Frequency control circuit of boost converter and boost converter

Abstract

The invention provides a boost converter and a frequency control circuit thereof, the boost converter comprises a main switch tube and a rectifier tube which are connected, the common connection end of the main switch tube and the rectifier tube is a first node, and the boost converter comprises a sampling hold circuit which samples and holds the voltage of the first node during the turn-off period of the main switch tube to obtain a first sampling signal; the integral circuit is used for integrating a second sampling signal representing the first sampling signal along with time to obtain a first integral signal during the turn-off period of the main switching tube; and the first comparator is used for comparing the first integral signal with an input sampling signal, when the first integral signal reaches the input signal, the main switch tube is controlled to be switched on, and the input sampling signal is proportional to the input voltage of the boost converter. The switching frequency of the boost converter can be controlled to be constant by controlling the turn-off time of the main switching tube.

Description

Technical Field

[0001] This invention relates to the field of power electronics, and in particular to a frequency control circuit for a boost converter and a boost converter. Background Technology

[0002] In boost converters, it is often necessary to control the switching frequency to achieve fixed-frequency or variable-frequency operation. Existing frequency control schemes require sampling the input and output voltages of the boost converter, designing the turn-off time of the main switch based on these voltages, and setting the switching frequency of the boost converter according to the magnitude of this turn-off time, thereby achieving switching frequency control.

[0003] Existing frequency control schemes require sampling of both output and input voltages. Furthermore, the relationship between input and output voltages differs between continuous conduction mode (CCM) and discontinuous conduction mode (DCM) of the boost converter. Different schemes are needed to achieve fixed-frequency control in different modes, making the control method quite complex. Summary of the Invention

[0004] The purpose of this invention is to provide a frequency control circuit and a boost converter. This invention can simultaneously achieve a constant switching frequency in both continuous conduction mode and intermittent conduction mode.

[0005] This invention also provides a frequency control circuit for a boost converter, the boost converter including a main switch, a rectifier, and an inductor, wherein the common connection terminal of the main switch and the rectifier is a first node, and the inductor is connected to the first node, including...

[0006] A sample-and-hold circuit samples and holds the voltage of the first node during the period when the main switch is turned off, to obtain a first sample signal;

[0007] An integrating circuit integrates the second sampling signal, which represents the first sampling signal, over time during the period when the main switch is off, to obtain a first integrated signal.

[0008] A first comparator compares the first integrated signal with the input sampling signal to generate a first control signal. When the first integrated signal reaches the input sampling signal, the first control signal controls the main switch to turn on.

[0009] The input sampling signal is proportional to the input voltage of the boost converter, and the proportionality coefficient is the first proportionality coefficient.

[0010] Optionally, it also includes a conversion unit to convert the first sampled signal into the second sampled signal, wherein the second sampled signal is proportional to the first sampled signal and the scaling factor is a second scaling factor.

[0011] Optionally, the second sampling signal is a current signal.

[0012] Optionally, the first proportionality coefficient is a constant value.

[0013] Optionally, the switching frequency of the boost converter is constant.

[0014] Optionally, the first proportional coefficient is adjustable, and the switching frequency of the boost converter can be adjusted by adjusting the first proportional coefficient.

[0015] Optionally, the second proportionality coefficient is a constant value.

[0016] Optionally, when the boost converter operates in continuous conduction mode, the turn-off time of the main switch is proportional to the ratio of the input voltage to the output voltage of the boost converter, and the proportionality coefficient is a third proportionality coefficient, which characterizes the switching frequency of the boost converter.

[0017] Optionally, the third proportional coefficient can be set according to the first proportional coefficient and the second proportional coefficient.

[0018] Optionally, when the boost converter operates in discontinuous conduction mode, the ratio of the integral of the output voltage over time during the freewheeling period of the inductor and the integral of the input voltage over time during the period when the inductor current is zero to the input voltage is a fourth proportionality coefficient, which represents the switching frequency of the boost converter.

[0019] Optionally, the fourth proportional coefficient can be set according to the first proportional coefficient and the second proportional coefficient.

[0020] Optionally, the sample-and-hold circuit includes a first resistor, a second resistor, and a sample-and-hold unit. The first resistor and the second resistor are connected in series and then connected to the first node. The sample-and-hold unit samples the voltage at the connection point of the first resistor and the second resistor during the off-state of the main switch and holds it during the on-state of the main switch to obtain the first sample signal.

[0021] Optionally, the conversion unit includes a third resistor, which controls the voltage across the third resistor to be equal to the first sampling signal, and obtains the second sampling signal based on the current in the third resistor.

[0022] Optionally, the conversion unit further includes a first operational amplifier, a first regulating transistor, and a current mirror. The regulating transistor and the third resistor are connected in series. The first input terminal of the first operational amplifier receives the first sampling signal. The second input terminal of the first operational amplifier is connected to the common connection terminal of the third resistor and the regulating transistor. The output terminal of the first operational amplifier is connected to the control terminal of the regulating transistor. The input terminal of the current mirror is connected to the regulating transistor. The output terminal of the current mirror outputs the second sampling signal.

[0023] Optionally, the integrating circuit includes a first capacitor and a first switch, the first switch and the first capacitor are connected in parallel, the second sampling signal charges the first capacitor to obtain the first integrating signal, and when the main switch is turned on, the first switch is turned on to reset the voltage of the first capacitor to zero.

[0024] The present invention also provides a boost converter, including a main switch, a rectifier, and an inductor. The main switch and the rectifier are connected, and the inductor is connected to the common connection terminal of the main switch and the rectifier. The converter also includes any of the frequency control circuits and driving units described above. The frequency control circuit outputs a first control signal to control the turn-off time of the main switch, and the driving unit receives the first control signal to drive the main switch.

[0025] Compared with existing technologies, this invention has the following advantages: This invention samples the node voltage at the connection point between the main switch and the rectifier diodes during the main switch turn-off period of the boost converter, and controls the turn-off time of the main switch based on this node voltage, thereby achieving fixed-frequency control of the boost converter. Whether the boost converter operates in CCM mode or DCM mode, this invention uses the same control scheme to achieve fixed-frequency control, eliminating the need to differentiate between the operating modes of the boost converter for separate control. The control scheme has a wide range of applications and is simple to implement. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the boost converter of the present invention;

[0027] Figure 2 This is a block diagram of the frequency control circuit of the present invention;

[0028] Figure 3 This is a schematic diagram of the frequency control circuit of the present invention;

[0029] Figure 4 This is a waveform diagram of the voltage at the first node of the present invention. Detailed Implementation

[0030] 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. The present invention covers any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the present invention.

[0031] To provide the public with a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the invention, but those skilled in the art can fully understand the invention without these details.

[0032] like Figure 1 The diagram illustrates the schematic of the boost converter of the present invention, including a main switch M1, a rectifier M2, an inductor L, an input capacitor Cin, an output capacitor Cout, and a switching control circuit. The first terminal of the inductor L is connected to the input capacitor Cin, receiving the input voltage Vin after filtering by Cin. The second terminal of the inductor L is connected to the common connection terminal of the main switch M1 and the rectifier M2, denoted as the first node. The first terminals of the main switch M1 and the rectifier M2 are connected, and the second terminal of the main switch M1 is grounded. The second terminal of the rectifier M2 is connected to the output capacitor Cout, and the voltage across the output capacitor Cout is the output voltage Vout of the boost converter. The rectifier M2 in the diagram is exemplified by an NMOS transistor, but it can also be a diode. The switching control circuit includes a frequency control circuit and a drive unit. The frequency control circuit samples the voltage of the first node during the off-state of the main switch M1 to obtain a sampling signal, and controls the off-state time of the main switch M1 based on this sampling signal to achieve frequency control of the boost converter. The fixed-frequency control circuit outputs a turn-off time control signal Toff. The drive unit receives this turn-off time control signal Toff to control the turn-on time of the main switch. The switch control circuit also includes an error amplifier and a comparator (not shown in the figure) to control the turn-off time of the main switch. The error amplifier amplifies the output feedback signal and reference signal of the boost converter to obtain a compensation signal. The comparator compares the compensation signal with the inductor current sampling signal. When the inductor current sampling signal reaches the compensation signal, the main switch is turned off. The design principle of the fixed-frequency control circuit of this invention is as follows:

[0033] When the boost converter operates in CCM mode, the switching period T, the turn-off time Toff of the main switch, the input voltage Vin, and the output voltage Vout satisfy the following:

[0034] T*Vin=Toff*Vout(1);

[0035] When Toff = k*Tc*Vin / Vout, and k*Tc is a constant, that is, when T = k*Tc, the switching frequency of the boost converter is constant. When k*Tc is adjustable, the switching frequency of the boost converter is adjusted accordingly.

[0036] When the boost converter operates in DCM mode, it satisfies the following:

[0037] (t1+t2)*Vin=t2*Vout (2);

[0038] Where t1 is the on-time of the main switch and t2 is the on-time of the rectifier. Adding t3*Vin to both sides of the equation (2), where t3 is the time when the main switch and the rectifier are simultaneously turned off, we get:

[0039] (t1+t2+t3)*Vin=t2*Vout+t3*Vin=T*Vin; (3);

[0040] When T = (t2*Vout + t3*Vin) / Vin = k*Tc, and k*Tc is a constant, the switching frequency / switching period of the boost converter is constant.

[0041] Based on the working principle of the boost converter described above, the following design is performed: Figure 2 The fixed-frequency control circuit shown is shown.

[0042] like Figure 2 The diagram illustrates a block diagram of a fixed-frequency control circuit, including a sample-and-hold circuit 01, a conversion circuit 02, an integrator circuit 03, and a comparator 04. The sample-and-hold circuit 01 samples the voltage Vsw of the first node during the main switch's off-time Toff and holds it to obtain a first sample signal VS1. The conversion circuit 02 receives the first sample signal VS1 and converts it into a second sample signal VS2. The second sample signal VS2 is proportional to the first sample signal VS1. Preferably, the second sample signal is a current signal obtained from the first sample signal. The integrator circuit 03 integrates the second sample signal over time during the main switch's off-time Toff to obtain an integrated signal VS2*Toff (assuming the integration coefficient of the integrator circuit 03 is 1). The comparator 04 compares the integrated signal with the input sample signal K1*Vin, where K1 is a proportionality coefficient greater than zero. When the integrated signal reaches the input sample signal K1*Vin, the main switch is turned off / turned on.

[0043] In CCM mode, during the main switch turn-off period / rectifier turn-on period, the voltage Vsw of the first node is approximately equal to the output voltage Vout. Therefore, the first sampling signal VS1 can be approximated as K2*Vout, and the second sampling signal VS2 can be denoted as K3*K2*Vout. K2 and K3 are both proportional coefficients greater than zero, and the integral signal is K3*K2*Vout*Toff. When the integral signal reaches the input sampling signal, that is, K3*K2*Vout*Toff=K1*Vin, we have Toff=(K1*K3 / K2)*Vin / Vout. According to equation (1), the switching period of the boost converter is equal to (K1*K3 / K2). Usually, (K1*K3 / K2) is a constant. Therefore, the switching period / switching frequency of the boost converter is a constant value. If (K1*K3 / K2) can be adjusted, the switching period / switching frequency of the boost converter can also be adjusted.

[0044] In DCM mode, during the time t2 when the main switch is off and the rectifier is on, the average value of the voltage Vsw at the first node is equal to Vout. During the time t3 when both the main switch and the rectifier are off, the voltage Vsw at the first node is approximately equal to the output voltage Vin. Therefore, the first sampled signal VS1 can be approximated as K2*(t2*Vout+t3*Vin) / (t2+t3).

[0045] The second sampled signal VS2 can be denoted as K3*K2*(t2*Vout+t3*Vin) / (t2+t3), where K2 and K3 are both proportional coefficients greater than zero. The integral signal is K3*K2*(t2*Vout+t3*Vin)*Toff / (t2+t3). When the integral signal reaches the input sampled signal, i.e., K3*K2*(t2*Vout+t3*Vin)*Toff / (t2+t3)=K1*Vin, we have

[0046] Toff=K1*Vin*(t2+t3) / (K3*K2*(t2*Vout+t3*Vin)), since the turn-off time of the main switch Toff=t2+t3, we have (t2*Vout+t3*Vin) / Vin=K1 / (K3*K2), combining with equation (3), we have T=K1 / (K3*K2), since K1 / (K3*K2) is a constant, the switching period / switching frequency of the boost converter is constant. If K1 / (K3*K2) is an adjustable coefficient, the switching period / switching frequency of the boost converter can be adjusted accordingly. Among them, any one or more parameters of K1, K2, K3 can be adjusted, and K1 / (K3*K2) can be adjusted.

[0047] Since both the first sampling signal VS1 and the second sampling signal VS2 are obtained from the voltage Vsw of the first node and are proportional to the voltage Vsw, a sampling signal proportional to Vsw can be directly obtained from the voltage of the first node. This sampling signal can then be integrated over the turn-off time Toff of the main switch to obtain the integrated signal. Any scheme that, according to the present invention, samples the voltage of the first node during the turn-off period of the main switch, integrates the sampling signal representing the voltage of the first node over the turn-off time of the main switch, and uses this integration to control the turn-off time of the main switch to achieve fixed-frequency control, is within the scope of protection of this invention.

[0048] like Figure 3 The diagram shown illustrates the schematic of the fixed-frequency control circuit of the present invention, based on... Figure 2 The block diagram of the design shows that the sample-and-hold circuit 01 includes voltage divider resistors R1 and R2 and a sample-and-hold unit 101. Resistors R1 and R2 are connected in series to the first node and are used to divide and sample the voltage Vsw of the first node. The sample-and-hold unit 101 receives the voltage at the connection of resistors R1 and R2 and performs sampling and holding during the turn-off period of the main switch transistor Toff to obtain the first sample signal R2*Vsw / (R1+R2). The conversion circuit 02 includes operational amplifier 201, regulating transistor M201, resistor R3, and a current mirror formed by connecting regulating transistors M202 and M203. Assuming that regulating transistors M202 and M203 have the same size, the non-inverting input terminal of operational amplifier 201 receives voltage R2*Vsw / (R1+R2), its inverting input terminal is connected to the common connection terminal of regulating transistor S1 and resistor R3, and its output terminal is connected to the control terminal of regulating transistor S1. Regulating transistors M201 and M202 and resistor R3 are connected in series. The output current of regulating transistor M203 is R2*Vsw / ((R1+R2)*R3), which serves as the second sampling signal.

[0049] The integrator circuit 03 includes a capacitor C1 and a first switch S1 connected in parallel. When the main switch is off, the first switch S1 is off, and the output current of the regulating transistor M203 charges the capacitor C1. The voltage VC1 on the capacitor C1 (C1 also represents the capacitance value) is VC1 = Toff*R2*Vsw / ((R1+R2)*R3*C1). The capacitance value of the capacitor C1 serves as the integration coefficient of the integrator circuit 03, and is a constant greater than zero. The comparator 04 compares the voltage VC1 on the capacitor C1 with the input sampling signal K1*Vin. When VC1 = K1*Vin, the output signal of the comparator 04 flips, controlling the main switch to turn on. After the main switch is turned on, the first switch S1 is turned on, and the voltage of the capacitor C1 is reset to zero.

[0050] In CCM mode, when the main switch is turned off, the voltage Vsw of the first node is approximately equal to Vout. Further, we have VC1 = Toff * R2 * Vout / ((R1 + R2) * R3 * C1). When VC1 = K1 * Vin, we have Toff = (K1 * ((R1 + R2) * R3 * C1) / R2) * Vin / Vout. Since K1, R1, R2, R3, and C1 are all constants, according to equation (1), T = K1 * ((R1 + R2) * R3 * C1) / R2 is also a constant. Therefore, the switching frequency / switching period of the boost converter is constant. Optionally, if K1 is an adjustable coefficient, the switching frequency / switching period can be adjusted accordingly, for example, from one constant switching frequency to another.

[0051] In DCM mode, combined with the above... Figure 2 Based on the analysis, when the main switch is turned off, the voltage Vsw at the first node is approximately equal to (t2*Vout+t3*Vin) / (t2+t3).

[0052] Furthermore, we have VC1 = Toff * R2 * (t2 * Vout + t3 * Vin) / ((t2 + t3)(R1 + R2) * R3). When VC1 = K1 * Vin, we have Toff = K1 * Vin * (t2 + t3)(R1 + R2) * R3 / (R2 * (t2 * Vout + t3 * Vin)). Since Toff = t2 + t3, we have t2 * Vout + t3 * Vin = (K1 * (R1 + R2) * R3 / R2) * Vin. Since K1, R1, R2, R3, and C1 are all constants, according to equation (3), T = K1 * (R1 + R2) * R3 / R2 is also a constant. Therefore, the switching frequency / switching period of the boost converter is constant. Optionally, if K1 is an adjustable coefficient, the switching frequency / switching period can be adjusted accordingly.

[0053] Based on the above analysis, the boost converter of the present invention controls the turn-off time of the main switch by sampling the voltage Vsw of the first node during the turn-off period of the main switch, thereby controlling the switching frequency of the boost converter to be constant. Regardless of whether it is operating in CCM mode or DCM mode, the boost converter of the present invention can achieve fixed frequency control.

[0054] like Figure 4The diagram illustrates the waveform of the first node voltage of the boost converter of the present invention. Vsw_CCM represents the voltage waveform of the first node when the boost converter operates in CCM mode, and Vsw_DCM represents the voltage waveform of the first node when the boost converter operates in DCM mode. In CCM mode, time t1 is the on-time of the main switch. When the main switch is on, the voltage Vsw_CCM of the first node is ground voltage (assuming the voltage drop of the main switch is zero), and the waveform is low. Time t2+t3 is the off-time of the main switch. When the main switch is off, the rectifier diode is on, and the voltage Vsw_CCM of the first node is approximately equal to the output voltage, and the waveform is high. In DCM mode, time t1 is the on-time of the main switch. When the main switch is on, the voltage at the first node is Vsw_DCM ground voltage (assuming the main switch on-time voltage drop is zero), and the waveform is low. Time t2 is the time when the main switch is off and the rectifier is on. The voltage at the first node, Vsw_DCM, is approximately equal to the output voltage. Time t3 is the time when the main switch and the rectifier are off simultaneously. The voltage at the first node, Vsw_DCM, is approximately equal to the input voltage, lower than the output voltage, and higher than the ground voltage. Therefore, the Vsw_CCM waveform during time t3 is higher than the Vsw_CCM waveform during time t1, but lower than the Vsw_CCM waveform during time t2.

[0055] The invention is described more specifically in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the drawings are in a simplified form and use non-precise proportions, in order to facilitate and clearly illustrate the purpose of the embodiments of the invention.

[0056] Although the embodiments are described and illustrated separately above, some common technologies are involved. Those skilled in the art can replace and integrate them between the embodiments. If there is any content not explicitly described in one embodiment, then another embodiment that is described can be referred to.

[0057] The embodiments described above do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the above embodiments should be included within the scope of protection of this technical solution.

Claims

1. A frequency control circuit of a boost converter, the boost converter comprising a main switch, a rectifier and an inductor, a common connection of the main switch and the rectifier being a first node, the inductor connecting the first node, characterized in that: comprising a sample-and-hold circuit, which samples and holds the voltage of the first node during the off period of the main switch to obtain a first sample signal; an integration circuit, which integrates the second sample signal representing the first sample signal over time to obtain a first integration signal during the off period of the main switch; a first comparator, which compares the first integration signal with an input sample signal to generate a first control signal, and when the first integration signal reaches the input sample signal, the first control signal controls the main switch to turn on; wherein the input sample signal is proportional to the input voltage of the boost converter, and the proportional coefficient is a first proportional coefficient.

2. The frequency control circuit of claim 1, wherein: further comprising a conversion unit, which converts the first sample signal into the second sample signal, and the second sample signal is proportional to the first sample signal, and the proportional coefficient is a second proportional coefficient.

3. The frequency control circuit of claim 1, wherein: the second sample signal is a current signal.

4. The frequency control circuit of claim 1, wherein: the first proportional coefficient is a constant value.

5. The frequency control circuit of claim 4, wherein: the switching frequency of the boost converter is constant.

6. The frequency control circuit of claim 1, wherein: the first proportional coefficient is adjustable, and the switching frequency of the boost converter is adjusted by adjusting the first proportional coefficient.

7. The frequency control circuit of claim 2, wherein: the second proportional coefficient is a constant value.

8. The frequency control circuit of claim 2, wherein: when the boost converter works in continuous conduction mode, the off time of the main switch is proportional to the ratio of the input voltage to the output voltage of the boost converter, and the proportional coefficient is a third proportional coefficient, and the third proportional coefficient represents the switching frequency of the boost converter.

9. The frequency control circuit of claim 8, wherein: the third proportional coefficient is set according to the first proportional coefficient and the second proportional coefficient.

10. The frequency control circuit of claim 2, wherein: when the boost converter works in discontinuous conduction mode, the ratio of the sum of the integral of the output voltage over time during the freewheeling period of the inductor to the integral of the input voltage over time during the period when the inductor current is zero to the input voltage is a fourth proportional coefficient, and the fourth proportional coefficient represents the switching frequency of the boost converter.

11. The frequency control circuit of claim 10, wherein: the fourth proportional coefficient is set according to the first proportional coefficient and the second proportional coefficient.

12. The frequency control circuit of claim 1, wherein: the sample-and-hold circuit comprises a first resistor, a second resistor, and a sample-and-hold unit, the first resistor and the second resistor are connected in series and connected to the first node, and the sample-and-hold unit samples the voltage at the connection end of the first resistor and the second resistor during the off period of the main switch and holds it during the on period of the main switch to obtain the first sample signal.

13. The frequency control circuit of claim 3, wherein: the conversion unit comprises a third resistor, the conversion unit controls the voltage across the third resistor to be equal to the first sample signal, and the second sample signal is obtained according to the current of the third resistor.

14. The frequency control circuit of claim 13, wherein: the conversion unit further comprises a first operational amplifier, a first adjusting tube, and a current mirror, the adjusting tube and the third resistor are connected in series, the first input end of the first operational amplifier receives the first sample signal, the second input end of the first operational amplifier is connected to the common connection end of the third resistor and the adjusting tube, the output end of the first operational amplifier is connected to the control end of the adjusting tube, and the input end of the current mirror is connected to the adjusting tube. The output end of the current mirror outputs the second sample signal.

15. The frequency control circuit of claim 3, wherein: The integration circuit comprises a first capacitor and a first switch, the first switch and the first capacitor are connected in parallel, the first capacitor is charged by the second sampling signal to obtain the first integration signal, and the first switch is turned on to reset the voltage of the first capacitor to zero when the main switch tube is turned on.

16. A boost converter comprising a main switch, a rectifier and an inductor, the main switch and the rectifier being connected, the inductor connecting a common connection of the main switch and the rectifier, characterized in that: The frequency control circuit and the driving unit are also included, and the frequency control circuit outputs a first control signal for controlling the off time of the main switch tube, and the driving unit receives the first control signal to drive the main switch tube.

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