Control circuit and control method of switching circuit, and switching circuit

Abstract

The present invention discloses a control circuit, control method, and switching circuit for a switching circuit. A reference voltage is fed back to the control circuit to output a compensation voltage. A voltage representing the inductor current of the switching circuit is obtained and proportionally adjusted according to an adjustment parameter to output an adjustment voltage. The compensation voltage and the adjustment voltage are obtained, and the difference between the two is taken to output a corrected compensation voltage for controlling the on-time of the main power transistor of the switching circuit. The present invention improves the waveform of the input current, thereby effectively reducing THD.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a control circuit and a control method of a switching circuit, and a switching circuit. Background Art

[0002] Switching converter circuits are widely used in the field of power electronics. In order to prevent the input current of the converter from polluting the power grid, it is usually required that the THD (total harmonic distortion) generated by the converter should be reduced as much as possible and meet specific national or industry standards. Constant on-time (COT) control is a common way to control switching circuits. It is particularly suitable for applications with high power factor (HPF) and near-continuous conduction (BCM) inductor voltage. It is simple to control, does not require sampling the input voltage, has good efficiency and EMI effects, and is widely used. The constant on-time control block diagram is shown in the figure below. Figure 1 As shown, the reference voltage Vref and the feedback voltage V FB After the difference is made, the error signal e passes through the compensator to obtain the compensation voltage Vc. After comparing it with the sawtooth wave, the MOS conduction time T is obtained. ON For high PF applications, the system bandwidth is low and the Vc voltage remains basically unchanged during the power frequency cycle, so T ON The time does not change within the power frequency cycle.

[0003] In the Boost circuit, theoretically, the input current and input voltage have a proportional relationship, and the THD of the input current will be very small. However, in actual applications, due to the influence of MOS drive delay and zero-crossing detection delay, the actual inductor current I in When operating in the discontinuous state, the inductor and various parasitic capacitors and RC snubber circuit capacitors may resonate, and the inductor peak current during the switching cycle is no longer proportional to the input voltage, as shown in Figure 2(a). In addition, when the grid voltage V in Near zero crossing, the existence of negative current makes the inductor current I in The average value will reach 0 too early, which is called a "dead zone" phenomenon, as shown in Figure 2(b). As a result, the current waveform distortion generated in the actual application of the boost circuit, especially the more serious "dead zone" phenomenon, will cause a large THD of the input current. Summary of the Invention

[0004] In view of this, an object of the present invention is to provide a control method and a control circuit for a switching circuit, which can effectively reduce the THD of the input current of the switching circuit.

[0005] Based on the above objectives, the present invention provides a control circuit for a switch circuit, the control circuit comprising:

[0006] A compensation voltage generating circuit outputs a compensation voltage by feedback compensation based on a reference voltage;

[0007] A characterization voltage adjustment circuit obtains a characterization voltage of the inductor current of the switching circuit, proportionally adjusts the characterization voltage according to an adjustment parameter, and outputs an adjusted voltage;

[0008] The correction circuit obtains the compensation voltage and the adjustment voltage, takes a difference between the two, and outputs a corrected compensation voltage for controlling the conduction time of the main power tube of the switching circuit.

[0009] Optionally, the adjustment parameter is positively correlated with the compensation voltage.

[0010] Optionally, the control circuit further includes:

[0011] a conduction time calculation circuit, which compares the corrected compensation voltage with a sawtooth wave signal to obtain a first conduction control signal. When the sawtooth wave signal does not reach the corrected compensation voltage, the first control signal controls the main power tube to conduct normally;

[0012] A delay logic circuit, when the sawtooth wave signal reaches the corrected compensation voltage, if the characterization voltage is less than the threshold voltage, the delay logic circuit controls the on-time of the main power tube to be extended, and when the extended on-time of the main power tube reaches the threshold time, the delay logic circuit controls the main power tube to be turned off; or, when the characterization voltage is greater than or equal to the threshold voltage, the delay logic circuit controls the main power tube to be turned off, and the extended on-time of the main power tube is less than or equal to the threshold time.

[0013] The present invention also provides a control method for a switch circuit, comprising the steps of:

[0014] The reference voltage is used to output a compensation voltage through feedback compensation;

[0015] Acquiring a representative voltage of the inductive current of the switching circuit, proportionally adjusting the representative voltage according to an adjustment parameter, and outputting an adjusted voltage;

[0016] The compensation voltage and the adjustment voltage are obtained, and after taking a difference between the two, a corrected compensation voltage is output for controlling the conduction time of the main power tube of the switching circuit.

[0017] Optionally, when the sawtooth wave signal reaches the corrected compensation voltage, when the sawtooth wave signal reaches the corrected compensation voltage, if the characterization voltage is less than the threshold voltage, the conduction time of the main power tube is extended, and when the extended conduction time of the main power tube reaches the threshold time, the delay logic circuit controls the main power tube to turn off; or, when the characterization voltage is greater than or equal to the threshold voltage, the main power tube is turned off, and the extended conduction time of the main power tube is less than or equal to the threshold time.

[0018] The present invention also provides a switch circuit, comprising any one of the control circuits described above.

[0019] This invention offers the following advantages over existing technologies: It considers the adverse effects of inductor current on the input circuit waveform in actual switching circuit applications. It uses an adjustment voltage representative of the inductor current to modify the compensation voltage, thereby adjusting the on / off time of the switching circuit, thereby optimizing the input circuit waveform and reducing THD. In some specific technical solutions, the invention further adjusts the on / off time of the switching circuit by extending the on-time or comparing conditions, thereby further reducing THD. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The following schematically shows a structural block diagram of a constant control circuit based on the prior art.

[0021] Figure 2 schematically shows the voltage and current change curves in the switching circuit based on the prior art, where Figure 2(a) is a comparison of the input current Iin change over time with a standard sine curve, and Figure 2(b) is a comparison of the input voltage Vin and input current Iin change over time.

[0022] Figure 3 The schematic diagram of the circuit principle for generating the corrected compensation voltage of the present invention is shown.

[0023] Figure 4 The control circuit principle diagram of the switch circuit of the present invention is schematically shown.

[0024] Figure 5 schematically shows the voltage and current change curves in the switching circuit of the present invention, wherein Figure 5(a) is a comparison of the input current Iin change over time according to the scheme of the present invention with the standard sine curve and the prior art, and Figure 5(b) is a comparison of the input voltage Vin and input current Iin change over time according to the technical scheme of the present invention with the prior art. DETAILED DESCRIPTION

[0025] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments and covers any substitution, modification, equivalent method and solution made within the spirit and scope of the present invention.

[0026] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the drawings are simplified and not to exact proportions, and are only used for the purpose of conveniently and clearly illustrating the embodiments of the present invention.

[0027] Figure 3 The control circuit structure block diagram of an embodiment of the present invention is schematically shown. The control circuit includes: a compensation voltage generating circuit 110, which outputs a compensation voltage Vc by feedback compensation from a reference voltage Vref; a characterizing voltage adjusting circuit 120, which obtains a characterizing voltage Vcs of the inductor current of the switching circuit, and proportionally adjusts the characterizing voltage Vcs according to an adjustment parameter k, and outputs an adjustment voltage k*Vcs; a correction circuit 130, which obtains the compensation voltage Vc and the adjustment voltage k*Vcs, takes the difference between the two, and outputs a corrected compensation voltage Vc1 for controlling the on-time Ton of the switching circuit. The compensation voltage generating circuit 110 is a common part in a constant control circuit, that is, it generates a compensation voltage Vc1 by a reference voltage Vref and a feedback voltage V FB After subtraction, the error signal passes through the compensator to obtain the compensation voltage Vc. In the prior art, the compensation voltage Vc is used to control the on-time Ton of the MOS. However, according to the present invention, the compensation voltage Vc is not directly used to control the on-off of the MOS, but is instead corrected in some way. The characterizing voltage adjustment circuit 120 first obtains the voltage Vcs that characterizes the inductor current in the switching circuit. However, Vcs cannot generally be used directly to correct the compensation voltage Vc. According to the present invention, an adjustment parameter k is provided. After adjusting the characterizing voltage Vcs by the adjustment parameter k, it can be used to correct the compensation voltage Vc. The correction circuit obtains the compensation voltage Vc and the adjustment voltage k*Vcs, takes the difference between the two, and outputs a corrected compensation voltage Vc1. The relationship between the three is Vc1 = Vc - k*Vcs. The corrected compensation voltage Vc1 can be used to control the on-off of the switching circuit. The adjustment parameter k is a constant that determines the degree of Vcs voltage compensation. A too small value will not achieve effective compensation, while a too large value will degrade THD. The value should take into account factors such as input and output voltages, the main inductor, and the parasitic capacitances of the MOS and diode. In the control loop, negative inductor current feedback (Vc1 = Vc - kVcs) is introduced. This increases the MOS conduction time near grid valleys and shortens it near peaks, compensating for the negative inductor current's effect on input current THD.

[0028] Figure 4The control circuit principle diagram according to the present invention is schematically shown, including a first comparator U01, a second comparator U03, a delay logic circuit U04, a first trigger U02, a second trigger U05 and a zero-crossing comparator (ZCD) U06. When the inductor current crosses zero, the zero-crossing comparator U06 controls the main power tube of the switch circuit to turn on. The first comparator U01 compares the corrected compensation voltage Vc1 with the ramp signal. When the ramp signal does not reach the corrected compensation voltage Vc1, the first comparator U01 outputs a low-level signal, the trigger U02 outputs a low-level signal, and the main power tube conducts normally. When the ramp signal reaches the corrected compensation voltage Vc1, the output signal of the first comparator U01 flips from a low level to a high level, and the output signal of the first trigger U02 flips from a low level to a high level. The second comparator U03 determines whether the voltage VCS representing the inductor current has reached the threshold voltage VREF1. If the voltage VCS has not reached the threshold voltage VREF1, the delay logic control circuit outputs a low-level signal, and the main power tube extends its on-time after normal conduction until the voltage VCS reaches the threshold voltage VREF1, and the extended on-time is less than or equal to the threshold time. In addition, the delay logic circuit itself sets a threshold time. When the voltage VCS has not yet reached the threshold voltage VREF1, but the extended on-time has reached the threshold time, the delay logic circuit outputs a high-level signal, and the main power tube is turned off.

[0029] FIG5 schematically shows the voltage and current variation curves in the switching circuit according to the present invention, wherein FIG5(a) is a comparison of the input current Iin variation with time according to the present invention and the standard sine curve and the prior art, and FIG5(b) is a comparison of the input voltage V according to the present invention. in And input current I in Comparison of the curves changing over time with the prior art. As shown in Figure 5(a), according to the technical solution of the present invention, since the Vcs signal basically follows the input voltage, the Vc1 signal is relatively high when the input voltage is low, and relatively low when the input voltage is high, that is, the TON time of the MOS is relatively small near the peak point of the input voltage and relatively large near the bottom. Compared with the traditional solution, the inductor current peak of the improved solution is relatively small at the peak point of the input voltage and relatively large at the bottom; therefore, the improved solution compensates for the input current distortion caused by the negative inductor current, thereby improving THD. As shown in Figure 5(b), where V in is the input voltage variation curve, I in-1 is the input current curve according to the prior art, I in This is the input current change curve according to the technical solution of the present invention. According to the solution of the present invention, since the inductor current is larger near the bottom of the grid voltage, more energy can be transmitted in each switching cycle, the filter capacitor voltage is lower, and the input current dead time is shorter, which compensates for the influence of the filter capacitor on the input current THD.

[0030] According to one embodiment, the present invention also proposes a switching circuit control method, comprising the steps of: outputting a compensation voltage from a reference voltage through feedback compensation; obtaining a representative voltage of the inductor current of the switching circuit, and proportionally adjusting the representative voltage according to an adjustment parameter to output an adjustment voltage; obtaining the compensation voltage and the adjustment voltage, taking the difference between the two, and outputting a corrected compensation voltage for controlling the conduction time of the switching circuit.

[0031] The present invention offers the following advantages over existing technologies: It considers the adverse effects of inductor current on the input circuit waveform in actual switching circuit applications. It uses an adjustment voltage representative of the inductor current to modify the compensation voltage, thereby adjusting the on-off time of the switching circuit, thereby optimizing the input current waveform and reducing THD. In some specific technical solutions, the present invention further adjusts the on-off time of the switching circuit by adding a delay condition or a comparison condition, thereby further reducing THD.

[0032] The terms "a" or "an" used in this specification and claims should be understood to mean "at least one" unless explicitly stated otherwise or the context precludes such interpretation. Unless explicitly stated to the contrary, any method claimed in the specification and claims that includes more than one step or action is not limited to the order in which the steps or actions are recited.

[0033] The above-described embodiments do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the above-described embodiments shall be included in the scope of protection of this technical solution.

Claims

1. A control circuit for a switching circuit, characterized in that: The control circuit includes: A compensation voltage generating circuit outputs a compensation voltage by feedback compensation based on a reference voltage; A characterization voltage adjustment circuit obtains a characterization voltage of the inductor current of the switching circuit, proportionally adjusts the characterization voltage according to an adjustment parameter, and outputs an adjusted voltage; a correction circuit, which obtains the compensation voltage and the adjustment voltage, takes a difference between the two, and outputs a corrected compensation voltage for controlling the conduction time of the main power tube of the switching circuit; The conduction time calculation circuit compares the modified compensation voltage with a sawtooth wave signal to obtain a first conduction control signal. When the sawtooth wave signal does not reach the modified compensation voltage, the first conduction control signal controls the main power tube to conduct normally.

2. The control circuit according to claim 1, wherein: The adjustment parameter is positively correlated with the compensation voltage.

3. The control circuit according to claim 1, wherein: Further including: A delay logic circuit, when the sawtooth wave signal reaches the modified compensation voltage, if the characterization voltage is less than the threshold voltage, the delay logic circuit controls the on-time of the main power tube to be extended, and when the extended on-time of the main power tube reaches the threshold time, the delay logic circuit controls the main power tube to be turned off; or, when the characterization voltage is greater than or equal to the threshold voltage, the delay logic circuit controls the main power tube to be turned off, and the extended on-time of the main power tube is less than or equal to the threshold time.

4. A control method for a switching circuit, characterized in that: Including steps: The reference voltage is used to output a compensation voltage through feedback compensation; Acquiring a representative voltage of the inductive current of the switching circuit, proportionally adjusting the representative voltage according to an adjustment parameter, and outputting an adjusted voltage; Obtaining the compensation voltage and the adjustment voltage, taking a difference between the two, and outputting a corrected compensation voltage for controlling the conduction time of the main power tube of the switching circuit; The modified compensation voltage is compared with a sawtooth wave signal, and when the sawtooth wave signal does not reach the modified compensation voltage, the main power tube is controlled to be normally turned on.

5. The control method of the switch circuit according to claim 4, characterized in that: When the sawtooth wave signal reaches the modified compensation voltage, if the representative voltage is less than a threshold voltage, the on-time of the main power tube is extended, and when the extended on-time of the main power tube reaches the threshold time, the main power tube is controlled to be turned off; Alternatively, when the characterizing voltage is greater than or equal to a threshold voltage, the main power tube is turned off, and the extended on-time of the main power tube is less than or equal to a threshold time.

6. A switching circuit, characterized in that: The method comprises the control circuit according to any one of claims 1 to 3.

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