TW201935825A - LLC quasi-resonant switching power supply - Google Patents

Abstract

The invention provides an LLC quasi-resonant switching power supply. The LLC quasi-resonant switching power supply comprises a first power switch, a second power switch, a transformer and a control chip, wherein the first power switch and the second power switch are connected in series, the control chip can be used for operatively switching on the first power switch or the second power switch according to change slope of a voltage of a connection node between the first power switch and the second power switch, an output voltage representation voltage repressing an output voltage of the LLC quasi-resonant switching power supply is generated by sampling a voltage of an auxiliary winding of the transformer, an output current representation voltage repressing an output current of the LLC quasi-resonant switching power supply is generated by sampling a current passing through the second power switch, and the first power switch or the second power switch is switched off according to one of the output voltage representation voltage and the output current representation voltage. According to the LLC quasi-resonant switching power supply provided by the embodiment of the invention, controlof the output current and the output voltage can be simultaneously achieved, and zero-voltage conduction of the power switches also can be achieved.

Description

LLC Quasi-Resonant Switching Power Supply

The present invention relates to the field of circuits, and more particularly to an LLC quasi-resonant switching power supply.

Figure 1 shows the circuit schematic of a conventional LLC quasi-resonant switching power supply. In the LLC quasi-resonant switching power supply shown in Figure 1, the resonance of the inductors Lp, Ls and the resonant capacitor Cr is achieved by turning on and off the power switches S1 and S2; the resonant cavity current lags behind the resonant cavity voltage to achieve power Necessary conditions for zero voltage conduction of switches S1, S2; when the input voltage is too low, the operating frequency is too low, which will cause it to work in the capacitive region and fail to achieve zero voltage conduction of the power switches S1, S2. Therefore, the traditional LLC quasi-resonant switching power supply can only work under a single voltage condition with an AC input voltage of 230V, and it is necessary to add a Boost power factor correction (ie, Boost-PFC) circuit to the front stage to achieve wide voltage input and high power factor. .

In view of one or more of the problems described above, the present invention provides a novel LLC quasi-resonant switching power supply.

An LLC quasi-resonant switching power supply according to an embodiment of the present invention includes: a first power switch and a second power switch connected in series; a transformer; and a control chip operable to: based on the first power switch and the second power switch The slope of the voltage change at the connection node between the two. Turn on the first power switch or the second power switch, and sample the voltage on the auxiliary winding of the transformer to generate an output voltage characterization voltage that characterizes the output voltage of the LLC quasi-resonant switching power supply. Sampling the current flowing through the second power switch to generate an output current characterizing voltage that characterizes the output current of the LLC quasi-resonant switching power supply, and turning off the first power switch based on one of the output voltage characterizing voltage and the output current characterizing voltage. Or a second power switch.

The LLC quasi-resonant switching power supply according to the embodiment of the present invention can not only realize the control of the output current and the output voltage at the same time, but also realize the zero voltage conduction of the power switch to reduce Small switching losses, improved power supply efficiency, and high power factor.

S1, S2‧‧‧ Power Switch

Vout‧‧‧Output voltage

Lp, Ls‧‧‧Inductance

CC_comp‧‧‧Constant current control voltage

Cr‧‧‧Resonant capacitor

CV_comp‧‧‧Constant voltage control voltage

I _LS ‧‧‧Inductor current

Io‧‧‧Output current

Rcs‧‧‧Current Sampling Resistor

Vref_cc‧‧‧Controls the reference voltage of the output current

Cboost‧‧‧Capacitor

comp‧‧‧Control voltage

t0-t6‧‧‧ Duty cycle

VCin‧‧‧Voltage on input capacitor Cin

Cin‧‧‧input capacitor

D1‧‧‧diode

V _AC ‧‧‧LLC AC input voltage of quasi-resonant switching power supply

Turn ratio of primary side and secondary side of N‧‧‧ transformer

GATEH, V _HV, Vcr, V _Cboost, Vcs‧‧‧Voltage

VFB, CS, RV, VDD‧‧‧ terminals

ramp, Vref_cv, Vref_cc‧‧‧ reference voltage

t0-t1, t1-t2, t2-t3, t4-t5, t5-t6‧‧‧

HV‧‧‧ Half-bridge intermediate node

T1a‧‧‧Transformer first winding

T1b‧‧‧Transformer secondary winding

T1c‧‧‧Transformer main winding

GND‧‧‧Reference ground

Cout‧‧‧ output capacitor

Rfb1‧‧‧first sampling voltage divider resistor

Rfb2‧‧‧Second sampling voltage dividing resistor

NC‧‧‧No connection

The present invention can be better understood from the following description of specific embodiments of the present invention with reference to the accompanying drawings, wherein: FIG. 1 shows a circuit schematic diagram of a conventional LLC quasi-resonant switching power supply; and FIG. 2 shows a circuit diagram according to the present invention. The circuit schematic diagram of the LLC quasi-resonant switching power supply according to the embodiment of the invention; FIG. 3 shows a timing chart of some signals in the LLC quasi-resonant switching power supply shown in FIG. 2; The equivalent circuit diagram of the LLC quasi-resonant switching power supply during t0-t1 shown in Figure 3; Figure 5 shows the LLC quasi-resonant switching power supply shown in Figure 2 during t1-t2 shown in Figure 3 Figure 6 shows the equivalent circuit diagram of the LLC quasi-resonant switching power supply shown in Figure 2 during t2-t3 shown in Figure 3; Figure 7 shows the equivalent circuit shown in Figure 2 The equivalent circuit diagram of LLC quasi-resonant switching power supply during t3-t4 shown in FIG. 3; FIG. 8 shows the LLC quasi-resonant switching power supply shown in FIG. 2 during t4-t5 shown in FIG. 3. Equivalent circuit diagram; Figure 9 shows the equivalent circuit diagram of the LLC quasi-resonant switching power supply shown in Figure 2 during t5-t6 shown in Figure 3; FIG. 10 shows a schematic block diagram of a control chip in the LLC quasi-resonant switching power supply shown in FIG. 2; and FIG. 11 shows a simplified circuit diagram of the constant current and constant voltage control module shown in FIG. 10.

The features and exemplary examples 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 those skilled in the art that the present invention can be used without To be implemented without 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 shows a circuit schematic diagram of an LLC quasi-resonant switching power supply according to an embodiment of the present invention. In the LLC quasi-resonant switching power supply shown in FIG. 2, the required output voltage and / or output current is achieved by turning on and off the power switches S1 and S2.

FIG. 3 shows a timing diagram of some signals in the LLC quasi-resonant switching power supply shown in FIG. 2. In the timing chart shown in FIG. 3, GATEH indicates the voltage at the GATEH terminal of the control chip shown in FIG. 2 (that is, the driving voltage of the power switch S1), and GATEL indicates the GATEL of the control chip shown in FIG. 2. The voltage at the terminals (ie, the driving voltage of the power switch S2), V _HV represents the voltage at the connection node (ie, the HV point shown in Figure 2) between the power switches S1 and S2, and Vcr represents the resonance capacitor Cr V _Cboost represents the voltage on the capacitor Cboost, I _LS represents the inductor current flowing through the inductor Ls, and Vcs represents the voltage on the current sampling resistor Rcs.

As shown in Figure 3, the on-times of the power switches S1 and S2 are completely the same, so the currents flowing through the power switches S1 and S2 are equal, that is, the current flowing through the current sampling resistor Rcs is the inductor current I _Ls flowing through the inductor _Ls . half.

T0-t6 shown in FIG. 3 is a duty cycle of the LLC quasi-resonant switching power supply shown in FIG. 2. The following describes in detail the working process of the LLC quasi-resonant switching power supply shown in FIG. 2 with reference to FIGS. 2 to 9.

Fig. 4 shows an equivalent circuit diagram of the LLC quasi-resonant switching power supply shown in Fig. 2 during the period t0-t1 shown in Fig. 3. As shown in Figure 4, during t0-t1, the power switch S1 is turned on, and the voltage on the input capacitor Cin charges the inductors Lp and Ls while charging the resonant capacitor Cr and the capacitor Cboost in the forward direction, and the inductor current I _Ls increases; The current I _{Ls is} transmitted from the primary side of the transformer to the secondary side of the transformer, and then flows to the output terminal through the diode D1; when the voltage on the capacitor Cboost reaches V _Cin -V _AC , this phase ends. Among them, V _Cin represents the voltage on the input capacitor Cin, and V _AC represents the alternating current (AC) input voltage of the LLC quasi-resonant switching power supply.

Fig. 5 shows an equivalent circuit diagram of the LLC quasi-resonant switching power supply shown in Fig. 2 during the period t1-t2 shown in Fig. 3. As shown in Figure 5, during t1-t2, the power switch S1 is turned on, the AC input voltage V _AC charges the inductors Lp and Ls and charges the resonant capacitor Cr in the forward direction, and the inductor current I _Ls increases; the inductor current I _Ls starts from The primary side of the transformer is transmitted to the secondary side of the transformer, and then flows to the output terminal through the diode D1; this phase ends when the power switch S1 is turned off.

Fig. 6 shows an equivalent circuit diagram of the LLC quasi-resonant switching power supply shown in Fig. 2 during the period t2-t3 shown in Fig. 3. As shown in FIG. 6, at time t2, the power switch S1 is turned off, and the body diode of the power switch S2 is turned on; the control chip detects the body diode of the power switch S2 by the slope change of the voltage V _HV at the HV point. After being turned on, the power switch S2 is turned on to achieve zero-voltage conduction of the power switch S2; during t2-t3, the inductors Lp and Ls discharge the resonant capacitor Cr in the forward direction; the inductor current I _{Ls is} transmitted from the primary side of the transformer to the secondary side of the transformer. The side, then flows to the output terminal through the diode D1; when the inductor current I _Ls drops to zero and the voltage V _Cr on the resonant capacitor _Cr reaches the maximum forward value, this phase ends.

FIG. 7 shows an equivalent circuit diagram of the LLC quasi-resonant switching power supply shown in FIG. 2 during t3-t4 shown in FIG. 3. As shown in Figure 7, during t3-t4, the capacitor Cboost and the resonant capacitor Cr discharge the inductance Lp and Ls; the voltage V _Cboost on the capacitor _Cboost and the voltage Vcr on the resonant capacitor Cr decrease, and the inductor current I _{Ls is} negative Increase; the inductor current I _{Ls is} transmitted from the primary side of the transformer to the secondary side of the transformer, and then flows to the output terminal through the diode D2; when the voltage V _Cboost on the capacitor _Cboost decreases to 0V, this phase ends.

Fig. 8 shows an equivalent circuit diagram of the LLC quasi-resonant switching power supply shown in Fig. 2 during the period t4-t5 shown in Fig. 3. As shown in Figure 8, during t4-t5, the resonant capacitor Cr discharges the inductors Lp and Ls; the voltage Vcr on the resonant capacitor Cr decreases, and the inductor current I _LS increases negatively; the inductor current I _Ls decreases from the original transformer The side is transmitted to the secondary side of the transformer, and then flows to the output through the diode D2; when the power switch S2 is turned off, this phase ends.

Fig. 9 shows an equivalent circuit diagram of the LLC quasi-resonant switching power supply shown in Fig. 2 during the period t5-t6 shown in Fig. 3. As shown in FIG. 9, at time t5, the power switch S2 is turned off, and the body diode of the power switch S1 is turned on; the control chip detects the body diode of the power switch S1 through the slope change of the voltage V _HV at the HV point. After being turned on, the power switch S1 is turned on to realize zero-voltage conduction of the power switch S1; during t5-t6, the inductors Lp and Ls discharge the resonant capacitor Cr in the reverse direction; the inductor current I _{Ls is} transmitted from the primary side of the transformer to the transformer's secondary side. Side, and then flows to the output terminal through the diode D2; when the inductor current I _LS drops to zero and the voltage V _Cr on the resonant capacitor _Cr reaches the reverse maximum, this phase ends.

FIG. 10 shows a schematic block diagram of a control chip in the LLC quasi-resonant switching power supply shown in FIG. 2. In the control chip shown in FIG. 10, the voltage on the auxiliary winding of the transformer is sampled through the VFB terminal to obtain an output voltage characterization voltage representing the output voltage Vout; and the current flowing through the power switch S2 is sampled through the CS terminal to obtain The output current characterization voltage that characterizes the output current (ie, the output current of the LLC quasi-resonant switching power supply); the constant current and constant voltage control module generates a constant current control voltage CC_comp and constant voltage control based on the output current characterization voltage and output voltage characterization voltage Voltage CV_comp; when the constant current control voltage CC_comp is higher than the constant voltage control voltage CV_comp, the comparator determines the off time of the power switch S1 or S2 by comparing the constant voltage control voltage CV_comp with the reference voltage ramp generated by the oscillator; when When the constant voltage control voltage CV_comp is higher than the constant current control voltage CC_comp, the comparator determines the off time of the power switch S1 or S2 by comparing the constant current control voltage CC_comp with the reference voltage ramp generated by the oscillator; when the power switch S1 is turned off when off, via a falling edge of the voltage V _HV at point HV RV detection terminal determines the power of the body diode of switch S2 Conduction time, and then outputs a high level GATEL terminal S2 to turn on the power switch, to achieve zero-voltage turn-on of the power switch S2; S2 when the power switch is turned off, the voltage V _HV to rising through the terminal HV was detected at the point RV The body diode of the power switch S1 is determined to be turned on, and then a high level is output at the GATEH terminal to turn on the power switch S1 to achieve zero-voltage conduction of the power switch S1.

Since the current flowing through the power switch S2 is sampled through the CS terminal, and the current flowing through the power switch S2 is half of the inductor current ILs, the output current can be calculated as follows:

Among them, Io represents the output current, Vref_cc represents the reference voltage for controlling the output current, and N represents the turns ratio of the primary side and the secondary side of the transformer.

Figure 11 shows a simplified diagram of the constant current and constant voltage control module shown in Figure 10. Circuit diagram. As shown in Figure 11, the output voltage characterization voltage at the VFB terminal is sent to the operational amplifier together with the reference voltage Vref_cv to generate a constant voltage control voltage CV_comp through capacitance compensation. The output current characterization voltage at the CS terminal is rectified to take the absolute value and reference The voltage Vref_cc is sent to the operational amplifier together to generate a constant current control voltage CC_comp through capacitance compensation.

When the LLC quasi-resonant power supply shown in Figure 2 is connected to an alternating current (AC) input voltage, in the control chip shown in Figure 10: the voltage at the VDD terminal increases; when the voltage at the VDD terminal reaches the first threshold Under voltage lock out (UVLO) module controls other modules to start working; the constant current and constant voltage control module is based on the output voltage characterization voltage and output current characterization voltage at the VFB terminal and CS terminal to generate Constant-current control voltage CC_comp and constant-voltage control voltage CV_comp; analog and soft-start module based on constant-current control voltage CC_comp and constant-voltage control voltage CV_comp to generate a control voltage comp that ultimately controls the operating frequency of the LLC quasi-resonant power supply (when constant current control When the voltage CC_comp is higher than the constant voltage control voltage CV_comp, the constant frequency control voltage CV_comp is used to control the operating frequency of the LLC quasi-resonant power supply; when the constant voltage control voltage CV_comp is higher than the constant current control voltage CC_comp, the constant current control voltage CC_comp is used to control the LLC standard The operating frequency of the resonant power supply); at the same time, the control voltage comp of the analog and soft-start modules gradually rises from 0V to the constant current control voltage CC_comp or the constant voltage control voltage CV_ The comp process is controlled, and a current fault indication signal is generated when the output current characteristic voltage indicates that the output current is too small; the analog and control voltage comp generated by the soft-start module is sent to a pulse-width modulation (PWM) comparison The reverse input of the comparator; the fixed-rate rising reference voltage ramp generated by the oscillator module is sent to the forward input of the PWM comparator; when the reference voltage ramp rises to the control voltage comp, the PWM comparator generates Turn off the shutdown signal of the power switch S1 or S2; the zero-voltage switch (ZVS) detection module detects the slope of the voltage VHV at the HV point through the RV terminal; when the slope of the voltage VHV at the HV point decreases to At the second threshold, the ZVS detection module generates an opening signal for turning on the power switch S1 or S2; the internal over-temperature protection module determines whether an over-temperature occurs in the control chip and generates an over-temperature characterization signal (for example, in the control chip) High-temperature over-temperature characterization voltage is generated when over-temperature occurs; the fault module is based on the current fault indication signal from the analog control and soft-start modules and the over-temperature from the internal over-temperature module. Temperature characterization signal to generate fault indication signal; the logic module is based on the opening signal from the ZVS detection module. The shutdown signal from the PWM comparator and the fault indication signal from the fault module generate switching signals for controlling the power switches S1 and S2; the first driver and the second driver module are generated based on the switching signals from the logic module The driving signals for driving the power switches S1 and S2 cause the power switches S1 and S2 to be turned on alternately.

The LLC quasi-resonant switching power supply according to the embodiment of the present invention can not only control output current and output voltage at the same time, but also realize zero voltage conduction of the power switch to reduce switching loss, improve power efficiency, and achieve high power factor.

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 present embodiments are to be considered in all respects as illustrative and not restrictive, the scope of the present invention is defined by the appended claims rather than the above description, and falls within the meaning and equivalent of the claims All changes within the scope are thus included in the scope of the present invention.

Claims (5)

An LLC quasi-resonant switching power supply includes: a first power switch and a second power switch connected in series; a transformer; and a control chip operable to: based on the first power switch and the second power switch. The slope of the voltage change at the connection node between the two nodes is turned on. The first power switch or the second power switch is turned on, and the voltage on the auxiliary winding of the transformer is sampled to generate the characteristic of the LLC quasi-resonant switching power supply. The output voltage characterizing voltage of the output voltage is obtained by sampling the current flowing through the second power switch to generate an output current characterizing voltage characterizing the output current of the LLC quasi-resonant switching power supply, and characterizing the voltage and the voltage based on the output voltage. One of the output current characterization voltages turns off the first power switch or the second power switch. The LLC quasi-resonant switching power supply according to item 1 of the scope of patent application, wherein when the output voltage characteristic voltage is higher than the output current characteristic voltage, the control chip determines the first An off time of a power switch or the second power switch. The LLC quasi-resonant switching power supply according to item 1 of the scope of patent application, wherein when the output current characteristic voltage is higher than the output voltage characteristic voltage, the control chip determines the An off time of a power switch or the second power switch. The LLC quasi-resonant switching power supply according to item 1 of the scope of patent application, wherein, when the first power switch is turned off, the control chip is based on the distance between the first power switch and the second power switch. The falling edge of the voltage at the connection node determines the on-time of the second power switch. The LLC quasi-resonant switching power supply according to item 1 of the scope of patent application, wherein, when the second power switch is turned off, the control chip is based on a voltage between the first power switch and the second power switch. The rising edge of the voltage at the connection node determines the on-time of the first power switch.