WO2024007555A1 - 一种应用于隔离变换器的励磁电流无损采样电路 - Google Patents

一种应用于隔离变换器的励磁电流无损采样电路 Download PDF

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WO2024007555A1
WO2024007555A1 PCT/CN2022/143355 CN2022143355W WO2024007555A1 WO 2024007555 A1 WO2024007555 A1 WO 2024007555A1 CN 2022143355 W CN2022143355 W CN 2022143355W WO 2024007555 A1 WO2024007555 A1 WO 2024007555A1
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circuit
voltage
sampling
resistor
sampling circuit
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PCT/CN2022/143355
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French (fr)
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钱钦松
丁松
聂春燕
周远航
孙伟锋
时龙兴
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东南大学
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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  • the invention discloses a lossless sampling circuit for excitation current applied to an isolation converter. It relates to a lossless sampling technology for the current of an isolation converter. It is suitable for sampling the excitation current of a DCM type isolation converter and a resonance type isolation converter, and belongs to the technology of basic electronic circuits. field.
  • the current detection circuit is mainly used to monitor the output current to obtain the current working status of the power supply in real time.
  • a common current sampling method is to place a sampling resistor or current transformer on the current branch that needs to be detected, but this method will produce an additional power loss, thereby reducing the working efficiency of the converter.
  • MOSFET-R DS to sample the current flowing through the tube.
  • this sampling method is lossless, it is greatly affected by temperature, process, etc., and the current detection accuracy is low. In some circuits that require relatively high efficiency and accuracy, the above sampling method is not applicable. Therefore, the current sampling scheme must be further improved to meet the needs of higher performance circuits.
  • the purpose of the present invention is to address the deficiencies of the above background technology and provide a lossless sampling circuit for excitation current applied to an isolation converter, which filters and integrates the voltage at both ends of the primary winding of the isolation converter through a large time constant filter.
  • the purpose of the invention of lossless sampling of the excitation current of the isolated converter can be achieved without the need for a series sampling resistor or current transformer, and solves the technical problems of existing non-destructive current detection circuits that reduce the overall efficiency of the converter and have low detection accuracy.
  • a lossless sampling circuit for the excitation inductor current of an isolated converter includes an isolation transformer.
  • the primary winding of the isolation transformer is connected in parallel with a primary power conversion circuit, and the secondary winding is connected in parallel with a secondary circuit.
  • the input end of the excitation current lossless sampling circuit is connected to the primary side of the isolation transformer to sample the voltage at both ends of the primary winding of the isolation transformer.
  • the output end of the excitation current lossless sampling circuit is directly connected to one input end of the comparison circuit; on the other hand, it is connected to the other input end of the comparison circuit through the sampling and holding circuit.
  • the comparison circuit outputs a control signal or protection signal control to achieve volt-second balance. Power switch status, thereby protecting the system and peripheral components.
  • the excitation current lossless sampling circuit includes a first voltage sampling circuit, a second voltage sampling circuit and a subtraction circuit composed of an operational amplifier.
  • the first and second voltage sampling circuits respectively sample the voltages at both ends of the primary winding of the isolation transformer, recorded as V a and V b respectively, and sample the excitation inductor AC by detecting the voltage difference (V a -V b ) between the two ends of the primary winding of the isolation transformer. current. It can be known from the relationship between inductor voltage and current That is, the excitation inductor current is obtained by making a difference between the integral value of the voltage across the primary winding of the isolation transformer over time.
  • a large time constant RC low-pass filter circuit that is, an integrating circuit, is introduced as a voltage sampling circuit.
  • the primary winding voltage of the isolation converter sampled by the first and second voltage sampling circuits is divided, filtered and integrated to obtain the final sampled output voltages V aS and V bS , which are the outputs of the first and second voltage sampling circuits.
  • the output of the voltage sampling circuit is connected to the two input terminals of the subtractor respectively, and the output terminal of the subtractor is used as the output terminal of the excitation current sampling circuit, recorded as V sen .
  • the present invention also superimposes a DC bias voltage on the forward input end of the subtractor, so that the output V sen of the excitation current sampling circuit is the superimposed DC amount of the excitation inductor current.
  • the circuit for realizing volt-second balance in the present invention includes a sampling and holding circuit and a comparison circuit.
  • the sampling and holding circuit is triggered by the pulse signal, and samples and holds the excitation current sampling output V sen at the rising edge of the pulse.
  • the sampling and holding result is recorded as V SH .
  • a small positive slope is also added to the output end of the sample and hold circuit to make the controlled power tube change state in advance to prevent system instability caused by delayed state flipping.
  • the two input terminals of the comparison circuit are respectively connected to the excitation current sampling output V sen and the holding circuit output V SH . When V sen changes to V SH , the output state of the comparison circuit flips, and the output of the comparison circuit is used as the power tube control signal.
  • the present invention is applied to the excitation current lossless sampling circuit of the isolated converter. It abandons the traditional excitation inductor current sampling scheme of series resistors or current transformers and directly samples the voltage at both ends of the primary winding of the transformer in the isolated converter. It achieves lossless sampling of the excitation inductor current without causing additional power loss and improves the overall converter efficiency. At the same time, the present invention abandons the lossless sampling scheme of detecting the excitation current flowing through the MOS tube, and has the advantage of high detection accuracy.
  • the present invention uses a large time constant RC circuit as a sampling circuit for the primary winding voltage of the isolation converter.
  • the RC circuit By selecting the parameters of the RC circuit, the RC circuit not only has a low-pass frequency response but also has an integrating function, realizing the RC circuit's
  • the voltage division, filtering and integration of the primary winding voltage of the isolation converter are used to obtain a sampling signal that effectively filters out high-frequency noise.
  • the present invention uses two RC sampling circuits to sample the voltage at both ends of the primary winding of the isolation converter, and uses the offset introduced in the difference between the two sampling signals to perform difference and amplification processing on the two sampling signals.
  • the positive input terminal of the subtraction circuit is superimposed with the bias voltage used to eliminate the offset, and the effective value of the excitation inductor current can be collected throughout the control cycle.
  • the present invention also proposes a solution to realize the volt-second balance of the excitation inductor current.
  • the lossless sampling signal of the excitation current is used as the reference signal.
  • the primary side power in the isolation converter is obtained.
  • the control signal that the tube turn-off time is consistent with the excitation inductor current volt-second balance time achieves the purpose of protecting the system and peripheral components.
  • Figure 1 is a functional block diagram of the excitation current lossless sampling circuit applied to the isolation converter and the realization of volt-second balance control according to the present invention.
  • Figure 2 is a specific circuit diagram for applying the excitation current lossless sampling circuit and realizing volt-second balance control in the embodiment of the present invention.
  • Figure 3 is a waveform diagram of an excitation current lossless sampling circuit used to collect the AC current of the excitation inductor of a buck-boost converter in discontinuous mode (DCM) in an embodiment of the present invention.
  • Figure 4 is a waveform diagram of the excitation current lossless sampling circuit used to collect the AC current of the excitation inductor of the buck-boost converter in critical conduction mode (CrCM) in the embodiment of the present invention.
  • CrCM critical conduction mode
  • Figure 5 is a waveform diagram of an excitation current lossless sampling circuit used to collect the alternating current of the excitation inductor of the flyback converter in discontinuous mode (DCM) in an embodiment of the present invention.
  • Figure 6 is a waveform diagram of the excitation current lossless sampling circuit used to collect the AC current of the excitation inductor of the flyback converter in the critical conduction mode (CrCM) in the embodiment of the present invention.
  • L r is the primary leakage inductance
  • L m is the excitation inductance
  • R L is the equivalent loss resistance
  • R0 is the voltage dividing resistor
  • C0 is the filter capacitor
  • C VSB the voltage holding capacitor
  • R1 ⁇ R5 are the The first to fifth resistors
  • R up is the pull-up resistor
  • OPA is the operational amplifier
  • SW is the switch
  • CMP is the comparator.
  • the isolation converter includes an isolation transformer.
  • the primary winding of the isolation transformer is connected in parallel with a primary power conversion circuit, and the secondary winding is connected in parallel with a primary power conversion circuit. Secondary circuit.
  • the excitation current lossless sampling circuit divides, filters and integrates the voltage at both ends of the primary winding of the isolation transformer to obtain the sampling value of the voltage at both ends of the primary winding of the isolation transformer, and then calculates the difference between the voltage sampling values at both ends of the primary winding of the isolation transformer. The value is amplified and compensated to obtain a voltage signal representing the excitation current.
  • the excitation current lossless sampling circuit includes: a first voltage sampling circuit, a second voltage sampling circuit and a subtraction circuit composed of an operational amplifier.
  • the lossless sampling signal of the excitation current is applied to the volt-second balance control method, and the control signal is obtained by detecting the moment when the increment is 0 within the period of the current sampling signal.
  • the circuit to achieve volt-second balance includes a sample and hold circuit and a comparison circuit.
  • the isolation converter includes an isolation transformer. The two ends of the primary winding of the isolation transformer are terminals a and b. The endpoint voltages are V a and V b .
  • the turns ratio between the primary winding and the secondary winding of the isolation transformer is
  • the primary side of the equivalent circuit of the isolation transformer includes the excitation inductance L m , the primary leakage inductance L r and the equivalent loss resistance R L .
  • the excitation inductor current is recorded as The secondary current i sec , then the voltage difference across the primary winding of the isolation transformer satisfies the following frequency domain model:
  • the excitation inductor current sampling circuit is connected to the primary side of the isolation transformer in the isolation converter and includes a first voltage sampling circuit, a second voltage sampling circuit and a subtraction circuit.
  • the first voltage sampling circuit is connected to terminal a of the primary winding of the isolation transformer, and the sampling output terminal of the first voltage sampling circuit is connected to the non-inverting input terminal of the subtractor.
  • the second voltage sampling circuit is connected to terminal b of the primary winding of the isolation transformer, and the sampling output terminal of the second voltage sampling circuit is connected to the inverting input terminal of the subtractor.
  • the output terminal of the subtractor is the output terminal of the excitation current sampling circuit.
  • the first and second voltage sampling circuits are both the same large time constant RC circuit to achieve integration of the detection voltage, in which the first resistor R 1 and the voltage dividing resistor R 0 form a voltage dividing network to control the primary winding a of the isolation transformer.
  • the sampling voltage at the terminal is divided, and the filter capacitor C 0 , the first resistor R 1 and the voltage dividing resistor R 0 form a low-pass filter circuit to filter out high-frequency noise.
  • the two voltage sampling circuits respectively sample the voltages V a and V b across the primary windings a and b of the isolation transformer, and obtain the sampling output frequency domain models of the first and second voltage sampling circuits:
  • the poles of the RC filter are Control at zero point and zero point between.
  • the subtraction circuit consists of the second resistor R 2 , the third resistor R 3 , the fourth resistor R 4 , the fifth resistor R 5 and the operational amplifier OPA. Its output signal is calculated according to the characteristics of the operational amplifier:
  • K is used to amplify the sampled excitation current signal, and the K value is selected so that the detected V sen signal is easy to distinguish.
  • the output result of the excitation current sampling circuit of the present invention is an excitation inductor current signal superimposed with a DC amount, in which the setting of the DC bias voltage V Bias satisfies the conditions:
  • the specific circuit used by the excitation current sampling circuit of the present invention to realize volt-second balance control is shown in Figure 2.
  • the circuit that realizes the volt-second balance includes the excitation current lossless sampling circuit, the sampling and holding circuit and the comparison circuit.
  • the comparison circuit is a fast comparator.
  • the excitation current sampling output V sen is connected to the inverting input terminal of the comparator CMP on the one hand, and is connected to the non-inverting input terminal of the comparator CMP through the sampling and holding circuit on the other hand.
  • the sampling and holding circuit includes switch SW, voltage holding capacitor C VSB and pull-up resistor R up .
  • the switch SW is controlled by a single pulse trigger, and at the beginning of the cycle, the excitation current sampling output V sen is sampled and held through the voltage holding capacitor C VSB .
  • the voltage holding capacitor C VSB is charged through the pull-up resistor R up , and a small positive slope signal is obtained, which is used to control the state flip of the power tube in advance to prevent the system from being unstable due to untimely state changes.
  • the pull-up resistor R up is a maximum resistance, which can be taken to the megohm level.
  • the sampling and holding signal V SH output by the sampling and holding circuit is connected to the positive input terminal of the comparator CMP.
  • the comparator compares V sen and V SH . When V sen drops to V SH , the comparator outputs a high level, which controls the power tube to turn off.
  • FIGS 3 and 4 are respectively test diagrams of a four-switch buck-boost converter using the circuit of this embodiment in discontinuous mode (DCM) and critical conduction mode (CrCM).
  • V sen is the voltage signal obtained by sampling the excitation current
  • V SH is the voltage signal sampled and held
  • i L is the actual inductor current
  • the falling edge of the Q3 signal is determined by the volt-second balance control circuit. It can be seen that the waveform of the excitation inductor current sampling signal V sen is accurate and consistent with the actual excitation inductor current.
  • the volt-second balance control circuit turns off Q3 and ends the demagnetization process.
  • FIGS 5 and 6 are respectively test diagrams of the flyback converter in discontinuous mode (DCM) and critical conduction mode (CrCM), using the circuit of this embodiment to determine volt-second balance. It can be seen that the excitation inductor current sampling is used The control signal (Q3) obtained by the signal is consistent with the secondary side synchronous rectification signal (Q5).
  • DCM discontinuous mode
  • CrCM critical conduction mode

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Abstract

一种应用于隔离变换器的励磁电流无损采样电路，包括第一电压采样电路、第二电压采样电路和一个由运算放大器构成的减法电路。第一、二电压采样电路分别采样隔离变换器中隔离变压器原边绕组的两端电压，两电压采样电路的输出分别接至减法电路的两输入端，减法电路的输出为励磁电流无损采样电路输出。励磁电流无损采样电路与保持电路和比较器实现伏秒平衡，比较器通过比较采样保持结果和电流采样结果输出控制信号。

Description

一种应用于隔离变换器的励磁电流无损采样电路 技术领域
本发明公开一种应用于隔离变换器的励磁电流无损采样电路，涉及隔离变换器电流无损采样技术，适用于DCM类隔离变换器及谐振类隔离变换器的励磁电流采样，属于基本电子电路的技术领域。
背景技术
现代电力电子技术水平不断提高，逐渐趋于高频率、高效率和高功率密度，主要依靠电力电子技术的开关电源也不断向着小型化、高频化发展。其中，作为关键器件的MOSFET、IGBT等大功率复合器件，承受短时过载的能力弱，当功率管因过压或过流而积聚能量时，容易引起击穿进而损坏器件。因此在实际应用中，必须考虑功率管保护电路的设计，以免器件损坏影响整个系统正常工作。保护电路是通过器件或电路结构对系统的某些参数指标进行检测，再通过控制电路控制功率管关断或导通时间来达到保护的功能。过流保护是DC-DC电路设计中必不可少的一部分，因此电流检测电路是功率集成电路中重要的功能模块。
电流检测电路主要用于对输出电流进行监控，以实时得到电源的当前工作状态。常见的电流采样方法有在需要检测的电流支路上放置采样电阻或电流互感器，但这种方式会产生一个额外的功率损耗，从而降低了变换器的工作效率。还有通过MOSFET-R DS来采样流过该管的电流，虽然该采样方式无损，但因受温度、工艺等的影响大，电流检测精度低。在一些对效率和精度要求相对高的电路中，上述采样方法并不适用。因此，必须对电流采样方案进一步改善，以满足更高性能的电路需求。
发明内容
本发明的发明目的是针对上述背景技术的不足，提供一种应用于隔离变换器的励磁电流无损采样电路，通过大时间常数滤波器对隔离变换器原边绕组两端电压进行滤波和积分处理，不需要串联采样电阻或电流互感器即可实现无损耗采样隔离变换器励磁电流的发明目的，解决现有电流无损检测电路降低变换器整体效率且检测精度低的技术问题。
本发明为实现上述发明目的采用如下技术方案：
一种隔离式变换器励磁电感电流的无损采样电路，隔离式变换器中包含一隔离变压器，隔离变压器原边绕组并联一原边功率变换电路，副边绕组并联一副边电路。励磁电流无损采样电路的输入端与隔离变压器原边相连，用以采样隔离变压 器原边绕组两端点的电压。励磁电流无损采样电路的输出端一方面直接连接比较电路的一个输入端，另一方面经过采样保持电路再接到比较电路另一输入端，比较电路输出实现伏秒平衡的控制信号或保护信号控制功率开关管状态，进而保护系统及外围元器件。
励磁电流无损采样电路包括第一电压采样电路、第二电压采样电路和一个运算放大器构成的减法电路。第一、二电压采样电路分别采样隔离变压器原边绕组两端电压，分别记为V a、V b，通过检测隔离变压器原边绕组两端压差(V a-V b)以采样励磁电感交流电流。由电感电压与电流的关系可知
Figure PCTCN2022143355-appb-000001
即对隔离变压器原边绕组两端电压随时间的积分值作差得到励磁电感电流。因此引入大时间常数的RC低通滤波电路也即积分电路作为电压采样电路。第一、第二电压采样电路采样的隔离变换器原边绕组电压经分压、滤波和积分后得到最终采样输出电压V aS、V bS，即第一、二电压采样电路的输出。电压采样电路的输出分别接至减法器的两输入端，减法器的输出端作为励磁电流采样电路的输出端，记为V sen。
本发明还在减法器的正向输入端叠加了一个直流偏置电压，使得励磁电流采样电路输出V sen为叠加了直流量的励磁电感电流。
本发明实现伏秒平衡的电路包括采样保持电路以及比较电路。采样保持电路由脉冲信号触发，在脉冲上升沿对励磁电流采样输出V sen进行采样保持，记采样保持结果为V SH。采样保持电路的输出端还加入一个小的正斜坡，使所控制的功率管提前改变状态，用于防止状态翻转不及时导致的系统不稳定。比较电路两输入端分别接励磁电流采样输出V sen以及保持电路输出V SH，当V sen变化到V SH时，比较电路输出状态翻转，比较电路的输出作为功率管控制信号。
本发明采用上述技术方案，具有以下有益效果：
(1)本发明应用于隔离式变换器的励磁电流无损采样电路，摒弃了串接电阻或电流互感器的传统励磁电感电流采样方案，通过直接采样隔离变换器中变压器原边绕组两端的电压来实现励磁电感电流的无损采样，不产生额外功率损耗，提高整体变换器效率；同时，本发明摒弃了检测流过MOS管电流检测励磁电流的无损采样方案，具有检测精度高的优势。
(2)本发明采用大时间常数RC电路作为隔离变换器原边绕组电压的采样电路，通过对RC电路的参数进行选取，使得RC电路不仅具有低通频率响应还具有积分功能，实现RC电路对隔离变换器原边绕组电压的分压、滤波和积分处理，获取有效滤除高频噪声的采样信号。
(3)本发明采用两个RC采样电路对隔离变换器原边绕组两端的电压进行采 样，对两个采样信号差值中引入的偏移量，在对两个采样信号进行作差和放大处理的减法电路的正向输入端叠加用于消除偏移量的偏置电压，能够在整个控制周期内都采集到励磁电感电流的有效值。
(4)本发明还提出了一种实现励磁电感电流伏秒平衡的方案，以励磁电流无损采样信号为基准信号，通过比较基准信号和经采样保持后的基准信号，得到隔离变换器中原边功率管关断时间与励磁电感电流伏秒平衡时间一致的控制信号，实现保护系统及外围元器件的目的。
附图说明
图1为本发明应用于隔离变换器的励磁电流无损采样电路及实现伏秒平衡控制的原理框图。
图2为本发明实施例中应用励磁电流无损采样电路及实现伏秒平衡控制的具体电路图。
图3为本发明实施例中应用励磁电流无损采样电路采集断续模式(DCM)下buck-boost变换器励磁电感交流电流的波形图。
图4为本发明实施例中应用励磁电流无损采样电路采集临界导通模式(CrCM)下buck-boost变换器励磁电感交流电流的波形图。
图5为本发明实施例中应用励磁电流无损采样电路采集断续模式(DCM)下反激变换器励磁电感交流电流的波形图。
图6为本发明实施例中应用励磁电流无损采样电路采集临界导通模式(CrCM)下反激变换器励磁电感交流电流的波形图。图中标号说明：L r为原边漏感，L m为励磁电感，R L为等效损耗电阻，R0为分压电阻，C0为滤波电容，C VSB为电压保持电容，R1～R5为第一至第五电阻，R up为上拉电阻，OPA为运算放大器，SW为开关，CMP为比较器。
具体实施方式
下面结合附图对发明的技术方案进行详细说明。
本发明励磁电流无损采样电路及实现伏秒平衡控制的原理框图如图1所示，隔离式变换器中包含一隔离变压器，隔离变压器原边绕组并联一原边功率变换电路，副边绕组并联一副边电路。励磁电流无损采样电路对隔离变压器原边绕组两端电压进行分压、滤波和积分处理后得到隔离变压器原边绕组两端电压的采样值，再对隔离变压器原边绕组两端电压采样值的差值进行放大和补偿，得到表征励磁电流的电压信号。励磁电流无损采样电路包括：第一电压采样电路、第二电压采样电路以及一个运算放大器构成的减法电路。励磁电流无损采样信号应用于伏秒 平衡控制方法，通过检测电流采样信号周期内增量为0的时刻，得到控制信号。实现伏秒平衡的电路包括采样保持电路与比较电路。隔离变换器中包括一隔离变压器，记隔离变压器原边绕组的两端为a、b端，端点电压为V a、V b，隔离变压器原边绕组与副边绕组的匝数比为
Figure PCTCN2022143355-appb-000002
隔离变压器等效电路原边包括励磁电感为L m、原边漏感L r以及等效损耗电阻R L，记励磁电感电流为
Figure PCTCN2022143355-appb-000003
副边电流i sec，则隔离变压器原边绕组两端的电压压差满足下述频域模型：
Figure PCTCN2022143355-appb-000004
本实施例励磁电流无损采样电路的具体电路如图2所示，励磁电感电流采样电路连接于隔离变换器中的隔离变压器原边，包括第一电压采样电路、第二电压采样电路和减法电路。第一电压采样电路接至隔离变压器原边绕组a端，第一电压采样电路的采样输出端接至减法器同相输入端。第二电压采样电路接至隔离变压器原边绕组b端，第二电压采样电路的采样输出端接至减法器的反相输入端。减法器的输出端即为励磁电流采样电路的输出端。
第一、第二电压采样电路都为相同的大时间常数RC电路以实现对检测电压的积分，其中，第一电阻R 1和分压电阻R 0构成分压网络以对隔离变压器原边绕组a端采样电压进行分压，滤波电容C 0与第一电阻R 1及分压电阻R 0组成低通滤波电路以滤除高频噪声。两电压采样电路分别采样隔离变压器原边绕组a、b两端电压V a、V b，得到第一、二电压采样电路的采样输出频域模型：
Figure PCTCN2022143355-appb-000005
Figure PCTCN2022143355-appb-000006
两电压采样电路输出信号压差满足下述表达式：
Figure PCTCN2022143355-appb-000007
通过选取第一电阻R 1、分压电阻R 0、滤波电容C 0的参数值，将RC滤波器的极点
Figure PCTCN2022143355-appb-000008
控制在零点
Figure PCTCN2022143355-appb-000009
和零点
Figure PCTCN2022143355-appb-000010
之间。
将上述频域模型转换至时域得：
Figure PCTCN2022143355-appb-000011
从上述表达式可知，两采样输出电压压差中引入了一个偏移量V offset，则本实施例中，在减法电路的同相输入端叠加了一个直流偏置电压V Bias，以保证减法电路的输出恒为正值。则减法电路同相输入信号V +(t)满足下述表达式：
Figure PCTCN2022143355-appb-000012
减法电路由第二电阻R 2、第三电阻R 3、第四电阻R 4、第五电阻R 5及运算放大器OPA构成，根据运算放大器的特性计算其输出信号：
Figure PCTCN2022143355-appb-000013
在上述表达式中第二电阻R 2、第三电阻R 3、第四电阻R 4、第五电阻R 5的阻值满足R 3＝R 5＝K*R 2＝K*R 4，即可得到：
Figure PCTCN2022143355-appb-000014
其中，K用于放大采样得到的励磁电流信号，K值的选取使得检测得到的V sen信号易于分辨即可。
通过上述表达式可以得出本发明励磁电流采样电路的输出结果为一个叠加了直流量的励磁电感电流信号，其中，直流偏置电压V Bias的设置满足条件：
Figure PCTCN2022143355-appb-000015
Figure PCTCN2022143355-appb-000016
本发明励磁电流采样电路用于实现伏秒平衡控制的具体电路如图2所示。实现伏秒平衡的电路包括励磁电流无损采样电路、采样保持电路和比较电路，比较电路为一个快速比较器。励磁电流采样输出V sen一方面接至比较器CMP的反相输入端，另一方面通过采样保持电路接至的比较器CMP的同相输入端。采样保持电 路中包括开关SW，电压保持电容C VSB以及上拉电阻R up。其中，开关SW由单脉冲触发控制，在周期开始时通过电压保持电容C VSB对励磁电流采样输出V sen进行采样保持。在采样保持的结果信号V SH上通过上拉电阻R up对电压保持电容C VSB充电，得到一个小的正斜坡信号，用于提前控制功率管状态翻转，以防状态改变不及时导致系统不稳定，其中，上拉电阻R up为极大电阻，可取到兆欧级。
采样保持电路输出的采样保持信号V SH接至比较器CMP的正向输入端。比较器对V sen以及V SH进行比较，当V sen降低至V SH时，比较器输出高电平，即控制功率管关断。
图3和图4分别为四开关buck-boost变换器在断续模式(DCM)和临界导通模式(CrCM)下，应用本实施例电路的测试图。图中，V sen是励磁电流采样得到的电压信号，V SH是采样保持的电压信号，i L是实际的电感电流，Q3信号的下降沿受伏秒平衡控制电路决定。可以看出励磁电感电流采样信号V sen波形准确，与实际的励磁电感电流一致，且在电感电流基本下降至0时，伏秒平衡控制电路关断Q3，结束去磁过程。
图5和图6分别为反激变换器在断续模式(DCM)和临界导通模式(CrCM)下，应用本实施例电路进行伏秒平衡判断的测试图，可以看出利用励磁电感电流采样信号得到的控制信号(Q3)与副边同步整流信号(Q5)一致。
这里的实施例只用于举例说明，并不用于限制本申请。此外，在不背离本发明的精神或基本特征的情况下，能够以其他形式实现本发明。本发明的范围由所附权利要求而不是上述说明限定，并且对于本领域技术人员显而易见的变化都应包括在所附权利要求的范围内。

Claims (10)

  1. 一种应用于隔离变换器的励磁电流无损采样电路，其特征在于，包括：
    第一电压采样电路，接隔离变换器中隔离变压器原边绕组的电流输入端，对所述隔离变压器原边绕组电流输入端的电压进行采样、滤波、积分处理，输出所述隔离变压器原边绕组电流输入端的电压采样值；
    第二电压采样电路，接隔离变换器中隔离变压器原边绕组的电流输出端，对所述隔离变压器原边绕组电流输出端的电压进行采样、滤波、积分处理，输出所述隔离变压器原边绕组电流输出端的电压采样值；及，
    减法电路，其正相输入端接第一电压采样电路的输出端，其反相输入端接第二电压采样电路的输出端，输出励磁电感电流采样信号。
  2. 根据权利要求1所述一种应用于隔离变换器的励磁电流无损采样电路，其特征在于，所述第一电压采样电路和第二电压采样电路相同，均为具有大时间常数的RC滤波器。
  3. 根据权利要求1所述一种应用于隔离变换器的励磁电流无损采样电路，其特征在于，所述第一电压采样电路和第二电压采样电路相同，均为具有大时间常数的高通滤波器级联积分电路。
  4. 根据权利要求2所述一种应用于隔离变换器的励磁电流无损采样电路，其特征在于，所述RC滤波器包括：第一电阻、分压电阻、滤波电容，所述第一电阻的一端接隔离变压器原边绕组的一端，所述分压电阻的一端与第一电阻另一端的连接点为电压采样电路的输出端，分压电阻的另一端接地，所述滤波电容并联在分压电阻的两端。
  5. 根据权利要求4所述一种应用于隔离变换器的励磁电流无损采样电路，其特征在于，依据所述RC滤波器的极点
    Figure PCTCN2022143355-appb-100001
    在零点
    Figure PCTCN2022143355-appb-100002
    和零点
    Figure PCTCN2022143355-appb-100003
    之间的原则确定第一电阻、分压电阻、滤波电容的参数值，其中，L m为励磁电感，R L为等效损耗电阻，L r为原边漏感。
  6. 根据权利要求5所述一种应用于隔离变换器的励磁电流无损采样电路，其特征在于，所述减法电路包括第二电阻、第三电阻、第四电阻、第五电阻、运算放大器，其中，所述第二电阻的一端接第一电压采样电路的输出端，第二电阻的另一端、第三电阻的一端均与运算放大器的同相输入端连接，第三电阻的另一端接有用于抵消两个电压采样电 路输出信号差值中的偏移量的直流偏置电压，所述第四电阻的一端接第二电压采样电路的输出端，第四电阻的另一端、第五电阻的一端均与运算放大器的反相输入端连接，第五电阻的另一端与运算放大器的输出端连接。
  7. 根据权利要求6所述一种应用于隔离变换器的励磁电流无损采样电路，其特征在于，所述直流偏置电压满足
    Figure PCTCN2022143355-appb-100004
    这一约束，其中，V Bias为直流偏置电压，K为放大系数，
    Figure PCTCN2022143355-appb-100005
    为励磁电感电流波谷值，V offset为两个电压采样电路输出信号差值中的偏移量。
  8. 根据权利要求7所述一种应用于隔离变换器的励磁电流无损采样电路，其特征在于，所述减法电路输出的励磁电感电流采样信号为：
    Figure PCTCN2022143355-appb-100006
    Figure PCTCN2022143355-appb-100007
    其中，V sen为励磁电感电流采样信号，
    Figure PCTCN2022143355-appb-100008
    为励磁电感电流的时域信号。
  9. 一种实现励磁电感电流伏秒平衡的控制电路，其特征在于，包括：
    采样保持电路，其输入端接权利要求1至8中任意一项所述励磁电流无损采样电路输出的励磁电感电流采样信号，输出采样保持信号；及，
    比较电路，其反相输入端接权利要求1至8中任意一项所述励磁电流无损采样电路的输出的励磁电感电流采样信号，其同相输入端接采样保持电路输出的采样保持信号，输出在励磁电感电流采样信号降低至采样保持信号时关断隔离变换器原边电路中功率开关管的控制信号。
  10. 根据权利要求9所述一种实现励磁电感电流伏秒平衡的控制电路，其特征在于，所述采样保持电路包括：开关、电压保持电容、上拉电阻，所述开关的一端作为采样电路的输入端，开关的另一端与电压保持电容的正极板、上拉电阻的一端连接后作为采样保持电路的输出端，所述开关的控制端接单脉冲触发信号，所述电压保持电容的负极板接地，所述上拉电阻的另一端接直流电压源。
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