CN103715898B

CN103715898B - Feedback voltage sample circuit, feedback voltage blanking circuit and method

Info

Publication number: CN103715898B
Application number: CN201410034017.9A
Authority: CN
Inventors: 黄秋凯; 胡志亮; 徐孝如; 白永江
Original assignee: Hangzhou Silergy Semiconductor Technology Ltd
Current assignee: Hangzhou Silergy Semiconductor Technology Ltd
Priority date: 2014-01-24
Filing date: 2014-01-24
Publication date: 2016-01-13
Anticipated expiration: 2034-01-24
Also published as: CN103715898A

Abstract

The present invention relates to feedback voltage sample circuit, feedback voltage blanking circuit and method.Described feedback voltage blanking circuit comprises blanking time control circuit and blanking filter circuit; The voltage parameter that blanking time control circuit is used for according to characterizing load condition generates blanking time control signal; Blanking filter circuit is connected between feedback voltage input and blanking output, for exporting the first voltage signal synchronously changed with feedback voltage in the blanking time interval of correspondence according to blanking time control signal, the second voltage signal that feedback voltage described in output delay obtains outside blanking time interval.The invention also discloses the feedback voltage sample circuit of corresponding feedback voltage blanking method and the described feedback voltage blanking circuit of application.The present invention arranges the blanking time according to load condition, both effectively can prevent feedback voltage sampling by mistake, and circuit can also be avoided in loss that is unloaded or underloading.

Description

Feedback voltage sampling circuit, feedback voltage blanking circuit and method

Technical Field

The invention relates to the power electronic technology, in particular to a feedback voltage sampling circuit, a feedback voltage blanking circuit and a feedback voltage blanking method.

Background

Isolated converters are widely used in various off-line power supply systems. An isolated converter typically includes a primary-side circuit and a secondary-side circuit, which are isolated by a transformer having a primary winding and a secondary winding. For an isolated converter, the current of the primary winding may be controlled by a switching tube so that the isolated converter outputs a constant voltage and/or current.

For the isolated converter, the primary side control mode has the advantages of few devices, simple structure, low cost and the like. In the primary side control mode, feedback sampling of the output voltage is achieved by sampling the voltage on the auxiliary winding. When the primary power switch of the isolated converter is on, the voltage of the auxiliary winding is proportional to the input voltage of the isolated converter. When a primary side power switch of the isolation type converter is turned off, the secondary side diode carries out follow current, and the follow current of the secondary side diode is linearly reduced from the peak value. When the follow current of the secondary side diode is gradually close to zero, the voltage of the auxiliary winding is proportional to the output voltage of the isolated converter, and the voltage of the auxiliary winding is sampled to be used as the feedback of the output voltage, so that the control of the output voltage is realized. When the freewheeling current of the secondary diode is equal to zero, the auxiliary winding voltage is not clamped by the output voltage of the isolated converter, and oscillation occurs, that is, the auxiliary winding voltage has a large drop, and the time when the drop starts is usually used as the sampling time of the output voltage feedback. At the same time, the primary side power switch of the isolated converter is turned on again.

However, after the primary power switch of the isolated converter is turned off, the voltage on the auxiliary winding may oscillate due to the existence of the transformer leakage inductance and the reverse recovery of the parasitic diode, and thus the feedback voltage may be sampled incorrectly. The prior art usually sets a predetermined blanking time, and does not perform feedback sampling of the output voltage within the predetermined blanking time after the primary power switch is turned off. However, the oscillation time of the auxiliary winding is not fixed, and the preset longer blanking time can cause the loss of the circuit to be high when the circuit is in idle or light load.

Disclosure of Invention

In view of the above, the technical problem to be solved by the present invention is to provide a feedback voltage sampling circuit, a feedback voltage blanking circuit and a method thereof, which are used for performing primary side control on an isolated converter, so as to avoid the loss of the circuit caused by unnecessary blanking time during light load or no load.

In a first aspect, a feedback voltage blanking circuit is provided for blanking a feedback voltage of a primary side controlled isolated converter, where the feedback voltage blanking circuit includes a blanking time control circuit and a blanking filter circuit;

the blanking time control circuit is used for generating a blanking time control signal according to the voltage parameter representing the load state, and the blanking time control signal indicates a blanking time interval which is changed along with the voltage parameter representing the load state;

the blanking filter circuit is connected between the feedback voltage input end and the blanking output end and used for outputting a first voltage signal which is synchronously changed along with the feedback voltage in a corresponding blanking time interval according to the blanking time control signal and outputting a second voltage signal obtained by delaying the feedback voltage outside the blanking time interval.

Preferably, the blanking time control circuit comprises a charging current source, a voltage-controlled current source, a charging capacitor, a discharging switch and a blanking comparator;

the charging capacitor, the discharging switch and the voltage-controlled current source are connected in parallel between a charging voltage output end and a grounding point, and the discharging switch is controlled to be conducted by a control pulse corresponding to a feedback voltage zero crossing point or a power switch control signal falling edge; the voltage-controlled current source is controlled by the voltage parameter representing the load state;

the charging current source is connected to the charging voltage output end and is used for charging the charging capacitor;

the input end of the blanking comparator is respectively connected with the charging voltage output end and the first reference voltage, and the output end of the blanking comparator outputs the blanking time control signal.

Preferably, the blanking filter circuit comprises a blanking switch, a filter resistor and a filter capacitor;

the blanking switch and the filter resistor are connected in parallel between a feedback voltage input end and the blanking output end;

the filter capacitor is connected between the blanking output end and a grounding point;

the blanking switch is controlled by the blanking time control signal, is switched on in a blanking time interval and is switched off outside the blanking time interval.

Preferably, the blanking filter circuit comprises a blanking switch, a filter resistor, a first filter capacitor and a second filter capacitor;

the filter resistor is connected in series between the feedback voltage input end and the blanking output end;

the first filter capacitor is connected between the blanking output end and a grounding point;

the second filter capacitor and the blanking switch are connected in series between the blanking output terminal and a ground point;

the blanking switch is controlled by the blanking time control signal, is switched off within a blanking time interval and is switched on outside the blanking time interval.

Preferably, the voltage parameter representing the load state is an output voltage of the voltage control loop or a peak signal of the primary current detection signal.

In a second aspect, a feedback voltage blanking circuit is provided for blanking a feedback voltage of a primary side controlled isolated converter, where the feedback voltage blanking circuit includes a blanking time control circuit and a blanking filter circuit;

the blanking time control circuit is used for generating a first blanking time control signal and a second blanking time control signal according to a voltage parameter representing a load state, wherein the first blanking time control signal and the second blanking time control signal respectively indicate a first blanking time interval and a second blanking time interval which change along with the voltage parameter representing the load state, the first blanking time interval and the second blanking time interval have the same starting time, and the second blanking time interval is larger than the first blanking time interval;

the blanking filter circuit is connected between a feedback voltage input end and a blanking output end and used for switching off the electric connection between the feedback voltage input end and the blanking output end in a first blanking time interval according to the blanking time control signal, outputting a first voltage signal which synchronously changes along with the feedback voltage outside the first blanking time interval and in a second blanking time interval, and outputting a second voltage signal obtained by delaying the feedback voltage outside the second blanking time interval.

Preferably, the blanking time control circuit comprises a charging current source, a voltage-controlled current source, a charging capacitor, a discharging switch, a first blanking comparator and a second blanking comparator;

the input end of the first blanking comparator is respectively connected with the charging voltage output end and a second reference voltage, and the output end of the first blanking comparator outputs a first blanking time control signal;

the input end of the second blanking comparator is respectively connected with the charging voltage output end and a third reference voltage; the output end of the second blanking comparator outputs a second blanking time control signal;

the second reference voltage is less than the third reference voltage.

Preferably, the blanking filter circuit comprises a first blanking switch, a second blanking switch, a filter resistor and a filter capacitor;

the second blanking switch is connected with the filter resistor in parallel to form a channel selection circuit; the channel selection circuit is connected in series with the first blanking switch between the feedback voltage input and the blanking output;

the first blanking switch is controlled by the first blanking time control signal, is switched off in a first blanking time interval and is switched on outside the first blanking time interval;

the second blanking switch is controlled by the second blanking time control signal, is switched on in a second blanking time interval and is switched off outside the second blanking time interval.

Preferably, the blanking filter circuit comprises a first blanking switch, a second blanking switch, a filter resistor, a first filter capacitor and a second filter capacitor;

the filter resistor and the first blanking switch are connected in series between the feedback voltage input terminal and the blanking output terminal;

the second filter capacitor and the second blanking switch are connected in series between the blanking output terminal and a ground point;

the second blanking switch is controlled by the second blanking time control signal, is switched off in a second blanking time interval, and is switched on outside the second blanking time interval.

In a third aspect, a feedback voltage sampling circuit is provided, which is used for sampling a feedback voltage of a primary side controlled isolated converter, and the feedback voltage sampling circuit includes a voltage source, a sampling comparator, a sampling execution circuit, and the feedback voltage blanking circuit as described above;

the voltage source is connected between a feedback voltage input end and a first input end of the sampling comparator; the blanking output end of the feedback voltage blanking circuit is connected with the second input end of the sampling comparator and the input end of the sampling execution circuit;

the output end of the sampling comparator outputs a sampling control signal, and the sampling control signal controls the sampling execution circuit to sample the voltage signal output by the feedback voltage blanking circuit.

In a fourth aspect, a feedback voltage blanking method is provided, including:

generating a blanking time control signal according to a voltage parameter representing a load state, wherein the blanking time control signal indicates a blanking time interval which changes along with the voltage parameter representing the load state;

and outputting a first voltage signal which synchronously changes with the feedback voltage in a corresponding blanking time interval according to the blanking time control signal, and outputting a second voltage signal obtained by delaying the feedback voltage outside the blanking time interval.

In a fifth aspect, a feedback voltage blanking method is provided, including:

generating a first blanking time control signal and a second blanking time control signal according to a voltage parameter representing a load state, wherein the first blanking time control signal and the second blanking time control signal respectively indicate a first blanking time interval and a second blanking time interval which are changed along with the voltage parameter representing the load state, the first blanking time interval and the second blanking time interval have the same starting time, and the second blanking time interval is larger than the first blanking time interval;

and according to the blanking time control signal, the electric connection between the feedback voltage input end and the blanking output end is cut off in a first blanking time interval, a first voltage signal which is synchronously changed along with the feedback voltage is output outside the first blanking time interval and in a second blanking time interval, and a second voltage signal obtained by delaying the feedback voltage is output outside the second blanking time interval.

Based on the characteristic that the oscillation time of the auxiliary winding changes along with the load state, the blanking time control signal is generated in a self-adaptive mode according to the voltage parameter representing the load state, the blanking time control signal indicates the blanking time changing along with the voltage parameter representing the load state, the blanking time is smaller when the load is light, the blanking time is larger when the load is heavy, the blanking time is matched with the oscillation time of the auxiliary winding, the feedback voltage is prevented from being sampled mistakenly due to oscillation, and the loss caused by the fact that a dummy load is added to meet the blanking time when the load is light or no load is avoided.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

FIG. 1 is a circuit schematic of an isolated converter using an auxiliary winding to achieve feedback in accordance with an embodiment of the present invention;

FIG. 2 is a schematic diagram of a switch control circuit according to an embodiment of the present invention;

FIG. 3 is a schematic waveform diagram of signal parameters in an isolated converter in accordance with an embodiment of the present invention;

FIG. 4A is a circuit schematic of a feedback voltage sampling circuit according to a first embodiment of the present invention;

FIG. 4B is a schematic circuit diagram of the feedback voltage blanking circuit according to the first embodiment of the present invention;

FIG. 4C is a waveform diagram of the feedback voltage and the delayed feedback voltage in the first embodiment of the present invention;

FIG. 4D is a schematic diagram of an alternative circuit for the blanking filter circuit of the first embodiment of the present invention;

FIG. 5A is a circuit diagram of a feedback voltage blanking circuit according to a second embodiment of the present invention;

FIG. 5B is a schematic diagram of an alternative circuit for the blanking filter circuit of the second embodiment of the present invention;

FIG. 6 is a flow chart of a feedback voltage blanking method according to a third embodiment of the present invention;

fig. 7 is a flowchart of a feedback voltage blanking method according to a fourth embodiment of the present invention.

Detailed Description

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. While the invention will be described in conjunction with the following preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments alone. In the following detailed description of the present invention, certain specific details are set forth. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details. Well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.

Further, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.

Meanwhile, it should be understood that "circuit" refers to a conductive loop constituted by at least one element or sub-circuit through electrical or electromagnetic connection. When an element or circuit is referred to as being "connected to" another element or circuit is referred to as being "connected between" two nodes, it may be directly coupled or connected to the other element or intervening elements may be present, and the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, it is intended that there are no intervening elements present. Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, what is meant is "including, but not limited to".

In the description of the present invention, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.

The present invention can be applied to any primary side controlled isolated converter, and in the following detailed description, the specific operation principle of the present invention is explained only by taking a flyback converter as an example.

Fig. 1 is a circuit schematic of an isolated converter using an auxiliary winding to achieve feedback in accordance with an embodiment of the present invention. As shown in fig. 1, the isolated converter 10 includes a transformer T, a power switch S, a switch control circuit 11, a voltage feedback circuit 12, a secondary rectification circuit 13, a power supply circuit 14, and a current sampling resistor R_sen. The transformer T comprises a primary winding L1, and a secondary winding L2 and an auxiliary winding L3 which are coupled with the primary winding L1; the secondary rectifying circuit 13 is connected to the secondary winding L2, and rectifies the voltage across the secondary winding L2 to output a constant voltage and/or current, and in fig. 1, the secondary rectifying circuit 13 includes a secondary rectifying diode D and a secondary output capacitor C.

The power supply circuit 14 is connected to the auxiliary winding L3, rectifies the voltage across the auxiliary winding L3, and outputs a stable bias voltage to supply power to the switching control circuit 11. The switch control circuit 11 comprises a bias voltage input terminal V_bA current detection signal input terminal SEN, a feedback voltage input terminal FB, a signal ground terminal GND and a switch control signal output terminal DRV, and the output terminal of the power supply circuit 14 is connected to a bias voltage input terminal V_b. Current sampling resistor R_senThe current flowing through the power switch S is converted into a voltage signal, the common terminal connected to the power switch S is connected to the current detection signal input terminal SEN of the switch control circuit 11, and the primary side current detection signal is input to the switch control circuit 11. In fig. 1, the voltage feedback circuit 12 is a voltage dividing circuit connected to both ends of the auxiliary winding L3, and divides the voltage across the auxiliary winding L3 and inputs the divided voltage to the feedback voltage input terminal FB of the switching control circuit 11. In general,the switch control circuit 11 may be manufactured as an integrated circuit, either alone or with the power switches in the isolated converter.

Fig. 2 is a schematic structural diagram of a switch control circuit according to an embodiment of the present invention. As shown in fig. 2, the switch control circuit 11 includes a feedback voltage sampling circuit 111, a set pulse generating circuit 112, a voltage error amplifier 113, a pulse width modulation comparator 114, and a logic control circuit 115.

The input terminal of the feedback voltage sampling circuit 111 is connected to the feedback voltage input terminal FB, and is configured to sample the secondary output voltage of the auxiliary winding when the current of the auxiliary winding changes to zero or approaches zero.

The output end of the feedback voltage sampling circuit 111 is connected to the set pulse generating circuit 112, and the set pulse generating circuit 112 generates a set pulse signal for controlling the frequency of the switching control signal according to the voltage value sampled by the feedback voltage sampling circuit 111.

Meanwhile, a voltage error amplifier 113 is connected to the feedback voltage sampling circuit 111 for comparing the voltage value sampled by the feedback voltage sampling circuit 111 with respect to an internal reference voltage value V_refAnd amplifying the error to output an error voltage V_comp. The output of the voltage error amplifier 113 constitutes the output of the voltage control loop of the switch control circuit 11. Error voltage V_comp(i.e., the output voltage of the voltage control loop) can characterize the load condition of the isolated converter, and when the load is large, the error voltage V_compLarge, error voltage V under light or no load_compIs smaller.

Similarly, the primary side current detection signal V_SENThe peak value signal of (2) can also represent the load state, when the load is larger, the primary side current detection signal V_SENThe peak value signal of (3) is larger, and when the load is smaller, the primary side current detection signal V is larger_SENThe peak signal of (a) is small.

The input terminals of the PWM comparator 114 and the output terminal of the voltage error amplifier 113An output terminal connected to the current detection signal input terminal for outputting the error voltage V from the voltage error amplifier 113_compAnd a current sampling resistor R in the primary side circuit_senSampling obtained primary side current detection signal V_SENAnd comparing to generate a zero pulse signal.

The logic control circuit 115 generates a switch control signal for controlling the power switch according to the zero pulse signal output from the pwm comparator 114 and the set pulse signal output from the set pulse generating circuit 112, and an output terminal of the logic control circuit 115 is connected to the switch control signal output terminal DRV.

The logic control circuit 115 may include an RS flip-flop, and a set pulse signal is input to an S terminal of the RS flip-flop to control the conduction of the power switch. And the zero setting pulse signal is input to the R end of the RS trigger to control the turn-off of the power switch.

Optionally, the logic control circuit 115 may further include a driving circuit connected to the output of the RS flip-flop, and the driving circuit provides driving for the power switch S.

Fig. 3 is a waveform diagram of signal quantities in an isolated converter in accordance with an embodiment of the present invention. V_DRVIs a switching control signal which is a square wave signal, I_PFor the current flowing through the primary winding, I_SFor the current flowing through the secondary winding, V_AUXIs the voltage across the auxiliary winding, which is related to the feedback voltage V_FBIs in direct proportion. As shown in fig. 3, the switch control signal V_DRVControlling the duration of the power switch conduction, i.e. at time t₀To time t₁During the period, the inductive current of the primary winding continuously rises, the primary winding continuously stores energy, and the feedback voltage V_FBIs proportional to the input terminal voltage (i.e., the dc bus voltage) of the isolated converter.

At switch control signal V_DRVAfter the power switch is controlled to be turned off, i.e. at time t₁To time t₂Period, primary winding current I_PBecomes zero, the stored energy of the primary winding is transferred to the secondary winding, and the current I of the secondary winding is changed_SUnder the constant action ofAnd reducing until the current is reduced to zero, and completely transferring the stored energy of the secondary winding to the load.

The secondary winding feeds back voltage V at the end of discharge_FBIs proportional to the output voltage of the power stage circuit, and therefore, at t₂Near the moment to the feedback voltage V_FBThe sampling voltage obtained by sampling can reflect the condition of the output voltage.

After the inductive current of the secondary winding is reduced to zero until the primary power switch is turned on again, i.e. at time t₂To time t₃In the period, the leakage inductance of the primary winding generates resonance with the power switch and the parasitic capacitance of the circuit, and then the feedback voltage drops greatly. The feedback voltage sampling circuit 111 can determine the sampling time of the feedback voltage by detecting the drop of the feedback voltage, and ensure that the voltage obtained by sampling is at the time t₂Or around that time, the condition of the output voltage of the isolated converter can be accurately obtained.

Meanwhile, as shown in fig. 3, a period of time after the power switch is turned off, that is, a time t in fig. 3₁To time t_offDuring which the voltage across the auxiliary winding oscillates. During oscillation, the voltages at the two ends of the auxiliary winding are high and low, when the voltages at the two ends of the auxiliary winding are too low, the feedback voltage can be mistakenly sampled, the voltage obtained by mistaken sampling is not related to the output voltage of the isolated converter, and the power switch can be mistakenly controlled. In order to avoid erroneous sampling of the feedback voltage, it is necessary to set a blanking time during which the feedback voltage is not sampled during the period in which the auxiliary winding oscillates. The existing blanking time is set to a fixed value so that the loss at no load or light load becomes high. Meanwhile, the oscillation time of the voltage across the auxiliary winding increases as the output load increases, and thus the blanking time can be adaptively set according to a parameter reflecting the load state.

Fig. 4A is a circuit diagram of a feedback voltage sampling circuit according to a first embodiment of the present invention. As shown in fig. 4A, the feedback voltage sampling circuit 111 includes a feedback voltage blanking circuit 41, a voltage source 42, a sampling comparator 43, and a sampling execution circuit 44.

Wherein the voltage source 42 is connected between the feedback voltage input terminal FB and the first input terminal of the sampling comparator 43; the blanking output OFF of the feedback voltage blanking circuit 41 is connected to a second input of the sampling comparator 43 and to an input of the sampling execution circuit 44.

The output terminal of the sampling comparator 43 outputs a sampling control signal P_STo control the sampling execution circuit 44 to sample the voltage signal output by the feedback voltage blanking circuit.

In fig. 4A, the negative pole of the voltage source 42 is connected to the feedback voltage input terminal FB, the positive pole is connected to the sampling comparator 43, and the voltage value of the voltage source is preset to Δ V, so that the voltage inputted to the sampling comparator is higher than the feedback voltage V_FBA predetermined voltage value av. In fig. 4A, the first input terminal is an inverting input terminal of the sampling comparator 43, and the second input terminal is a non-inverting input terminal of the sampling comparator 43. Thus, the change of the output voltage at the blanking output terminal OFF is larger than V_FBAt + Δ V, the sampling comparator 43 outputs high level.

As shown in fig. 4A, the sampling execution circuit 44 includes a sampling switch S1 connected between the input terminal and the output terminal, and a sampling capacitor C1 connected between the output terminal and ground. The sampling switch S1 is controlled according to the sampling control signal P_SIs turned on at the sampling time, the sampling capacitor C1 is charged until the voltage across the sampling capacitor C1 equals the voltage output by the blanking output, then the sampling switch S1 is turned off and the voltage across the sampling capacitor C1 remains until the sampling switch S1 is turned on again.

Fig. 4B is a circuit diagram of the feedback voltage blanking circuit according to the first embodiment of the present invention. As shown in fig. 4B, the feedback voltage blanking circuit 41 includes a blanking time control circuit 411 and a blanking filter circuit 412.

The blanking time control circuit 411 is used for generating a blanking time control signal P according to the voltage parameter representing the load state_OFFBlanking time controlSignal P_OFFIndicating a blanking time interval as a function of the voltage parameter indicative of the load condition.

In the present embodiment, the larger the load, the longer the blanking time.

A blanking filter circuit 412 is connected between the feedback voltage input terminal FB and the blanking output terminal OFF for controlling the signal P according to the blanking time_OFFAnd outputting a first voltage signal which is synchronously changed along with the feedback voltage in a corresponding blanking time interval, and outputting a second voltage signal obtained by delaying the feedback voltage outside the blanking time interval.

Since the feedback voltage blanking circuit 41 outputs the first voltage signal varying in synchronization with the feedback voltage at the blanking output terminal OFF during the blanking time period, the voltage of the second input terminal of the sampling comparator 43 is smaller than the voltage of the first input terminal, and thus the sampling comparator 43 outputs a low level.

Outside the blanking time interval, the feedback voltage blanking circuit 41 outputs a second voltage signal obtained by delaying the feedback voltage at a blanking output terminal OFF when the feedback voltage is gently changed (at time t in fig. 3)_offTo time t₂) The voltage at the second input of the sampling comparator 43 is still less than the voltage at the first input. However, when the discharge of the secondary winding L2 is completed, the feedback voltage starts to rapidly decrease. See FIG. 4C, V_FBFor feeding back the voltage waveform, V_FB' is the feedback voltage waveform delayed by Δ t. Since the voltage at the second input of the sampling comparator 43 is the feedback voltage delayed by Δ t, at t₂At + Δ t (i.e., Δ t after the discharge of the secondary winding L2 ends), the voltage feedback V of the second input terminal_FB' Voltage value and t₂Feedback voltage V of time_FBAre equal in voltage value. At this time, the voltage at the first input terminal of the sampling comparator 43 is the feedback voltage at the present moment plus the voltage Δ V of the voltage source, and t is decreased rapidly due to the feedback voltage₂The feedback voltage at time + Δ t is less than t₂The feedback voltage at the moment. When Δ t and Δ V are set appropriately, at t₂At time + Δ t, the second input of comparator 43 is sampledThe voltage of the input end is changed from the voltage smaller than the first input end to the voltage larger than the first input end. Thus, the sampling comparator 43 outputs a high level, the rising edge of the output signal of which indicates the sampling instant, i.e. instant t₂+Δt。

It will be understood by those skilled in the art that the first input terminal and the second input terminal of the sampling comparator 43 can be interchanged according to the form of the sampling control signal, that is, the first input terminal is a non-inverting input terminal, and the second input terminal is an inverting input terminal, and the falling edge of the output signal of the sampling comparator 43 indicates the sampling time. At the same time, the control signal P is sampled_SThe form of the sampling switch S1 can be selected according to the actual situation as long as the sampling switch S1 can sample the control signal P_SAnd conducting at the sampling moment.

The sampling execution circuit 44 outputs the sampling control signal P according to the sampling comparator 43_SAnd sampling the voltage of the hidden output end OFF at the sampling moment. Also, since the voltage at the blanking output OFF is now equal to t₂The feedback voltage at that moment, and therefore the sampled voltage, can be used to characterize the condition of the isolated converter output voltage.

The blanking time control circuit 411 includes a charging current source a1, a voltage controlled current source a2, a charging capacitor C2, a discharging switch S2, and a blanking comparator 411 a.

The charging capacitor C2, the discharging switch S2, and the voltage controlled current source a2 are connected in parallel between the charging voltage output terminal and ground. The discharge switch S2 is controlled by the feedback voltage zero crossing point or the control pulse P corresponding to the power switch control signal falling edge_ZAnd controlling the conduction.

The charging current source A1 is connected to the charging voltage output terminal to charge the charging capacitor C2. The voltage-controlled current source A2 is controlled by a voltage parameter V representing the load state_LOADAnd (5) controlling. As described above, the output voltage of the voltage control loop in the switch control circuit can represent the load state, and thus, can be used to control the voltage-controlled current source a2 of the present embodiment.

Similarly, the current detection signal V_SENCan also characterize the load state, so that the current detection signal V can also be used when a current peak detection circuit is present in the switch control circuit_SENTo control the voltage controlled current source a 2.

The input terminal of the blanking comparator 411a is connected to the charging voltage output terminal and the first reference voltage V1, respectively, and the blanking comparator 411a outputs the blanking time control signal P according to the comparison condition of the input terminal voltage_OFF. Although in fig. 4B, the charging voltage output terminal is connected to the inverting input terminal of the blanking comparator 411a and the first reference voltage V1 is inputted to the non-inverting input terminal, those skilled in the art will readily understand that the connection relationship can be reversed, that is, the charging voltage output terminal is connected to the non-inverting input terminal of the blanking comparator 411a and the first reference voltage V1 is inputted to the inverting input terminal.

Discharge switch S2 is controlled by control pulse P_ZThe discharging switch S2 is turned off when the falling edge of the switch control signal or the zero-crossing point of the feedback voltage is turned on, so that the charging capacitor C2 is discharged until the voltage across the charging capacitor C2 becomes zero. After the discharging switch S2 is turned off, the charging current source a1 starts to charge the charging capacitor C2, and the output of the blanking comparator 411a jumps when the voltage across the charging capacitor C2 rises to the first reference voltage V1. At the same time, a part of the current of the charging current source a1 flows into the voltage controlled current source a 2. Because the output current of the voltage-controlled current source is along with the control voltage V_LOADIn other words, when the load is small, the output current of the voltage-controlled current source is small, and the charging current flowing to the charging capacitor C2 is large, so that the voltage across the charging capacitor C2 rises quickly, and the time required for the voltage to rise to the first reference voltage V1 is short, so that the blanking comparator 411a outputs the blanking time control signal P with a small blanking time interval_OFF. Correspondingly, when the load is larger, the output current of the voltage-controlled current source is larger, and the charging current flowing to the charging capacitor C2 is smaller, so that the voltage across the charging capacitor C2 rises at a slower speed, and the time required for the voltage to rise to the first reference voltage V1 is longer, therefore, the blanking comparator 411a outputs a blanking time interval in a longer blanking time intervalLong blanking time control signal P_OFF。

The blanking filter circuit 412 includes a blanking switch S_OFFFilter resistor R_OFFAnd a filter capacitor C_OFF。

Blanking switch S_OFFAnd a filter resistor R_OFFConnected in parallel between the feedback voltage input terminal FB and the blanking output terminal OFF.

Filter capacitor C_OFFConnected between the blanking output OFF and ground.

Blanking switch S_OFFBy blanking-time control signal P_OFFAnd controlling to be switched on in the blanking time interval and switched off outside the blanking time interval.

In blanking switch S_OFFWhen conducting, the filter resistor R_OFFIs short-circuited, the filter capacitor C_OFFThe voltages at the two ends change synchronously with the feedback voltage.

In blanking switch S_OFFWhen turned off, the filter resistor R_OFFAnd a filter capacitor C_OFFAnd forming an RC delay circuit, and outputting the feedback voltage after delaying.

Fig. 4D is a schematic diagram of an alternative circuit for the blanking filter circuit of the first embodiment of the present invention. As shown in FIG. 4D, the blanking filter circuit 412 includes a blanking switch S_OFFFilter resistor R_OFFA first filter capacitor C_OFF1And a second filter capacitor C_OFF2。

Filter resistor R_OFFConnected between the feedback voltage input terminal FB and the blanking output terminal OFF.

A first filter capacitor C_OFF1Connected between the blanking output terminal OFF and ground; a second filter capacitor C_OFF2And blanking switch S_OFFConnected in series between the blanking output terminal OFF and ground. Preferably, a second filter capacitor C_OFF2Is larger than the first filter capacitor C_OFF1。

Blanking switch S_OFFFrom the blanking time P_OFFThe control signal controls the switch-off in the blanking time interval and the switch-on outside the blanking time interval.

In blanking switch S_OFFWhen turned off, the filter resistor R_OFFAnd a first filter capacitor C_OFF1The RC delay circuit with a small time constant is formed, when the resistance value of the filter resistor is selected to be small, the OFF voltage of the blanking output end changes with the feedback voltage with extremely small delay, and the OFF voltage can be considered to change synchronously with the feedback voltage.

In blanking switch S_OFFWhen conducting, the filter resistor R_OFFAnd a first filter capacitor C_OFF1And a second filter capacitor C_OFF2And forming an RC delay circuit with a larger time constant, and outputting the feedback voltage after delaying.

The blanking time control signal is generated in a self-adaptive mode according to the voltage parameter representing the load state based on the characteristic that the oscillation time of the auxiliary winding changes along with the load state, the blanking time control signal indicates the blanking time changing along with the voltage parameter representing the load state, the blanking time is smaller when the load is light, the blanking time is larger when the load is heavy, the blanking time is matched with the oscillation time of the auxiliary winding, the feedback voltage mis-sampling caused by oscillation is avoided, and the loss caused by the fact that the blanking time is met by adding a dummy load when the load is light or no load is avoided.

Fig. 5A is a circuit diagram of a feedback voltage blanking circuit according to a second embodiment of the present invention. The feedback voltage blanking circuit may be applied to the feedback voltage sampling circuit described in fig. 4A. As shown in fig. 5A, the feedback voltage blanking circuit 41 includes a blanking time control circuit 411 and a blanking filter circuit 412.

The blanking time control circuit 411 is used for controlling the voltage parameter V according to the characteristic load state_LOADGenerating a first blanking time control signal P_OFF1And a second blanking time control signal P_OFF2The first blanking time control signal P_OFF1And a second blanking time control signal P_OFF2Are respectively indicatedVoltage parameter V representing load state_LOADThe blanking device comprises a first blanking time interval and a second blanking time interval which are changed, wherein the first blanking time interval and the second blanking time interval have the same starting time, and the second blanking time interval is larger than the first blanking time interval.

A blanking filter circuit 412 is connected between the feedback voltage input terminal FB and the blanking output terminal OFF for controlling the signal P according to the blanking time_OFF1And P_OFF2And the electric connection between the feedback voltage input end and the blanking output end is cut off in a first blanking time interval, a first voltage signal which is synchronously changed along with the feedback voltage is output outside the first blanking time interval and in a second blanking time interval, and a second voltage signal obtained by delaying the feedback voltage is output outside the second blanking time interval.

In this embodiment, the turn-off period of the power switch is divided into three intervals by two blanking time control signals, and in the first interval, that is, the first blanking time interval, the turn-off time of the power switch is short, the oscillation amplitude of the feedback voltage is large, and at this time, the electrical connection between the feedback voltage input end and the blanking output end is turned off, so that the circuit is prevented from being damaged due to the excessively large oscillation voltage amplitude. And outputting a first voltage signal synchronously changing with the feedback voltage in a second interval, namely outside the first blanking interval and in the second blanking interval, so as to prevent the sampling comparator from outputting wrong sampling time. In a third interval, the oscillation of the feedback voltage is finished, and a second voltage signal obtained by delaying the feedback voltage is output, so that the sampling comparator can detect the drop of the feedback voltage, and the sampling time is accurately captured.

Specifically, as shown in fig. 5A, the blanking time control circuit 411 includes a charging current source a1, a voltage-controlled current source a2, a charging capacitor C2, a discharging switch S2, a first blanking comparator 411a, and a second blanking comparator 411 b.

The charging capacitor C2, the discharging switch S2 and the voltage-controlled current source A2 are connected in parallel between the charging voltage output end and the grounding point, and the discharging switch S2 passes the zero point or work from the feedback voltageThe control pulse corresponding to the falling edge of the rate switch control signal controls the conduction; the voltage-controlled current source A2 is controlled by a voltage parameter V representing the load state_LOADAnd (5) controlling.

As described above, the output voltage of the voltage control loop in the switch control circuit can represent the load state, and thus, can be used to control the voltage-controlled current source a2 of the present embodiment.

Similarly, the primary side current detection signal V_SENCan also characterize the load condition, and thus the current detection signal V can also be used when a current peak detection circuit is present in the switch control circuit_SENTo control the voltage controlled current source a 2.

The charging current source A1 is connected to the charging voltage output terminal to charge the charging capacitor C2.

The input terminal of the first blanking comparator 411a is connected to the charging voltage output terminal and the second reference voltage V2, and the output terminal of the first blanking comparator 411a outputs the first blanking time control signal P_OFF1。

The input terminal of the second blanking comparator 411b is connected to the charging voltage output terminal and the third reference voltage V3, respectively; the output terminal of the second blanking comparator 411b outputs a second blanking time control signal P_OFF2。

Discharge switch S2 is controlled by control pulse P_ZThe discharging switch S2 is turned off when the falling edge of the switch control signal or the zero-crossing point of the feedback voltage is turned on, so that the charging capacitor C2 is discharged until the voltage across the charging capacitor C2 becomes zero. After the discharging switch S2 is turned off, the charging current source a1 starts to charge the charging capacitor C2, and when the voltage across the charging capacitor C2 rises to the second reference voltage V2, the output of the first blanking comparator 411a jumps; the output of the second blanking comparator 411b jumps until the voltage across the charging capacitor C2 rises to the third reference voltage V3.

By setting the second reference voltage V2 to be smaller than the third reference voltage V3, the corresponding first blanking time interval can be made smaller than the second blanking time interval.

Similar to the first embodiment, a part of the current of the charging current source a1 flows into the voltage-controlled current source a 2. Because the output current of the voltage-controlled current source is along with the control voltage V_LOADIn the variation, when the load is small, the blanking comparator 411a and the blanking comparator 411b respectively output the first blanking time control signal P with a small blanking time interval_OFF1And a second blanking time control signal P_OFF2(ii) a When the load is large, the blanking comparator 411a and the blanking comparator 411b respectively output the first blanking time control signal P with a large blanking time interval_OFF1And a second blanking time control signal P_OFF2。

Thus, the blanking time may be adaptively set as the load changes.

The blanking filter circuit 412 comprises a first blanking switch S_OFF1The second blanking switch S_OFF2Filter resistor R_OFFAnd a filter capacitor C_OFF。

Filter capacitor C_OFFConnected between the blanking output OFF and ground.

Second blanking switch S_OFF2And a filter resistor R_OFFThe parallel connection forms a channel selection circuit; channel selection circuit and first blanking switch S_OFF1Connected in series between the feedback voltage input terminal FB and the blanking output terminal OFF.

First blanking switch S_OFF1By the first blanking-time control signal P_OFF1And controlling to be switched off in the first blanking time interval and to be switched on outside the first blanking time interval.

Second blanking switch S_OFF2By the second blanking-time control signal P_OFF2And controlling to be switched on in the second blanking time interval and switched off outside the second blanking time interval.

The first blanking time interval and the second blanking time interval have the same starting time, and the second blanking time interval is largeIn a first blanking time interval, in the first blanking time interval, a first blanking switch S_OFF1Off and the second blanking switch S_OFF2Is conducted, the electrical connection between the feedback voltage input terminal FB and the blanking output terminal OFF is switched on by the first blanking switch S_OFF1And (6) turning off.

Outside the first blanking interval and in the second blanking interval, the first blanking switch S_OFF1Conducting and second blanking switch S_OFF2Conducting, filtering resistor R_OFFIs short-circuited, the filter capacitor C_OFFThe voltages at the two ends change synchronously with the feedback voltage.

Outside the second blanking interval, the first blanking switch S_OFF1Conducting and the second blanking switch S_OFF2Turn-off, filter resistor R_OFFAnd a filter capacitor C_OFFAnd forming an RC delay circuit, and outputting the feedback voltage after delaying.

Fig. 5B is a schematic diagram of an alternative circuit for the blanking filter circuit of the second embodiment of the present invention. As shown in FIG. 5B, the blanking filter circuit 412 includes a first blanking switch S_OFF1The second blanking switch S_OFF2Filter resistor R_OFFA first filter capacitor C_OFF1And a second filter capacitor C_OFF2。

Filter resistor R_OFFAnd a first blanking switch S_OFF1Connected in series between the feedback voltage input terminal FB and the blanking output terminal OFF.

A first filter capacitor C_OFF1Connected between the blanking output OFF and ground.

A second filter capacitor C_OFF2And a second blanking switch S_OFF2Connected in series between the blanking output terminal OFF and ground.

Second blanking switch S_OFF2By the second blanking-time control signal P_OFF2And controlling to be switched off in the second blanking time interval and to be switched on outside the second blanking time interval.

Since the first blanking interval and the second blanking interval have the same starting time and the second blanking interval is greater than the first blanking interval, the first blanking switch S is turned off during the first blanking interval_OFF1And a second blanking switch S_OFF2Are all turned OFF, the electrical connection between the feedback voltage input terminal FB and the blanking output terminal OFF is switched OFF by the first blanking switch S_OFF1And (6) turning off.

Outside the first blanking interval and in the second blanking interval, the first blanking switch S_OFF1Conducting and the second blanking switch S_OFF2Turn-off, filter resistor R_OFFAnd a first filter capacitor C_OFF1The RC delay circuit with a small time constant is formed, when the resistance value of the filter resistor is selected to be small, the OFF voltage of the blanking output end changes with the feedback voltage with extremely small delay, and the OFF voltage can be considered to change synchronously with the feedback voltage.

Outside the second blanking interval, the first blanking switch S_OFF1Conducting and second blanking switch S_OFF2Conducting, filtering resistor R_OFFAnd a first filter capacitor C_OFF1And a second filter capacitor C_OFF2And forming an RC delay circuit with a larger time constant, and outputting the feedback voltage after delaying.

In the embodiment, two blanking time intervals which are adaptively changed are set, so that in the first blanking time interval with larger oscillation amplitude of the feedback voltage, the electric connection between the feedback voltage input end and the rear-stage circuit is turned off, thereby providing better protection for the rear-stage circuit, and meanwhile, the blanking time is changed along with the voltage parameter representing the load state, thereby not only avoiding the feedback voltage mis-sampling caused by the voltage oscillation, but also avoiding the loss caused by light load or no load due to the fact that a dummy load is added to meet the blanking time.

Fig. 6 is a flowchart of a feedback voltage blanking method according to a third embodiment of the present invention. As shown in fig. 6, the method includes:

and 610, generating a blanking time control signal according to the voltage parameter representing the load state, wherein the blanking time control signal indicates a blanking time interval which is changed along with the voltage parameter representing the load state.

The voltage parameter representing the load state is the output voltage of the voltage control loop or the peak value signal of the primary side current detection signal.

And step 620, outputting a first voltage signal which is synchronously changed along with the feedback voltage in a corresponding blanking time interval according to the blanking time control signal, and outputting a second voltage signal obtained by delaying the feedback voltage outside the blanking time interval.

The blanking time control signal is generated in a self-adaptive mode according to the voltage parameter representing the load state based on the characteristic that the oscillation time of the auxiliary winding changes along with the load state, the blanking time which changes along with the voltage parameter representing the load state is indicated by the blanking time control signal, blanking is set to be small when the load is light, the blanking time is large when the load is heavy, the blanking time is matched with the oscillation time of the auxiliary winding, feedback voltage mis-sampling caused by oscillation is avoided, and loss caused by the fact that a dummy load is added to meet the blanking time when the load is light or no load is avoided.

Fig. 7 is a flowchart of a feedback voltage blanking method according to a fourth embodiment of the present invention. As shown in fig. 7, the method includes:

step 710, generating a first blanking time control signal and a second blanking time control signal according to the voltage parameter characterizing the load state, where the first blanking time control signal and the second blanking time control signal respectively indicate a first blanking time interval and a second blanking time interval that vary with the voltage parameter characterizing the load state, the first blanking time interval and the second blanking time interval have the same start time, and the second blanking time interval is greater than the first blanking time interval.

And 720, according to the blanking time control signal, the electric connection between the feedback voltage input end and the blanking output end is cut off in a first blanking time interval, a first voltage signal which is synchronously changed along with the feedback voltage is output outside the first blanking time interval and in a second blanking time interval, and a second voltage signal obtained by delaying the feedback voltage is output outside the second blanking time interval.

In the embodiment, two blanking time intervals which are adaptively changed are set, so that in the first blanking time interval with larger oscillation amplitude of the feedback voltage, the electric connection between the feedback voltage input end and the rear-stage circuit is turned off, thereby providing better protection for the rear-stage circuit, and meanwhile, the blanking time is changed along with the voltage parameter representing the load state, thereby not only avoiding the feedback voltage mis-sampling caused by oscillation, but also avoiding the loss caused by light load or no load due to the fact that a dummy load is added to meet the blanking time.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A feedback voltage blanking circuit is used for blanking feedback voltage of a primary side controlled isolation type converter and comprises a blanking time control circuit and a blanking filter circuit;

2. The feedback voltage blanking circuit of claim 1 wherein the blanking time control circuit comprises a charging current source, a voltage controlled current source, a charging capacitor, a discharging switch, and a blanking comparator;

3. The feedback voltage blanking circuit of claim 2 wherein the blanking filter circuit comprises a blanking switch, a filter resistor, and a filter capacitor;

4. The feedback voltage blanking circuit according to claim 2, wherein the blanking filter circuit comprises a blanking switch, a filter resistor, a first filter capacitor and a second filter capacitor;

5. The feedback voltage blanking circuit of claim 1 wherein the voltage parameter indicative of the load condition is an output voltage of a voltage control loop; or,

and the voltage parameter representing the load state is a peak signal of the primary side current detection signal.

6. A feedback voltage blanking circuit is used for blanking feedback voltage of a primary side controlled isolation type converter and comprises a blanking time control circuit and a blanking filter circuit;

7. The feedback voltage blanking circuit of claim 6, wherein the blanking time control circuit comprises a charging current source, a voltage controlled current source, a charging capacitor, a discharging switch, a first blanking comparator and a second blanking comparator;

the second reference voltage is less than the third reference voltage.

8. The feedback voltage blanking circuit of claim 7, wherein the blanking filter circuit comprises a first blanking switch, a second blanking switch, a filter resistor, and a filter capacitor;

9. The feedback voltage blanking circuit of claim 7, wherein the blanking filter circuit comprises a first blanking switch, a second blanking switch, a filter resistor, a first filter capacitor, and a second filter capacitor;

10. The feedback voltage blanking circuit of claim 6 wherein the voltage parameter indicative of the load condition is an output voltage of a voltage control loop; or,

11. A feedback voltage sampling circuit for sampling a feedback voltage of a primary side controlled isolated converter, the feedback voltage sampling circuit comprising a voltage source, a sampling comparator, a sampling execution circuit and a feedback voltage blanking circuit as claimed in any one of claims 1 to 10;

12. A feedback voltage blanking method, comprising:

13. A feedback voltage blanking method, comprising: