CN111711364B - Self-adaptive leading edge blanking circuit based on high-precision load current detection technology - Google Patents

Abstract

An adaptive leading edge blanking circuit based on high-precision load current detection technology includes a high-precision load current detection module and an adaptive leading edge blanking time setting module. Among them, the high-precision load current detection module is used to obtain the signal proportional to the load current and operating frequency of the primary side feedback flyback converter and transmit it to the adaptive leading edge blanking time setting module; the adaptive leading edge blanking time setting module is based on the original The load current and operating frequency of the side feedback flyback converter generate an adaptive front blanking signal to control the sampling time of the knee point voltage. When the primary side feedback flyback converter works at light load or low frequency, the adaptive front blanking signal The enabling time becomes shorter, and the enabling time of the adaptive leading edge blanking signal becomes longer when the primary-side feedback flyback converter operates under heavy load or high frequency. The invention can avoid wrong sampling, improve the output voltage precision of the primary side feedback flyback converter, and reduce light-load power consumption of voltage sampling at the same time.

Description

An Adaptive Leading Edge Blanking Circuit Based on High Precision Load Current Detection Technology

technical field

The invention belongs to the field of integrated circuits and switching power supplies, and more specifically relates to an adaptive leading edge blanking circuit based on high-precision load current detection technology.

Background technique

Traditional flyback converter adjustment is mainly divided into primary-side feedback adjustment and secondary-side feedback adjustment. Among them, the secondary-side feedback adjustment method requires optocoupler devices and related circuit components, which increases system cost and has a complex structure. The primary-side feedback adjustment method uses The primary winding or the auxiliary winding is used for feedback adjustment, which has a wider range of applications. Most of the small and medium power flyback converters work in discontinuous mode. By sampling the knee point voltage on the auxiliary winding, the purpose of adjusting the output voltage is achieved, and then the constant voltage output of the system is controlled.

Figure 1 shows the architecture diagram of a traditional primary-side feedback flyback converter system. The input voltage of the primary-side feedback flyback converter is V _IN , the output voltage is V _OUT , and V _BUS is the bus voltage. The primary side feedback flyback converter mainly includes a transformer T composed of primary winding N _P , secondary winding N _S and auxiliary winding N _A , the primary switching tube S ₀ connected to the same terminal of the primary winding, and the secondary winding The rectifier diode _D2 connected to the end of the same name, the anode of the rectifier diode _D2 is connected to the end of the same name of the secondary winding, the cathode is connected to the output end of the system, and there is a clamping capacitor C connected to the drain of the primary switching tube _S0 and the opposite end of the primary winding _CLAMP , clamp resistor R _CLAMP and clamp diode D ₁ .

In the flyback converter system with primary side feedback adjustment, when the primary side switch S ₀ is turned off, the inductance energy of the secondary winding starts to supply power to the load, and when the secondary side current drops to zero, the influence of the output line impedance reaches the minimum, at this time The voltage on the waveform corresponding to the signal V _AUX of the auxiliary winding is the knee point voltage V _KNEE , the flyback converter samples and holds the knee point voltage V _KNEE , and converts through the equivalent relationship to obtain the output voltage information, which is used as the primary side feedback flyback conversion The constant voltage output of the device, so it is very important to accurately sample the knee point voltage information.

During the conduction phase of the primary side switch tube, the input voltage charges the primary side inductance, and most of the energy is stored in the excitation inductance; however, there is a small amount of magnetic flux in the primary side winding that is not coupled to the secondary side winding through the magnetic core, but returns through air closure Therefore, the leakage inductance energy of the primary side is not completely transmitted to the secondary side, and part of the energy is in the leakage inductance and parasitic capacitance. When the power tube of the primary side is turned off, the auxiliary winding will oscillate. As the load current increases, the oscillation becomes more severe, which easily leads to false sampling of the knee point voltage.

Specifically, there is leakage inductance in the transformer in the primary side feedback flyback converter, and the leakage inductance energy cannot be transmitted to the secondary side. Most of the leakage inductance energy will be clamped by the clamping diode D ₁ , The RCD circuit composed of the clamping capacitor C _CLAMP and the clamping resistor R _CLAMP absorbs and consumes, but due to the parasitic effects such as the forward voltage drop and reverse recovery of the clamping diode, the leakage inductance energy cannot be completely consumed, and there is still a part of the leakage The inductive energy is stored in the parasitic inductance and capacitance of the system; when the primary power tube is turned off, this part of the energy resonates in the loop, and produces high-frequency oscillations on the primary winding and auxiliary winding waveforms, which easily leads to voltage missampling. Thus the direct flyback converter affects the output voltage accuracy.

The energy stored in the leakage inductance is mainly related to the leakage inductance value, the current value flowing through the leakage inductance, and the current change rate dI/dt. Through the equivalent relationship, the magnitude of the current flowing through the leakage inductance can be equivalent to the weight of the load. When the system transformer After being determined, the leakage inductance value itself is small and will not produce large fluctuations, and the leakage inductance energy is mainly affected by the load current and operating frequency. During each switching cycle, the voltage oscillation on the auxiliary winding varies with the load current. When the load is light and the operating frequency is low, the current flowing through the leakage inductance is small, and the current change rate is small, so the energy stored in the leakage inductance is small. When the primary side power tube is turned off, the leakage inductance energy is The oscillation amplitude generated on the auxiliary winding is low, and the oscillation decay time is short; when the load is heavy and the operating frequency is high, the current flowing through the leakage inductance is large, and the current change rate is large, so it is stored in the leakage inductance The energy of the leakage inductance is relatively high, and when the power tube of the primary side is turned off, the oscillation amplitude generated by the leakage inductance energy on the auxiliary winding is relatively high, and the oscillation attenuation time is relatively long.

The traditional flyback converter current detection circuit directly reflects the load current information by detecting the peak current of the primary side, but when the operating frequency of the system changes, the leakage inductance energy is greatly affected by the current change rate, and the traditional peak current detection circuit of the primary side cannot Detecting the load current parameters including the operating frequency information may cause the leading-edge blanking time signal to be unable to effectively shield the high-frequency oscillation of the auxiliary winding, resulting in false sampling of the knee point voltage.

In order to solve the impact of auxiliary winding waveform oscillation on voltage sampling, the traditional method is to add a fixed period of leading edge blanking time or to delay sampling for a fixed period of time when the oscillation waveform is detected to be less than the threshold. The above methods have introduced a period of fixed blanking time signal , however, when the load current becomes larger or the system operating frequency increases, the too short leading edge blanking time may not be enough to shield the voltage oscillation of the auxiliary winding; The blanking time will not only increase the power consumption of the system, but also completely shield the voltage waveform of the auxiliary winding, which will affect the system voltage feedback regulation.

Contents of the invention

Aiming at the inaccurate knee point voltage sampling problem caused by the fixed leading edge blanking time in the knee point voltage detection technology of the above-mentioned primary side feedback flyback converter, the present invention proposes an adaptive leading edge blanking technology based on high-precision load current detection technology. The hidden circuit can generate an automatically adjusted adaptive pre-blanking signal according to the load current and operating frequency of the primary-side feedback flyback converter to control the knee-point voltage sampling of the primary-side feedback flyback converter, which can improve the accuracy of the knee-point voltage sampling degree, while reducing circuit power consumption.

Technical scheme of the present invention is:

An adaptive leading edge blanking circuit based on high-precision load current detection technology, which can be used to generate an adaptive front blanking signal to control the knee point voltage sampling of the primary side feedback flyback converter; the adaptive leading edge blanking circuit includes High-precision load current detection module and adaptive leading edge blanking time setting module,

The high-precision load current detection module includes a primary current peak sampling unit, a first voltage-current conversion unit, a degaussing time integration unit and an average value unit,

The primary-side current peak sampling unit is used to sample the source terminal voltage of the primary-side switching tube to obtain a sampling voltage when the primary-side switching tube of the primary-side feedback flyback converter is turned on, and to obtain a sampling voltage when the primary-side switching tube is turned off. Hold the obtained peak value of the sampling voltage when it is off, and the primary current peak sampling unit clears the sampling voltage to zero at the beginning of each switching cycle of the primary switching tube;

The first voltage-current conversion unit is used to convert the sampling voltage output by the primary current peak sampling unit into a corresponding sampling current;

The degaussing time integration unit includes a fifth switch, a sixth switch, a seventh switch and a third capacitor, one end of the fifth switch is connected to the sampling current, and the other end is connected to one end of the third capacitor and serves as the degaussing time integration unit. The output terminal, the other end of the third capacitor is grounded; the sixth switch is connected between the output terminal of the degaussing time integration unit and the ground, and the seventh switch is connected between the output terminal of the degaussing time integration unit and the ground; wherein The fifth switch is closed only during the degaussing time of the secondary winding, and the degaussing time of the secondary winding is the time from when the primary switching tube is turned off to when the current of the secondary winding of the primary feedback flyback converter drops to zero ; The sixth switch is only closed when the primary side switch tube is just turned off, and the seventh switch is only closed when the current of the secondary winding of the primary side feedback flyback converter drops to zero;

The average value unit is used to filter and average the output signal of the degaussing time integration unit to generate the output signal of the high-precision load current detection module, and the output signal of the high-precision load current detection module is consistent with the The load current of the primary side feedback flyback converter is proportional to the operating frequency;

The adaptive leading edge blanking time setting module includes a first switch, a first current source, a second current source, a second voltage-current conversion unit, a first capacitor, a first inverter and a second inverter,

The first current source is a constant current source; the second voltage-current conversion unit is used to convert the output signal of the high-precision load current detection module into a corresponding current signal to act on the second current source, so that the second current source The current value is proportional to the output signal of the high-precision load current detection module;

One end of the first capacitor is connected to the input end of the first inverter and grounded after passing through the first switch, and the other end is grounded; the first capacitor is charged by the first current source and discharged by the second current source; the first switch is controlled by the The gate control signal of the primary switch tube controls its switching action;

The input end of the second inverter is connected to the output end of the first inverter, and the output end of the second inverter outputs the adaptive pre-blanking signal.

Specifically, the drain of the primary switching tube is connected to the same-named terminal of the primary winding in the primary feedback flyback converter, and its source is connected to the input terminal of the primary current peak sampling unit and grounded after passing through the sampling resistor ;

The primary current peak sampling unit includes a first operational amplifier, a second switch, a second capacitor and a fourth switch, the input of the first operational amplifier is used as the input of the primary current peak sampling unit, and its output is passed through Connect one end of the second capacitor after the second switch and output the sampling voltage as the output terminal of the primary current peak sampling unit, and the other end of the second capacitor is grounded; the fourth switch is connected to the primary current peak sampling unit between the output terminal of the primary side switch and the ground; the switching action of the second switch is controlled by the gate control signal of the primary side switching tube; the fourth switch is only closed at the beginning of each switching cycle of the primary side switching tube.

Specifically, the averaging unit includes a second operational amplifier, a first resistor and a fourth capacitor, the input of the second operational amplifier is connected to the output signal of the degaussing time integration unit, and its output is connected to one end of the first resistor, The other end of the first resistor outputs the output signal of the high-precision load current detection module and is grounded after passing through the fourth capacitor.

The beneficial effects of the present invention are: the knee point voltage sampling of the primary-side feedback flyback converter is controlled by using the self-adaptive pre-blanking signal generated by the present invention, and the load of the primary-side feedback flyback converter becomes heavier or the operating frequency of the system increases In this case, the leading edge blanking time required for knee point voltage sampling will be lengthened adaptively and synchronously, so as to avoid the false sampling of knee point voltage caused by oscillation; when the load of the primary side feedback flyback converter becomes lighter or the operating frequency of the system is reduced, the The leading edge blanking time required for knee point voltage sampling is shortened adaptively and synchronously, which will not completely shield the auxiliary winding voltage waveform, and will not affect the system voltage feedback adjustment; when the primary side feedback flyback converter system is light-loaded or empty When the load is output, the knee point voltage sampling with a relatively fixed leading edge blanking time is adopted; on the one hand, the present invention can make the knee point voltage sampling of the primary side feedback flyback converter more accurate, avoiding false sampling caused by high-frequency noise of the auxiliary winding, and improving The output voltage accuracy and working stability of the primary-side feedback flyback converter are improved. On the other hand, the adaptive control of the leading edge blanking time in the knee point voltage sampling process can reduce the light-load power consumption of the voltage sampling circuit and improve system efficiency.

Description of drawings

Figure 1 is a circuit block diagram of the primary side feedback flyback converter.

FIG. 2 is a circuit block diagram of a primary side feedback flyback converter using an adaptive leading edge blanking circuit based on high precision load current detection technology proposed by the present invention.

FIG. 3 is an implementation circuit diagram of a high-precision load current detection module in an embodiment of an adaptive leading edge blanking circuit based on high-precision load current detection technology proposed by the present invention.

FIG. 4 is an implementation circuit diagram of an adaptive leading edge blanking time setting module in an embodiment of an adaptive leading edge blanking circuit based on high-precision load current detection technology proposed by the present invention.

FIG. 5 is a waveform diagram of a light-load working example of a primary-side feedback flyback converter using an adaptive leading edge blanking circuit based on a high-precision load current detection technology proposed by the present invention.

FIG. 6 is a waveform diagram of a heavy-load working example of a primary-side feedback flyback converter using an adaptive leading edge blanking circuit based on a high-precision load current detection technology proposed by the present invention.

FIG. 7 is a waveform diagram of a low-frequency working example of a primary-side feedback flyback converter using an adaptive leading edge blanking circuit based on a high-precision load current detection technology proposed by the present invention.

FIG. 8 is a waveform diagram of a high-frequency working example of a primary-side feedback flyback converter using an adaptive leading edge blanking circuit based on high-precision load current detection technology proposed by the present invention.

Detailed ways

In order to make the public have a deeper understanding of the present invention, a specific embodiment of the present invention will be described and analyzed in detail below in conjunction with the accompanying drawings, and the working principle and practicability of the present invention will be introduced, but the present invention is not limited to this specific embodiment . The present invention covers any modifications, alternative methods and schemes within the spirit and scope of the present invention.

As shown in FIG. 2 , an adaptive leading edge blanking circuit based on high-precision load current detection technology proposed by the present invention includes a high-precision load current detection module 201 and an adaptive leading edge blanking time setting module 202 . Among them, the high-precision load current detection module 201 is used to sample the voltage signal V _CS at the upper end of the source sampling resistor R _CS of the primary-side switching tube _S0 of the primary-side feedback flyback converter, as shown in FIG. 2 , the primary-side switching tube S The drain of ₀ is connected to the terminal with the same name of the primary winding in the primary feedback flyback converter, and its source is grounded after passing through the sampling resistor R _CS . The high-precision load current detection module 201 generates the output signal V _SAMPLE of the high-precision load current detection module including the load current of the primary-side feedback flyback converter and the system operating frequency information, and sends it to the adaptive leading edge blanking time setting module 202 . The adaptive leading edge blanking time setting module 202 generates an adaptive leading edge blanking signal V _{LEB according to the output signal V SAMPLE of} the high-precision load current detection module 201 and sends it to the knee point voltage sampling circuit for controlling the primary side feedback flyback converter in The sampling time of the knee point voltage sampling circuit in the current switching cycle. The first input data of the knee voltage sampling circuit 203 is the auxiliary winding voltage signal V _AUX , the second input data is the adaptive leading edge blanking signal V _LEB , and the output data is the knee voltage sampling signal V _KNEE . The input data of the waveform modulation drive circuit 204 is the knee point voltage sampling signal V _KNEE , and the output data is the gate control signal V _GATE of the primary switch, which is used to control the turn-on and turn-off of the primary switch S ₀ . When the adaptive leading edge blanking signal V _LEB is enabled, the knee point voltage sampling circuit stops sampling the auxiliary winding voltage signal V _AUX ; when the adaptive leading edge blanking signal V _LEB is disabled, the knee point voltage sampling circuit starts sampling the auxiliary winding voltage signal V AUX The winding voltage signal V _AUX is sampled; the adaptive leading edge blanking signal V _LEB generated by the adaptive leading edge blanking circuit proposed by the present invention is positively correlated with the load current and system operating frequency of the primary side feedback flyback converter with its enabling width relation.

As shown in Figure 3, the high-precision load current detection module includes a primary current peak sampling unit, a first voltage-current conversion unit, a degaussing time integration unit, and an average value unit, where the primary current peak sampling unit is used to receive the primary switch The voltage signal V _CS at the upper end of the sampling resistor at the source of the tube S ₀ , when the primary switch tube S ₀ is turned on, samples the voltage signal V _CS at the upper end of the sampling resistor to obtain the sampling voltage; when the primary switch tube S ₀ is turned off, the peak value of the primary current The voltage hold value of the sampling unit is the peak value of the sampling voltage. Figure 3 shows a specific implementation structure of the primary current peak sampling unit, including the first operational amplifier U ₃ , the second switch S ₂ , the second capacitor C ₂ and the fourth switch S ₄ , the first operational amplifier The input terminal of U ₃ is used as the input terminal of the primary current peak sampling unit to connect to the upper terminal voltage signal V _CS of the source sampling resistor of the primary switching tube S ₀ , and its output terminal is connected to one end of the second capacitor C ₂ after passing through the second switch S ₂ And as the output terminal of the primary current peak sampling unit to output the sampling voltage V _{CS_PK} , the other end of the second capacitor C ₂ is grounded; the fourth switch S ₄ is connected between the output terminal of the primary current peak sampling unit and the ground. The switching action of the second switch S ₂ is controlled by the gate control signal V _GATE of the primary switching tube; the fourth switch S ₄ is only closed at the beginning of each switching cycle of the primary switching tube to clear the voltage on the second capacitor C ₂ That is, the sampling voltage V _{CS_PK} .

The first voltage-current conversion unit receives the sampling voltage V _{CS_PK} output by the primary current peak sampling unit and converts it into a current signal matching the voltage information, that is, the sampling current.

The degaussing time integration unit is used to receive the secondary winding degaussing time signal V _TDIS and the sampling current output by the first voltage-current conversion unit, and obtain the voltage signal reflecting the load current information of the primary feedback flyback converter through capacitance integration. As shown in Figure 3, the degaussing time integration unit includes a fifth switch S ₅ , a sixth switch S ₆ , a seventh switch S ₇ and a third capacitor C ₃ , and one end of the fifth switch S ₅ is connected to the output of the first voltage-current conversion unit The sampling current, the other end is connected to one end of the third capacitor _C3 and used as the output end of the degaussing time integration unit, the other end of the third capacitor _C3 is grounded; the sixth switch _S6 is connected to the output end of the degaussing time integration unit and the ground Between, the seventh switch _S7 is connected between the output terminal of the degaussing time integration unit and the ground. The fifth switch is controlled by the secondary winding degaussing time signal V _TDIS and is only closed during the secondary winding degaussing time, so that the degaussing time integration unit performs capacitance integration within the secondary winding degaussing time, wherein the secondary winding degaussing time is from the primary side The time from when the switch tube S ₀ is turned off to when the current of the secondary winding of the primary feedback flyback converter drops to zero. The sixth switch _S6 is only closed when the primary side switch _S0 is just turned off, and the seventh switch _S7 is only closed when the current of the secondary winding of the primary side feedback flyback converter drops to zero, so that the third capacitor _C3 The voltage is cleared when the primary side switching tube S ₀ is just turned off and when the current of the secondary winding of the primary side feedback flyback converter drops to zero.

The average value unit receives the output signal V _CH of the degaussing time integration unit and performs filtering and averaging to generate the output signal V _SAMPLE of the high-precision load current detection module. The output signal V _SAMPLE of the high-precision load current detection module is inverted from the primary feedback The load current of the excitation converter is directly proportional to the operating frequency. As shown in Figure 3, a specific implementation circuit of the average value unit is given, including the second operational amplifier U ₄ , the first resistor R ₄ and the fourth capacitor C ₄ , the input terminal of the second operational amplifier U ₄ is connected to the degaussing time The output signal V _CH of the integrating unit is connected to one end of the first resistor R ₄ , and the other end of the first resistor R ₄ outputs the output signal V _SAMPLE of the high-precision load current detection module and is grounded after passing through the fourth capacitor C ₄ .

The working principle of the high-precision load current detection module in this embodiment is as follows:

The second switch S ₂ controls its switching state through the gate control signal V _GATE of the primary switch tube. When the second switch S ₂ is closed, the voltage signal V _CS at the upper end of the source sampling resistor of the primary switch tube is transmitted to the second capacitor C ₂ , the voltage on the second capacitor C ₂ is V _{CS_PK} , and the clearing signal V _RT1 controls the fourth switch S ₄ , so that the fourth switch S ₄ is closed at the beginning of each switching cycle of the primary side switch S ₀ so that the second capacitor The voltage V _{CS_PK} on C ₂ is cleared; the voltage V _{CS_PK} on the second capacitor C ₂ is converted into the third current source I ₃ containing the voltage information through the first voltage-current conversion unit; the fifth switch S ₅ is passed through the secondary The side winding degaussing time signal V _TDIS controls its switch state, so that the fifth switch S ₅ can only be turned off during the degaussing time of the secondary winding (that is, the current from the primary side switching tube S ₀ to the secondary winding of the primary side feedback flyback converter time to zero) is closed, when the fifth switch _S5 is closed, the third current source _I3 integrates the third capacitor _C3 to obtain the voltage signal _VCH at the upper end of the third capacitor _C3 , which is the output signal of the degaussing time integration unit V _CH ; the clear signal V _RT2 controls the sixth switch S ₆ , and closes the sixth switch S ₆ when the secondary winding starts to degauss, thereby clearing the voltage V _CH of the third capacitor C ₃ , and the clear signal V _RT3 controls The seventh switch S ₇ closes the seventh switch S ₇ at the end of the degaussing time to clear the voltage V _CH of the third capacitor C ₃ ; the voltage signal V _CH at the upper end of the third capacitor C ₃ is obtained by the average value unit The output signal V _SAMPLE of the high-precision load current detection module.

As shown in Figure 4, the adaptive leading edge blanking time setting module includes a first switch S ₁ , a first current source I ₁ , a second current source I ₂ , a second voltage-current conversion unit, a first capacitor C ₁ , a second An inverter U ₁ and a second inverter U ₂ , the first current source I ₁ is a constant current source; the second voltage-current conversion unit is used to convert the output signal V _SAMPLE of the high-precision load current detection module into a corresponding The current signal acts on the second current source _I2 , so that the current value of the second current source _I2 is proportional to the output signal V _SAMPLE of the high-precision load current detection module; one end of the first capacitor _C1 is connected to the first inverter The input terminal of _U1 is grounded after passing through the first switch _S1 , and the other end is grounded; the first capacitor _C1 is charged by the first current source _I1 , and discharged by the second current source _I2 ; the first switch _S1 is controlled by The gate control signal V _GATE of the primary switching tube controls its switching action; the input terminal of the second inverter _U2 is connected to the output terminal of the first inverter _U1 , and its output terminal outputs an adaptive front blanking signal V _LEB .

The first capacitor _C1 and the first switch _S1 are connected in parallel, the first capacitor _C1 is charged by the first current source _I1 , the second current source _I2 discharges the first capacitor _C1 , the voltage on the first capacitor _C1 is V _C1 ; the first inverter _U1 compares the voltage V _C1 on the first capacitor _C1 with its own threshold voltage, and when V _C1 is greater than the first inverter _U1’s own threshold voltage, the first inverter U ₁ output is inverted, and the output signal of the first inverter U ₁ is inverted and shaped by the second inverter U ₂ to obtain the adaptive leading edge blanking signal V _LEB . When the primary-side feedback flyback converter works at light load or low frequency, the peak value of the voltage signal V _CS at the upper end of the source sampling resistor of the primary-side switching tube S ₀ is small, and the current change rate di/dt is low, so the high-precision load current The output voltage V _SAMPLE of the detection module is reduced, so that the enabling time of the adaptive leading edge blanking signal V _LEB is shortened, and the time for the knee point voltage sampling circuit to stop sampling the auxiliary winding voltage signal V _AUX is shortened, and the auxiliary winding will not be The voltage waveform is completely shielded and does not affect the system voltage feedback regulation. When the primary side feedback flyback converter works under heavy load or high frequency, the peak value of the voltage signal V _CS signal at the upper end of the source sampling resistor of the primary switching tube S ₀ is relatively large, and the current change rate di/dt is relatively high, so the high precision The output voltage V _SAMPLE of the load current detection module increases, so that the enabling time of the adaptive leading edge blanking signal V _LEB becomes longer, and the time for the knee point voltage sampling circuit to stop sampling the auxiliary winding voltage signal V _AUX becomes longer, which is enough to shield The voltage of the auxiliary winding oscillates.

As shown in Figure 5, the waveform diagram of the working example under the light load of this embodiment, the primary side feedback flyback converter works in the inductor current discontinuous mode, when the primary side switching tube _S0 is turned off, the residual energy of the transformer leakage inductance is small, so the energy stored in the parasitic parameters of the circuit is also relatively small, the auxiliary winding voltage signal V _AUX oscillation amplitude is small, and the decay time is short, and the adaptive leading edge blanking time set by the present invention is short, so that the knee point The voltage sampling circuit can sample accurately.

As shown in Figure 6, it is the waveform diagram of the working example under the heavy load of the present embodiment. When the primary switch tube _S0 is turned off, the energy left by the leakage inductance of the transformer is relatively large, so the energy stored in the circuit parasitic parameters is also relatively large. The amplitude of the auxiliary winding voltage signal V _AUX is larger and the decay time is longer. The self-adaptive leading edge blanking time set by the present invention is longer, which avoids false sampling caused by the high-frequency oscillation of the auxiliary winding.

As shown in Figure 7, it is the waveform diagram of the low-frequency working example of the present embodiment. The circuit works in the inductive current discontinuous mode. When the primary switch tube _S0 is turned off, the residual energy of the transformer leakage inductance is small, so the parasitic parameters stored in the circuit The energy of V AUX is relatively small, the amplitude of the auxiliary winding voltage signal V _AUX is small, and the decay time is short. The adaptive leading edge blanking time set by the present invention is short, so that the knee point voltage sampling circuit can accurately sample.

As shown in Figure 8, it is the waveform diagram of the example of high-frequency operation of this embodiment. When the primary switch tube _S0 is turned off, the residual energy of the transformer leakage inductance is relatively large, so the energy stored in the parasitic parameters of the circuit is also relatively large, and the auxiliary winding The oscillation amplitude of the voltage signal V _AUX is relatively large, and the decay time is relatively long. The self-adaptive leading edge blanking time set by the present invention is relatively long, which avoids mis-sampling caused by high-frequency oscillation of the auxiliary winding.

As can be seen from the above specific embodiments, the adaptive leading edge blanking circuit proposed by the present invention generates an adaptive leading edge blanking signal according to the load current of the primary side feedback flyback converter and the system operating frequency information, avoiding external input factors and load changes In this case, the knee point voltage of the system is wrongly sampled. When the load becomes heavier or the operating frequency of the system increases, after the primary switching tube is turned off, the amplitude of the auxiliary winding voltage oscillation becomes larger and the decay time becomes longer. Adapt to synchronous lengthening to avoid false sampling of the knee point voltage caused by oscillation; when the load becomes lighter or the operating frequency of the system decreases, and the primary side switch is turned off, the auxiliary winding voltage oscillation amplitude becomes smaller, the decay time becomes shorter, and the knee point voltage of the system The leading edge blanking time required for sampling is shortened adaptively and synchronously; when the system is light-loaded or no-load output, compared with the knee point voltage sampling with a fixed leading edge blanking time, the power consumption is reduced, the system efficiency is improved, and the The system error sampling probability improves the working stability of the primary side feedback flyback converter. The self-adaptive leading edge blanking circuit based on the high precision load current detection technology of the present invention can be applied to the primary side feedback flyback converter system in any occasion.

Through a specific embodiment above, a kind of self-adaptive frontier blanking circuit based on high-precision load current detection technology of the present invention has been described and analyzed in detail, those of ordinary skill in the art can make according to these technical revelations disclosed in the present invention Various other specific modifications and combinations without departing from the essence of the present invention, these modifications and combinations are still within the protection scope of the present invention.

Claims (3)

1. an adaptive leading edge blanking circuit based on high-precision load current detection technology, which can be used to generate adaptive front blanking signals to control the knee point voltage sampling of the primary side feedback flyback converter; it is characterized in that the automatic The adaptive leading edge blanking circuit includes a high-precision load current detection module and an adaptive leading edge blanking time setting module, The high-precision load current detection module includes a primary current peak sampling unit, a first voltage-current conversion unit, a degaussing time integration unit and an average value unit, The primary-side current peak sampling unit is used to sample the source terminal voltage of the primary-side switching tube to obtain a sampling voltage when the primary-side switching tube of the primary-side feedback flyback converter is turned on, and to obtain a sampling voltage when the primary-side switching tube is turned off. Hold the obtained peak value of the sampling voltage when it is off, and the primary current peak sampling unit clears the sampling voltage to zero at the beginning of each switching cycle of the primary switching tube; The first voltage-current conversion unit is used to convert the sampling voltage output by the primary current peak sampling unit into a corresponding sampling current; The degaussing time integration unit includes a fifth switch, a sixth switch, a seventh switch and a third capacitor, one end of the fifth switch is connected to the sampling current, and the other end is connected to one end of the third capacitor and serves as the degaussing time integration unit. The output terminal, the other end of the third capacitor is grounded; the sixth switch is connected between the output terminal of the degaussing time integration unit and the ground, and the seventh switch is connected between the output terminal of the degaussing time integration unit and the ground; wherein The fifth switch is closed only during the degaussing time of the secondary winding, and the degaussing time of the secondary winding is the time from when the primary switching tube is turned off to when the current of the secondary winding of the primary feedback flyback converter drops to zero ; The sixth switch is only closed when the primary side switch tube is just turned off, and the seventh switch is only closed when the current of the secondary winding of the primary side feedback flyback converter drops to zero; The average value unit is used to filter and average the output signal of the degaussing time integration unit to generate the output signal of the high-precision load current detection module, and the output signal of the high-precision load current detection module is consistent with the The load current of the primary side feedback flyback converter is proportional to the operating frequency; The adaptive leading edge blanking time setting module includes a first switch, a first current source, a second current source, a second voltage-current conversion unit, a first capacitor, a first inverter and a second inverter, The first current source is a constant current source; the second voltage-current conversion unit is used to convert the output signal of the high-precision load current detection module into a corresponding current signal to act on the second current source, so that the second current source The current value is proportional to the output signal of the high-precision load current detection module; One end of the first capacitor is connected to the input end of the first inverter and grounded after passing through the first switch, and the other end is grounded; the first capacitor is charged by the first current source and discharged by the second current source; the first switch is controlled by the The gate control signal of the primary switch tube controls its switching action; The input end of the second inverter is connected to the output end of the first inverter, and the output end of the second inverter outputs the adaptive pre-blanking signal. 2. The adaptive leading edge blanking circuit based on high-precision load current detection technology according to claim 1, wherein the drain of the primary switch tube is connected to the primary winding in the primary feedback flyback converter The terminal with the same name, its source is connected to the input terminal of the primary current peak sampling unit and grounded after passing through the sampling resistor; The primary current peak sampling unit includes a first operational amplifier, a second switch, a second capacitor and a fourth switch, the input of the first operational amplifier is used as the input of the primary current peak sampling unit, and its output is passed through Connect one end of the second capacitor after the second switch and output the sampling voltage as the output terminal of the primary current peak sampling unit, and the other end of the second capacitor is grounded; the fourth switch is connected to the primary current peak sampling unit between the output terminal of the primary side switch and the ground; the switching action of the second switch is controlled by the gate control signal of the primary side switching tube; the fourth switch is only closed at the beginning of each switching cycle of the primary side switching tube. 3. the adaptive leading edge blanking circuit based on high-precision load current detection technology according to claim 1 or 2, is characterized in that, described average value unit comprises the second operational amplifier, the first resistance and the 4th electric capacity, the 3rd The input end of the two operational amplifiers is connected to the output signal of the degaussing time integration unit, and its output end is connected to one end of the first resistor, and the other end of the first resistor outputs the output signal of the high-precision load current detection module and passes through the fourth capacitor back to ground.

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