, a comparator circuit and a switch control circuit. Op amp U1 equalizes the voltage across resistor R2 to the voltage across resistor R1. The current flowing through resistor R2 also flows through resistor R3, and the voltage generated across R3 is:

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}$

Among them, I _in is the primary current of the power supply.

The comparator U2 detects the terminal voltage of the resistor R3 and compares it with the reference voltage U _ref . When the voltage across the resistor R3 is lower than the reference voltage, the comparator is turned off and outputs a low level; once the voltage across the resistor R3 is greater than the reference voltage, the comparator outputs a high level and the drive transistor Q3 is turned on. The collector of the transistor Q3 is connected to the oscillator port of the PWM controller of the switching power supply. After the transistor Q3 is turned on, the clock signal level of the oscillator pin is pulled down, the PWM controller stops working, the output of the switching power supply is turned off, and the over-current protection is completed. It can be seen that the condition for the overcurrent protection comparator to be turned on is:

U _RS = U _ref

The reference voltage input to the inverting input of op amp U2 determines the maximum value of the primary operating current:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; f</span>}}$

According to the requirements of different over-current protection parameters, the maximum current-limiting value of the primary current can be adjusted by changing the reference voltage input to the non-inverting terminal of the operational amplifier U3.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (7)

1. A high-precision overcurrent detection circuit is characterized in that: comprise a signal amplifying circuit, a comparator circuit and a switch control circuit; Described signal amplifying circuit comprises operational amplifier U1, MOSFET tube Q2 and resistance R2; Described The comparator circuit includes an operational amplifier U2 and a resistor R3; the switch control circuit includes a triode Q3 and a resistor R4. 2 . The drive circuit according to claim 1 , wherein the non-inverting input terminal of the operational amplifier U1 is connected to one end of the resistor R2 ; the inverting input terminal of the operational amplifier U1 is grounded. 3. The drive circuit according to claim 1, characterized in that: the gate of the MOSFET Q2 is connected to the output terminal of the operational amplifier U1; the drain of the MOSFET Q2 is connected to the non-inverting input terminal of the operational amplifier U1; The source of the MOSFET Q2 is connected to one end of the resistor R3. 4 . The driving circuit according to claim 1 , wherein: the non-inverting input terminal of the operational amplifier U2 is connected to the source of the MOSFET Q2 ; the inverting input terminal of the operational amplifier U2 is connected to a reference voltage. 5. The drive circuit according to claim 1, characterized in that: the base of the transistor Q3 is connected to one end of the resistor R4; the other end of the resistor R4 is connected to the output end of the operational amplifier U2; the set of the transistor Q3 The electrodes are connected to the oscillator port of the PWM controller. 6. The drive circuit according to any one of claims 1 to 3, wherein the MOSFET Q2 is an N-channel MOSFET. 7. The drive circuit according to any one of claims 1 to 5, wherein the transistor Q3 is an NPN transistor.