CN204030996U - A kind of reverse exciting switching voltage regulator circuit - Google Patents

Abstract

The utility model relates to a kind of reverse exciting switching voltage regulator circuit, comprise: current rectifying and wave filtering circuit, flyback switching circuit, output filter circuit, feedback sampling circuit, power supply circuits, drive circuit, input voltage power down detecting and X capacitance detecting and discharge circuit and control circuit, described control circuit comprises control chip, the first resistance, thermal-shutdown circuit and the second resistance, and described control chip comprises: drive pin; Output feedback pin; System protection pin, described system protection pin is connected with described flyback switching circuit via described the first resistance, and is connected to ground via thermal-shutdown circuit; Power supply input pin; Current sample pin, described current sample pin is connected with unearthed one end of the sampling resistor of the transformer primary avris of described flyback switching circuit via described the second resistance; High voltage startup pin, described high voltage startup pin and described input voltage power down detecting and X capacitance detecting and discharge circuit are connected; And chip lower margin.

Description

A flyback switching power supply circuit

technical field

The utility model technology relates to a switching power supply circuit, in particular to a novel switching power supply circuit with a flyback structure. the

Background technique

In today's era, human society is facing the pressure of excessive energy consumption and serious environmental damage. Energy conservation and emission reduction are imminent. In order to reduce energy consumption for electrical equipment and electronic products, their power converters must be optimized to achieve higher conversion efficiency and lower energy consumption. The static standby power consumption. In the field of small and medium power, the flyback structure is widely used because of its low cost and simple design. The conversion efficiency, standby power consumption and other technical indicators of the flyback switching power supply currently on the market still have room for further improvement. With the introduction of various new energy standards and safety regulations, higher technical requirements will be placed on existing power converters. the

Utility model content

The purpose of the utility model is to provide a flyback switching power supply conversion circuit which overcomes at least one of the above technical bottlenecks. the

According to the flyback switching power supply circuit of the present utility model, it comprises: a rectification and filtering circuit (1), which is rectified by an input alternating current and performs electromagnetic interference filtering; a flyback switching circuit (2), which is connected with the rectification and filtering circuit (1) The output terminal is connected; Output filter circuit (3), it is connected with the output terminal of described flyback switch circuit (2); Feedback sampling circuit (4), it is sampled to the output of described output filter circuit (3); A power supply circuit (6), which is connected between the control circuit (5) and the flyback switch circuit (2), supplies power to the control circuit; a drive circuit (8), which is connected between the control circuit and the Between the flyback switch circuit (2), the on-off of the flyback switch circuit (2) is controlled; input voltage power-down detection and X capacitance detection and discharge circuit (9), its two input terminals are connected with The parallel connection of the X capacitor of the rectification and filtering circuit (1), the output end is connected with the high voltage starting pin (HV) of the control chip (U1); the control circuit (5), the control circuit (5) includes the control chip (U1) , a first resistor (Rovp), an over-temperature protection circuit (OTP), and a second resistor (Rocp), the control chip (U1) includes: a drive pin (GATE), the drive pin (GATE) and the drive The circuit (8) is connected; the output feedback pin (FB), the output feedback pin (FB) is connected to the output end of the feedback sampling circuit (4); the system protection pin (PRT), the system protection pin (PRT) The first resistor (Rovp) is connected to the connection point of the flyback switch circuit (2) and the power supply circuit for overvoltage protection, and the system protection pin (PRT) is connected to the connection point of the flyback switch circuit (2) through the overtemperature protection circuit (OTP ) is connected to the ground for over-temperature protection; the power supply input pin (VDD), the power supply input pin (VDD) is connected to the power supply circuit (6), and is used to supply power to the control chip (U1); the current sampling pin (CS), the current sampling pin (CS) is connected to the flyback switch circuit (2) via the second resistor (Rocp); the high voltage starting pin (HV), the high voltage starting pin (HV) is connected to the The input voltage power-down detection and the output terminal of the X capacitor detection and discharge circuit (9) are connected; and the chip ground pin (GND), the chip ground pin (GND) is grounded. the

According to the above-mentioned flyback switching power supply circuit, wherein, the flyback switching circuit (2) is a series connection of a flyback transformer, a switching tube, and a primary current sampling resistor, and the power supply circuit (6) is connected to the flyback transformer The auxiliary group winding is connected, the drive circuit (8) is connected to the gate of the switching tube, and the second resistor (Rocp) is connected to the ungrounded end of the primary current sampling resistor. the

According to the above flyback switching power supply circuit, wherein, when the switching tube is turned on, the output of the feedback sampling circuit (4) is input to the output feedback pin (FB), and the flyback switching circuit (2 ) current sampling signal flows into the current sampling pin (CS) via the second resistor (Rocp), and the control chip (U1) outputs a driving pulse signal through the driving pin (GATE) based on the above two sampling signals . the

According to the above flyback switching power supply circuit, wherein, when the switch tube of the flyback switching circuit (2) is turned off, the control chip (U1) flows out current from the current sampling pin (CS), and the outflow The current generates a voltage on the second resistor (Rocp), which is used for overcurrent protection compensation, and the resistance value of the second resistor (Rocp) is adjustable. the

According to the above-mentioned flyback switching power supply circuit, wherein, when the switch tube is cut off, the control chip (U1) detects an oscillating voltage from the flyback switching circuit (2) via the drive circuit (8), The demagnetization time is calculated internally based on this oscillating voltage. the

According to the above-mentioned flyback switching power supply circuit, wherein, the over-temperature protection circuit (OTP) is a series combination of a diode and a negative temperature coefficient resistor (NTC), the anode of the diode is connected to the system protection pin (PRT), and the The system protection pin (PRT) is grounded through the over-temperature protection circuit (OTP). the

According to the above-mentioned flyback switching power supply circuit, wherein, the over-temperature protection circuit (OTP) also has a third resistor, and the third resistor is connected to the diode, the negative temperature coefficient resistor ( NTC) connected in series. the

According to the above flyback switching power supply circuit, there is also an overshoot absorbing circuit (7), and the overshoot absorbing circuit (7) is connected to both ends of the primary winding of the flyback transformer. the

According to the above flyback switching power supply circuit, wherein, one end of the first resistor (Rovp) is connected to the system protection pin (PRT), and the other end is connected to the auxiliary winding of the flyback transformer and the power supply circuit ( 6), the system protection pin (PRT) detects the output voltage signal obtained by the current flowing into the control chip (U1) through the first resistor (Rovp), so as to perform overvoltage protection when the output is overvoltage , shut down the system. the

According to the above flyback switching power supply circuit, wherein, when the switching tube is turned off, the system protection pin (PRT) is connected to the connection between the first resistor (Rovp) and the over-temperature protection circuit (OTP) point, the first resistor (Rovp), the diode, and the negative temperature coefficient resistor (NTC) are connected in sequence, and the voltage information of the auxiliary winding, demagnetization information, and transformer The resonance information of the primary winding is used for demagnetization detection. the

According to the flyback switching power supply circuit of the utility model, functions such as overvoltage protection, overtemperature protection, overcurrent protection compensation, demagnetization detection, and power-off protection are realized, and it has low standby power consumption, high efficiency, short startup time, and EMI Low radiation characteristics, and can meet various safety standards

Description of drawings

Fig. 1 is the schematic diagram of the flyback switching power supply circuit that the utility model relates to;

Fig. 2 is a circuit for showing OVP and OTP protection time-sharing detection;

Fig. 3 is the figure showing the concrete connection of OTP circuit;

Fig. 4 is a figure showing the two-point connection method of the absorption circuit AB;

Fig. 5 is a figure showing the connection method between two points of the driving circuit CD;

Figure 6 is a schematic diagram showing an overcurrent protection adjustment circuit and a drive circuit as a demagnetization detection circuit;

Fig. 7 is a figure showing the connection method between two points of the power supply circuit GH;

Figure 8 is a waveform diagram of the voltage at the corresponding position during demagnetization detection and OCP compensation;

FIG. 9 is a schematic diagram of an input voltage power-down detection circuit, an X capacitor detection and discharge circuit. the

Detailed ways

Features and exemplary embodiments of various aspects of the present invention will be described in detail below. The following description covers numerous specific details in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is only to provide a clearer understanding of the present invention by showing examples of the present invention. The utility model is by no means limited to any specific configuration proposed below, but covers any modification, substitution and improvement of related elements or components without departing from the spirit of the utility model. the

The utility model circuit is developed based on the flyback switching power supply circuit, and Fig. 1 is a schematic diagram of the flyback switching power supply circuit involved in the utility model. With reference to the accompanying drawings, the utility model is described. The flyback switching power supply circuit includes AC input rectification, EMI (electromagnetic interference) filter circuit 1, flyback switching circuit 2, output filter circuit 3, feedback sampling circuit 4, control circuit 5, power supply circuit 6, overshoot absorption circuit (also called A sink circuit) 7, a drive circuit 8, and an input voltage brownout detection and X capacitance detection and discharge circuit 9. the

Next, each circuit component included in the flyback switching power supply circuit according to the embodiment of the present invention will be described in detail. in:

The rectification and EMI filter circuit 1 consists of a fuse FUSE, a two-stage common-mode filter inductor, an X capacitor (CX1), a varistor MOV, a rectifier bridge, and an output filter capacitor. the

Flyback switch circuit 2 is connected with the output end of described rectification filter circuit 1, and comprises flyback transformer T, switch MOSFET tube (field effect transistor), primary side current sampling resistor. the

The output filter circuit 3 is connected to the output end of the flyback switch circuit 2, and includes two main parts, an output rectifier diode and a filter capacitor. A resistance-capacitance absorption circuit (hereinafter referred to as an RC absorption circuit) is connected in parallel to the rectifier diode, and the RC absorption circuit can be adjusted or not used as required. In addition, for different output ripple requirements, the output filter circuit can add a π-type filter circuit or a common-mode filter circuit. the

The feedback sampling circuit 4 samples the output of the output filter circuit 3, and comprises a voltage stabilizing circuit (such as TL431), an optocoupler (hereinafter referred to as an optocoupler), and a feedback resistor and capacitor to sample the output voltage and pass through the TL431 loop Road regulation, feedback to the primary side control chip, to adjust the duty cycle of the switch MOSFET. the

The control circuit 5 is used as a control module, and its main components are a PWM control chip and necessary peripheral auxiliary components. The PWM control chip is, for example, OB2282 or a control chip with similar functions. The PWM control chip contains a total of 8 pins, which are:

① The gate drive pin GATE is used to control the switch of the switching tube (MOSFET) and is connected to the drive circuit. This pin is also used for demagnetization detection when the driver is turned off. the

② The output feedback pin FB is connected to the output terminal of the feedback sampling circuit 4, that is, connected to the optical coupler, and the feedback signal is input into the chip through the optical coupler. the

③The system protection pin PRT is used for system over-temperature protection, external output over-voltage (OVP) protection, and detection of demagnetization and valley opening. The system protection pin PRT is an output over-voltage protection and over-temperature (OTP) protection multiplex pin. It is connected to the flyback switch circuit 2 through the Rocp resistor (detection output over-voltage protection resistor), that is, connected to the intersection of the auxiliary winding and the power supply circuit. The point is used to obtain the output voltage information by sampling the current flowing into the chip from the demagnetization platform on the power supply winding, and to protect when the output overvoltage occurs. the

The system protection pin can be connected to an OTP protection circuit to ground to realize over-temperature protection while realizing output over-voltage protection. OTP protection and OVP protection do not interfere with each other, and this function can be realized separately or at the same time. the

In addition to the above functions, this pin can also be used to detect the demagnetization time and perform valley turn-on detection. the

④ The power supply input pin VDD is connected to the power supply circuit 6 for chip power supply. the

⑤The current sampling pin CS is used to sample the voltage signal of the primary current of the transformer on the sampling resistor. At the same time, this pin flows out a current after the MOSFET tube is turned off, which is used to compensate the output over-current protection (OCP) threshold. the

⑥The high-voltage starting pin HV is connected with the output end of the input voltage power-down detection and X capacitor detection and discharge circuit 9, and is used for high-voltage startup, power-down (Brownout) detection, input plug power-off detection and X-capacitor discharge detection, and The input voltage power-down detection is connected with the output end of the X capacitor detection and discharge circuit 9 . the

⑦ Chip ground GND, the reference ground of the chip. the

Here, the current sampling pin CS flows into this pin after the current sampling signal is filtered by RC. The output feedback pin FB and the current sampling pin CS generate PWM (pulse width adjustment) output through the internal operation of the chip. the

The system protection pin PRT is an output voltage detection and temperature detection multiplexing pin. The output voltage signal is detected through the Rovp resistor. If the output overvoltage protection (OVP) occurs, the system will be shut down. One end of the detection output overvoltage protection (OVP) resistor Rovp is connected to the junction of the system protection pin PRT and OTP, and the other end is connected to the connection point between the power supply circuit and the auxiliary winding. the

Fig. 2 is a circuit for showing time-division detection of OVP and OTP protection. the

In the circuit shown in Figure 2, one end of the Rovp resistor is connected to the auxiliary winding, and the other end is connected to the OTP circuit. When the switching MOSFET is turned off, the voltage information and demagnetization information of the auxiliary winding can be detected on the system protection pin PRT. In addition to detecting the demagnetization time, the circuit shown in Figure 2 can also be used to detect the bottom of the primary side resonance and realize the opening of the quasi-resonant (QR) bottom. the

This circuit is different from the ordinary QR resonant chip. The main difference is that the demagnetization detection of the ordinary QR chip is realized by resistor division, while the PWM control chip OB2282 not only adds a diode in series with the divider resistor, but also uses a negative The temperature coefficient resistor NTC realizes the voltage division. the

Figure 3 is a diagram of the specific connection method of the OTP circuit. The negative temperature coefficient resistor (temperature-sensitive resistor) NTC, the resistor R and the diode are connected in series to the ground, and the reference current flowing out is in the negative temperature coefficient resistor (thermo-sensitive resistor) NTC, resistor The voltage generated on the branch connected in series with R and the diode changes with the temperature to detect the system temperature. When the system temperature is too high, the chip will have input over-temperature protection and stop driving the output. Among them, the resistor R, the negative temperature coefficient resistor NTC and the diode can exchange positions, and R can also be omitted, as shown in Figure 3, but it is not limited to the three connection methods shown in Figure 3. the

4 is a diagram showing how to connect two points in the sink circuit AB, FIG. 5 is a diagram showing how to connect two points in the drive circuit CD, and FIG. 7 is a diagram showing how to connect two points in the power supply circuit GH. the

The absorption circuit 7 is connected to two points A and B in the circuit, and can be connected in various ways as shown in FIG. 4 . The drive circuit 8 is connected between the control circuit 5 and the flyback switch circuit 2, supplies power to the control circuit 5, and is connected to two points C (gate drive pin GATE) and D in the circuit, as shown in FIG. 5 various methods of connection. The power supply circuit 6 is connected to G (power supply input pin VDD) and H two points in the circuit, and can be connected in various ways as shown in Figure 7. The connection of the above-mentioned absorption circuit 7, drive circuit 8 and power supply circuit 6 is not limited to As shown in the diagram, it can be changed according to different system requirements. the

FIG. 6 is a schematic diagram showing an overcurrent protection adjustment circuit and a drive circuit as a demagnetization detection circuit. FIG. 8 is a waveform diagram of voltages at corresponding positions during demagnetization detection and OCP compensation. the

The dotted arrow in FIG. 6 shows the schematic diagram when the driving circuit is used as the demagnetization detection circuit. The drive circuit 8 can be used as a demagnetization detection circuit after the switching MOSFET is turned off, because after the gate drive pin GATE is turned off and the demagnetization is completed, the primary inductance of the transformer and the junction capacitance of the MOSFET form a resonance. When the resonance occurs, as shown by the dotted line in Figure 6 Capacitance and arrows, and as shown in Figure 8, the oscillating voltage is coupled to the gate drive pin GATE through the junction capacitance of the MOSFET drain and gate, and the chip internally detects this oscillating voltage, which is shown in Figure 8. As shown in the voltage diagram of GATE, the demagnetization time can be calculated through the oscillating voltage inside the chip. This demagnetization time cooperates with the internal algorithm circuit to achieve precise over-current protection (OCP) function. the

In addition to the built-in precise OCP protection loop, the PWM control chip OB2282 can also realize the external adjustment of OCP protection. As shown by the arrow shown by the solid line in Figure 6, the external adjustment is performed as follows: when the gate drive pin GATE is turned off, a current flows from the current sampling pin CS inside the chip, and a voltage is generated on the Rocp resistor through the current, This voltage is detected inside the chip. This voltage is shown as CS in Figure 8 and is used to compensate the output OCP threshold. Therefore, the OCP threshold can be adjusted by adjusting the resistance value of the Rocp resistor. the

FIG. 9 is a schematic diagram of the input voltage power-down detection circuit and the X-capacitor detection and discharge circuit 9 . the

PWM control chip OB2282 high-voltage starting pin HV is connected to the cathodes of two diodes through a resistor. After plugging in, the current flows into the chip through the diode and resistor, and charges the capacitor at the power supply input pin VDD. When the capacitor voltage at VDD reaches the rated voltage, the chip Start working. During normal operation, the high-voltage startup pin HV detects the AC input voltage across the X capacitor through the circuit shown in Figure 9. When the voltage is lower than the set value of the chip datasheet (datasheet), brownout protection occurs and the gate is stopped. Drive pin GATE output. After unplugging, the AC waveform disappears. The chip can detect the above phenomenon through the cooperation of the circuit shown in Figure 9 and the internal circuit, and after detection, it will act through the X capacitor discharge circuit to quickly discharge the stored charge of the X capacitor to meet the safety requirements. the

The utility model has been described above with reference to the specific embodiments of the utility model, but those skilled in the art will understand that various modifications, combinations and changes can be made to these specific embodiments without departing from the requirements set by the appended claims or Its equivalents define the spirit and scope of the present invention. Furthermore, any signal arrows in the figures should be considered as illustrative only, and not restrictive, unless specifically indicated otherwise. Combinations of components or steps are also considered to have been recited when terms are foreseen to obscure the ability to separate or combine. the

Claims (10)

1. a reverse exciting switching voltage regulator circuit, comprising:

Current rectifying and wave filtering circuit (1), it is transfused to alternating current and carries out rectification and carry out EMI Filtering;

Flyback switching circuit (2), it is connected with the output of described current rectifying and wave filtering circuit (1);

Output filter circuit (3), it is connected with the output of described flyback switching circuit (2);

Feedback sampling circuit (4), its output to described output filter circuit (3) is sampled;

Power supply circuits (6), it is connected between control circuit (5) and described flyback switching circuit (2), to described control circuit power supply;

Drive circuit (8), it is connected between described control circuit and described flyback switching circuit (2), and the break-make of described flyback switching circuit (2) is controlled;

Input voltage power down detecting and X capacitance detecting and discharge circuit (9), the X electric capacity of two input and described current rectifying and wave filtering circuit (1) in parallel, output is connected with the high voltage startup pin (HV) of control chip (U1);

Control circuit (5); described control circuit (5) comprises control chip (U1), the first resistance (Rovp), thermal-shutdown circuit (OTP) and the second resistance (Rocp), and described control chip (U1) comprising:

Drive pin (GATE), described driving pin (GATE) is connected with described drive circuit (8);

Output feedback pin (FB), described output feedback pin (FB) is connected with the output of described feedback sampling circuit (4);

System protection pin (PRT), described system protection pin (PRT) is connected to described flyback switching circuit (2) via described the first resistance (Rovp) and carries out overvoltage protection with the tie point of described power supply circuits, and described system protection pin (PRT) carries out overheat protector via thermal-shutdown circuit (OTP) with being connected to;

Power supply input pin (VDD), described power supply input pin (VDD) is connected with described power supply circuits (6), for powering to described control chip (U1);

Current sample pin (CS), described current sample pin (CS) is connected with described flyback switching circuit (2) via described the second resistance (Rocp);

High voltage startup pin (HV), described high voltage startup pin (HV) is connected with the output of described input voltage power down detecting and X capacitance detecting and discharge circuit (9); And

Chip lower margin (GND), described chip lower margin (GND) ground connection.

2. reverse exciting switching voltage regulator circuit as claimed in claim 1, wherein,

Described flyback switching circuit (2) is being connected in series of flyback transformer, switching tube, primary current sampling resistor, described power supply circuits (6) are connected with auxiliary group of winding of described flyback transformer, described drive circuit (8) is connected with the grid of described switching tube, and described the second resistance (Rocp) is connected with unearthed one end of described primary current sampling resistor.

3. reverse exciting switching voltage regulator circuit as claimed in claim 2, wherein,

In the time that described switching tube is connected, the output of described feedback sampling circuit (4) is imported into described output feedback pin (FB), the current sampling signal of described flyback switching circuit (2) flow into described current sample pin (CS) via described the second resistance (Rocp), and described control chip (U1) is exported drive pulse signal based on above-mentioned two sampled signals by described driving pin (GATE).

4. reverse exciting switching voltage regulator circuit as claimed in claim 2, wherein,

Have when described flyback switching circuit (2) switching tube cut-off time; described control chip (U1) flows out electric current from described current sample pin (CS); this outflow electric current is at the upper voltage that produces of described the second resistance (Rocp); for overcurrent protection compensation, the resistance value of described the second resistance (Rocp) is adjustable.

5. reverse exciting switching voltage regulator circuit as claimed in claim 2, wherein,

In the time of described switching tube cut-off, described control chip (U1) detects concussion voltage via described drive circuit (8) from described flyback switching circuit (2), to calculate the demagnetization time in inside based on this concussion voltage.

6. reverse exciting switching voltage regulator circuit as claimed in claim 2, wherein,

Described thermal-shutdown circuit (OTP) is the tandem compound of diode and negative temperature coefficient resister (NTC); the anode of diode is connected with described system protection pin (PRT), and described system protection pin (PRT) is ground connection via described thermal-shutdown circuit (OTP).

7. reverse exciting switching voltage regulator circuit as claimed in claim 6, wherein,

Described thermal-shutdown circuit (OTP) also has the 3rd resistance, and described the 3rd resistance is connected in series at cathode side and described diode, the described negative temperature coefficient resister (NTC) of described diode.

8. reverse exciting switching voltage regulator circuit as claimed in claim 2, wherein,

Also have overshoot absorbing circuit (7), described overshoot absorbing circuit (7) is connected to the two ends of the former limit winding of described flyback transformer.

9. reverse exciting switching voltage regulator circuit as claimed in claim 2, wherein,

One end of described the first resistance (Rovp) is connected to described system protection pin (PRT); the other end is connected to the auxiliary winding of described flyback transformer and the tie point of described power supply circuits (6); described system protection pin (PRT) detects the output voltage signal being obtained by the electric current of ramp metering chip (U1) by described the first resistance (Rovp); to carry out overvoltage protection, shutdown system in the time that overvoltage occurs in output.

10. reverse exciting switching voltage regulator circuit as claimed in claim 6, wherein,

In the time that described switching tube turn-offs; described system protection pin (PRT) is connected to the tie point of described the first resistance (Rovp) and described thermal-shutdown circuit (OTP); described the first resistance (Rovp), described diode, described negative temperature coefficient resister (NTC) are connected successively; detect the resonance information of information of voltage, demagnetization information and the transformer primary side winding of auxiliary group of winding by the signal of described system protection pin, the detecting of demagnetizing.