A method and circuit for eliminating the over-standard ripple at the critical point of a Buck-boost power module

Abstract

The present invention discloses a method and a circuit for eliminating the over-standard ripple at the critical point of a Buck-boost power module, belonging to the technical field of switching power supplies. The method is that when the supply voltage of the Buck-boost non-isolated DC / DC power module drops to be close to or equal to the critical point, by reducing the supply voltage of the Buck-boost non-isolated DC / DC power module, it is completely converted into the boost step-up working mode to avoid the critical point where the ripple exceeds the standard. The circuit performs comparison operations through a voltage comparison circuit and a gate circuit, and then drives the relay to be attracted or disconnected to control whether the buck circuit is connected in series to the power supply line, so as to avoid the critical point of the Buck-boost non-isolated DC / DC power module. The circuit of the present invention is composed of discrete devices, with a simple structure and low cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of switching power supplies, and particularly relates to a method and a circuit for eliminating excessive ripple at the critical point of a Buck-boost type non-isolated DC / DC power module. Background Art

[0002] When powered by a Buck-boost type non-isolated DC / DC power module, when the supply battery voltage drops from a higher voltage to a value very close to or equal to the output voltage, that is, when it drops to the critical point, the critical point is a range, generally within Vout±0.5V of the output voltage. Since the module switches between buck and boost modes, it will generate several times more ripple than usual. For example, for the commonly used NQ60W60HGC40NRF-G non-isolated Buck-boost power module, the normal ripple is within 250KHZ, 200mVp-p. However, when the input voltage drops to the critical point of 24.6V±0.5V (at this time the output voltage Vout is 25V), the ripple has exceeded 500mVp-p, seriously exceeding the standard. This is a Bug (defect) existing in the Buck-boost type non-isolated DC / DC power module, which is determined by the Buck-boost topology form, and this defect cannot be eradicated at present.

[0003] Figure 1 It is the topology diagram of the Buck-boost type non-isolated DC / DC power module, which is described according to the following parameters:

[0004] The battery supply voltage range is 21V to 32V, the input voltage range of the Buck-boost type non-isolated DC / DC power module is 9V to 60V, and the output voltage (Vout) is adjusted to 25V.

[0005] During normal operation, the battery supply voltage gradually decreases. When the battery output voltage Vin is higher than the output voltage Vout of the DC / DC non-isolated Buck-boost power module, the DC / DC module operates in the Buck bucking topology mode. The upper MOS transistor on the output side SW2 is directly connected, and the lower MOS transistor is turned off. The upper and lower MOS transistors on the input side SW1 are alternately turned on, and the output voltage Vout is adjusted by adjusting the duty cycle.

[0006] When the output voltage of the battery is lower than the output voltage Vout of the Buck-boost non-isolated DC / DC power module, the DC / DC module operates in the Boost boosting topology mode. The upper MOS transistor on the input side SW1 is directly connected, and the lower MOS transistor is turned off. The output voltage Vout is adjusted by adjusting the duty cycle of the upper and lower MOS transistors on the output side SW2.

[0007] When the battery output voltage Vin is close to or equal to the input voltage of the Buck-boost non-isolated DC / DC power module, the module enters the buck-boost rotation mode (see Figure 2 ), that is:

[0008] During t0 to t1 and t2 to t3, the module enters the freewheeling mode, and the upper MOS transistors on the input side SW1 and the output side SW2 are turned on simultaneously, while the other two MOS transistors are turned off;

[0009] During t1 to t2, the module enters the charging mode, and the upper MOS transistor on the input side SW1 and the lower MOS transistor on the output side SW2 are turned on simultaneously, while the other two MOS transistors are turned off simultaneously, and the inductor L1 voltage is equal to the input voltage Vin;

[0010] During t3 to t4, the module enters the discharging mode, and the lower MOS transistor on the input side SW1 and the upper MOS transistor on the output side SW2 are turned on simultaneously, while the other two MOS transistors are turned off simultaneously, and the inductor L1 voltage is equal to the output voltage Vout;

[0011] It can be seen from the above example that when the input voltage is very close to or equal to the output voltage, although the internal management chip of the Buck-boost non-isolated DC / DC power module also sets a sampling hysteresis, there is always a certain error in the chip sampling, which causes the power supply to misjudge the Buck-boost mode and results in excessive ripple. This is determined by the Buck-boost topology mode and cannot be overcome at present. The ripple will seriously affect the normal operation of the subsequent equipment.

[0012] Currently, the solutions adopted by engineers are as follows:

[0013] One is to increase the battery output cut-off voltage, that is, to make the battery output cut-off voltage higher than the critical point of the Buck-boost power module. In this way, the Buck-boost non-isolated DC / DC power module always operates in the Buck bucking topology mode. Without entering the critical point, there will be no excessive ripple. In fact, the boost function of the module is cut off, weakening the "wide input range" advantage of the Buck-boost non-isolated DC / DC power module, and the battery utilization rate is low, wasting equipment resources, funds, etc.

[0014] Second, increase the output capacitance to tens of thousands of μF. Generally, electrolytic capacitors with tens of thousands of μF have a very large volume and there may be no space inside the device to install them, and the effect is not ideal. Because the switching frequency between Buck and Boost modes at the input voltage critical point is very low, about several hundred hertz. When the device current is about 20 A, according to the ripple and capacitance relationship formula: σVout = (Iout * D * Ts) / C (σVout is the ripple amplitude, C is the capacitance value, Iout is the output current magnitude, Ts is the ripple period, D is the duty cycle), if the ripple is limited within 200 mVp-p, electrolytic capacitors with tens of thousands of μF or even larger need to be configured, and this method is not ideal. Summary of the Invention

[0015] The technical problem to be solved by the present invention is to provide a method and circuit for eliminating the excessive ripple at the critical point of a Buck-boost type non-isolated DC / DC power module by using the transfer critical point.

[0016] To solve the above problems, the technical solutions adopted by the present invention are as follows:

[0017] A method for eliminating the excessive ripple at the critical point of a Buck-boost type non-isolated DC / DC power module is that when the supply voltage of the Buck-boost type non-isolated DC / DC power module drops to be close to or equal to the critical point, by reducing the supply voltage of the Buck-boost type non-isolated DC / DC power module, it is completely converted into the boost operating mode to avoid the critical point where the ripple exceeds the standard. The critical point is a range, and specifically includes the following steps:

[0018] A) Real-time monitor the output voltage of the battery supplying power to the Buck-boost type non-isolated DC / DC power module, and compare it with the first set voltage and the second set voltage;

[0019] B) When the battery output voltage is greater than the first set voltage, the battery directly supplies power to the Buck-boost type non-isolated DC / DC power module, that is, the battery output voltage is equal to the input voltage of the Buck-boost type non-isolated DC / DC power module;

[0020] C) When the battery output voltage is less than or equal to the first set voltage and greater than the second set voltage, reduce the battery output voltage by a certain fixed voltage and then supply power to the Buck-boost type non-isolated DC / DC power module, that is, the input voltage of the Buck-boost type non-isolated DC / DC power module is the battery output voltage minus a certain fixed voltage;

[0021] D) When the battery output voltage is less than or equal to the second set value, the battery directly powers the Buck-boost non-isolated DC / DC power module, that is, the battery output voltage is equal to the input voltage of the Buck-boost non-isolated DC / DC power module;

[0022] The above-mentioned first set voltage must be greater than the upper limit of the critical point of the Buck-boost non-isolated DC / DC power module, and the second set voltage must be less than the lower limit of the critical point of the Buck-boost non-isolated DC / DC power module.

[0023] Preferably, the first set voltage and the second set voltage are obtained through a voltage dividing circuit respectively. The battery output voltage monitored in real time is obtained through the voltage dividing circuit, and the comparison between the battery output voltage and the first set voltage and the second set voltage is realized by a voltage comparison circuit.

[0024] Preferably, the way that the battery powers the Buck-boost non-isolated DC / DC power module after reducing a certain fixed voltage is to connect a buck circuit in series in the power supply line between the battery and the Buck-boost non-isolated DC / DC power module.

[0025] A circuit for eliminating the excessive ripple at the critical point of the Buck-boost non-isolated DC / DC power module includes a voltage comparison circuit for comparing the first set voltage, the second set voltage with the battery output voltage monitored in real time, a gate circuit for performing logical operations on the output signal of the voltage comparison circuit, a relay drive circuit for driving a relay, and a buck circuit connected in parallel with the relay contacts and then connected in series in the power supply line between the battery and the Buck-boost non-isolated DC / DC power module; wherein after the output of the voltage comparison circuit is logically operated by the gate circuit, the relay of the relay drive circuit is attracted or disconnected to control whether the buck circuit is connected in the power supply line to avoid the critical point of the Buck-boost non-isolated DC / DC power module.

[0026] Preferably, the gate circuit includes a NOT gate and an OR gate. The NOT gate is used for logically inverting the comparison result between the first set voltage and the battery output voltage monitored in real time, and the OR gate is used for performing logical operations on the comparison result between the second set voltage and the battery output voltage monitored in real time and the output of the NOT gate.

[0027] Preferably, the buck circuit is a diode buck circuit, which is composed of one diode or multiple diodes connected in series in sequence, and the number of the diodes is 4.

[0028] Preferably, the step-down circuit is a diode step-down circuit, which is composed of multiple diode series components connected in parallel. Each diode series component is composed of one diode or multiple diodes connected in series in sequence. The number of diodes in each diode series component is 4, and the number of diode series components is more than 2 groups.

[0029] The beneficial effects of adopting the above technical solution are as follows:

[0030] The present invention uses a step-down circuit connected in series in the power supply circuit. When the battery voltage drops to the critical point of the Buck-boost non-isolated DC / DC power module, the diode step-down circuit is used to reduce the supply voltage of the module, successfully avoiding the critical point of the Buck-boost non-isolated DC / DC power module. When the battery voltage is lower than the critical point, the supply voltage of the module is restored to the battery voltage, effectively eliminating the excessive ripple at the critical point of the Buck-boost non-isolated DC / DC power module. The circuit of the present invention is composed of discrete devices, with a simple structure and low cost. Description of the Drawings

[0031] Figure 1 is the topology diagram of the Buck-boost non-isolated DC / DC power module;

[0032] Figure 2 is the voltage time sequence curve diagram when the input voltage of the Buck-boost non-isolated DC / DC power module works in the buck and boost rotation modes at the critical point;

[0033] Figure 3 is the circuit schematic diagram of the present invention. Detailed Embodiments

[0034] The following further describes the invention in detail with reference to the drawings:

[0035] In order to effectively remove the excessive ripple at the critical point of the input voltage of the Buck-boost non-isolated DC / DC power module, the present invention provides a method and a circuit for eliminating the excessive ripple at the critical point of the Buck-boost non-isolated DC / DC power module.

[0036] The method for eliminating the excessive ripple is as follows: When the supply voltage of the Buck-boost non-isolated DC / DC power module drops to be close to or equal to the critical point, by reducing the supply voltage of the Buck-boost non-isolated DC / DC power module, it is completely converted into the boost step-up working mode to avoid the critical point where the excessive ripple occurs. The critical point is a range, and the specific steps are as follows:

[0037] A) Monitor the output voltage of the battery that powers the Buck - boost non - isolated DC / DC power module in real - time, and compare it with the first set voltage and the second set voltage;

[0038] B) When the battery output voltage is greater than the first set voltage, the battery directly powers the Buck - boost non - isolated DC / DC power module, that is, the battery output voltage is equal to the input voltage of the Buck - boost non - isolated DC / DC power module;

[0039] C) When the battery output voltage is less than or equal to the first set voltage and greater than the second set voltage, reduce the battery output voltage by a certain fixed voltage and then power the Buck - boost non - isolated DC / DC power module, that is, the input voltage of the Buck - boost non - isolated DC / DC power module is the battery output voltage minus a certain fixed voltage;

[0040] D) When the battery output voltage is less than or equal to the second set value, the battery directly powers the Buck - boost non - isolated DC / DC power module, that is, the battery output voltage is equal to the input voltage of the Buck - boost non - isolated DC / DC power module;

[0041] The above - mentioned first set voltage must be greater than the upper limit of the critical point of the Buck - boost non - isolated DC / DC power module, and the second set voltage must be less than the lower limit of the critical point of the Buck - boost non - isolated DC / DC power module.

[0042] The above - mentioned first set voltage and second set voltage are obtained through voltage - dividing circuits respectively. The real - time monitored battery output voltage is obtained through a voltage - dividing circuit. The comparison between the battery output voltage and the first set voltage and the second set voltage is realized by a voltage - comparison circuit. The voltage - comparison circuit consists of two - way hysteresis comparators; the method of reducing the battery output voltage by a certain fixed voltage and then powering the Buck - boost non - isolated DC / DC power module is to connect a step - down circuit in series in the power - supply line between the battery and the Buck - boost non - isolated DC / DC power module.

[0043] In order to implement the above method at low cost, the ripple-eliminating circuit of the present invention includes a voltage comparison circuit for comparing a first set voltage, a second set voltage with the battery output voltage monitored in real time, a gate circuit for performing a logical operation on the output signal of the voltage comparison circuit, a relay drive circuit for driving a relay, and a buck circuit connected in parallel with the relay contacts and then connected in series in the power supply line between the battery and the Buck-boost non-isolated DC / DC power module; after the output of the voltage comparison circuit is logically operated by the gate circuit, the relay of the relay drive circuit is attracted or disconnected to control whether the buck circuit is connected in series in the power supply line to avoid the critical point of the Buck-boost non-isolated DC / DC power module.

[0044] The gate circuit includes a NOT gate and an OR gate. The NOT gate is used for logically inverting the comparison result of the first set voltage and the battery output voltage monitored in real time, and the OR gate is used for performing a logical operation on the comparison result of the second set voltage and the battery output voltage monitored in real time and the output of the NOT gate.

[0045] In order to ensure the supply current of the Buck-boost non-isolated DC / DC power module and effectively avoid the critical point, the buck circuit of the present invention adopts a diode buck circuit, which is composed of a plurality of diode series components connected in parallel. The diode series component is composed of one diode or a plurality of diodes connected in series in sequence; the number of diodes in each diode series component is 4. Among them, the number of diodes in series is determined according to the voltage range of the critical point to be avoided. According to the model of the Buck-boost non-isolated DC / DC power module and the working current that the diode series component can provide, the number of diode series components can be one group or more than 2 groups.

[0046] Principle description:

[0047] Figure 3 The following is the circuit schematic diagram of an embodiment of the present invention. The specific description is as follows:

[0048] In this embodiment, the battery output voltage range is 21V to 32V, the model of the Buck-boost non-isolated DC / DC power module is NQ60W60HGC40NRF-G, and the output voltage is 25V. When the output voltage is 25V, the critical point of the input voltage of this module is 24.6V ± 0.5V (obtained by experimental measurement, generally the critical point of the module is at Vout ± 0.5V of the output voltage). By connecting this embodiment in series between the battery and the Buck-boost non-isolated DC / DC power module, within the entire battery supply voltage range of 21V to 32V, the output ripple of the Buck-boost non-isolated DC / DC power module will not exceed the standard.

[0049] The step-down circuit in this embodiment uses 4 diodes in series and then in parallel. In this way, the voltage drop is 0.7 * 4 = 2.8V. At this time, the voltage critical point range to be avoided is 24.6 ± 1.4V, that is, 23.2V to 26V. When the battery voltage drops to 26V (the first set voltage), the step-down circuit is connected. At this time, the input voltage of the Buck-boost non-isolated DC / DC power module is 26V - 2.8V = 23.2V, and the input voltage directly skips the critical point. The Buck-boost non-isolated DC / DC power module directly switches from the Buck step-down mode to the Boost step-up mode. When the battery voltage drops to 23.2V (the second set voltage), the connection of the step-down circuit is cancelled, and power is directly supplied through the relay contacts to reduce power consumption.

[0050] The reference voltage of the first set voltage is input to the non-inverting terminal of comparator U1A through resistors R10 and R15 in series for voltage division and then through resistor R6. Resistor R8 is the feedback resistor, and positive feedback is added through the feedback resistor R8. Comparator U1A forms a hysteresis comparator. The reference voltage of the second set voltage is input to the non-inverting terminal of comparator U1B through resistors R7 and R14 in series for voltage division and then through resistor R3. Resistor R5 is the feedback resistor, and positive feedback is added through the feedback resistor R5. Comparator U1B forms a hysteresis comparator. The real-time monitored battery output voltage is input to the inverting terminal of U1A through resistors R1 and R2 in series for voltage division, and input to the inverting terminal of U1B through resistors R4 and R13 in series for voltage division. The comparison between the real-time battery output voltage and the first set voltage and the second set voltage is completed by the inverting-input hysteresis comparators U1A and U1B formed. To ensure the stability of the comparator level flip, this embodiment uses a hysteresis comparator, and the hysteresis voltage is about 0.1V. The hysteresis voltage can be adjusted according to the actual situation.

[0051] According to the voltage critical point range to be avoided, the critical point voltage value for avoidance is set by adjusting the resistance values of resistors R1, R2, R4, and R13.

[0052] When the battery voltage in this embodiment is lower than 26V (the first set voltage), the output voltage of comparator U1A needs to be inverted to a high level, and then output as a low level to OR gate U2 through NOT gate U3. Calculate the input voltage of the inverting terminal of U1A through the first set voltage: R2 / (R1+R2)*26V = 2.49V. Since comparator U1A and its peripheral circuit form a hysteresis comparator, the voltage input to the non-inverting terminal of comparator U1A after the series voltage division of resistors R10 and R15 and through resistor R6 is in a range of 2.49V to 2.59V, that is, Vref*R8 / (R6+R8)+5V*R6 / (R6+R8)=2.59V, Vref*R8 / (R6+R8)-0V*R6 / (R6+R8)=2.49V, then Vref = R15 / (R10+R15)*5V = 2.54V. An example given in this embodiment is: R15 = 2k7, then R10 = R15*5V / 2.54V - R15 = 2K7*5V / 2.54V - 2K7 = 2K6.

[0053] Similarly, when the battery voltage is lower than 23.2V (the second set voltage), an example given in this embodiment is: R14 is 2K7, then R7 is 3K1.

[0054] The resistance values of the above resistors R1, R2, R4, R7, R14, and R15 can be selected and calculated according to the actual situation. In order to ensure the sampling accuracy, the above resistors use 1% precision resistors.

[0055] When the battery output voltage is less than 32V and greater than 26V, comparator U1A outputs a low level, which is output as a high level after passing through NOT gate U3. Comparator U1B outputs a low level. The output signals of NOT gate U3 and comparator U1B are operated by OR gate U2 and then output as a high level to drive transistor Q1 to conduct, and relay J1 is attracted. The normally open contact of relay J1 shorts the buck circuit, and the positive electrode of the battery directly supplies power to the Buck - boost non - isolated DC / DC power module through the normally open contact of relay J1.

[0056] When the battery voltage drops to less than or equal to 26V and greater than 23.2V, the output of comparator U1A flips to high level, and after passing through the NOT gate U3, a low level is output. The output of comparator U1B remains low. At this time, the output of OR gate U2 is low, transistor Q1 is cut off, and relay J1 is disconnected. The positive pole of the battery is supplied to the Buck - boost non - isolated DC / DC power module after passing through the buck circuit (high - power diodes D1, D2, D3, Dn, D21, D22, D23, D2n). The buck range selected in this embodiment is 2.8V. In this way, the supply voltage provided to the subsequent Buck - boost non - isolated DC / DC power module is 26V - 2.8V = 23.2V, thus avoiding the critical point range of 24.6V ± 0.5V of the Buck - boost non - isolated DC / DC power module and eliminating the excessive ripple.

[0057] When the battery voltage continues to drop to less than or equal to 23.2V, the output of comparator U1A remains high, and through the NOT gate U3, a low level is output. The output of comparator U1B flips to high level. After the two signals pass through the OR gate U2, a high level is output. Transistor Q1 conducts, and relay J1 is pulled in. The positive pole of the battery directly supplies power to the Buck - boost non - isolated DC / DC power module through the normally - open contact of relay J1. At this time, the supply voltage is 23.2V, which has avoided the critical point voltage of 24.6V ± 0.5V.

[0058] The above is only a specific embodiment of the present invention. Due to the differences in the Buck - boost non - isolated DC / DC power module and its output voltage, the circuit parameters need to be adjusted. Therefore, the setting of the above parameters does not limit the protection scope of the present invention.

[0059] The voltage critical point is determined by the output voltage of the Buck - boost non - isolated DC / DC power module. Generally, the input voltage critical point of the Buck - boost non - isolated DC / DC power module is in the range of about the output voltage Vout ± 0.5V. After finding the critical point, determine the buck magnitude. If the buck range is too small, it may not completely cover the critical point; if it is too large, it will waste energy, and heat dissipation needs to be considered, such as adding heat sinks, fans, etc.

[0060] According to the determined buck range, select the forward voltage drop Vf value of the diode, and based on the current demand of the device, determine how many diodes need to be used in series and parallel. In addition, the contact current of relay J1 should be greater than the maximum load current.

Claims

1. A method for eliminating the excessive ripple at the critical point of a Buck-boost non-isolated DC / DC power module is that when the supply voltage of the Buck-boost non-isolated DC / DC power module drops to equal the critical point, by reducing the supply voltage of the Buck-boost non-isolated DC / DC power module, it is completely converted to the boost operating mode to avoid the critical point where the ripple exceeds the standard. The critical point is a voltage range, specifically including the following steps: A) Monitor the output voltage of the battery supplying power to the Buck-boost non-isolated DC / DC power module in real time and compare it with the first set voltage and the second set voltage; B) When the battery output voltage is greater than the first set voltage, the battery directly supplies power to the Buck-boost non-isolated DC / DC power module, that is, the battery output voltage is equal to the input voltage of the Buck-boost non-isolated DC / DC power module; C) When the battery output voltage is less than or equal to the first set voltage and greater than the second set voltage, the battery output voltage is reduced by a certain fixed voltage and then supplies power to the Buck-boost non-isolated DC / DC power module, that is, the input voltage of the Buck-boost non-isolated DC / DC power module is the battery output voltage minus a certain fixed voltage; D) When the battery output voltage is less than or equal to the second set voltage, the battery directly supplies power to the Buck-boost non-isolated DC / DC power module, that is, the battery output voltage is equal to the input voltage of the Buck-boost non-isolated DC / DC power module; The above-mentioned first set voltage must be greater than the upper limit of the critical point of the Buck-boost non-isolated DC / DC power module, and the second set voltage must be less than the lower limit of the critical point of the Buck-boost non-isolated DC / DC power module.

2. A method for eliminating the excessive ripple at the critical point of a Buck-boost non-isolated DC / DC power module according to claim 1, characterized in that: The first set voltage and the second set voltage are respectively obtained through a voltage division circuit. The battery output voltage monitored in real time is obtained through a voltage division circuit. The comparison between the battery output voltage and the first set voltage and the second set voltage is realized by a voltage comparison circuit.

3. A method for eliminating the excessive ripple at the critical point of a Buck-boost non-isolated DC / DC power module according to claim 1 or 2, characterized in that: The way that the battery output voltage is reduced by a certain fixed voltage and then supplies power to the Buck-boost non-isolated DC / DC power module is to connect a buck circuit in series in the power supply line between the battery and the Buck-boost non-isolated DC / DC power module.

4. A circuit for implementing the method for eliminating the excessive ripple at the critical point of a Buck-boost non-isolated DC / DC power module described in any one of claims 1 to 3, characterized in that: It includes a voltage comparison circuit for comparing a first set voltage, a second set voltage with the battery output voltage monitored in real time, a gate circuit for performing logical operations on the output signal of the voltage comparison circuit, a relay drive circuit for driving a relay, and a buck circuit connected in parallel with the relay contacts and then connected in series to the power supply line between the battery and the Buck-boost non-isolated DC / DC power module; after the output of the voltage comparison circuit is logically operated by the gate circuit, the relay of the relay drive circuit is attracted or disconnected to control whether the buck circuit is connected in series to the power supply line to avoid the critical point of the Buck-boost non-isolated DC / DC power module.

5. A circuit for eliminating the excessive ripple of the Buck-boost non-isolated DC / DC power module at the critical point according to claim 4, characterized in that: the gate circuit includes a NOT gate and an OR gate, the NOT gate is used for logically inverting the comparison result of the first set voltage and the battery output voltage monitored in real time, and the OR gate is used for performing logical operations on the comparison result of the second set voltage and the battery output voltage monitored in real time and the output of the NOT gate.

6. A circuit for eliminating the excessive ripple of the Buck-boost non-isolated DC / DC power module at the critical point according to claim 4 or 5, characterized in that: the buck circuit is a diode buck circuit, which is composed of one diode or multiple diodes connected in series in sequence.

7. A circuit for eliminating the excessive ripple of the Buck-boost non-isolated DC / DC power module at the critical point according to claim 6, characterized in that: the number of the diodes is 4.

8. A circuit for eliminating the excessive ripple of the Buck-boost non-isolated DC / DC power module at the critical point according to claim 4 or 5, characterized in that: the buck circuit is a diode buck circuit, which is composed of multiple diode series components connected in parallel, and the diode series component is composed of one diode or multiple diodes connected in series in sequence.

9. A circuit for eliminating the excessive ripple of the Buck-boost non-isolated DC / DC power module at the critical point according to claim 8, characterized in that: the number of diodes in each diode series component is 4, and the number of diode series components is more than 2 groups.

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