Voltage sampling and supply circuit for an isolated forward converter

Abstract

The application discloses a voltage sampling and power supply circuit of an isolated forward converter, comprising an output voltage error compensation circuit, an error signal sampling circuit, an isolated double-winding transformer, a primary rectifier circuit and a clock circuit, the output voltage error compensation circuit samples the converter output voltage, and outputs an error signal after comparison with a reference voltage; the error signal sampling circuit discretizes the error signal to make it pass through the isolated transformer, and simultaneously supplies power to a secondary chip; the isolated double-winding transformer realizes primary-secondary side isolation of the isolated forward converter; the primary rectifier circuit restores the discrete error signal to a time-domain continuous signal, which is provided to a converter master control chip for subsequent control; and the clock circuit provides a clock pulse signal for the whole circuit. The application can realize output of the isolated converter, reduce the number of winding of the isolated transformer, reduce the system volume and weight, simplify the working mode, and improve the system integration and reliability while ensuring sampling accuracy.

Description

Technical Field

[0001] This invention discloses a voltage sampling and power supply circuit for an isolated forward converter, which relates to voltage sampling technology for isolated converters and belongs to the field of basic electronic circuits. Background Technology

[0002] With the continuous development of modern power electronics technology, power supply equipment is gradually becoming more high-frequency, high-efficiency, integrated, and modular. As a typical DC-DC converter topology, the forward converter topology has advantages such as isolated step-up / step-down voltage, simple topology structure, and low output voltage ripple, and is widely used in fields such as computers, electronic communications, and aerospace. Because the forward converter requires input-output isolation, its control loop also needs to be designed with isolation. The voltage sampling circuit is an important component of the forward converter topology control loop. Its main function is to sample the output voltage signal, generate an error signal through compensation amplification, pass this error signal through an isolation transformer, and finally output it to the main control chip for subsequent control.

[0003] Crane Aerospace & Electronics has developed a voltage sampling circuit suitable for forward converter topologies. This solution uses a three-winding transformer to isolate the primary and secondary sides. The three windings are connected to the error signal loop, the primary rectifier circuit, and the clock circuit, respectively. The clock circuit provides a periodic pulsating signal, which allows the error signal to be transmitted to the rectifier circuit through the isolation transformer and then output to the main control chip.

[0004] 1. Error voltage signal sampling phase t0-t1

[0005] When the clock circuit outputs a high-level signal, that is, when the clock signal is in the first half of the cycle t0-t1, the winding connected to the rectifier circuit stops working, the sampling part of the error signal sampling circuit works, so that the non-same-name terminal of the secondary side of the winding obtains the error voltage signal, the same-name terminal of the secondary side of the winding is low-level, the diode D3 freewheels, and the power supply part is powered by the capacitor C2.

[0006] 2. Rectification phase t1-t2

[0007] When the clock circuit outputs a low-level signal, that is, when the clock signal is in the second half of the cycle t1-t2, the rectifier circuit works normally, the secondary side terminal is at a high level, and the capacitor C2 is charged through diode D4.

[0008] This scheme allows for more accurate sampling of the forward converter, achieving input-output isolation. The use of a three-winding transformer increases the overall size, weight, and heat generation of the power system, hindering miniaturization and integration of power equipment. Therefore, improved transformer design is needed to enhance the integration level of the power system. Summary of the Invention

[0009] Technical Problem: The purpose of this invention is to address the technical shortcomings of the isolation transformer and related circuits in the voltage sampling circuit of an isolated forward converter. It proposes an isolated forward converter voltage sampling circuit that utilizes the alternating operation principle of the clock circuit and rectifier circuit in the voltage sampling circuit, and modifies the number of windings in the isolation transformer. This improves the integration and power density of the voltage sampling circuit and the power supply system without altering the function and performance of the voltage sampling circuit.

[0010] Technical solution: To achieve the above-mentioned objectives, this invention employs a voltage sampling and power supply circuit for an isolated forward converter, comprising:

[0011] The output voltage error compensation circuit is connected to the output voltage of the forward converter at its input terminal. It samples, compares, and compensates the output voltage of the forward converter, and outputs an error signal V obtained by comparing it with a reference voltage. err ;

[0012] The error signal sampling circuit receives the error signal output by the output voltage error compensation circuit, discretizes the error signal so that it can pass through the isolation double-winding transformer, and simultaneously supplies power to the comparator of the output voltage error compensation circuit.

[0013] An isolation dual-winding transformer receives the output of the error signal sampling circuit and transmits the discretized error signal to the primary side, thereby achieving primary-secondary isolation of the sampling circuit of the isolation-type forward converter.

[0014] The primary-side rectifier circuit rectifies the error signal transmitted to the primary side through the discretization process and outputs the COMP comparison signal.

[0015] The clock circuit uses an operational amplifier to generate clock pulse signals through self-oscillation, which helps to transmit error signals to the primary side.

[0016] The output voltage error compensation circuit divides the output voltage of the forward converter through resistors and inputs it to the inverting input of the comparator. The non-inverting input of the comparator is connected to a 2.5V reference voltage source to perform pole and zero compensation on the comparison signal. The output of the comparator outputs the error signal V. err .

[0017] The error signal sampling circuit receives the error voltage signal, changes the base potential of the first transistor by charging and discharging the first capacitor, thereby changing the on-resistance of the first transistor, and thus characterizes the discrete error signal. The discrete error signal is transmitted to the same-name terminal of the secondary side of the isolated double-winding transformer.

[0018] The primary-side rectifier circuit receives discrete error signals, restores AC pulsating signals to continuous error signals, and outputs COMP comparison signals.

[0019] The clock circuit uses an operational amplifier to generate a periodic pulse signal through self-oscillation, which is then transmitted to the primary side of the isolated double-winding transformer.

[0020] The isolated dual-winding transformer has its primary winding terminal connected to the clock circuit output and the primary rectifier circuit input, and its non-primary winding terminal grounded; the secondary winding terminal is connected to the error signal sampling circuit, and its non-secondary winding terminal supplies power to the comparator of the output voltage error compensation circuit.

[0021] In the error signal sampling circuit, when the error signal is low, the first transistor is turned on, and the same-name terminal of the secondary side of the isolation double-winding transformer is at a pulsating low level; when the error signal is high, the first transistor is turned off, and the same-name terminal of the secondary side of the isolation double-winding transformer is at a high level; the non-same-name terminal of the secondary side of the isolation double-winding transformer charges the filter capacitor through the fourth diode, providing a DC voltage SVCC to the secondary circuit.

[0022] When the clock signal is high, the clock circuit of the isolated double-winding transformer operates, transmitting a high-level signal to the secondary side; when the clock signal is low, the primary-side rectifier circuit operates, providing a sampling error signal to the primary side.

[0023] The isolated double-winding transformer has a turns ratio of 1:1.

[0024] The voltage sampling and power supply circuit includes an output voltage error compensation circuit, an error signal sampling circuit, an isolated dual-winding transformer, a primary-side rectifier circuit, and a clock circuit. The output of the isolated forward converter is connected to the output voltage error compensation circuit. The output voltage signal is divided by a voltage divider circuit and transmitted to the inverting input of the comparator, where it is compared with the DC reference voltage signal at the non-inverting input. An error signal is generated through proportional and integral operations. The output of the output voltage error compensation circuit is connected to the error signal sampling circuit, which can be divided into two parts, connected to the same-name terminal and the non-same-name terminal of the secondary side of the isolated dual-winding transformer, respectively. On one hand, the error voltage signal, by changing the base potential of the transistor in the sampling circuit and adjusting the transistor's on-resistance, is superimposed with the clock signal from the primary side to form a discrete error signal. On the other hand, the discrete signal from the non-same-name terminal is rectified and filtered to form a DC voltage, which powers the secondary-side chip. The same-name terminal of the primary side of the isolated dual-winding transformer is connected to the input of the primary-side rectifier circuit and the output of the clock circuit, while the non-same-name terminal is grounded.

[0025] This invention utilizes the alternating operation of the primary-side rectifier circuit and the clock circuit, as well as the hold function of the primary-side rectifier circuit, and employs a two-winding transformer instead of a three-winding transformer. The clock circuit consists of a self-oscillating circuit built with operational amplifiers and an amplification circuit, generating a high-frequency pulsating signal. When the clock signal is high, the primary-side rectifier circuit stops working and only charges the capacitor. The corresponding terminal on the secondary side of the isolated two-winding transformer is high, which is superimposed on the error signal to generate a sampling error signal. When the clock signal is low, the primary-side rectifier circuit operates. The discrete error voltage signal generated by the error signal sampling circuit is transmitted to the primary-side rectifier circuit through the isolated two-winding transformer. After rectification, the error voltage signal is restored and transmitted to the main control chip for subsequent control operations.

[0026] Beneficial effects: The voltage sampling and power supply circuit of the isolated forward converter proposed in this invention has the following advantages compared with existing technologies:

[0027] (1) This invention utilizes the characteristic that the primary-side rectifier circuit and the clock circuit can work alternately, and uses an isolated double-winding transformer to replace the isolated triple-winding transformer, thereby reducing the system size and weight and improving the system power density and reliability.

[0028] (2) The primary winding of the isolation double-winding transformer of the present invention is not directly connected to the primary voltage source V. cc Connected, a self-excited oscillation circuit is used to directly generate a clock signal, reducing the voltage source V on the primary side. cc The impact of fluctuations on system function and stability;

[0029] (3) The present invention utilizes the voltage signal of the non-same terminal of the secondary side of the isolated double winding transformer, and uses it to power the secondary chip through rectification, filtering and amplification, thereby reducing system heat loss and improving system energy utilization and temperature performance. Attached Figure Description

[0030] Figure 1 This is a system block diagram of the voltage sampling and power supply circuit of the isolated forward converter of the present invention.

[0031] Figure 2 This is a schematic diagram of the error signal sampling circuit of the present invention.

[0032] Figure 3 The waveforms of the ripple-containing output voltage of the analog isolated forward converter and the output error voltage signal of the output voltage error compensation circuit are shown in the figure.

[0033] Figure 4 The waveforms of capacitor C1 voltage and sampled discrete error voltage signal in the error signal sampling circuit of this invention are shown.

[0034] Figure 5This is a detailed waveform diagram of the discrete error voltage signal sampled in this invention.

[0035] Figure 6 This is a waveform comparison diagram of the sampling voltage signal output by the primary rectifier circuit of the present invention, the voltage signal at the same terminal of the primary side of the isolation double-winding transformer, and the clock signal.

[0036] Figure 7 This is a detailed waveform diagram of the voltage signal and clock signal at the primary side of the isolation double-winding transformer of the present invention.

[0037] Figure 8 This is an equivalent circuit diagram of the voltage sampling and power supply circuit of an isolated forward converter according to the present invention, in operating mode 1.

[0038] Figure 9 This is an equivalent circuit diagram of the voltage sampling and power supply circuit of an isolated forward converter according to the present invention, operating mode 2.

[0039] The diagram shows: comparator b1, first capacitor C1, filter capacitor C2, third capacitor C3, first transistor Q1, second transistor Q2, first diode D1, second diode D2, third diode D3, and fourth diode D4. Detailed Implementation

[0040] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0041] This invention discloses a voltage sampling and power supply circuit for an isolated forward converter, comprising the following circuit modules: an output voltage error compensation circuit, connected to the output terminal of the isolated forward converter, which samples, compares, and compensates the output voltage of the forward converter, and outputs an error signal obtained by comparing it with a reference voltage; an error signal sampling circuit, which receives the error signal output by the output voltage error compensation circuit, discretizes the error signal so that it can pass through the isolation transformer and simultaneously power the secondary-side chip; an isolation dual-winding transformer, connected to the error signal sampling circuit, transmits the discrete error signal to the primary side, realizing primary-secondary isolation of the sampling circuit of the isolated forward converter; a primary-side rectifier circuit, which rectifies the discrete error signal transmitted to the primary side and outputs the rectified signal to the main control chip; and a clock circuit, in which an operational amplifier self-oscillates to generate a clock pulse signal to assist in the transmission of the error signal to the primary side.

[0042] The output voltage error compensation circuit divides the output voltage through resistors and inputs it to the inverting input of comparator B1. The non-inverting input of comparator B1 is connected to a 2.5V reference voltage source to perform pole and zero compensation on the comparison signal. The output of comparator B1 outputs the error signal. The error signal sampling circuit receives the error voltage signal and changes the base potential of the transistor by charging and discharging the capacitor, thereby changing the transistor's on-resistance and characterizing the error signal. This discrete error signal is transmitted to the secondary side terminal of the isolated double-winding transformer. The primary-side rectifier circuit receives the discrete error signal and restores the AC pulsating signal to a continuous error signal. This signal is then transmitted to the main control chip through a common-collector amplifier circuit, which acts as a buffer and isolation circuit. The clock circuit uses an operational amplifier to generate a periodic pulse signal through self-oscillation and transmits it to the primary side terminal of the isolated double-winding transformer. An isolated double-winding transformer has its primary winding's same-name terminal connected to the clock circuit output and the primary rectifier circuit input, while its non-same-name terminal is grounded. The secondary winding's same-name terminal is connected to the error signal sampling circuit, and its non-same-name terminal supplies power to the secondary chip. In the error signal sampling circuit, when the error signal is low, the transistor is turned on, and the secondary winding's same-name terminal of the isolated double-winding transformer is at a pulsating low level; when the error signal is high, the transistor is turned off, and the secondary winding's same-name terminal of the isolated double-winding transformer is at a high level. The non-same-name terminal of the secondary winding of the isolated double-winding transformer charges the filter capacitor through a diode, providing DC voltage to the secondary circuit. When the clock signal is high, the clock circuit operates, transmitting a high-level signal to the secondary side; when the clock signal is low, the primary rectifier circuit operates, providing a sampling error signal to the primary side. The isolated double-winding transformer has a turns ratio of 1:1.

[0043] The system principle block diagram of the voltage sampling and power supply circuit of the isolated forward converter of the present invention is as follows: Figure 1 As shown. The voltage sampling and power supply circuit system of the isolated forward converter includes an output voltage error compensation circuit, an error signal sampling circuit, an isolated two-winding transformer, a primary-side rectifier circuit, and a clock circuit. For example... Figure 3 As shown, let the output voltage V of the isolated forward converter be... out The input is a 15V DC voltage containing a sinusoidal ripple of 8V peak-to-peak and 1kHz frequency. The input of the output voltage error compensation circuit is connected to the output voltage of the isolated forward converter. After being divided by a 6:1 ratio, it is compared with a 2.5V reference voltage, and an error voltage signal is generated using dual-pole and dual-zero compensation.

[0044] For a detailed circuit diagram of the error signal sampling circuit in this embodiment of the invention, please refer to... Figure 2 .like Figure 3 As shown, the output voltage error compensation circuit outputs an error voltage signal V. err This is a rectangular wave signal. The circuit operation principle under each error signal state is described in detail below.

[0045] 1. Error voltage signal high level t0-t1

[0046] like Figure 2 As shown, when the error voltage signal is high, the signal charges the first capacitor C1 through resistor R1, the base potential of the first transistor Q1 increases, the emitter-base voltage difference decreases, which increases the on-resistance of the first transistor Q1, thus increasing the voltage V at the same terminal of the secondary side of the isolation double-winding transformer. s An increase is represented by a high level.

[0047] 2. Error voltage signal low level t1-t2

[0048] like Figure 2 As shown, when the error voltage signal is low, the voltage of capacitor C1 decreases, the base potential of the first transistor Q1 decreases accordingly, and the emitter-base voltage difference increases, which reduces the on-resistance of the first transistor Q1 and decreases the voltage V at the same terminal of the secondary side of the isolation double-winding transformer. s A decrease is represented by a low level.

[0049] The time-domain discretization process of the error voltage signal is explained further below. For example... Figure 5 The figure shows the error voltage signal V. err When the voltage level is high, the voltage V at the same terminal of the secondary side of the isolation double-winding transformer is... s Detailed waveform diagram.

[0050] 1. Error voltage signal sampling phase t0-t1

[0051] When the clock signal is high, i.e., when the clock signal is in the first half of the cycle t0-t1, the equivalent circuit is as follows: Figure 8 As shown, the clock signal supplies energy to the secondary side through an isolated double-winding transformer. The first diode D1 is off, and the second diode D2 is on. At this time, V... s This manifests as the error voltage signal being in the same state.

[0052] 2. Rectification phase t1-t2

[0053] When the clock signal is low, i.e., when the clock signal is in the second half-cycle t1-t2, the equivalent circuit is as follows: Figure 9 As shown, the second diode D2 is cut off, and the first diode D1 is conducting to provide freewheeling current, returning energy to the isolation double-winding transformer. At this time, the signal passes through the isolation double-winding transformer, and the primary-side rectifier circuit operates, as shown. Figure 6 As shown, the output sampling voltage signal COMP is generated.

[0054] The error signal sampling circuit in this embodiment of the invention has a secondary power supply function; please refer to [reference needed]. Figure 2 The specific principles of power supply are explained below.

[0055] 1. Discharge stage of filter capacitor C2 t0-t1

[0056] When the clock signal is high, the equivalent circuit is as follows: Figure 8 As shown, the fourth diode D4 is cut off, and the third diode D3 is turned on to provide freewheeling current to the circuit. At this time, the filter capacitor C2 supplies power to the common-base amplifier circuit and provides voltage SVCC to the secondary chip.

[0057] 2. Charging stage of filter capacitor C2: t1-t2

[0058] When the clock signal is low, the equivalent circuit is as follows: Figure 9 As shown, the non-same-name terminals on the secondary side of the isolation dual-winding transformer are at a high level, the third diode D3 is cut off, and the fourth diode D4 is turned on. This voltage charges the filter capacitor C2 and simultaneously supplies power to the common-base amplifier circuit.

[0059] In this embodiment of the invention, an isolation two-winding transformer is used instead of an isolation three-winding transformer, and the secondary-side power supply function is realized, reducing the primary-side voltage source V. cc The fluctuations have an impact on system function and stability, reduced system heat loss, improved system energy utilization and temperature performance, reduced system size and weight, and improved system power density and reliability.

[0060] While this specification describes certain exemplary embodiments in detail, it should be understood that those skilled in the art, upon understanding the foregoing, can readily conceive of modifications, variations, and equivalents of these embodiments.

[0061] The embodiments of the present invention can be modified and altered in various ways without departing from the spirit and scope of the invention. Therefore, it should be understood that the embodiments of the present invention are not limited to the exemplary embodiments described above, but should be subject to the limitations set forth in the claims and any of their equivalents.

Claims

1. A voltage sampling and power supply circuit for an isolated forward converter, characterized in that, include: The output voltage error compensation circuit has its input terminal connected to the output voltage of the forward converter. It samples, compares, and compensates the output voltage of the forward converter and outputs an error signal Verr obtained by comparing it with the reference voltage. The error signal sampling circuit receives the error signal output by the output voltage error compensation circuit, discretizes the error signal so that it can pass through the isolation double-winding transformer, and simultaneously supplies power to the comparator (b1) of the output voltage error compensation circuit. An isolation dual-winding transformer receives the output of the error signal sampling circuit and transmits the discretized error signal to the primary side, thereby achieving primary-secondary isolation of the sampling circuit of the isolation forward converter. The primary-side rectifier circuit rectifies the error signal transmitted to the primary side through the discretization process and outputs the COMP comparison signal. The clock circuit uses an operational amplifier to generate clock pulse signals through self-oscillation, which helps to transmit error signals to the primary side. in, The output voltage error compensation circuit divides the output voltage of the forward converter through resistors and inputs it to the inverting input of the comparator (b1). The non-inverting input of the comparator (b1) is connected to a 2.5V reference voltage source to perform pole and zero compensation on the comparison signal. The output of the comparator (b1) outputs the error signal Verr. The error signal sampling circuit receives the error voltage signal, and changes the base potential of the first transistor (Q1) by charging and discharging the first capacitor (C1), thereby changing the on-resistance of the first transistor (Q1) and thus characterizing the discrete error signal. The discrete error signal is transmitted to the same-name terminal of the secondary side of the isolated double-winding transformer. The primary-side rectifier circuit receives discrete error signals, restores AC pulsating signals to continuous error signals, and outputs COMP comparison signals. The clock circuit uses an operational amplifier to generate a periodic pulse signal through self-excited oscillation, which is then transmitted to the primary side of the isolation double-winding transformer. The isolated dual-winding transformer has its primary winding terminal connected to the clock circuit output and the primary rectifier circuit input, and its non-primary winding terminal grounded; the secondary winding terminal is connected to the error signal sampling circuit, and its non-secondary winding terminal supplies power to the comparator (b1) of the output voltage error compensation circuit.

2. The voltage sampling and power supply circuit of the isolated forward converter according to claim 1, characterized in that, In the error signal sampling circuit, when the error signal is low, the first transistor (Q1) is turned on, and the same-name terminal of the secondary side of the isolation double-winding transformer is at a pulsating low level; when the error signal is high, the first transistor (Q1) is turned off, and the same-name terminal of the secondary side of the isolation double-winding transformer is at a high level; the non-same-name terminal of the secondary side of the isolation double-winding transformer charges the filter capacitor (C2) through the fourth diode (D4), providing a DC voltage SVCC to the secondary circuit.

3. The voltage sampling and power supply circuit of the isolated forward converter according to claim 1, characterized in that, When the clock signal is high, the clock circuit of the isolated double-winding transformer operates, transmitting a high-level signal to the secondary side; when the clock signal is low, the primary-side rectifier circuit operates, providing a sampling error signal to the primary side.

4. The voltage sampling and power supply circuit of the isolated forward converter according to claim 3, characterized in that, The isolated double-winding transformer has a turns ratio of 1:1.

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