TW201308842A - Buck converter and its control circuit and control method - Google Patents

Abstract

A buck converter and its control circuit and control method, wherein the buck converter comprises a rectifier that converts alternating current into all wave signals with diode, output inductor, and buck output level for the switch to turn on/off on the basis of the control signal for all wave signal buck. Voltage sampling circuit samples all wave signals to generate sampling signal with identical position with the all wave signal. The first signal is generated by detecting whether the current that passes through output inductor via zero current detecting circuit is zero, and the current detecting circuit detects the current that passes through the switch to generate a second signal after comparing with the sampling signal to drive the circuit. On the basis of the first and second signal, control signal is generated. The first signal turns on the switch while the second signal turns off the switch.

Description

Buck converter and its control circuit and control method

This creation is related to a power converter, and in particular to a buck converter and its control circuit and control method.

The types of conventional power converters include a buck converter, a boost converter, a buck-boost converter, a flyback converter, and a forward-looking type. Converter converters and the like, in which the circuit of the buck converter is the simplest and has the advantage of low cost. When the input is AC power, it needs to go through the steps of filtering and rectifying, but the generated current waveform will be deformed. If the harmonic content is too large, the power factor will be reduced, which will affect the stable operation of the load current. To effectively solve this problem, it is necessary to perform power factor correction (PFC) on the electrical equipment to fundamentally eliminate the harmonic source. At present, in the PFC function, the single-phase boost (Boost) circuit operating in the discontinuous conduction mode (DCM) with the inductor current is mainly due to the simple circuit structure, low cost and high power factor. Has received wide attention. However, in this mode, the MOSFET switch is controlled by the error signal of the output voltage, and the switching period is constant. The disadvantage of this PFC technology is mainly because the input current is a pulsating triangular wave, and the higher peak switching current will bring Large switch losses and high output voltages can cause large switching stresses in the latter stage of the corrector. However, in a single-phase buck circuit operating in discontinuous current mode (DCM), when the input voltage is lower than the output voltage, the input current waveform will be deformed to reduce the power factor.

Therefore, a buck converter with high power supply is what it is.

The object of the present invention is to provide a buck converter with high power supply and a control circuit and control method thereof.

According to the present invention, a buck converter includes a rectifier coupled to an AC power source for generating a full-wave signal to a first voltage terminal, and a buck output stage coupled to the first voltage terminal includes a diode, an output inductor, and a switch, according to The control signal turns on or off the switch to step down the full-wave signal, and the voltage sampling circuit coupled to the first voltage terminal samples the full-wave signal to generate a sampling signal having the same phase as the full-wave signal, and the zero-current detecting circuit Detecting whether the current flowing through the output inductor is zero to generate a first signal, the current sensing circuit detecting a current flowing through the switch, generating a second signal compared with the sampling signal; and coupling the zero current detecting circuit and The driving circuit of the current sensing circuit generates the control signal according to the first signal and the second signal, wherein the first signal triggers the conduction of the switch, and the second signal triggers the closing of the switch.

According to the present invention, a buck converter control method, wherein the buck converter includes a diode, an output inductor, and a switch, the control method includes rectifying an AC power source to generate a full-wave signal, and sampling the full-wave signal to generate a sampling signal having the same phase as the full-wave signal, detecting whether the current flowing through the output inductor is zero, generating a first signal, detecting a current flowing through the switch, and generating a second signal according to the sampling signal, according to The first signal and the second signal generate a control signal, wherein the first signal triggers the turn-on of the switch, the second signal triggers the switch to be turned off, and the full-wave signal is stepped down according to the control signal turning the switch on or off .

According to the present invention, a control circuit for a buck converter, wherein the buck converter includes a rectifier coupled to an AC power source to generate a full-wave signal to a first voltage terminal, and a buck output stage coupled to the first voltage terminal includes a diode The body, the output inductor and the switch, the full-wave signal is stepped down according to the control signal being turned on or off, and the control circuit includes a voltage sampling circuit coupled to the first voltage terminal to sample the full-wave signal to generate the full-wave signal a sampling signal having the same phase, the zero current detecting circuit detects whether the current flowing through the output inductor is zero to generate a first signal, and the current sensing circuit detects a current flowing through the switch, and generates a second comparison with the sampling signal. And the driving circuit coupled to the zero current detecting circuit and the current sensing circuit generates the control signal according to the first signal and the second signal, wherein the first signal triggers conduction of the switch, and the second signal triggers The switch is turned off.

The buck converter of the invention can detect the zero current state, enable the power control circuit to operate in a transition mode, and has a current sense circuit to correct the power factor (Power) Factor correction, PFC) can be used in the step-down circuit, and can improve the efficiency of the step-down circuit and reduce the total harmonic distortion (THD). It is suitable for driving and controlling the light-emitting diode (LED) illumination. .

1 is an embodiment of a buck converter of the present invention including a rectifier 10, a buck output stage 12, and a control circuit 14. The rectifier 10 is configured to convert the half-wave AC power source AC into an input voltage Vin, which is a full-wave signal having an m-shaped waveform. In addition, the rectifier 10 further includes a filter composed of capacitors C1 and C2 and an inductor L1. To filter out electromagnetic interference (EMI). The buck output stage 12 includes a diode D1, an output inductor Lout, an output capacitor Cout, a MOSFET switch Qsw, and a resistor Rcs. The MOSFET switch Qsw is turned on or off according to the control signal Sc to step down the input voltage Vin to a desired output current. Or a voltage is supplied to the load, and the resistor Rcs is connected in series between the MOSFET switch Qsw and the ground. When the current Isw of the MOSFET switch Qsw flows through the resistor Rcs, a voltage Vcs related to the current Isw is generated. The control circuit 14 includes a zero current detecting circuit 16, a driving circuit 18, a current sensing circuit 20, and a voltage sampling circuit 24. The zero current detecting circuit 16 is configured to detect whether the current IL flowing through the output inductor Lout is zero, and generate a signal S1. When the current IL is zero, the signal S1 triggers the driving circuit 18 to control the conduction of the MOSFET switch Qsw. The voltage sampling circuit 24 is a voltage divider composed of resistors R1, R2 and a capacitor C3. The input voltage Vin is divided to generate a signal S3. The signal S3 is the same as the input voltage Vin, and has an m-shaped waveform. The current sensing circuit 18 The comparator 22 in the comparator compares the signal Vcs with the signal S3 to generate the signal S2. When the voltage Vcs exceeds the signal S3, the signal S2 triggers the drive circuit 18 to control the closing of the MOSFET switch Qsw. In an embodiment, the driver circuit 18 is an SR flip-flop that generates a control signal Sc to control the MOSFET switch Qsw based on the signals S1, S2.

2 is an embodiment of the zero current detection circuit 16 of FIG. The zero current detecting circuit 16 includes an auxiliary inductor L2, a hysteresis comparator 26, and a logic controller 28. The auxiliary inductor L2 generates a current according to the influence of the inductor current IL, and uses the resistor Rzcd to generate a voltage signal S4 related to the inductor current IL. When the voltage signal S4 is greater than Vth, the comparator 26 generates a signal S5 at a high level. When the signal S4 is at Vth, the generated signal S5 is at a low level, and the logic controller 28 can generate the signal S1 according to the signal S5, and thus detecting the zero current state, the buck converter can be operated in the transfer mode.

Referring to FIG. 3, this is an operational waveform diagram of the input voltage Vin sine wave of the half-cycle of the buck converter of the zero current detecting circuit 16 of the present invention, which shows the input voltage of the half cycle, the sine wave, and the generated inductor current IL. And the waveform result of the voltage signal S4. The buck converter of the present invention turns on the MOSFET switch Qsw when the inductor current IL is zero, so that the current increases. When the current sensing circuit 20 detects that the current Isw is too large, the MOSFET switch Qsw is turned off, so that the current is reduced, due to zero current detection. The measuring circuit 16 can accurately detect the zero current state so that the MOSFET switch Qsw can be accurately turned on or off to generate a complete sawtooth inductor current IL. When the input voltage Vin is low, the duty cycle (D) is long. When the input voltage Vin is high, the duty cycle is short.

Since the AC power supply AC in various countries is not fixed at the same level, and may be 110V or 220V, in order to make the buck converter of the present invention applicable, another embodiment of the sampling circuit 24 is proposed in FIG. In addition to the voltage divider, a multiplier 30 and a voltage compensation circuit 32 are further included. The pass voltage compensation circuit 32 generates a compensation signal (V2-Vref) according to the voltage level of the input voltage Vin, and compensates the signal Vs generated by the voltage divider via the multiplier 30, so that the input voltage of the sampling circuit at different voltage levels Under Vin, a signal S3 of the same voltage level can be generated for use in the power supply circuit 20. The voltage compensation circuit 32 is composed of resistors R3 R R7 and capacitors C4 and C5 and an error amplifier 34. The combination of the resistor R3 and the capacitor C4 forms a low-pass filter 36, and the cutting off frequency must be much smaller than 60Hz, and resistors R6, R7 and C5 form a loop compensation circuit 38 connected between the negative input terminal and the output terminal of the error amplifier 34 to form a feedback path. Through the circuit analysis, the following formula can be obtained

R4=2×R7, Equation 4

Among them, V2 ₁₁₀ is a V2 voltage that is customized when the input voltage Vin is 110V, V2 ₂₂₀ is a V2 voltage that is customized when the input voltage Vin is 220V, Vref is a reference voltage, and I1 is a current flowing through the resistor 5. In addition, the transfer function of the feedback circuit formed by the error amplifier 34 and the loop compensation circuit 38 and the resistor R5 is

Using the above formula, find the values of resistors R3~R7 and capacitors C4 and C5 to enable the same circuit to be used at different input voltages. The signal S3 output by the multiplier 30 is subject to the following formula

S3=C×Vs×(V2-Vref)

Where C is the custom magnification parameter of the multiplier. By the implementation of this sampling circuit, the same output signal S3 can be generated when the input voltage is 110V or 220V, while passing through the same multiplier 30, so that the load maintains the same current.

In the implementation of the buck converter of the present invention, an over current protection (OCP) circuit, an over voltage protection (OVP) circuit, a startup circuit, etc. may be further included to provide more complete functions, such as 5 is another embodiment of the current sensing circuit 20 of FIG. 1. In addition to the original comparator 22, a shutter 42 is added, an overcurrent protection comparator 44, and a comparator 22, 44 are connected. The output gate 46 is used to generate the signal S2. The shutter 42 is connected between the comparators 22, 44 and the resistor Rcs for avoiding the judgment of some of the surge noise interference comparator 22 or the overcurrent protection comparator 44. The overcurrent protection comparator 44 is for applying the voltage Vcs with Another threshold value Vocp is compared. If the voltage Vcs is greater than Vocp, it means that the current Isw flowing through the MOSFET switch Qsw is too large, which means that the current flowing through the load is too large, and the load will be damaged for a long time. Therefore, the overcurrent protection comparator When it is known that the current Isw is too large, the signal S6 of the high level is immediately generated, and the gate 46 is driven to the drive circuit 18 to control the closing of the MOSFET switch Qsw to achieve the effect of overcurrent protection.

The above description of the preferred embodiments of the present invention is intended to be illustrative, and is not intended to limit the scope of the present invention. It is possible to make modifications or variations based on the above teachings or learning from the embodiments of the present invention. The embodiments are described and illustrated in the practical application by the skilled person in the various embodiments using the present invention. The technical idea of the present invention is determined by the following claims and their equals. .

10. . . Rectifier

12. . . Buck output stage

14. . . Control circuit

16. . . Zero current detection circuit

18. . . Drive circuit

20. . . Current sensing circuit

twenty two. . . Comparators

twenty four. . . Voltage sampling circuit

26. . . Hysteresis comparator

28. . . Logic controller

30. . . Multiplier

32. . . Voltage compensation circuit

34. . . Low pass filter

36. . . Error amplifier

38. . . Loop compensation circuit

40. . . Subtractor

42. . . Shader

44. . . Comparators

46. . . Gate

1 is an embodiment of a buck converter of the present invention;

2 is an embodiment of the zero current detecting circuit 16 of FIG. 1;

3 is an operational waveform diagram of an input voltage Vin sine wave of a buck converter of the present invention at a half cycle;

4 is another embodiment of the sampling circuit 24 of FIG. 1;

FIG. 5 is another embodiment of the current sensing circuit 20 of FIG.

10. . . Rectifier

12. . . Buck output stage

14. . . Control circuit

16. . . Zero current detection circuit

18. . . Drive circuit

20. . . Current sensing circuit

twenty two. . . Comparators

twenty four. . . Voltage sampling circuit

Claims (22)

A buck converter includes: a rectifier coupled to an AC power source for generating a full-wave signal to a first voltage terminal; and a buck output stage coupled to the first voltage terminal, including a diode, an output inductor, and a switch, The full-wave signal is stepped down according to the control signal being turned on or off; the voltage sampling circuit is coupled to the first voltage terminal, and samples the full-wave signal to generate a sampling signal having the same phase as the full-wave signal; zero current a detecting circuit that detects whether a current flowing through the output inductor is zero to generate a first signal; a current sensing circuit detects a current flowing through the switch, and generates a second signal compared with the sampling signal; and a driving circuit, The zero current detecting circuit and the current sensing circuit are coupled to generate the control signal according to the first signal and the second signal, wherein the first signal triggers the conduction of the switch, and the second signal triggers the closing of the switch. The buck converter of claim 1, wherein the zero current detecting circuit comprises: an auxiliary inductor that senses a current of the output inductor to generate a third signal; a hysteresis comparator coupled to the auxiliary inductor to allow the third signal The fourth signal is generated in comparison with the threshold value, and a logic circuit generates the first signal based on the fourth signal. The step-down converter of claim 1, wherein the voltage sampling circuit comprises: a voltage divider coupled to the first voltage terminal, and dividing the full-wave signal to form a third signal; and a voltage compensation circuit coupled to the first a voltage terminal, generating a fourth signal according to a level of the full wave signal; and a multiplier, multiplying the third signal by the fourth signal to generate the sampling signal, so that the sampling signal is at an AC power source of different voltage levels Both can be maintained at the same level. The buck converter of claim 3, wherein the voltage compensation circuit comprises a low pass filter connected to the first voltage terminal to filter out a low frequency in the full wave signal, the cutoff frequency is much less than 60 Hz; the error amplifier has a positive input terminal, a negative input terminal and an output terminal, the filtered full-wave signal is input to the negative input terminal, and the reference voltage is input to the positive input terminal to generate a fifth signal; the first resistor is connected to the negative input terminal and Between the low pass filters; a second resistor connected between the low pass filter and the ground; and a loop compensation circuit connected between the negative input and the output to feed the fifth signal Up to the negative input terminal; a subtractor that subtracts the reference signal from the fifth signal to generate the fourth signal. The buck converter of claim 1, wherein the buck output stage further comprises a resistor connected in series between the switch and the ground to generate a third signal related to current flowing through the switch. The buck converter of claim 5, wherein the current sensing circuit includes a comparator that compares the third signal and the sampled signal to generate the second signal. The buck converter of claim 5, wherein the current sensing circuit further comprises an overcurrent protection comparator that compares whether the third signal exceeds a limit value to generate the second signal. The buck converter of claim 1, wherein the driving circuit comprises an SR flip-flop, and the control signal is generated according to the first signal and the second signal. A buck converter control method, wherein the buck converter comprises a diode, an output inductor and a switch, the control method comprises: rectifying an AC power source to generate a full-wave signal; sampling the full-wave signal, generating and The wave signal has a sampling signal of the same phase; detecting whether the current flowing through the output inductor is zero, generating a first signal; detecting a current flowing through the switch, and generating a second signal compared with the sampling signal; The signal and the second signal generate a control signal, wherein the first signal triggers the conduction of the switch, the second signal triggers the closing of the switch; and the full-wave signal is stepped down by turning the switch on or off according to the control signal. The control method of claim 9, wherein the detecting the current flowing through the output inductor is zero, and the step of generating the first signal comprises: sensing an electric current of the output inductor by using an auxiliary inductor to generate a third signal; The third signal is compared to a threshold value to generate the fourth signal; and the first signal is generated based on the fourth signal. The control method of claim 9, wherein the step of sampling the full-wave signal to generate a sampling signal having the same phase as the full-wave signal comprises: dividing the full-wave signal into a third signal; according to the full-wave signal The level is generated by the fourth signal; and the third signal is multiplied by the fourth signal to generate the sampling signal, so that the sampling signal can be maintained at the same level under the AC power source of different voltage levels. The control method of claim 9, wherein the detecting the current flowing through the switch and comparing the sampling signal to generate the second signal comprises using a resistor in series with the switch to generate a third associated with current flowing through the switch signal. The control method of claim 12, wherein the detecting the current flowing through the switch and comparing the sampling signal to generate the second signal comprises comparing the third signal and the sampling signal to generate the second signal. The control method of claim 12 further includes comparing whether the third signal exceeds a limit value, and generating the second signal triggers the closing of the switch. A buck converter control circuit, wherein the buck converter includes a rectifier coupled to an AC power source to generate a full-wave signal to a first voltage terminal, and a buck output stage coupled to the first voltage terminal includes a diode, an output inductor And a switch, the full-wave signal is stepped down according to the control signal being turned on or off, the control circuit comprising: a voltage sampling circuit coupled to the first voltage terminal, sampling the full-wave signal, generating and having the full-wave signal a sampling signal of the same phase; a zero current detecting circuit detecting whether the current flowing through the output inductor is zero, generating a first signal; and a current sensing circuit detecting a current flowing through the switch, and generating a comparison with the sampling signal a second signal; and a driving circuit coupled to the zero current detecting circuit and the current sensing circuit, generating the control signal according to the first signal and the second signal, wherein the first signal triggers conduction of the switch, the first The two signals trigger the closing of the switch. The control circuit of claim 15, wherein the zero current detecting circuit comprises: an auxiliary inductor that senses a current of the output inductor to generate a third signal; a hysteresis comparator coupled to the auxiliary inductor to allow the third signal to be thresholded Comparing the values, generating the fourth signal; and logic circuitry generating the first signal based on the fourth signal. The control circuit of claim 15, wherein the voltage sampling circuit comprises: a voltage divider coupled to the first voltage terminal, the partial wave signal is divided to form a third signal; and the voltage compensation circuit is coupled to the first voltage terminal And generating a fourth signal according to the level of the full wave signal; and a multiplier, multiplying the third signal by the fourth signal to generate the sampling signal, so that the sampling signal is under an alternating current power source of different voltage levels Can be maintained at the same level. The control circuit of claim 17, wherein the voltage compensation circuit comprises a low pass filter connected to the first voltage terminal to filter out a low frequency in the full wave signal, the cutoff frequency is much less than 60 Hz; the error amplifier has a positive input a negative input terminal and an output terminal, the filtered full-wave signal is input to the negative input terminal, and the reference voltage is input to the positive input terminal to generate a fifth signal; the first resistor is connected to the negative input terminal and the low terminal a second resistor connected between the low pass filter and the ground; and a loop compensation circuit connected between the negative input terminal and the output terminal, and the fifth signal is fed back to the a negative input terminal; a subtractor that subtracts the reference signal from the fifth signal to generate the fourth signal. The buck converter of claim 15, wherein the buck output stage further comprises a resistor coupled in series between the switch and the ground to generate a third signal associated with current flowing through the switch. The buck converter of claim 19, wherein the current sensing circuit includes a comparator that compares the third signal and the sampled signal to generate the second signal. The buck converter of claim 19, wherein the current sensing circuit further comprises an overcurrent protection comparator that compares whether the third signal exceeds a limit value to generate the second signal. The buck converter of claim 15, wherein the driving circuit comprises an SR flip-flop, and the control signal is generated according to the first signal and the second signal.