TWI622258B - System for quickly starting switching power supply - Google Patents

Abstract

The invention relates to a system for quickly starting a switching power supply. A system for quickly starting a switching power supply is provided, including: an electromagnetic interference filter circuit, an input rectification circuit, a startup circuit, and an output rectification circuit, wherein the input end of the electromagnetic interference filter circuit is connected to an AC power source, and the output end is connected to a rectifier The circuit is connected; the input of the input rectification circuit is connected to the output of the electromagnetic interference filter circuit, and the output is connected to the input of the start circuit; the input of the start circuit is connected to the output of the input rectification circuit, and the output is The input terminal of the feedback sampling circuit is connected; one end of the feedback sampling circuit is connected to the input terminal of the startup circuit, and the other end is grounded; and wherein the startup circuit includes a first resistor, a Zener diode, a first diode, a first Two diodes, a first transistor, a second transistor, an under-voltage sensing circuit, a driver, a capacitor, a second resistor, and a third resistor.

Description

System for quickly starting switching power supply

The present invention relates to the field of circuits, and more particularly to a system for quickly starting a switching power supply.

In recent years, the switching power supply technology has been continuously developed and has a broad application prospect. However, because the control circuit in the switching power supply is relatively complicated, the ability of the transistor and integrated device to withstand electrical and thermal shocks is poor, which brings great inconvenience to the user during use. In order to protect the safety of the switching power supply itself and the load, according to the principles and characteristics of the switching power supply, overheat protection, overcurrent protection, overvoltage protection, and soft-start protection circuits are designed.

Generally speaking, an AC / DC (direct current / alternating current) power supply system implements an IC (Integrate Circuit, IC) startup by connecting a startup resistor from a bulk capacitor to the IC VDD, as shown in Figure 1 below. FIG. 1 is a diagram showing the application of a conventional AC / DC system.

In Figure 1, the resistor R1 charges the VDD (Virtual Device Driver) capacitor C1. When the voltage on the C1 capacitor is higher than the UVLO (Under Voltage Lock Out) voltage, the IC completes the startup and starts working; Efficiency. Generally speaking, the resistance value of R1 is as large as possible, but the resistance value of R1 is too large, it will cause the time for charging capacitor C1 to increase, and it will cause the startup time to be too long. At the same time, when the input AC voltage is different, the startup time is also different. For example: assuming R1 is 3Mohm and C1 is 4.7uF; and assuming that the IC UVLO (undervoltage sensing circuit) voltage is 16V, the circuit startup time at 90V AC is 1.8S, and the startup time at 264V AC is 0.6S , And the startup resistor R1 consumes 46mW. The startup resistor dissipates more power.

In view of the problems described above, the present invention provides a method for switching power supplies. Quick start system.

According to an aspect of the present disclosure, a system for quickly starting a switching power supply is provided, including: an electromagnetic interference filter circuit, a rectifier circuit, a startup circuit, and a rectifier circuit, wherein an input end of the electromagnetic interference filter circuit is connected to an AC power source. The output end is connected to the rectification circuit; the input end of the rectification circuit is connected to the output end of the electromagnetic interference filter circuit, and the output end is connected to the input end of the startup circuit; the input end of the startup circuit is connected to the output end of the rectification circuit, The output end is connected to the input end of the feedback sampling circuit; one end of the feedback sampling circuit is connected to the input end of the startup circuit, and the other end is grounded; and wherein the startup circuit includes a first resistor connected in series, a Zener diode, a first One diode, second diode, first metal oxide semiconductor field effect transistor (MOSFET M1), second metal oxide semiconductor field effect transistor (MOSFET M2), VDD undervoltage sensing circuit (UVLO) , Driver, capacitor (C1), second resistor (R0), third resistor (R1). One end of the capacitor is grounded and connected in series with the negative electrode of the first resistor, the second diode, the second resistor, and the zener diode. The third resistor is usually connected at one end to the positive pole of the rectified power source and at the other end. The Zener diode is negative, one end of the undervoltage sensing circuit is connected to the capacitor, and the other end is connected to the driver, and the driver is connected to the undervoltage sensing circuit and the first diode.

According to an embodiment of the present application, a system for quickly starting a switching power supply is provided, which has a lower power loss. Depending on the embodiment, one or more benefits may also be obtained. These benefits, as well as various additional objects, features, and advantages of the present invention can be fully understood with reference to the following detailed description and accompanying drawings.

AC‧‧‧DC

DC‧‧‧ Exchange

C1‧‧‧Capacitor

Rc‧‧‧First resistor

R0‧‧‧Second resistor

R1‧‧‧Third resistor

UVLO‧‧‧Undervoltage sensing circuit

por‧‧‧ output

Icharge‧‧‧Starting current

D1, D2‧‧‧ diodes

Z1‧‧‧Zina Diode

PWM‧‧‧Pulse Width Modulation

PFM‧‧‧Pulse Frequency Modulation

M1‧‧‧The first metal oxide semiconductor field effect transistor

M2‧‧‧Second Metal Oxide Semiconductor Field Effect Transistor

GATE, SW, VDD, FB, GND, CS‧‧‧ pins

Hereinafter, the features, advantages, and technical effects of the exemplary embodiments of the present invention will be described with reference to the accompanying drawings. Similar reference numerals in the drawings represent similar elements, of which: FIG. 1 shows a conventional AC / DC Illustration of system applications.

FIG. 2 is an exemplary diagram illustrating an AC / DC of a quick start secondary side regulation (SSR) according to an embodiment of the present disclosure.

FIG. 3 illustrates a quick start primary adjustment according to an embodiment of the present disclosure (PSR) Exemplary illustration of AC / DC.

Features and exemplary embodiments of various aspects of the invention will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to a person skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is merely for providing a better understanding of the present invention by showing examples of the present invention. The invention is by no means limited to any specific configuration and algorithm proposed below, but covers any modification, replacement and improvement of elements, components and algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.

FIG. 2 is an exemplary diagram illustrating an AC / DC of a quick start secondary side regulation (SSR) according to an embodiment of the present disclosure. This figure is only an example, and it should not unduly limit the scope of patent application. Those of ordinary skill in the art should understand many variations, substitutions, and modifications.

As shown in Figure 2, the secondary side of the AC / DC power supply system includes an electromagnetic interference (EMI) filter circuit and an output rectification filter circuit. Depending on the application, the EMI filter circuit can include one or two inductors, or it can include only one common-mode inductor (while including one or more high-voltage electrolytic capacitors); it can include only one high-voltage electrolytic capacitor (including one or more Simultaneous two inductors or one common mode inductor); and in some cases may not include ESD (Electrostatic Discharge, electrostatic discharge) discharge resistance. In the embodiment shown in FIG. 2, the output rectification filter circuit includes four output rectification diodes, and optionally includes a filter capacitor. For different output ripple requirements, the output rectification filter circuit can add a π -type filter circuit or a common mode filter circuit to improve the filtering effect. Those skilled in the art can set different connection methods for the diodes according to the needs to achieve different ripple requirements. The rectifier diode can be combined with an RC absorption circuit, and the RC absorption circuit can be adjusted or not used as required.

The AC / DC power supply system also includes a Pulse Width Modulation (PWM) control chip and necessary peripheral auxiliary components. Among them, the PWM control chip has comprehensive protection functions. AC / DC power systems also include UVLO components. After the power is turned on, the UVLO element puts the internal circuit in a standby state until the input voltage (VIN) of the DC / DC converter reaches the UVLO voltage, thereby reducing power consumption and avoiding misoperation.

According to an embodiment of the present disclosure, the AC / DC power supply system further includes a startup system. The starting system includes a first resistor Rc, a Zener diode Z1, a diode D1, a diode D2, a first power transistor, a second power transistor, a VDD undervoltage sensing circuit (UVLO), a driver, The capacitor (C1), the second resistor (R0), and the third resistor (R1). In one example, the power transistor is a bipolar junction transistor. In yet another example, the power transistor is an Insulated Gate Bipolar Transistor (IGBT). Preferably, the power transistor is a field effect transistor (eg, a metal oxide semiconductor field effect transistor (MOSFET)). The driver is connected in series with the starting resistor R1, the Zener diode Z1, the diode D1, and the diode D2.

FIG. 3 is an exemplary diagram illustrating an AC / DC of Quick Start Primary Side Regulation (PSR) according to an embodiment of the present disclosure. This figure is only an example, and it should not unduly limit the scope of patent application. Those of ordinary skill in the art should understand many variations, substitutions, and modifications. Similar components have been described with reference to FIG. 2 and will not be repeated here.

According to an embodiment of the present disclosure, the primary side of the AC / DC power supply system may further include a feedback sampling circuit. The feedback sampling circuit may include a feedback element, a sample and hold element, and an error amplifier. The feedback sampling circuit can, for example, sample the output voltage of the power supply circuit, adjust the sampling voltage through TL431 (Controllable Precision Stable Voltage Source), and feed back the adjusted sampling voltage to the PWM control chip, and then the Duty cycle.

According to an embodiment of the present disclosure, after the AC / DC power supply system is powered on, due to the low voltage, the integrated circuit IC is initially in a UVLO state. The output from the UVLO element to the driver's output por is "0", and the M2 MOS tube (metal oxide semiconductor diode) is in the off state. Discharge the start resistor R1 and pull up the voltage at the GATE pin until the Zener diode Z1 and diode D1 are turned on. The resistance value of the starting resistor R1 can be set by a person skilled in the art according to actual needs, and the resistance value can be very large. At this time, the voltage VGATE at the GATE pin remains as follows: VGATE = VDD + Vz + Vd1 (Equation 1)

Among them, VDD is the voltage of capacitor C1; Vz is the breakdown voltage of Zener diode Z1; and Vd1 is the on-voltage of diode D1.

As the VGATE pin rises, the MOS M1 tube is turned on, so current flows from the buck capacitor to M1 (M1 can be integrated inside the integrated circuit or connected outside the integrated circuit), SW pin, diode D2, resistor Rc to VDD pin to charge capacitor C1. Among them, a resistor R0 is set between GATE-SW to give a certain state to the power MOS M1 tube to prevent a large large current from flowing through the M1 tube at the moment of AC startup or repeated DC on / off, causing the circuit to overload, or even Device is damaged.

The resistance of R0 can be 1/5 ~ 1/10 of the resistance of R1. Assuming that the turn-on threshold of the M1 MOS transistor is Vth, the current flowing through the R0 resistor is Vth / R0. Because the R0 resistance is large and the Vth threshold is small (for example, about 3V), the current flowing through the R0 resistor is far. Is less than the resistance current flowing through R1, so the voltage drop VRc on the resistor Rc is calculated as follows: VRc = VGATE-Vth-Vd2-VDD (Equation 2)

Among them, Vth is the turn-on threshold of the M1 MOS tube; VDD is the voltage of capacitor C1; Vd2 is the voltage drop of diode D2; and VGATE is the voltage at the GATE pin.

From equation (1), we know that VGATE is VDD + Vz + Vd1, so VRc can be calculated from the voltage on resistor Rc as follows: VRc = Vz + Vd1-Vd2-Vth (Equation 3)

Therefore, the charging current for capacitor C1 is: Ich arg e = ( Vz + Vd 1- Vd 2- Vth ) / R (Equation 4)

Where R is the resistance of the resistor Rc.

As can be seen from Equation 4, the charging current Icharge is a fixed value and does not change with the AC input voltage. Therefore, the startup time is the same under different input voltages. Can adjust Rc Resistance value to achieve different charging currents.

The start-up time Ton of the integrated circuit IC can be calculated as follows: Ton = C1 * Vuvlo / Icharge (Equation 5)

Set Vz = 6V, Vd1 = Vd2 = 0.7V, Vth = 3V; Rc is 20Kohm, R1 is 100Mohm, R0 is 20Mohm, C1 = 4.7uF, IC UVLO is Vuvlo = 16V; then Icharge = (6+ 0.7-0.7-3) / 20 = 150uA.

Substituting Icharge = 150uA into Equation 5, we can get the IC startup time: Ton = 4.7 * 16/150 = 0.5s.

The startup resistor R1 (100Mohm) consumes 1.4mW at 264V, compared to the 46mW power consumption of the conventional startup resistor R1 = 3Mohm, which is only 1/33. System efficiency.

Those skilled in the art will understand that the startup time can be controlled by adjusting the resistance value R of the Rc resistor. From Equation 4 and Equation 5, Ton = C1 * Vuvlo * R / (Vz + Vd1-Vd2-Vth) (Equation 6)

It can be known that the resistance value R of the Rc resistor is proportional to the startup time Ton of the integrated circuit IC. The larger the set R, the longer the time required for the IC circuit to start. For example, in alternative embodiments, a higher Rc resistor R may be set to obtain a longer startup time; or a lower Rc resistor R may be set to obtain a shorter startup time .

The present invention may be implemented in other specific forms without departing from the spirit and essential characteristics thereof. For example, the algorithms described in particular embodiments may be modified without the system architecture departing from the basic spirit of the invention. Therefore, the current embodiment is considered in all respects to be exemplary rather than limiting, the scope of the present invention is defined by the scope of the attached patent application rather than the above description, and the meanings and equivalents falling within the scope of the patent application All changes within the scope of the substance are thus included in the scope of the present invention.

Some or all of the elements of the various embodiments of the invention, alone and / or in combination with at least another element, are one of one or more software elements, one or more hardware elements, and / or software and hardware elements Or multiple combinations to achieve. In another example, the invention Some or all of the elements in one embodiment are implemented in one or more circuits alone and / or in combination with at least another element, such as in one or more analog circuits and / or one or more digital circuits . In yet another example, various embodiments and / or examples of the present invention may be combined.

Although specific embodiments of the present invention have been described, those skilled in the art will appreciate that there are other embodiments equivalent to the described embodiments. Therefore, it will be understood that the present invention is not limited by the specific embodiments shown, but is limited only by the scope of patent application.

Claims (8)

A system for quickly starting a switching power supply includes an electromagnetic interference filter circuit, an input rectification circuit, a startup circuit, and an output rectification circuit, wherein an input end of the electromagnetic interference filter circuit is connected to an AC power source, and an output end is connected to an AC power source. The input rectification circuit is connected; the input terminal of the input rectification circuit is connected to the output terminal of the electromagnetic interference filter circuit, and the output terminal is connected to the input terminal of the startup circuit; the input terminal of the startup circuit is connected to all The output terminal of the rectifier circuit is connected, the output terminal is connected to the input terminal of the feedback sampling circuit; one end of the feedback sampling circuit is connected to the input terminal of the startup circuit, and the other end is grounded; and wherein the startup circuit includes First resistor, Zener diode, first diode, second diode, first transistor, second transistor, undervoltage sensing circuit, driver, capacitor, second resistor, and third A resistor, wherein one end of the capacitor is grounded, and is connected to the first resistor, the second diode, the second resistor, and the Zener The negative electrode of the electrode body is connected in series, one end of the third resistor is connected to the positive electrode of the rectified power source, and the other end is connected to the negative electrode of the Zener diode. Said driver, said driver being connected to said under-voltage sensing circuit and said first diode. The system of claim 1, wherein the first transistor and the second transistor are metal oxide semiconductor field effect transistors. The system of claim 1, wherein the value of the resistance of the first resistor is variable. According to the system of claim 1, the value of the resistance of the second resistor is between 1/5 and 1/10 of the value of the resistance of the third resistor. The system according to item 1 of the scope of patent application, wherein the charging current of the capacitor is determined according to the following formula: Ich arg e = ( Vz + Vd 1- Vd 2- Vth ) / R, where Icharge represents the capacitor's Charging current, Vz represents the breakdown voltage of the Zener diode, Vd1 represents the on-voltage of the first diode, Vd2 represents the on-voltage of the second diode, and Vth represents the first voltage The turn-on threshold of the crystal, R represents the resistance value of the first resistor. The system according to item 1 of the patent application scope, wherein the electromagnetic interference filtering circuit comprises a π-type filtering circuit and / or a common mode filtering circuit. The system according to item 1 of the patent application scope, wherein the electromagnetic interference filtering circuit includes an inductor and a high-voltage electrolytic capacitor. The system according to item 1 of the patent application scope, wherein the electromagnetic interference filtering circuit further comprises an electrostatic discharge resistor.