CN108377099B - Two-stage input boost DC constant voltage output converter - Google Patents

Abstract

The invention discloses a two-stage input boosting DC constant voltage output converter which comprises a 12V or 24V power supply input, an auxiliary power supply circuit, an automatic frequency switching circuit, a PWM (pulse-width modulation) regulating circuit, a boosting output rectifying and filtering circuit, a potential logic protection circuit, a push-pull boosting topological circuit and an output constant voltage automatic switching circuit. The invention judges the potential logic monitoring according to different states (under voltage, overvoltage and normal) of the input bus voltage, thereby controlling the start and stop of the whole circuit by controlling the PWM module. The output constant voltage automatic switching circuit ensures safe and stable voltage output under different input voltages. The high-frequency step-up transformer connected with the push-pull topology is specially designed in winding distribution so as to adapt to two different input voltages. The automatically switched output constant voltage circuit after the step-up transformer can ensure constant voltage output at different inputs.

Description

A dual-stage input step-up DC constant voltage output converter

technical field

The invention relates to the technical field of constant voltage output circuit design, in particular to a double-stage input boost type DC constant voltage output converter.

Background technique

With the rise of green renewable energy such as photovoltaic power generation, the application of inverter power supply and related research are becoming more and more extensive and in-depth. It is widely used in home, company server, satellite relay station and even aerospace industry. The boost circuit is a key part of the inverter power supply, and its key indicators such as working stability, safety, and response sensitivity all affect the normal operation of the entire inverter power supply system.

Multi-input step-up DC constant voltage output converter is a common component in inverter power supply. In the boost circuit, the commonly used methods are: Push-Pull (push-pull topology), Weinberg Circuit (Weinberg circuit topology), Half-Bridge (half-bridge topology), Full-Bridge (full-bridge topology) ) and so on, the most commonly used one is Push-Pull (push-pull topology). For these topologies, the input voltage is limited to a relatively narrow range to ensure a fixed transformation ratio. When the input voltage changes greatly, the voltage of the boost output part will be too high, which may burn the high-voltage power part. Although the output voltage is too high, the purpose of setting the voltage output can be achieved through PWM modulation, but this will reduce the power conversion efficiency (at this time, the pulse width of the PWM driving signal is very narrow, resulting in a lower power conversion rate). Therefore, in the coupling scheme of the multi-input switching converter, each input corresponds to its own power conversion circuit or passes through a more complex control circuit. Although this can adapt to the situation of different input voltages, the cost of the system solution is high and the economy is reduced.

On the other hand, in order to ensure the normal operation of the system, it is necessary to judge the state of the input signal in time to respond. If the voltage signal is used as the input, it is necessary to make judgments on the three working states of the input voltage: undervoltage, overvoltage and normal. When an abnormal input voltage is detected, that is, undervoltage or overvoltage, the system needs to stop running or automatically Implement protection. The same is true for multi-voltage level (hereinafter referred to as multi-level) input. If any input is abnormal, corresponding protection measures need to be activated. As far as multi-level input logic judgment is concerned, the current common microcontrollers implement functions through software design, which has the disadvantages of lagging response and high cost.

There are generally two ways to detect the state of the multi-level input voltage and make logical judgments, that is, the hardware circuit method and the single-chip software programming method.

When the hardware circuit method is used, the voltage signal is generally compared and detected by the comparator to obtain the logic potential, and then the detected logic potential signal is directly transmitted to the logic composite circuit for logic judgment, and an actual control signal is obtained for the potential protection circuit. Pure hardware circuits are often used for single input voltage state detection.

When using the single-chip software programming method, the voltage signal must be sampled and detected through the analog-to-digital conversion module, and then the logic judgment is made through the single-chip software programming, which can conveniently judge the multi-level input signal.

The response speed of the hardware circuit method and the MCU software programming method is also affected by the constraints of semiconductor materials and working environment, and the MCU software programming method is also affected by the MCU clock signal, the conversion accuracy of the analog-to-digital conversion module, and the sampling voltage range. Impact.

Although the response speed of semiconductor devices is getting faster and faster under the current high-speed development wave, the performance of the single-chip software programming method is more restricted than the hardware circuit method. Therefore, compared with the software programming method, the hardware circuit method has a more timely and sensitive response to the direct logic judgment of the voltage signal, and has a wide potential measurement range, a small error range, and a low overall circuit implementation cost. In the case of the same performance, the response of the single-chip software programming method will not be as timely as the hardware circuit method, and it is not easy to integrate, and the implementation cost of the overall circuit is relatively high.

Contents of the invention

The purpose of the present invention is to provide a dual-stage input step-up DC constant voltage output converter to overcome The existing deficiencies of the prior art.

The technical solution of the present invention to solve its technical problems is: a dual-stage input boost DC constant voltage output converter, including 12V or 24V low voltage power input, auxiliary power supply circuit, automatic frequency switching circuit, PWM control circuit, boost output The rectification filter circuit is characterized in that: it also includes a potential logic protection circuit, a push-pull boost topology circuit, and an output constant voltage automatic switching circuit; the auxiliary power supply circuit is respectively connected to the automatic frequency switching circuit, the potential logic protection circuit, and the automatic frequency switching The circuit adjusts the parameters of the oscillation circuit according to the input voltage level to ensure that the PWM frequency adapts. The push-pull boost topology circuit is driven by the PWM signal and is connected in sequence with the output constant voltage automatic switching circuit and the boost output rectification filter circuit; the output constant voltage is automatically The switching circuit includes a push-pull transformer, a transfer switch K1, a switch drive circuit, and a rectification and filtering circuit. The push-pull transformer is connected to the rectification and filtering circuit through the transfer switch K1. The input winding of the push-pull transformer includes two windings with the same number of turns. A winding with a center tap, its output winding is two independent windings with the same number of turns, the switch driving circuit includes a triode, a Zener diode, a resistor, and a capacitor, and the anode end of the Zener diode is connected to the base of the triode. The cathode terminal of the voltage diode is connected to the DC power supply through the resistor R2; the base circuit of the triode is composed of a parallel connection of the resistor R1 and the capacitor C4, and one end of the base circuit is grounded; the collector terminal of the triode is connected to the relay coil of the transfer switch K1, and is connected to the relay A freewheeling diode D7 is connected in parallel with the coil, and the freewheeling diode D7 is connected to the DC power supply with the relay coil; the transfer switch K1 is a double-pole double-throw relay, and its normally closed contacts are respectively connected to the B and B of the two output windings of the push-pull transformer. C port, the normally open contact is connected to the A and D ports, so that when the relay armature is in the released state, the two output winding ports connected by the normally closed contact are in an internal short-circuit state and are not connected to the rectifier and filter circuit, so that the push-pull transformer The two output windings are output in series; and when the relay armature is in the pull-in state, the two output windings of the push-pull transformer are output in parallel.

The reference value of the Zener diode is selected from 15V to 21V.

The Zener diodes include Zener diodes D5 and D6 connected in series, and satisfy: 15V<(VD5+VD6)<21V.

The rectification and filtering circuit includes diodes D1-D4.

The rectification and filtering circuit includes two aluminum electrolytic capacitors connected in parallel.

The potential logic protection circuit includes a comparator circuit and a logic composite circuit. The comparator circuit has n sets of comparators, n threshold point potentials U_set_1,..., U_set_n, and each set of comparators has two comparators to obtain 2n comparative output voltages U_out_1,..., U_out_2n, the undervoltage and overvoltage sampling of the input compared voltage U_in are divided into two independent voltage-dividing branches, the undervoltage sampling voltage-dividing branch includes resistors R ₁ and R ₂ , the overvoltage sampling voltage dividing branch includes resistors R ₃ and R ₄ ; the inverting terminal of the even-numbered comparator is connected and connected to the voltage dividing circuit composed of R ₁ and R ₂ , so that R ₁ and R ₂ are divided The voltage obtained after pressing is sent to the inverting terminal of the even-numbered comparator, and compared with the threshold potential of the same-phase terminal, so that the even-numbered comparator obtains the undervoltage state of each of the n channels; the same-phase terminal of the odd-numbered comparator is connected to And connect to the voltage divider circuit composed of R ₃ and R ₄ , so that the voltage obtained after the voltage division of R ₃ and R ₄ is respectively sent to the non-inverting terminal of the odd-numbered comparator, and compared with the threshold potential of the inverting terminal, so that the odd number The sequence number comparator obtains the overvoltage status of each of the n channels.

The logic composite circuit includes n groups of logic input signals, and each group of logic input signals is input by n two-input OR logic gates to obtain n operation output signals, and the n operation output signals are sent to the AND logic gate to finally obtain the composite output signal U_out .

The parameters of resistors R ₁ , R ₂ , R ₃ , and R ₄ are determined according to the following formula:

in,

The beneficial effects of the present invention are:

1) The present invention proposes a switching power supply with integrated power conversion for 12V and 24V dual-input, and designs a potential logic monitoring circuit, a winding distribution of a high-frequency step-up transformer and a corresponding output constant voltage automatic switching circuit. The potential logic monitoring circuit can judge according to different states of the input bus voltage (undervoltage, overvoltage, normal), so as to control the start and stop of the entire circuit by controlling the PWM module. The output constant voltage automatic switching circuit ensures safe and stable voltage output under different input voltages. The high-frequency step-up transformer connected to the push-pull topology has a special winding distribution design to adapt to two different input voltages. The automatic switching output constant voltage circuit after the step-up transformer can ensure a constant voltage output for different inputs.

The invention adopts a pure hardware circuit design scheme, has fast response and high reliability, and does not have the problem of "crash" of programs in the software during long-term operation. For the dual-input state, a dual-channel composite window voltage comparator circuit is designed to realize potential logic protection; the winding structure of the traditional push-pull step-up high-frequency transformer is improved, and a constant voltage switching circuit matching it is designed ; And for the output constant voltage switching mode, a series/parallel solution is proposed. The design schemes of these key technologies can provide reference for practical engineering applications.

The invention adopts an improved window comparator, and adopts a pure hardware design scheme for the state detection and logic judgment circuit of multi-level voltage input, which has fast response and high reliability, and there is no "crash" of the program in the software during long-term operation question. Based on the simple and basic threshold voltage window comparator circuit, the dual-level window voltage comparator is analyzed, and a dual-level and multi-level composite window voltage comparator is designed, and applied to the state detection and logic of 12V and 24V two-level voltage input On the judging circuit, the rationality and practicability of the multi-level composite voltage window comparator are verified through simulation and experiment, which can provide reference for practical related engineering applications.

2) The above design scheme is applied to the actual inverter power supply, and strict tests are carried out under different input voltages (12V and 24V), and the transient response test for high-power loads is passed. The dual-input function reduces the stringent requirements on the input power supply, which is practical.

Description of drawings

Fig. 1 is a schematic diagram of the circuit structure of the push-pull transformer of the present invention.

Fig. 2 is a schematic block diagram of the circuit of the present invention.

Fig. 3 is a circuit diagram of a series or parallel output constant voltage conversion circuit of the present invention.

Fig. 4 is a schematic diagram of the equivalent principle of a series or parallel output constant voltage conversion circuit of the present invention, wherein Fig. 4 (a) is an equivalent schematic diagram of a series output constant voltage conversion circuit, and Fig. 4 (b) is a parallel output constant voltage conversion circuit Equivalent schematic.

Fig. 5 is a characteristic diagram of multi-stage output of the circuit of the present invention.

Fig. 6 is a circuit diagram of a multi-level composite window comparator of the present invention.

Fig. 7 is a logic composite circuit diagram of the present invention.

Fig. 8 is an input dual voltage level logic protection circuit of the present invention.

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals designate the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

In describing the present invention, it is to be understood that the terms "central", "lateral", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", The orientation or positional relationship indicated by "outside" is based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, Constructed and operative in a particular orientation and therefore are not to be construed as limitations of the invention. Unless stated otherwise, "plurality" means two or more.

In the description of the present invention, it should be noted that unless otherwise specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection; it can also be a detachable connection. Connection, or integral connection; it can be mechanical connection or electrical connection; it can be direct connection or indirect connection through an intermediary, and it can be the internal communication of two components. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention according to specific situations.

Referring to Figures 1-4, the present invention provides a dual-stage input step-up DC constant voltage output converter, including 12V or 24V low-voltage power input, auxiliary power supply circuit, automatic frequency switching circuit, PWM control circuit, boost output rectification filter The circuit is characterized in that: it also includes a potential logic protection circuit, a push-pull boost topology circuit, and an output constant voltage automatic switching circuit; the auxiliary power supply circuit is respectively connected to the automatic frequency switching circuit and the potential logic protection circuit, and the automatic frequency switching circuit is The input voltage level adjusts the parameters of the oscillation circuit to ensure that the PWM frequency is adapted. The push-pull boost topology circuit is driven by the PWM signal and is connected in sequence with the output constant voltage automatic switching circuit and the boost output rectification filter circuit; the output constant voltage automatic switching circuit It includes a push-pull transformer, a transfer switch K1, a switch drive circuit, and a rectification and filtering circuit. The push-pull transformer is connected to the rectification and filtering circuit through the transfer switch K1. The input winding of the push-pull transformer includes two windings with the same number of turns, A winding with a center tap, and its output winding is two independent windings with the same number of turns. The switch drive circuit includes a triode, a Zener diode, a resistor, and a capacitor. The anode end of the Zener diode is connected to the base of the triode, and the Zener diode The cathode terminal of the triode is connected to the DC power supply through the resistor R2; the base circuit of the triode is composed of a parallel connection of the resistor R1 and the capacitor C4, and one end of the base circuit is grounded; the collector terminal of the triode is connected to the relay coil of the transfer switch K1, and is connected to the relay coil A freewheeling diode D7 is connected in parallel, and the freewheeling diode D7 is connected to the DC power supply with the relay coil; the transfer switch K1 is a double-pole double-throw relay, and its normally closed contacts are respectively connected to the B and C ports of the two output windings of the push-pull transformer , the normally open contact is connected to the A and D ports, so that when the relay armature is in the released state, the two output winding ports connected by the normally closed contact are in an internal short-circuit state and are not connected to the rectifier and filter circuit, so that the two push-pull transformers The output windings are output in series; and when the relay armature is in the pull-in state, the two output windings of the push-pull transformer are output in parallel. The specific description is as follows:

Multi-voltage level input step-up DC constant voltage output converter is a common component in inverter power supply. The present invention focuses on the design scheme of an automatic constant voltage switching circuit for a 12V and 24V dual voltage level (hereinafter referred to as dual level) input switching power supply. The output constant voltage automatic switching circuit ensures safe and stable voltage output under different input voltages. The potential logic monitoring circuit can judge according to the different states of the input bus voltage (undervoltage, overvoltage, normal), so as to control the start and stop of the entire circuit by controlling the PWM module.

In the push-pull topology (Push-Pull), the input and output windings of the transformer generally consist of two sets of symmetrical windings with taps in the middle. The symmetrical input winding makes the transformer core work in the third type of working state, and the power topology has a good core utilization rate during the conversion process. In the case of input DC voltage U _i , if the transformation ratio is K, the output voltage satisfies U _o = U _i /K; if the new DC voltage U _i '=2U _i is taken as input at this time, then at this time The new output voltage satisfies U _o '=U _i '/K=2U _o . It can be seen that under different input voltage conditions, an overvoltage output phenomenon will occur.

In order to solve the above problems, the output of the transformer of the push-pull topology circuit is designed as two independent windings, as shown in Figure 1. And switch the series or parallel connection of two independent output windings through the peripheral circuit, or switch the rectification method corresponding to the AC voltage of the output winding of the transformer, so that the circuit output is a constant voltage, thereby solving the overvoltage phenomenon. The input winding of the transformer is composed of two windings with the same number of turns, and has a center tap, and the number of turns is represented by n ₁₁ and n ₁₂ respectively. The output winding is composed of two independent windings with the same number of turns, and the numbers of turns are represented by n ₂₁ and n ₂₂ respectively. Suppose the number of turns n ₁₁ =n ₁₂ =N ₁ , and the number of turns n ₂₁ =n ₂₂ =N ₂ . According to the known conditions such as input voltage U _i , output voltage U _o , output power P _o , PWM frequency f and duty cycle D, the conversion efficiency η can be estimated, the coil current density j can be solved, and then the required transformer core can be selected Specifications and enameled wire diameter and other parameters. The values of N ₁ and N ₂ can be solved according to the following formula:

The automatic switching output constant voltage circuit after the step-up transformer can ensure constant voltage output when different inputs are applied to the boost circuit of the dual-stage input inverter power supply. The boost circuit of the dual-stage input inverter power supply is mainly composed of Push-pull boost topology circuit, PWM control circuit, potential logic protection circuit, automatic frequency switching circuit, output constant voltage automatic switching circuit, output overvoltage protection circuit, switching tube conduction voltage drop overcurrent protection circuit, boost output rectification The filter circuit and auxiliary power supply are composed of several parts. Its overall design block diagram is shown in Figure 2. A low-voltage power supply (12V or 24V) is used as the input of the entire power supply circuit. Output stable 15V and 5V through the auxiliary power supply circuit to provide the control circuit as a power supply; the automatic frequency switching circuit can adjust the parameters of the oscillation circuit according to the input voltage level to ensure that the PWM frequency adapts; the push-pull boost circuit is driven by the PWM signal, and the output constant Cooperate with the automatic voltage adjustment circuit, switch the circuit according to the automatic judgment of the input voltage (12V or 24V), convert different low-voltage DC inputs into a square wave high voltage with a constant output voltage of 380V (effective value), and then pass through the output rectification filter circuit Get a 380V post-stage bus high voltage.

The entire design scheme also includes overcurrent protection and overvoltage protection circuits, and the two protection circuits are introduced into the PWM enable terminal as feedback signals. The over-current protection circuit uses the internal resistance characteristics of the transistor to judge whether there is an over-current or short-circuit phenomenon during the boosting process by monitoring the conduction voltage drop of the transistor switch, and if so, it will turn off the PWM output in time; while the over-voltage protection circuit By monitoring the output voltage, the PWM output is immediately turned off in case of overvoltage.

The input winding of the transformer connected to the push-pull topology is composed of two N ₁ -turn coil windings, and the output winding is composed of two independent windings with N ₂ turns. When the input voltage is U _i , the two output windings each output a square wave voltage with an effective value of U _o ; when the input voltage is 2U _i , each output winding outputs a square wave voltage with an effective value of 2U _o . Based on this, the following output constant voltage automatic switching scheme is designed:

Referring to Fig. 3, when the input voltage is U _i =12V, the two output windings are differently connected in series to form a new 2N ₂ output winding, so that the high voltage output of 2U _o can be obtained from the principle formula of the transformer; when the input voltage is 2U _i = At 24V, the two output windings are connected in parallel to form a new output winding of N ₂ turns, and the high voltage output of 2U _o can be obtained from the principle formula of the transformer. Therefore, the principle of constant voltage is to design a series-parallel switching circuit.

In Figure 3, the two output windings of the step-up transformer are connected to a double-pole double-throw relay, and the relay coil K1 is controlled by a 17.1V voltage state reversal circuit composed of R2, D6, D5, R1, C4, and Q1.

When the input terminal voltage (V-BAT) is lower than 17.1V (12V input), the base drive voltage of Q1 is approximately 0V, which fails to meet the conduction condition of the triode, so the relay armature is in the released state (the state of the relay in Figure 3 ), it can be seen from the circuit analysis that at this time the ports 'OUT B' and 'OUT C' are in an internal short-circuit state and are not connected to the rectifier circuit, and the ports 'OUTA' and 'OUT D' are used as outputs, that is, the transformer The two output windings are output in series, that is, the number of turns of the coil formed after series connection is 2N ₂ , so the effective value of the output is a square wave voltage of 2U _o , and its equivalent principle is shown in Figure 4(a); similarly, when When the input terminal voltage (V-BAT) is higher than 17.1V (in the case of 24V input), the Q1 base drive voltage is approximately 0.7V (the triode PN junction clamping effect is equivalent to a diode connected in series from the base to the emitter), which satisfies the requirements of the triode The conduction condition, so the relay armature is in the pull-in state. According to the circuit analysis, at this time, the ports 'OUT A' and 'OUT C' and 'OUT B' and 'OUT D' are both internally short-circuited for output, that is, the two transformers Two output windings are output in parallel with the same name, that is, the number of turns of the coil formed after parallel connection is N ₂ , that is, the output effective value is a square wave voltage of 2U _o , and its equivalent principle is shown in Figure 4 (b). In this way, the purpose of constant voltage conversion is realized.

This scheme realizes the switching of constant voltage output for two different input voltages, and adopts bridge rectification circuit in the subsequent rectification circuit part. Four fast recovery diodes RHRP8120 (D4, D3, D1, D2 in the figure) are used here. In the output filter link, two parallel aluminum electrolytic capacitors (470uF/400V) are used to obtain a stable DC voltage output.

Referring to Figure 5-8, the potential logic protection circuit includes a comparator circuit and a logic composite circuit, and is characterized in that: the comparator circuit has n groups of comparators, n threshold point potentials U_set_1,..., U_set_n, and each group compares The device has two comparators to obtain 2n comparison output voltages U_out_1,..., U_out_2n, the undervoltage and overvoltage sampling of the input compared voltage U_in is divided into two independent voltage division branches, and the undervoltage sampling division The type branch includes resistors R ₁ and R ₂ , and the overvoltage sampling branch includes resistors R ₃ and R ₄ . The voltage obtained after dividing the voltage by R ₁ and R ₂ is respectively sent to the inverting terminal of the comparator with even numbers (A2, A4, ..., A 2n) in Figure 2, and compared with the threshold potential of the non-inverting terminal. At this time, the even number The comparator obtains the undervoltage state of each of the n channels (undervoltage state when the output is high, and non-undervoltage state when the output is low); the voltage obtained by dividing the voltage of R ₃ and R ₄ is respectively sent to the odd serial number (A1, A3, ..., A(2n-1)) the non-inverting terminal of the comparator, and compare it with the threshold potential of the inverting terminal. At this time, the odd-numbered comparator obtains the overvoltage state of each of the n channels (output high voltage It is usually in overvoltage state, and it is in non-overvoltage state when outputting low level). The specific description is as follows:

The design of this circuit is divided into two parts, one is a multi-stage composite window comparator circuit, and the other is a logic composite circuit. And its circuit output characteristic diagram is shown in Fig. 5 .

In Fig. 5, U_low_1, U_high_1, U_low_2, U_high_2, ..., U_low_n, U_high_n represent the first level low threshold potential point, the first level high threshold point potential, the second level low threshold point potential, the second level High threshold point potential, nth level low threshold point potential, nth level high threshold point potential (there are other levels of high and low threshold point potentials not marked). At the same time, the threshold point potential satisfies U_high_n>U_low_n>…>U_high_2>U_low_2>U_high_1>U_low_1. If U_in<U_low_x, it is called the undervoltage situation corresponding to the xth level; if U_low_x<U_in<U_high_x, it is called the normal situation corresponding to the xth level; if U_in>U_high_x, it is called the corresponding xth level overvoltage condition.

The structure of the multi-stage composite window comparator circuit is shown in Figure 6, and the structure of the logic composite circuit is shown in Figure 7.

The multi-level composite window comparator circuit has 2n comparators (A1, A2, A3, A4, ..., A(2n-1), A 2n), n threshold point potentials (U_set_1, U_set_2, ..., U_set_n), 2n comparison output voltages (U_out_1, U_out_2, U_out_3, U_out_4, . . . , U_out_(2n-1), U_out_2n).

Here, from the nature of the upper limit and lower limit of the potential at the threshold point, it can be known that the upper limit and lower limit of each level of potential in the n-level input satisfy U_high_n>U_low_n>U_high_(n-1)>U_low_(n-1)> ...>U_high_1>U_low_1. At the same time, the potentials of each threshold point of the multi-level composite window comparator circuit should satisfy U_set_n>U_set_(n-1)>...>U_set_1.

This circuit divides the undervoltage and overvoltage sampling of the input compared voltage U_in into two independent voltage division branches. The undervoltage sampling branch is composed of R ₁ and R ₂ in the figure, and the overvoltage sampling branch is composed of R ₃ and R ₄ in the figure.

Send the voltage obtained after dividing the voltage of _R1 and _R2 to the inverting terminal of the comparator with even numbers (A2, A4, ..., A2n), and compare it with the threshold potential of the non-inverting terminal. At this time, the comparator with even numbers gets The undervoltage state of each of the n roads (the undervoltage state when the output is high, and the non-undervoltage state when the output is low); the voltage obtained by dividing the voltage of R ₃ and R ₄ is respectively sent to the odd serial number in Figure 2 (A1, A3, ..., A(2n-1)) the non-inverting terminal of the comparator, and compare it with the threshold potential of the inverting terminal. At this time, the odd-numbered comparator obtains the overvoltage state of each of the n channels (output high voltage It is usually in overvoltage state, and it is in non-overvoltage state when outputting low level). Here, the comparative output voltages (U_out_1, U_out_2, U_out_3, U_out_4, ..., U_out_(2n-1), U_out_2n) obtained by the 2n comparators are logically combined through the logic circuit in Figure 2 to obtain a multi-level input Potential logic judgment signal output.

It can be seen that the lower limit values U_low_1, U_low_2, . . . , U_low_n and upper limit values U_high_1, U_high_2, . The input voltage is compared with U_set_1, U_set_2, ..., U_set_n after being valued by the voltage divider circuit, which is equivalent to the direct comparison of the input voltage with U_low_1, U_high_1, U_low_2, U_high_2..., U_low_n, U_high_n. This method converts the under-voltage and over-voltage areas into two circuits. Only n comparison threshold point potentials are needed in the circuit to form the required potential identification. The principle of the small number required on the threshold point potential lies.

The parameters of the design are determined according to the following formula:

in

In the process of designing and determining parameters, U_low_1, U_high_1, U_low_2, U_high_2..., U_low_n, U_high_n should be specified. Then, the values of U_set_1, U_set_2, ..., U_set_n can be determined first, and then R ₁ , R ₂ , R ₃ , and R ₄ can be determined by using the above formulas to realize the parameter setting of the entire circuit.

The multilevel composite window comparator circuit scheme is applied to electronic circuits with two different input voltage levels of 12V and 24V. The input dual voltage level logic protection circuit shown in Figure 8 is obtained. As shown in the figure, the undervoltage and overvoltage sampling of the input voltage (V-BAT) is divided into two independent voltage-dividing branches. The undervoltage sampling branch is composed of R ₁ and R ₂ in the figure, and the overvoltage sampling branch is composed of R ₃ and R ₄ in the figure.

At the same time, under the 12V input level, the undervoltage and overvoltage values are 10.5V and 15V respectively; under the 24V input level, the undervoltage and overvoltage values are 21V and 30V respectively.

By calculation, the four resistors can take values:

R ₁ =24K ohm, R ₂ =11K ohm, R ₃ =39K ohm, R ₄ =11K ohm. The two-way voltage-dividing sampling signals are respectively sent to the four comparator units A, B, C, and D of the LM339 chip. Two Zener diodes (Zener diodes, BZV55-B3V3) are connected in series to form the comparison reference voltage of four comparators, and each Zener diode is connected in parallel with a ceramic capacitor with a capacity of 10nF as a high-frequency bypass capacitor. In addition to comparing the reference voltage from the interference signal inside and outside the circuit. Because the LM339 comparator is an "open-drain" output type, a "pull-up" resistor with a resistance value of 2K ohm is added to the output terminal of each comparator unit to ensure that the correct state can be output.

The outputs of the four comparators are connected to subsequent logic gate circuits. Because of the working characteristics of the CMOS logic chip, and it works in the 5V mode, a voltage divider circuit is added at the output end of each comparator to make the input voltage reach the input standard of the CMOS logic chip. According to the circuit connection in Figure 2, when the output of the comparator is high, it means that the input voltage is undervoltage or overvoltage; when the output of the comparator is low, it means that the input voltage is within a reasonable working range.

It can be analyzed that when the output terminals OA and OB of the comparator units A and B output high levels, they correspond to the overvoltage and undervoltage protection outputs when the 12V battery is input; while the output terminals OC and OD of the comparator units C and D output When the level is high, it corresponds to the overvoltage and undervoltage protection output when the 24V battery is input.

The four logic signals OA, OB, OC, and OD are sent together into a logical composite circuit conforming to the logical expression "Control_out = OA·OD+OB+OC", and finally a composite output signal Control_out is obtained.

Although the embodiments of the present invention have been shown and described, those skilled in the art should understand that various changes, modifications, substitutions and modifications can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalent replacements, and improvements made without creative work shall be included in the protection scope of the present invention.

Claims (5)

1. A double-stage input step-up DC constant voltage output converter, comprising 12V or 24V low-voltage power input, auxiliary power supply circuit, automatic frequency switching circuit, PWM control circuit, boost output rectification filter circuit, is characterized in that: also It includes a potential logic protection circuit, a push-pull boost topology circuit, and an output constant voltage automatic switching circuit; the auxiliary power supply circuit is connected to the automatic frequency switching circuit and the potential logic protection circuit respectively, and the automatic frequency switching circuit adjusts the oscillation circuit parameters according to the input voltage level To ensure that the PWM frequency adapts, the push-pull boost topology circuit is driven by the PWM signal and is sequentially connected with the output constant voltage automatic switching circuit and the boost output rectification filter circuit; The output constant voltage automatic switching circuit includes a push-pull transformer, a transfer switch K1, a switch drive circuit, and a rectification and filtering circuit. The push-pull transformer is connected to the rectification and filtering circuit through the transfer switch K1, and the input winding of the push-pull transformer is It includes two windings with the same number of turns and a center tap, and its output winding is two independent windings with the same number of turns. The switch drive circuit includes a triode, a Zener diode, a resistor, a capacitor, and the anode terminal of the Zener diode Connect the base of the triode, the cathode of the Zener diode is connected to the DC power supply through the resistor R2; the base circuit of the triode is composed of a parallel connection of the resistor R1 and the capacitor C4, and one end of the base circuit is grounded; the collector of the triode is connected to the switch K1 Relay coil, and a freewheeling diode D7 is connected in parallel on the relay coil, and the freewheeling diode D7 is connected to the DC power supply with the relay coil; the transfer switch K1 is a double-pole double-throw relay, and its normally closed contacts are respectively connected to the push-pull transformer. The B and C ports of the two output windings, the normally open contacts are connected to the A and D ports, so that when the relay armature is in the released state, the two output winding ports connected by the normally closed contacts are in an internal short-circuit state and are not connected to the rectifier filter circuit. In this way, the two output windings of the push-pull transformer are output in series; and when the relay armature is in the pull-in state, the two output windings of the push-pull transformer are output in parallel; The reference value of the Zener diode is selected between 15V and 21V; The potential logic protection circuit includes a comparator circuit and a logic composite circuit. The comparator circuit has n sets of comparators, n threshold point potentials U_set_1,..., U_set_n, and each set of comparators has two comparators to obtain 2n comparative output voltages U_out_1,..., U_out_2n, the undervoltage and overvoltage sampling of the input compared voltage U_in are divided into two independent voltage-dividing branches, the undervoltage sampling voltage-dividing branch includes resistors R ₁ and R ₂ , the overvoltage sampling voltage dividing branch includes resistors R ₃ and R ₄ ; the inverting terminal of the even-numbered comparator is connected and connected to the voltage dividing circuit composed of R ₁ and R ₂ , so that R ₁ and R ₂ are divided The voltage obtained after pressing is sent to the inverting terminal of the even-numbered comparator, and compared with the threshold potential of the same-phase terminal, so that the even-numbered comparator obtains the undervoltage state of each of the n channels; the same-phase terminal of the odd-numbered comparator is connected to And connect to the voltage divider circuit composed of R ₃ and R ₄ , so that the voltage obtained after the voltage division of R ₃ and R ₄ is respectively sent to the non-inverting terminal of the odd-numbered comparator, and compared with the threshold potential of the inverting terminal, so that the odd number The sequence number comparator obtains the overvoltage status of each of the n channels. 2. The dual-stage input step-up DC constant voltage output converter according to claim 1, characterized in that: said Zener diodes include Zener diodes D5 and D6 connected in series, and satisfy: 15V<(VD5+VD6 )<21V. 3. The dual-stage input step-up DC constant voltage output converter according to claim 1 or 2, wherein the rectification and filtering circuit includes diodes D1-D4. 4 . The dual-stage input step-up DC constant voltage output converter according to claim 3 , wherein the rectification and filtering circuit comprises two parallel-connected aluminum electrolytic capacitors. 5. The dual-stage input step-up DC constant voltage output converter according to claim 1, characterized in that: said logic composite circuit includes n groups of logic input signals, and each group of logic input signals is input by n two-input or logic The gate obtains n operation output signals, and the n operation output signals are sent to the AND logic gate to finally obtain the composite output signal U_out.

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