A buck-boost converter mode switching circuit

Abstract

The present application belongs to the technical field of Buck-Boost converter control, and particularly relates to a Buck-Boost converter mode switching circuit. According to the switching of the working mode of the Buck-Boost converter, the output voltage of the error amplifier is processed, so that when switching between the buck mode, the extended buck mode, the extended boost mode and the boost mode, the output voltage of the error amplifier is compared with the inductance current information after being processed and superimposed with the slope compensation; thereby the inductance current change speed during mode switching is improved, the output voltage is more smoothly transitioned during mode switching, and the purpose of improving the output stability is achieved; in addition, the present application is simple to operate, does not need to increase complex devices, only needs to reuse the original modules in the circuit, and has a wide application range.

Description

Technical Field

[0001] This invention belongs to the field of Buck-Boost converter control technology, and particularly relates to a Buck-Boost converter mode switching circuit. Background Technology

[0002] Four-switch buck-boost converters possess both buck and boost capabilities, and feature input and output voltages of the same polarity, making them widely used in electric vehicles, energy harvesting, and battery power. When the input and output voltages differ significantly, control timings similar to boost and buck converters are employed for boost and buck modes, respectively. Due to limitations imposed by gate drive and other system non-ideal factors, the duty cycle of the half-bridge has upper and lower limits. This means that when the input and output voltages are close, the control timing of either the boost or buck converter cannot be used continuously; alternative control timings are required as transition modes. Different power stage control timings, combined with the control circuit, cause variations in the overall loop gain. The same input and output voltages and load currents correspond to different error amplifier outputs in different operating modes. However, the output change rate of the error amplifier is generally limited, leading to overshoot and undershoot in output voltage and current during mode switching, which may cause subsequent systems to malfunction. Summary of the Invention

[0003] To address the overshoot and undershoot of output voltage and current caused by mode switching between different operating modes, this invention proposes a four-switch buck-boost converter mode smoothing switching circuit, which can reduce the overshoot and undershoot during switching between boost, buck, and transition modes.

[0004] The technical solution of this invention is as follows:

[0005] A Buck-Boost converter mode switching circuit is characterized by comprising a power stage circuit and a control circuit. The power stage circuit includes a first switch, a second switch, a third switch, a fourth switch, an inductor, an input capacitor, and an output capacitor. The first and second switches are connected in series and parallel between the input terminal of the buck-boost converter and ground. The connection point SW1 between the first and second switches is connected to one end of the inductor. The third and fourth switches are connected in series and parallel between the output terminal of the buck-boost converter and ground. The connection point SW2 between the third and fourth switches is connected to the other end of the inductor. The input capacitor is connected between the input terminal and ground, and the output capacitor is connected between the output terminal and ground.

[0006] The control circuit includes an inductor current detection circuit, a load current detection circuit, a slope compensation generation circuit, a logic control circuit, a drive circuit, a comparator, an internal clock, an output voltage divider resistor, a voltage regulation error amplifier, a constant current error amplifier, a smooth switching auxiliary circuit, a type II compensation network, a bias current, and an internal power supply.

[0007] The output voltage divider resistors include a first resistor R1 and a second resistor R2. The first resistor R1 and the second resistor R2 are connected in series and connected between the output terminal of the buck-boost converter and ground. The connection point of the first resistor R1 and the second resistor R2 is connected to the negative input terminal of the voltage regulation error amplifier. The positive input terminal of the voltage regulation error amplifier is connected to the reference voltage V_REF.

[0008] One end of the load current detection circuit is connected to the output terminal of the buck-boost converter, and the other end of the load current detection circuit outputs load current information V_ILOAD and is connected to the negative input terminal of the constant current error amplifier and the first input terminal of the smooth switching auxiliary circuit. The positive input terminal of the constant current error amplifier is connected to the constant current control signal V_CTRL.

[0009] The output terminals of the constant current error amplifier and the voltage regulator error amplifier are connected together after taking the smaller value, and the output voltage V_C of the error amplifier is generated on the type II compensation network. The type II compensation network includes a compensation capacitor CC and a compensation resistor RC. The compensation capacitor CC and the compensation resistor RC are connected in series and parallel between the output voltage V_C of the error amplifier and ground. The bias current I_BIAS is connected between the internal power supply and the output voltage V_C of the error amplifier.

[0010] One end of the inductor current detection circuit is connected to SW1, and the other end is added to the slope compensation information to serve as the positive input of the comparator. The negative input of the comparator is connected to the output of the smooth switching auxiliary circuit.

[0011] The inputs of the logic control circuit are the output of the comparator, the input voltage of the buck-boost converter, the output voltage of the buck-boost converter, and the internal clock signal. The output of the logic control circuit generates control signals for the first, second, third, and fourth switching transistors through the driver circuit.

[0012] The second input terminal of the smooth switching auxiliary circuit is connected to the output voltage V_C of the error amplifier, the third input terminal of the smooth switching auxiliary circuit is connected to the mode switching control signal MODE generated by the logic control circuit, and the output V_C' of the smooth switching auxiliary circuit is used as the negative input terminal of the comparator.

[0013] The specific method for achieving smooth mode switching of a buck-boost converter through a smooth switching auxiliary circuit is as follows:

[0014] When the buck-boost converter switches modes, a different actual comparison voltage V_C' is output according to different operating modes to replace the error amplifier output voltage V_C and compare it with the inductor current information superimposed with slope compensation. When the buck-boost converter switches to buck mode, the mode switching control signal MODE selects the error amplifier output voltage V_C, K1 times the load current information V_ILOAD, and the first error voltage V_OS1 to be added as the actual comparison voltage V_C'. When the buck-boost converter switches to extended buck mode, the mode switching control signal MODE selects to directly output the actual comparison voltage V_C' without changing the error amplifier output voltage V_C. When the buck-boost converter switches to extended boost mode, the mode switching control signal MODE selects the error amplifier output voltage V_C and the third error voltage V_OS3 to be added as the actual comparison voltage V_C'. When the buck-boost converter switches to boost mode, the mode switching control signal MODE selects the error amplifier output voltage V_C and K2 times the load current... The information V_ILOAD, the second error voltage V_OS2, and the third error voltage V_OS3 are added together to output the actual comparison voltage V_C'. The expression for the first error voltage is -(Dmax-1)*Dmax*ma*TSW+(Dmax-1)^3*(Dmax+1)*V_ILOAD / ILOAD*TSW*VIN / 2 / Dmax / L, the expression for the second error voltage is -(1-Dmax)*Dmax*ma*TSW+(Dmax-1)^3*(Dmax+1)*V_ILOAD / ILOAD*TSW*VIN / 2 / Dmax^2 / L, and the expression for the third error voltage is -(1-2Dmax)*ma*TSW, where Dmax is the maximum duty cycle of the bridge arm composed of the first and second switches before mode switching, and is also the fixed duty cycle of the third and fourth switches in extended buck mode, ma is the slope of the ramp compensation voltage, TSW is the switching period, and ILOAD is the load current.

[0015] The beneficial effects of this invention are as follows: This invention processes the error amplifier output voltage according to the switching of the buck-boost converter's operating mode. This ensures that when switching between buck mode and extended buck mode, extended boost mode and boost mode, and extended buck mode and extended boost mode, the error amplifier output voltage is processed and then compared with the inductor current information superimposed with slope compensation. This improves the rate of change of the inductor current during mode switching, no longer limited by the error amplifier output voltage constrained by bandwidth and slew rate, resulting in a smoother transition of the output voltage during mode switching and improving output stability. Furthermore, this invention is simple to operate, requires no additional complex components, only reuses existing modules in the circuit, and has a wide range of applications. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0017] Figure 2 A functional diagram of the auxiliary circuit for smooth switching;

[0018] Figure 3 The waveforms of inductor current and switching control are shown before and after the buck converter switches between buck mode and extended buck mode, when the buck converter is operating in steady-state buck mode and extended buck mode.

[0019] Figure 4 The waveforms of inductor current and switching control are shown before and after the buck-boost converter switches between boost mode and extended buck mode, when the buck-boost converter is operating in steady-state boost mode and extended boost mode.

[0020] Figure 5 A comparison chart of inductor current and output voltage changes during mode switching between traditional peak current mode control and the smooth mode switching control adopted in this invention.

[0021] Figure 6 The simulation comparison chart shows the output voltage change when switching from traditional peak current mode control.

[0022] Figure 7 This is a simulation comparison diagram of the output voltage change during mode switching using the smooth mode switching control employed in this invention. Detailed Implementation

[0023] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0024] like Figure 1As shown, the buck-boost converter of the present invention includes a first switch Q1, a second switch Q2, a third switch Q3, a fourth switch Q4, and an inductor L. The first switch Q1 and the second switch Q2 are connected in series and parallel between the input voltage VIN of the buck-boost converter and ground, and their connection point is connected to one end of the inductor L. The third switch Q3 and the fourth switch Q4 are connected in series and parallel between the output voltage VOUT of the buck-boost converter and ground, and their connection point is connected to the other end of the inductor L. The inductor current detection circuit and the load current detection circuit in the buck-boost converter process the inductor current IL and the load current ILOAD to obtain the inductor current information V_IL and the load current information V_ILOAD. The two error amplifiers EA1 and EA2 in the buck-boost converter process the output voltage divider V_FB and the load current information V_ILOAD, and set according to the application requirements. They are then used to amplify the error with the voltage regulation control signal V_REF and the constant current control signal V_CTRL to generate the error amplification signal V_C. The smooth switching auxiliary circuit is controlled by the mode control signal MODE generated by the logic control circuit. Based on different modes and load current levels, it converts the error amplification signal V_C into an actual comparison voltage V_C'. The actual comparison voltage V_C' and the inductor current information V_IL are superimposed with the slope compensation signal V_SLOPE and compared to generate a peak current detection signal. The logic control circuit generates different switching transistor control signals according to different modes, based on the PWM clock CLK, the peak current detection signal, and the input / output voltages VIN and VOUT. These signals, after being driven by the driver circuit, generate TG1, BG1, TG2, and BG2, which control the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4, respectively, to change the operating mode of the buck-boost converter.

[0025] When switching modes, the relationship between inductor current and load current changes due to the change in operating timing. If the load current is to remain constant, the inductor current value needs to change rapidly. In peak current mode, the inductor current value is limited by the output of the error amplifier. However, due to the existence of a compensation network in the error amplifier's output, the output of the error amplifier changes rapidly, preventing the inductor current from changing quickly and causing instability in the output voltage VOUT. Based on this, this invention proposes a smooth mode switching control method. During mode switching, the output voltage V_C of the error amplifier is modified according to the mode change and the load current level to generate V_C'. This ensures that the rate of change of the inductor current during mode switching is not limited by the output voltage V_C of the error amplifier, making the output voltage more stable during mode transitions. Specifically, the load current information of the buck-boost converter is sampled and input into the smooth switching auxiliary circuit, and the actual comparison voltage V_C' is generated by the subsequent calculation unit.

[0026] This invention can be used in conjunction with a BUCK-BOOST operating mode consisting of an extended boost mode and an extended buck mode. It can also be used in conjunction with other current-mode controlled BUCK-BOOST operating modes to improve the transient fluctuations of the output voltage. The following description will use the control method of this invention in conjunction with a BUCK-BOOST operating mode consisting of an extended boost mode and an extended buck mode.

[0027] like Figure 3 As shown, the waveforms of inductor current and switching control timing of the buck-boost converter before and after switching between the same ratio buck mode and the extended buck mode are shown. Since the input and output voltages and the ratio remain unchanged before and after the mode switch, the waveform of the inductor current is fixed. Furthermore, the load current needs to remain as constant as possible before and after the mode switch to minimize the overshoot and undershoot of the output voltage. Within one cycle, the shaded area of ​​the inductor current equals the load current multiplied by the period (only when the third switch Q3 controlled by TG2 is turned on, at which time the inductor provides energy to the output load and charges the output capacitor, ensuring that when the third switch Q3 controlled by TG2 is turned off, the output capacitor can provide current to the output load and maintain the output voltage). Based on the relationship that the ratio, input and output voltages, and load current remain unchanged before and after the mode switch, the difference ΔV_C1 of the error amplifier output voltage V_C before and after the mode switch can be obtained under steady-state conditions without adding a smooth switching auxiliary circuit. ΔV_C1=(1-Dmax)*V_ILOAD / Dmax+ (Dmax-1)*Dmax*ma*TSW-(Dmax-1)^3*(Dmax+1)*V_ILOAD / ILOAD*TSW*VIN / 2 / Dmax / L (where Dmax is the maximum duty cycle of the bridge arm composed of Q1 and Q2 before mode switching, and is also the fixed duty cycle of Q3 and Q4 in extended buck mode, ma is the slope of the ramp compensation voltage, TSW is the switching period, and ILOAD is the load current). With the output voltage and load current remaining constant, ΔV_C1 can be expressed as ΔV_C1=k1*V_ILOAD+b1, where k1 and b1 are constants for a given application. When a smooth auxiliary switching circuit is used to convert the output voltage V_C of the error amplifier into V_C' for comparison, the rate of change of the inductor current during mode switching is no longer limited by the output voltage V_C of the error amplifier. Figure 5As shown, it is only limited by the slope of the inductor current and the operating timing. Similarly, when the buck-boost converter switches from boost mode to extended boost mode, the difference ΔV_C2 of the error amplifier output voltage V_C before and after the mode switch in steady state without adding a smooth switching auxiliary circuit is given by: ΔV_C2 = (1-Dmax)*V_ILOAD / Dmax^2 + (1-Dmax)*Dmax*ma*TSW - (Dmax-1)^3*(Dmax+1)*V_ILOAD / ILOAD*TSW*VIN / 2 / Dmax^2 / L. With the output voltage and load current remaining constant, ΔV_C2 can be expressed as ΔV_C1 = k2*V_ILOAD + b2, where k2 and b2 are constants for a given application.

[0028] An artificially set offset voltage can be superimposed on the output voltage V_C of the error amplifier in different operating modes of the buck-boost converter by a smooth switching auxiliary circuit, such as... Figure 2 As shown, when the buck-boost converter switches modes, different actual comparison voltages V_C' are output according to different operating modes to replace the V_C voltage output by the error amplifier and compare it with the inductor current information of the superimposed slope compensation. When the buck-boost converter switches to buck mode, the mode control signal selects the differential amplifier output V_C voltage, K1 times the load current information V_ILOAD, and the first error voltage V_OS1 to be added as the actual comparison voltage V_C'. When the buck-boost converter switches to extended buck mode, the mode control signal selects to directly output the actual comparison voltage V_C' without changing the differential amplifier output V_C voltage. When the buck-boost converter switches to extended boost mode, the mode control signal selects the differential amplifier output V_C voltage, the third error voltage V_OS3, and the third error voltage V_OS3 to be added as the actual comparison voltage V_C'. When the buck-boost converter switches to boost mode, the mode control signal selects the differential amplifier output V_C voltage, the K2 times the load current information V_ILOAD, and the third error voltage V_OS3 to be added as the actual comparison voltage V_C'.

[0029] In summary, this invention obtains the actual comparison voltage V_C' by superimposing an artificial offset voltage onto the error amplifier output voltage V_C during mode switching. This eliminates the limitation on the inductor current change rate during mode switching by the error amplifier output voltage V_C, thereby reducing output voltage overshoot and undershoot and resulting in a smoother transition during mode switching, thus improving the output stability of the buck-boost converter. As can be seen in the circuit simulation, as... Figure 6As shown, the four-switch buck-boost converter mode smoothing switching circuit used in this invention significantly reduces the overshoot and undershoot of the output voltage during mode switching compared to the basic peak current mode controlled four-switch buck-boost converter, making the mode switching smoother.

Claims

1. A Buck-Boost converter mode switching circuit, characterized in that, The system includes a power stage circuit and a control circuit. The power stage circuit includes a first switch, a second switch, a third switch, a fourth switch, an inductor, an input capacitor, and an output capacitor. The first and second switches are connected in series and parallel between the input terminal of the buck-boost converter and ground. The connection point SW1 between the first and second switches is connected to one end of the inductor. The third and fourth switches are connected in series and parallel between the output terminal of the buck-boost converter and ground. The connection point SW2 between the third and fourth switches is connected to the other end of the inductor. The input capacitor is connected between the input terminal and ground, and the output capacitor is connected between the output terminal and ground. The control circuit includes an inductor current detection circuit, a load current detection circuit, a slope compensation generation circuit, a logic control circuit, a drive circuit, a comparator, an internal clock, an output voltage divider resistor, a voltage regulation error amplifier, a constant current error amplifier, a smooth switching auxiliary circuit, a type II compensation network, a bias current, and an internal power supply. The output voltage divider resistors include a first resistor R1 and a second resistor R2. The first resistor R1 and the second resistor R2 are connected in series and connected between the output terminal of the buck-boost converter and ground. The connection point of the first resistor R1 and the second resistor R2 is connected to the negative input terminal of the voltage regulation error amplifier. The positive input terminal of the voltage regulation error amplifier is connected to the reference voltage V_REF. One end of the load current detection circuit is connected to the output terminal of the buck-boost converter, and the other end of the load current detection circuit outputs load current information V_ILOAD and is connected to the negative input terminal of the constant current error amplifier and the first input terminal of the smooth switching auxiliary circuit. The positive input terminal of the constant current error amplifier is connected to the constant current control signal V_CTRL. The outputs of the constant current error amplifier and the voltage regulator error amplifier are selected by the minimum value taking circuit, and the output voltage V_C of the error amplifier is generated on the type II compensation network. The type II compensation network includes a compensation capacitor CC and a compensation resistor RC. The compensation capacitor CC and the compensation resistor RC are connected in series and parallel between the output voltage V_C of the error amplifier and ground. The bias current I_BIAS is connected between the internal power supply and the output voltage V_C of the error amplifier. One end of the inductor current detection circuit is connected to SW1, and the other end is added to the slope compensation information to serve as the positive input of the comparator. The negative input of the comparator is connected to the output of the smooth switching auxiliary circuit. The inputs of the logic control circuit are the output of the comparator, the input voltage of the buck-boost converter, the output voltage of the buck-boost converter, and the internal clock signal. The output of the logic control circuit generates control signals for the first, second, third, and fourth switching transistors through the driver circuit. The second input terminal of the smooth switching auxiliary circuit is connected to the output voltage V_C of the error amplifier, the third input terminal of the smooth switching auxiliary circuit is connected to the mode switching control signal MODE generated by the logic control circuit, and the output V_C' of the smooth switching auxiliary circuit is used as the negative input terminal of the comparator. The specific method for achieving smooth mode switching of a buck-boost converter through a smooth switching auxiliary circuit is as follows: When the buck-boost converter switches modes, a different actual comparison voltage V_C' is output according to different operating modes to replace the error amplifier output voltage V_C and compare it with the inductor current information superimposed with slope compensation. When the buck-boost converter switches to buck mode, the mode switching control signal MODE selects the error amplifier output voltage V_C, K1 times the load current information V_ILOAD, and the first error voltage V_OS1 to be added as the actual comparison voltage V_C'. When the buck-boost converter switches to extended buck mode, the mode switching control signal MODE selects not to change the error amplifier output voltage V_C'. The first error voltage, V_C, is directly output as the actual comparison voltage V_C'. When the buck-boost converter switches to extended boost mode, the mode switching control signal MODE selects the error amplifier output voltage V_C, which is added to the third error voltage V_OS3 to output the actual comparison voltage V_C'. When the buck-boost converter switches to boost mode, the mode switching control signal MODE selects the error amplifier output voltage V_C, which is added to the load current information V_ILOAD (K2 times the load current), the second error voltage V_OS2, and the third error voltage V_OS3 to output the actual comparison voltage V_C'. The expression for the first error voltage is: The expression for the second error voltage is: The expression for the third error voltage is: Where Dmax is the maximum duty cycle of the bridge arm composed of the first and second switching transistors before mode switching, and is also the fixed duty cycle of the third and fourth switching transistors in extended buck mode. ma is the slope of the ramp compensation voltage, TSW is the switching period, ILOAD is the load current, VIN is the input voltage, and L is the inductance value.

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