CN103715898A - Feedback voltage sampling circuit, and feedback voltage blanking circuit and method - Google Patents
Feedback voltage sampling circuit, and feedback voltage blanking circuit and method Download PDFInfo
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- CN103715898A CN103715898A CN201410034017.9A CN201410034017A CN103715898A CN 103715898 A CN103715898 A CN 103715898A CN 201410034017 A CN201410034017 A CN 201410034017A CN 103715898 A CN103715898 A CN 103715898A
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Abstract
The invention relates to a feedback voltage sampling circuit, and a feedback voltage blanking circuit and method. The feedback voltage blanking circuit comprises a blanking time control circuit and a blanking filter circuit, wherein the blanking time control circuit is used for generating a blanking time control signal according to a voltage parameter representing a load state; the blanking filter circuit is connected between a feedback voltage input terminal and a blanking output terminal and is used for outputting a first voltage signal changed synchronous with a feedback voltage within a corresponding blanking time interval according to the blanking time control signal as well as outputting a second voltage signal obtained by delaying a feedback voltage outside the blanking time interval. The invention further discloses the corresponding feedback voltage blanking method and the feedback voltage sampling circuit employing the feedback voltage blanking circuit. The blanking time is set according to the load state, so that the error sampling of the feedback voltage is effectively prevented; the loss of the circuit in on-load or light-load state is also avoided.
Description
Technical field
The present invention relates to power electronic technology, be specifically related to a kind of feedback voltage sample circuit, feedback voltage blanking circuit and method.
Background technology
Isolated converter is widely used in various off-line electric power systems.Isolated converter generally includes former avris circuit and secondary lateral circuit, and both are by having the transformer isolation of former limit winding and secondary winding.For isolated converter, thereby can make isolated converter export constant voltage and/or electric current by the electric current of the former limit of switch controlled winding.
For isolated converter, it is few that former limit control mode has device, simple in structure and low cost and other advantages.In the control mode of former limit, output voltage feedback sample is that the voltage by sampling on auxiliary winding is realized.When the power switch conducting of the former limit of isolated converter, the auxiliary voltage of winding and the input voltage of isolated converter are proportional.When the former limit of isolated converter power switch turn-offs, secondary diode carries out afterflow, and the freewheel current of secondary diode starts linearity from peak value and reduces.When the freewheel current of secondary diode moves closer in zero time, the auxiliary voltage of winding is proportional with the output voltage of isolated converter, and the auxiliary winding voltage of now sampling is as the feedback of output voltage, thus the control of realization to output voltage.When the freewheel current of secondary diode equals zero; auxiliary winding voltage is not isolated the output voltage clamp of formula converter; and can vibrate; namely auxiliary winding voltage has larger falling, conventionally can be by falling the sampling instant of the moment of beginning as output voltage feedback.Meanwhile, the former limit power switch conducting again of isolated converter.
But, at the former limit of isolated converter power switch, close and to have no progeny, due to the reverse reason such as recoverys of the existence of transformer leakage inductance and parasitic diode, the voltage on auxiliary winding can vibrate, and the mistake that feedback voltage so likely occurs is sampled.Prior art can be set a predetermined blanking time conventionally, in former limit power switch closes the predetermined blanking time of having no progeny, does not carry out the feedback sample of output voltage.Yet the duration of oscillation of auxiliary winding is not what fix, the default longer blanking time can cause the loss of circuit when zero load or underloading to uprise.
Summary of the invention
In view of this, technical problem to be solved by this invention is to provide a kind of feedback voltage sample circuit, feedback voltage blanking circuit and method, for isolated converter is carried out to the control of former limit, avoid circuit that the unnecessary blanking time causes in underloading or loss when unloaded.
First aspect, provides a kind of feedback voltage blanking circuit, and for the feedback voltage of the isolated converter of former limit control is carried out to blanking, described feedback voltage blanking circuit comprises blanking time control circuit and blanking filter circuit;
Described blanking time control circuit is for generating blanking time control signal according to the voltage parameter that characterizes load condition, and described blanking time control signal indication is interval with the blanking time of the voltage parameter variation of described sign load condition;
Described blanking filter circuit is connected between feedback voltage input and blanking output, for exporting in corresponding blanking time interval according to described blanking time control signal with synchronous the first voltage signal changing of feedback voltage, the second voltage signal that described in output delay, feedback voltage obtains outside blanking time interval.
Preferably, described blanking time control circuit comprises charging current source, voltage-controlled current source, charging capacitor, discharge switch and blanking comparator;
Described charging capacitor, described discharge switch and described voltage-controlled current source are connected in parallel between charging voltage output and earth point, and described discharge switch is controlled conducting by feedback voltage zero crossing or the corresponding control impuls of power switch control signal trailing edge; Described voltage-controlled current source is controlled by the voltage parameter of described sign load condition;
Described charging current source is connected to described charging voltage output, for described charging capacitor is charged;
The input of described blanking comparator is connected with the first reference voltage with described charging voltage output respectively, and the output of described blanking comparator is exported described blanking time control signal.
Preferably, described blanking filter circuit comprises blanking switcher, filter resistance and filter capacitor;
Described blanking switcher and described filter resistance are connected in parallel between feedback voltage input and described blanking output;
Described filter capacitor is connected between described blanking output and earth point;
Described blanking switcher is controlled by described blanking time control signal, and conducting in blanking time interval is turn-offed outside blanking time interval.
Preferably, described blanking filter circuit comprises blanking switcher, filter resistance, the first filter capacitor and the second filter capacitor;
Described filter resistance is connected in series between described feedback voltage input and described blanking output;
Described the first filter capacitor is connected between described blanking output and earth point;
Described the second filter capacitor and described blanking switcher are connected in series between described blanking output and earth point;
Described blanking switcher is controlled by described blanking time control signal, turn-offs conducting outside blanking time interval in blanking time interval.
Preferably, the voltage parameter of described sign load condition is the peak signal of output voltage or the primary current detection signal of voltage control loop.
Second aspect, provides a kind of feedback voltage blanking circuit, and for the feedback voltage of the isolated converter of former limit control is carried out to blanking, described feedback voltage blanking circuit comprises blanking time control circuit and blanking filter circuit;
Described blanking time control circuit is for generating the first blanking time control signal and the second blanking time control signal according to the voltage parameter that characterizes load condition, described the first blanking time control signal and described the second blanking time control signal are indicated respectively with the first blanking time interval and second blanking time of the voltage parameter variation of described sign load condition interval, described the first blanking time interval and the second blanking time interval have identical initial time, and described the second blanking time interval is greater than described the first blanking time interval;
Described blanking filter circuit is connected between feedback voltage input and blanking output, for turn-off the electrical connection between described feedback voltage input and described blanking output in the first blanking time interval according to described blanking time control signal, outside the first blanking time interval, in the second blanking time interval, output is with synchronous the first voltage signal changing of feedback voltage, the second voltage signal of feedback voltage acquisition described in output delay the second blanking time interval outside.
Preferably, described blanking time control circuit comprises charging current source, voltage-controlled current source, charging capacitor, discharge switch, the first blanking comparator and the second blanking comparator;
Described charging capacitor, described discharge switch and described voltage-controlled current source are connected in parallel between charging voltage output and earth point, and described discharge switch is controlled conducting by feedback voltage zero crossing or the corresponding control impuls of power switch control signal trailing edge; Described voltage-controlled current source is controlled by the voltage parameter of described sign load condition;
Described charging current source is connected to charging voltage output, for described charging capacitor is charged;
The input of described the first blanking comparator is connected with the second reference voltage with described charging voltage output respectively, and the output of described the first blanking comparator is exported the first blanking time control signal;
The input of described the second blanking comparator is connected with the 3rd reference voltage with described charging voltage output respectively; The output of described the second blanking comparator is exported the second blanking time control signal;
Described the second reference voltage is less than described the 3rd reference voltage.
Preferably, described blanking filter circuit comprises the first blanking switcher, the second blanking switcher, filter resistance and filter capacitor;
Described filter capacitor is connected between described blanking output and earth point;
Described the second blanking switcher and the described filter resistance composition channel selection circuit that is connected in parallel; Described channel selection circuit and described the first blanking switcher are connected in series between described feedback voltage input and described blanking output;
Described the first blanking switcher is controlled by described the first blanking time control signal, turn-offs conducting outside the first blanking time interval in the first blanking time interval;
Described the second blanking switcher is controlled by described the second blanking time control signal, and conducting in the second blanking time interval is turn-offed outside the second blanking time interval.
Preferably, described blanking filter circuit comprises the first blanking switcher, the second blanking switcher, filter resistance, the first filter capacitor and the second filter capacitor;
Described filter resistance and described the first blanking switcher are connected in series between described feedback voltage input and described blanking output;
Described the first filter capacitor is connected between described blanking output and earth point;
Described the second filter capacitor and described the second blanking switcher are connected in series between described blanking output and earth point;
Described the first blanking switcher is controlled by described the first blanking time control signal, turn-offs conducting outside the first blanking time interval in the first blanking time interval;
Described the second blanking switcher is controlled by described the second blanking time control signal, turn-offs conducting outside the second blanking time interval in the second blanking time interval.
Preferably, the voltage parameter of described sign load condition is the peak signal of output voltage or the primary current detection signal of voltage control loop.
The third aspect, a kind of feedback voltage sample circuit is provided, for the feedback voltage of the isolated converter of former limit control is sampled, described feedback voltage sample circuit comprises voltage source, sampling comparator, sampling executive circuit and feedback voltage blanking circuit as above;
Described voltage source is connected between feedback voltage input and the first input end of described sampling comparator; The blanking output of described feedback voltage blanking circuit is connected with the input of the second input of described sampling comparator and described sampling executive circuit;
The output output sampling control signal of described sampling comparator, described sampling control signal is controlled described sampling executive circuit the voltage signal of described feedback voltage blanking circuit output is sampled.
Fourth aspect, provides a kind of feedback voltage blanking method, comprising:
According to the voltage parameter that characterizes load condition, generate blanking time control signal, described blanking time control signal indication is interval with the blanking time of the voltage parameter variation of described sign load condition;
According to described blanking time control signal, in corresponding blanking time interval, export with synchronous the first voltage signal changing of feedback voltage, the second voltage signal that described in output delay, feedback voltage obtains outside blanking time interval.
The 5th aspect, provides a kind of feedback voltage blanking method, comprising:
According to the voltage parameter that characterizes load condition, generate the first blanking time control signal and the second blanking time control signal, described the first blanking time control signal and described the second blanking time control signal are indicated respectively with the first blanking time interval and second blanking time of the voltage parameter variation of described sign load condition interval, described the first blanking time interval and the second blanking time interval have identical initial time, and described the second blanking time interval is greater than described the first blanking time interval;
According to described blanking time control signal, in the first blanking time interval, turn-off the electrical connection between feedback voltage input and blanking output, outside the first blanking time interval, in the second blanking time interval, output is with synchronous the first voltage signal changing of feedback voltage, the second voltage signal of feedback voltage acquisition described in output delay the second blanking time interval outside.
The present invention is based on the feature that auxiliary winding duration of oscillation changes with load condition, according to the voltage parameter adaptive generation blanking time control signal that characterizes load condition, the blanking time that blanking time control signal indication changes with the voltage parameter that characterizes load condition, when underloading, the blanking time is less, and when heavy duty the blanking time larger, blanking time and auxiliary winding duration of oscillation are matched, both avoided because vibration causes feedback voltage mistake sampling, and avoided again meeting underloading that the blanking time causes or loss when unloaded because increasing dummy load.
Accompanying drawing explanation
By the description to the embodiment of the present invention referring to accompanying drawing, above-mentioned and other objects, features and advantages of the present invention will be more clear, in the accompanying drawings:
Fig. 1 is the circuit diagram that the auxiliary winding of the use of the embodiment of the present invention is realized the isolated converter of feedback;
Fig. 2 is the structural representation of the ON-OFF control circuit of the embodiment of the present invention;
Fig. 3 is the waveform schematic diagram of each signal parameter in the isolated converter of the embodiment of the present invention;
Fig. 4 A is the circuit diagram of the feedback voltage sample circuit of first embodiment of the invention;
Fig. 4 B is the circuit diagram of the feedback voltage blanking circuit of first embodiment of the invention;
Fig. 4 C is the oscillogram of feedback voltage and delayed feedback voltage in first embodiment of the invention;
Fig. 4 D is the schematic diagram of a replacement circuit of the blanking filter circuit of first embodiment of the invention;
Fig. 5 A is the circuit diagram of the feedback voltage blanking circuit of second embodiment of the invention;
Fig. 5 B is the schematic diagram of a replacement circuit of the blanking filter circuit of second embodiment of the invention;
Fig. 6 is the flow chart of the feedback voltage blanking method of third embodiment of the invention;
Fig. 7 is the flow chart of the feedback voltage blanking method of fourth embodiment of the invention.
Embodiment
Below in conjunction with accompanying drawing, the preferred embodiments of the present invention are described in detail.Although the present invention is described in conjunction with following preferred embodiment, the present invention is not restricted to these embodiment.In below details of the present invention being described, detailed some specific detail sections of having described.Do not have to those skilled in the art the description of these detail sections can understand the present invention completely yet.For fear of obscuring essence of the present invention, known method, process, flow process, element and circuit do not describe in detail.
In addition, it should be understood by one skilled in the art that the accompanying drawing providing at this is all for illustrative purposes, and accompanying drawing is not necessarily drawn in proportion.
Meanwhile, should be appreciated that " circuit " refers to the galvanic circle being connected and composed by electrical connection or electromagnetism by least one element or electronic circuit.When claiming that element or circuit " are connected to " another element or claim that element or circuit " are connected to " between two nodes, it can be directly couple or be connected to another element or can have intermediary element, and the connection between element can be physically, in logic or its combination.On the contrary, when claiming element " to be directly coupled to " or during " being directly connected to " another element, meaning that both do not exist intermediary element.Unless context explicitly calls for, otherwise the implication that " comprising " in whole specification and claims, " comprising " etc., similar word should be interpreted as comprising rather than exclusive or exhaustive implication; That is to say, be the implication of " including but not limited to ".
In description of the invention, it will be appreciated that, term " first ", " second " etc. are only for describing object, and can not be interpreted as indication or hint relative importance.In addition,, in description of the invention, except as otherwise noted, the implication of " a plurality of " is two or more.
The present invention can be applied to the isolated converter that any former limit is controlled, and in the following detailed description, the inverse excitation type converter (flyback converter) of only take is explained specific works principle of the present invention as example.
Fig. 1 is the circuit diagram that the auxiliary winding of the use of the embodiment of the present invention is realized the isolated converter of feedback.As shown in Figure 1, isolated converter 10 comprises transformer T, power switch S, ON-OFF control circuit 11, voltage feedback circuit 12, secondary side rectification circuit 13 and power supply circuits 14 and current sampling resistor R
sen.Transformer T comprise former limit winding L 1 and with secondary winding L 2 and the auxiliary winding L 3 of its coupling; Secondary side rectification circuit 13 is connected with secondary winding L 2, and for the both end voltage of secondary winding L 2 being carried out to rectification with output constant voltage and/or electric current, in Fig. 1, secondary side rectification circuit 13 comprises secondary rectifier diode D and secondary output capacitance C.
Power supply circuits 14 are connected with auxiliary winding L 3, and by the both end voltage of auxiliary winding L 3 is carried out to rectification, and the bias voltage of stable output is ON-OFF control circuit 11 power supplies.ON-OFF control circuit 11 comprises bias voltage input V
b, current detection signal input SEN, feedback voltage input FB, signal ground end GND and switch controlling signal output DRV, the output of power supply circuits 14 is connected to bias voltage input V
b.Current sampling resistor R
senby the current conversion that flows through power switch S, be voltage signal, its common port being connected with power switch S is connected with the current detection signal input SEN of ON-OFF control circuit 11, and primary current detection signal is input to ON-OFF control circuit 11.In Fig. 1, voltage feedback circuit 12 is for being connected to the bleeder circuit at auxiliary winding L 3 two ends, and it will be input to the feedback voltage input FB of ON-OFF control circuit 11 after the voltage dividing potential drop at auxiliary winding L 3 two ends.Conventionally, ON-OFF control circuit 11 can be manufactured to integrated circuit separately or with the power switch in isolated converter.
Fig. 2 is the structural representation of the ON-OFF control circuit of the embodiment of the present invention.As shown in Figure 2, ON-OFF control circuit 11 comprises feedback voltage sample circuit 111, set pulse generative circuit 112, voltage error amplifier 113, pwm comparator 114 and logic control circuit 115.
Wherein, the input of feedback voltage sample circuit 111 is connected to feedback voltage input FB, for be changed to zero or while approaching zero at secondary winding current, the secondary output voltage of auxiliary winding is sampled.
The output of feedback voltage sample circuit 111 is connected with set pulse generative circuit 112, and the magnitude of voltage that set pulse generative circuit 112 samples according to feedback voltage sample circuit 111 generates the set pulse signal of control switch control signal frequency.
Meanwhile, voltage error amplifier 113 is connected with feedback voltage sample circuit 111, and the magnitude of voltage sampling for comparison feedback voltage sample circuit 111 is with respect to inner reference voltage value V
referror, and this error is amplified to rear output error voltage V
comp.The output of voltage error amplifier 113 has formed the output of the voltage control loop of ON-OFF control circuit 11.Error voltage V
comp(also, the output voltage of voltage control loop) can characterize the load condition of isolated converter, when load is larger, and error voltage V
complarger, when underloading or zero load, error voltage V
compless.
Similarly, primary current detection signal V
sENpeak signal also can characterize load condition, when load is larger, primary current detection signal V
sENpeak signal larger, in load hour, primary current detection signal V
sENpeak signal less.
The input of pwm comparator 114 is connected with output and the current detection signal input of voltage error amplifier 113 respectively, for the error voltage V that voltage error amplifier 113 is exported
compwith current sampling resistor R in former avris circuit
senthe primary current detection signal V that sampling obtains
sENrelatively, generate quenching pulse signal.
Alternatively, logic control circuit 115 can also comprise the drive circuit being connected with rest-set flip-flop output, and this drive circuit provides driving to power switch S.
Fig. 3 is the waveform schematic diagram of each signal parameter in the isolated converter of the embodiment of the present invention.V
dRVfor switch controlling signal, it is square-wave signal, I
pfor flowing through the electric current of former limit winding, I
sfor flowing through the electric current of secondary winding, V
aUXfor the voltage at auxiliary winding two ends, itself and feedback voltage V
fBbe directly proportional.As shown in Figure 3, switch controlling signal V
dRVduring power ratio control switch conduction, be also moment t
0to moment t
1during this time, the inductive current of former limit winding continues to rise, and former limit winding continues energy storage, feedback voltage V
fBbe directly proportional to the input terminal voltage (being also DC bus-bar voltage) of isolated converter.
At switch controlling signal V
dRVpower ratio control switch closes has no progeny, and is also moment t
1to moment t
2during this time, former limit winding current I
pvanishing, the energy storage of former limit winding is passed to secondary winding, secondary winding current I
scontinuous decrease, until electric current reduces to zero, the energy storage of secondary winding is all passed to load.
Secondary winding when electric discharge finishes, feedback voltage V
fBbe directly proportional to the output voltage of power stage circuit, therefore, at t
2constantly neighbouring to feedback voltage V
fBthe obtained sampled voltage of sampling can reflect the situation of output voltage.
After the inductive current of secondary winding drops to zero until former limit power switch again before conducting, also i.e. t constantly
2to moment t
3during this time, the leakage inductance of former limit winding and the parasitic capacitance of power switch and circuit produce resonance, and at this moment feedback voltage has larger falling.Feedback voltage sample circuit 111 can, by detecting the sampling instant of determining feedback voltage of falling of feedback voltage, guarantee that the voltage of sampling acquisition is at moment t
2or this constantly near, thus, situation that can the isolated converter output voltage of Obtaining Accurate.
Meanwhile, as shown in Figure 3, in power switch closes a period of time of having no progeny, also, moment t in Fig. 3
1to moment t
offduring this time, the voltage at auxiliary winding two ends can vibrate.During due to vibration, the voltage at auxiliary winding two ends can time low when high, when the both end voltage of auxiliary winding is too low, can cause the mistake sampling to feedback voltage, it is associated that the voltage that mistake sampling obtains and the output voltage of isolated converter do not have, and can cause power switch control to occur mistake.Mistake sampling for fear of for feedback voltage, need to arrange the blanking time, in the time period that occurs to vibrate, does not carry out feedback voltage sampling at auxiliary winding.The existing blanking time is set to fixed value, and the loss while making zero load or underloading uprises.Meanwhile, the duration of oscillation of the voltage at auxiliary winding two ends can increase and increase along with output loading, thus, can come self adaptation that the blanking time is set according to the parameter of reflected load state.
Fig. 4 A is the circuit diagram of the feedback voltage sample circuit of first embodiment of the invention.As shown in Figure 4 A, feedback voltage sample circuit 111 comprises feedback voltage blanking circuit 41, voltage source 42, sampling comparator 43 and sampling executive circuit 44.
Wherein, voltage source 42 is connected between feedback voltage input FB and the first input end of sampling comparator 43; The blanking output OFF of feedback voltage blanking circuit 41 is connected with the second input of sampling comparator 43 and the input of sampling executive circuit 44.
The output output sampling control signal P of sampling comparator 43
s, to control the voltage signal of 44 pairs of feedback voltage blanking circuit outputs of sampling executive circuit, sample.
In Fig. 4 A, the negative pole of voltage source 42 is connected with feedback voltage input FB, anodal is connected with sampling comparator 43, and the magnitude of voltage of voltage source is preset as Δ V, thereby makes to be input to the voltage of sampling in comparator higher than feedback voltage V
fBa scheduled voltage Δ V.In Fig. 4 A, first input end is the inverting input of sampling comparator 43, and the second input is the in-phase input end of sampling comparator 43.Thus, at the output voltage of blanking output OFF, be changed to and be greater than V
fBduring+Δ V, sampling comparator 43 output high level.
As shown in Figure 4 A, sampling executive circuit 44 comprise the sampling switch S1 being connected between input and output and be connected to output and earth point between sampling capacitance C1.Sampling switch S1 is according to sampling control signal P
sindication, in sampling instant conducting, give sampling capacitance C1 charging, until the voltage at sampling capacitance C1 two ends equals the voltage of blanking output output, then sampling switch S1 disconnects, the voltage on sampling capacitance C1 keeps, until sampling switch S1 conducting again.
Fig. 4 B is the circuit diagram of the feedback voltage blanking circuit of first embodiment of the invention.As shown in Figure 4 B, feedback voltage blanking circuit 41 comprises blanking time control circuit 411 and blanking filter circuit 412.
Blanking time control circuit 411 is for generating blanking time control signal P according to the voltage parameter that characterizes load condition
oFF, blanking time control signal P
oFFindication is interval with the blanking time of the voltage parameter variation of described sign load condition.
In the present embodiment, load is larger, and the blanking time is longer.
Due in blanking time interval, feedback voltage blanking circuit 41 is in blanking output OFF output with synchronous the first voltage signal changing of feedback voltage, and therefore, the voltage of sampling comparator 43 second inputs is less than the voltage of first input end, thus, sampling comparator 43 output low levels.
Outside blanking time interval, the second voltage signal that feedback voltage blanking circuit 41 obtains at feedback voltage described in blanking output OFF output delay, (moment t in Fig. 3 when feedback voltage smooth variation
offto moment t
2), the voltage of sampling comparator 43 second inputs is still less than the voltage of first input end.But after 2 electric discharges of secondary winding L finish, feedback voltage starts fast-descending.Referring to Fig. 4 C, V
fBfor feedback voltage waveform, V
fB' for postponing the feedback voltage waveform of Δ t.Because the voltage of sampling comparator 43 second inputs is for postponing the feedback voltage of Δ t, therefore, at t
2+ Δ t is (being also that 2 electric discharges of secondary winding L finish rear Δ t) constantly, the Voltage Feedback V of the second input
fB' magnitude of voltage and t
2feedback voltage V constantly
fBmagnitude of voltage equate.And the feedback voltage that the voltage of the first input end of the comparator 43 of now sampling is current time adds the voltage Δ V of voltage source, due to feedback voltage fast-descending, t
2+ Δ t feedback voltage is constantly less than t
2feedback voltage constantly.When Δ t and Δ V arrange suitable time, at t
2constantly, the voltage of the second input of sampling comparator 43 is the voltage that is greater than first input end by the voltage transformation that is less than first input end to+Δ t.Thus, sampling comparator 43 output high level, the rising edge of its output signal indicates sampling instant, is also moment t
2+ Δ t.
It will be appreciated by those skilled in the art that, according to the difference of the sampling control signal form of expression, first input end and second input of sampling comparator 43 also can exchange, also be, first input end is in-phase input end, the second input is inverting input, and at this moment, the trailing edge of sampling comparator 43 output signals indicates sampling instant.Meanwhile, sampling control signal P
sform also can select according to actual conditions, as long as can realize sampling switch S1 sampling control signal P
sin sampling instant conducting.
Sampling executive circuit 44 is according to the sampling control signal P of sampling comparator 43 outputs
sin sampling instant, the voltage of blanking output OFF is sampled.Equally, because the voltage of blanking output OFF now equals t
2feedback voltage constantly, therefore, the voltage that sampling obtains can be for characterizing the situation of isolated converter output voltage.
Blanking time control circuit 411 comprises charging current source A1, voltage-controlled current source A2, charging capacitor C2, discharge switch S2 and blanking comparator 411a.
Charging capacitor C2, discharge switch S2 and voltage-controlled current source A2 are connected in parallel between charging voltage output and earth point.Discharge switch S2 is by feedback voltage zero crossing or the corresponding control impuls P of power switch control signal trailing edge
zcontrol conducting.
Charging current source A1 is connected to charging voltage output, and charging capacitor C2 is charged.Voltage-controlled current source A2 is by the voltage parameter V that characterizes load condition
lOADcontrol.As previously mentioned, the output voltage of the voltage control loop in ON-OFF control circuit can characterize load condition, therefore, can be used to control the voltage-controlled current source A2 of the present embodiment.
Similarly, current detection signal V
sENpeak value also can characterize load condition, therefore, while there is current peak testing circuit in ON-OFF control circuit, also can use current detection signal V
sENpeak signal control voltage-controlled current source A2.
The input of blanking comparator 411a is connected with the first reference voltage V1 with charging voltage output respectively, and blanking comparator 411a is according to the comparison situation output blanking time control signal P of input terminal voltage
oFF.Although in Fig. 4 B, charging voltage output is connected with the inverting input of blanking comparator 411a, and the first reference voltage V1 is input to in-phase input end, those skilled in the art easily understand, above-mentioned annexation can be changed, also, charging voltage output is connected with the in-phase input end of blanking comparator 411a, and the first reference voltage V1 is input to inverting input.
The controlled pulse P of discharge switch S2
zcontrol, in trailing edge or the place's conducting of feedback voltage zero crossing of switch controlling signal, make charging capacitor C2 electric discharge until during its both end voltage vanishing, discharge switch S2 turn-offs.Discharge switch S2 closes and to have no progeny, and charging current source A1 starts the charging to charging capacitor C2, until charging capacitor C2 both end voltage is while rising to the first reference voltage V1, and the output generation saltus step of blanking comparator 411a.Meanwhile, the one part of current of charging current source A1 flows to voltage-controlled current source A2.Because the output current of voltage-controlled current source is with controlling voltage V
lOADchange, in load hour, the output current of voltage-controlled current source is less, the charging current that now flows to charging capacitor C2 is larger, make charging capacitor C2 both end voltage increase with fast speed, it is shorter that it rose to for the first needed time of reference voltage V1, and thus, blanking comparator 411a exports the less blanking time control signal P in blanking time interval
oFF.Accordingly, when load is larger, the output current of voltage-controlled current source is larger, the charging current that now flows to charging capacitor C2 is less, make charging capacitor C2 both end voltage to rise compared with jogging speed, it is longer that it rose to for the first needed time of reference voltage V1, and thus, blanking comparator 411a exports the longer blanking time control signal P in blanking time interval
oFF.
Blanking switcher S
oFFwith filter resistance R
oFFbe connected in parallel between feedback voltage input FB and blanking output OFF.
Filter capacitor C
oFFbe connected between blanking output OFF and earth point.
Blanking switcher S
oFFby blanking time control signal P
oFFcontrol, conducting in blanking time interval is turn-offed outside blanking time interval.
At blanking switcher S
oFFduring conducting, filter resistance R
oFFby short circuit, filter capacitor C
oFFboth end voltage synchronously changes with feedback voltage.
At blanking switcher S
oFFduring shutoff, filter resistance R
oFFwith filter capacitor C
oFFform RC delay circuit, feedback voltage is postponed to rear output.
Fig. 4 D is the schematic diagram of a replacement circuit of the blanking filter circuit of first embodiment of the invention.As shown in Figure 4 D, blanking filter circuit 412 comprises blanking switcher S
oFF, filter resistance R
oFF, the first filter capacitor C
oFF1with the second filter capacitor C
oFF2.
Filter resistance R
oFFbe connected between feedback voltage input FB and blanking output OFF.
The first filter capacitor C
oFF1be connected between blanking output OFF and earth point; The second filter capacitor C
oFF2with blanking switcher S
oFFbe connected in series between blanking output OFF and earth point.Preferably, the second filter capacitor C
oFF2be greater than the first filter capacitor C
oFF1.
Blanking switcher S
oFFby blanking time P
oFFcontrol signal is controlled, and turn-offs conducting outside blanking time interval in blanking time interval.
At blanking switcher S
oFFduring shutoff, filter resistance R
oFFwith the first filter capacitor C
oFF1form the RC delay circuit with less time constant, in filter resistance resistance, choose hour, blanking output OFF voltage changes with feedback voltage with minimum delay, can think that it synchronously changes with feedback voltage.
At blanking switcher S
oFFduring conducting, filter resistance R
oFFwith the first filter capacitor C
oFF1and the second filter capacitor C
oFF2form and there is the RC delay circuit compared with large time constant, feedback voltage is postponed to rear output.
The feature that the present embodiment changes with load condition based on auxiliary winding duration of oscillation, according to the voltage parameter adaptive generation blanking time control signal that characterizes load condition, the blanking time that blanking time control signal indication changes with the voltage parameter that characterizes load condition, when underloading, the blanking time is less, and when heavy duty the blanking time larger, blanking time and auxiliary winding duration of oscillation are matched, both avoided because vibration causes feedback voltage mistake sampling, and avoided again meeting underloading that the blanking time causes or loss when unloaded because increasing dummy load.
Fig. 5 A is the circuit diagram of the feedback voltage blanking circuit of second embodiment of the invention.Described feedback voltage blanking circuit can be applied to the feedback voltage sample circuit described in Fig. 4 A.As shown in Figure 5A, feedback voltage blanking circuit 41 comprises blanking time control circuit 411 and blanking filter circuit 412.
Blanking time control circuit 411 is for according to the voltage parameter V that characterizes load condition
lOADgenerate the first blanking time control signal P
oFF1with the second blanking time control signal P
oFF2, described the first blanking time control signal P
oFF1with the second blanking time control signal P
oFF2indicate respectively with the voltage parameter V that characterizes load condition
lOADthe the first blanking time interval and the second blanking time that change are interval, and the first blanking time interval and the second blanking time interval have identical initial time, and the second blanking time interval is greater than the first blanking time interval.
In the present embodiment, by two blanking time control signals, the blocking interval of power switch is divided into three intervals, in first interval, also be that in the first blanking time interval, the power switch turn-off time is short, the oscillation amplitude of feedback voltage is larger, now turn-off the electrical connection between feedback voltage input and described blanking output, prevent from that oscillating voltage amplitude is excessive circuit is caused damage.In second interval, also the first blanking time interval outer, in the second blanking time interval, output is with the first voltage signal of the synchronous variation of feedback voltage, the sampling instant of the comparator output error that prevents from sampling.In the 3rd interval, the vibration of feedback voltage finishes, the second voltage signal that feedback voltage obtains described in output delay, and the comparator that makes to sample can detect falling of feedback voltage, thereby accurately catches sampling instant.
Particularly, as shown in Figure 5A, blanking time control circuit 411 comprises charging current source A1, voltage-controlled current source A2, charging capacitor C2, discharge switch S2, the first blanking comparator 411a and the second blanking comparator 411b.
Charging capacitor C2, discharge switch S2 and voltage-controlled current source A2 are connected in parallel between charging voltage output and earth point, and discharge switch S2 controls conducting by feedback voltage zero crossing or the corresponding control impuls of power switch control signal trailing edge; Voltage-controlled current source A2 is by the voltage parameter V that characterizes load condition
lOADcontrol.
As previously mentioned, the output voltage of the voltage control loop in ON-OFF control circuit can characterize load condition, therefore, can be used to control the voltage-controlled current source A2 of the present embodiment.
Similarly, primary current detection signal V
sENpeak signal also can characterize load condition, therefore, while there is current peak testing circuit in ON-OFF control circuit, also can use current detection signal V
sENpeak signal control voltage-controlled current source A2.
Charging current source A1 is connected to charging voltage output, and charging capacitor C2 is charged.
The input of the first blanking comparator 411a is connected with the second reference voltage V2 with charging voltage output respectively, and the output of the first blanking comparator 411a is exported the first blanking time control signal P
oFF1.
The input of the second blanking comparator 411b is connected with the 3rd reference voltage V3 with charging voltage output respectively; The output of the second blanking comparator 411b is exported the second blanking time control signal P
oFF2.
The controlled pulse P of discharge switch S2
zcontrol, in trailing edge or the place's conducting of feedback voltage zero crossing of switch controlling signal, make charging capacitor C2 electric discharge until during its both end voltage vanishing, discharge switch S2 turn-offs.Discharge switch S2 closes and to have no progeny, and charging current source A1 starts the charging to charging capacitor C2, until charging capacitor C2 both end voltage is while rising to the second reference voltage V2, and the output generation saltus step of the first blanking comparator 411a; Until charging capacitor C2 both end voltage is while rising to the 3rd reference voltage V3, the output generation saltus step of the second blanking comparator 411b.
By being set, the second reference voltage V2 is less than the 3rd reference voltage V3, and can be so that the first corresponding blanking time interval be less than the second blanking time interval.
Similar with the first embodiment, an electric current part of charging current source A1 flows into voltage-controlled current source A2.Because the output current of voltage-controlled current source is with controlling voltage V
lOADchange, in load hour, blanking comparator 411a and blanking comparator 411b export respectively the first less blanking time control signal P of blanking time interval
oFF1with the second blanking time control signal P
oFF2; When load is larger, blanking comparator 411a and blanking comparator 411b export respectively the first larger blanking time control signal P of blanking time interval
oFF1with the second blanking time control signal P
oFF2.
Thus, the blanking time can be set adaptively along with the variation of load.
Filter capacitor C
oFFbe connected between blanking output OFF and earth point.
The second blanking switcher S
oFF2with filter resistance R
oFFcomposition channel selection circuit is connected in parallel; Channel selection circuit and the first blanking switcher S
oFF1be connected in series between feedback voltage input FB and blanking output OFF.
The first blanking switcher S
oFF1by the first blanking time control signal P
oFF1control, in the first blanking time interval, turn-off conducting outside the first blanking time interval.
The second blanking switcher S
oFF2by the second blanking time control signal P
oFF2control, conducting in the second blanking time interval is turn-offed outside the second blanking time interval.
Because the first blanking time is interval and the second blanking time interval has identical initial time, meanwhile, it is interval that the second blanking time interval was greater than for the first blanking time, in the first blanking time interval, and the first blanking switcher S
oFF1turn-off and the second blanking switcher S
oFF2conducting, the electrical connection between feedback voltage input FB and blanking output OFF is by the first blanking switcher S
oFF1turn-off.
Outside the first blanking time interval, in the second blanking time interval, the first blanking switcher S
oFF1conducting and the second blanking switcher S
oFF2conducting, filter resistance R
oFFby short circuit, filter capacitor C
oFFboth end voltage synchronously changes with feedback voltage.
Outside the second blanking time interval, the first blanking switcher S
oFF1conducting and the second blanking switcher S
oFF2turn-off filter resistance R
oFFwith filter capacitor C
oFFform RC delay circuit, feedback voltage is postponed to rear output.
Fig. 5 B is the schematic diagram of a replacement circuit of the blanking filter circuit of second embodiment of the invention.As shown in Figure 5 B, blanking filter circuit 412 comprises the first blanking switcher S
oFF1, the second blanking switcher S
oFF2, filter resistance R
oFF, the first filter capacitor C
oFF1with the second filter capacitor C
oFF2.
Filter resistance R
oFFwith the first blanking switcher S
oFF1be connected in series between feedback voltage input FB and blanking output OFF.
The first filter capacitor C
oFF1be connected between blanking output OFF and earth point.
The second filter capacitor C
oFF2with the second blanking switcher S
oFF2be connected in series between blanking output OFF and earth point.
The first blanking switcher S
oFF1by the first blanking time control signal P
oFF1control, in the first blanking time interval, turn-off conducting outside the first blanking time interval.
The second blanking switcher S
oFF2by the second blanking time control signal P
oFF2control, in the second blanking time interval, turn-off conducting outside the second blanking time interval.
Because the first blanking time is interval and the second blanking time interval has identical initial time, meanwhile, it is interval that the second blanking time interval was greater than for the first blanking time, in the first blanking time interval, and the first blanking switcher S
oFF1with the second blanking switcher S
oFF2all turn-off, the electrical connection between feedback voltage input FB and blanking output OFF is by the first blanking switcher S
oFF1turn-off.
Outside the first blanking time interval, in the second blanking time interval, the first blanking switcher S
oFF1conducting and the second blanking switcher S
oFF2turn-off filter resistance R
oFFwith the first filter capacitor C
oFF1form the RC delay circuit with less time constant, in filter resistance resistance, choose hour, blanking output OFF voltage changes with feedback voltage with minimum delay, can think that it synchronously changes with feedback voltage.
Outside the second blanking time interval, the first blanking switcher S
oFF1conducting and the second blanking switcher S
oFF2conducting, filter resistance R
oFFwith the first filter capacitor C
oFF1and the second filter capacitor C
oFF2form and there is the RC delay circuit compared with large time constant, feedback voltage is postponed to rear output.
The present embodiment is by arranging the blanking time interval of two adaptive changes; make in the first larger blanking time interval of feedback voltage oscillation amplitude; electrical connection between feedback voltage input and late-class circuit is turned off; thereby for late-class circuit provides better protection; simultaneously; blanking time changes with the voltage parameter that characterizes load condition; both avoided because voltage oscillation causes feedback voltage mistake sampling, and avoided again meeting underloading that the blanking time causes or loss when unloaded because increasing dummy load.
Fig. 6 is the flow chart of the feedback voltage blanking method of third embodiment of the invention.As shown in Figure 6, described method comprises:
Wherein, the voltage parameter of described sign load condition is the peak signal of output voltage or the primary current detection signal of voltage control loop.
The feature that the present embodiment changes with load condition based on auxiliary winding duration of oscillation, according to the voltage parameter adaptive generation blanking time control signal that characterizes load condition, the blanking time that blanking time control signal indication changes with the voltage parameter that characterizes load condition, when underloading, blanking arranges littlely, and when heavy duty the blanking time larger, blanking time and auxiliary winding duration of oscillation are matched, both avoided because vibration causes feedback voltage mistake sampling, and avoided again meeting underloading that the blanking time causes or loss when unloaded because increasing dummy load.
Fig. 7 is the flow chart of the feedback voltage blanking method of fourth embodiment of the invention.As shown in Figure 7, described method comprises:
Wherein, the voltage parameter of described sign load condition is the peak signal of output voltage or the primary current detection signal of voltage control loop.
The present embodiment is by arranging the blanking time interval of two adaptive changes; make in the first larger blanking time interval of feedback voltage oscillation amplitude; electrical connection between feedback voltage input and late-class circuit is turned off; thereby for late-class circuit provides better protection; simultaneously; blanking time changes with the voltage parameter that characterizes load condition; both avoided because vibration causes feedback voltage mistake sampling, and avoided again meeting underloading that the blanking time causes or loss when unloaded because increasing dummy load.
The foregoing is only the preferred embodiments of the present invention, be not limited to the present invention, to those skilled in the art, the present invention can have various changes and variation.All any modifications of doing, be equal to replacement, improvement etc., within protection scope of the present invention all should be included within spirit of the present invention and principle.
Claims (13)
1. a feedback voltage blanking circuit, carries out blanking for the feedback voltage of isolated converter that former limit is controlled, and described feedback voltage blanking circuit comprises blanking time control circuit and blanking filter circuit;
Described blanking time control circuit is for generating blanking time control signal according to the voltage parameter that characterizes load condition, and described blanking time control signal indication is interval with the blanking time of the voltage parameter variation of described sign load condition;
Described blanking filter circuit is connected between feedback voltage input and blanking output, for exporting in corresponding blanking time interval according to described blanking time control signal with synchronous the first voltage signal changing of feedback voltage, the second voltage signal that described in output delay, feedback voltage obtains outside blanking time interval.
2. feedback voltage blanking circuit according to claim 1, is characterized in that, described blanking time control circuit comprises charging current source, voltage-controlled current source, charging capacitor, discharge switch and blanking comparator;
Described charging capacitor, described discharge switch and described voltage-controlled current source are connected in parallel between charging voltage output and earth point, and described discharge switch is controlled conducting by feedback voltage zero crossing or the corresponding control impuls of power switch control signal trailing edge; Described voltage-controlled current source is controlled by the voltage parameter of described sign load condition;
Described charging current source is connected to described charging voltage output, for described charging capacitor is charged;
The input of described blanking comparator is connected with the first reference voltage with described charging voltage output respectively, and the output of described blanking comparator is exported described blanking time control signal.
3. feedback voltage blanking circuit according to claim 2, is characterized in that, described blanking filter circuit comprises blanking switcher, filter resistance and filter capacitor;
Described blanking switcher and described filter resistance are connected in parallel between feedback voltage input and described blanking output;
Described filter capacitor is connected between described blanking output and earth point;
Described blanking switcher is controlled by described blanking time control signal, and conducting in blanking time interval is turn-offed outside blanking time interval.
4. feedback voltage blanking circuit according to claim 2, is characterized in that, described blanking filter circuit comprises blanking switcher, filter resistance, the first filter capacitor and the second filter capacitor;
Described filter resistance is connected in series between described feedback voltage input and described blanking output;
Described the first filter capacitor is connected between described blanking output and earth point;
Described the second filter capacitor and described blanking switcher are connected in series between described blanking output and earth point;
Described blanking switcher is controlled by described blanking time control signal, turn-offs conducting outside blanking time interval in blanking time interval.
5. feedback voltage blanking circuit according to claim 1, is characterized in that, the voltage parameter of described sign load condition is the peak signal of output voltage or the primary current detection signal of voltage control loop.
6. a feedback voltage blanking circuit, carries out blanking for the feedback voltage of isolated converter that former limit is controlled, and described feedback voltage blanking circuit comprises blanking time control circuit and blanking filter circuit;
Described blanking time control circuit is for generating the first blanking time control signal and the second blanking time control signal according to the voltage parameter that characterizes load condition, described the first blanking time control signal and described the second blanking time control signal are indicated respectively with the first blanking time interval and second blanking time of the voltage parameter variation of described sign load condition interval, described the first blanking time interval and the second blanking time interval have identical initial time, and described the second blanking time interval is greater than described the first blanking time interval;
Described blanking filter circuit is connected between feedback voltage input and blanking output, for turn-off the electrical connection between described feedback voltage input and described blanking output in the first blanking time interval according to described blanking time control signal, outside the first blanking time interval, in the second blanking time interval, output is with synchronous the first voltage signal changing of feedback voltage, the second voltage signal of feedback voltage acquisition described in output delay the second blanking time interval outside.
7. feedback voltage blanking circuit according to claim 6, is characterized in that, described blanking time control circuit comprises charging current source, voltage-controlled current source, charging capacitor, discharge switch, the first blanking comparator and the second blanking comparator;
Described charging capacitor, described discharge switch and described voltage-controlled current source are connected in parallel between charging voltage output and earth point, and described discharge switch is controlled conducting by feedback voltage zero crossing or the corresponding control impuls of power switch control signal trailing edge; Described voltage-controlled current source is controlled by the voltage parameter of described sign load condition;
Described charging current source is connected to charging voltage output, for described charging capacitor is charged;
The input of described the first blanking comparator is connected with the second reference voltage with described charging voltage output respectively, and the output of described the first blanking comparator is exported the first blanking time control signal;
The input of described the second blanking comparator is connected with the 3rd reference voltage with described charging voltage output respectively; The output of described the second blanking comparator is exported the second blanking time control signal;
Described the second reference voltage is less than described the 3rd reference voltage.
8. feedback voltage blanking circuit according to claim 7, is characterized in that, described blanking filter circuit comprises the first blanking switcher, the second blanking switcher, filter resistance and filter capacitor;
Described filter capacitor is connected between described blanking output and earth point;
Described the second blanking switcher and the described filter resistance composition channel selection circuit that is connected in parallel; Described channel selection circuit and described the first blanking switcher are connected in series between described feedback voltage input and described blanking output;
Described the first blanking switcher is controlled by described the first blanking time control signal, turn-offs conducting outside the first blanking time interval in the first blanking time interval;
Described the second blanking switcher is controlled by described the second blanking time control signal, and conducting in the second blanking time interval is turn-offed outside the second blanking time interval.
9. feedback voltage blanking circuit according to claim 7, is characterized in that, described blanking filter circuit comprises the first blanking switcher, the second blanking switcher, filter resistance, the first filter capacitor and the second filter capacitor;
Described filter resistance and described the first blanking switcher are connected in series between described feedback voltage input and described blanking output;
Described the first filter capacitor is connected between described blanking output and earth point;
Described the second filter capacitor and described the second blanking switcher are connected in series between described blanking output and earth point;
Described the first blanking switcher is controlled by described the first blanking time control signal, turn-offs conducting outside the first blanking time interval in the first blanking time interval;
Described the second blanking switcher is controlled by described the second blanking time control signal, turn-offs conducting outside the second blanking time interval in the second blanking time interval.
10. feedback voltage blanking circuit according to claim 6, is characterized in that, the voltage parameter of described sign load condition is the peak signal of output voltage or the primary current detection signal of voltage control loop.
11. 1 kinds of feedback voltage sample circuits, for the feedback voltage of the isolated converter of former limit control is sampled, described feedback voltage sample circuit comprises voltage source, sampling comparator, sampling executive circuit and the feedback voltage blanking circuit as described in any one in claim 1-10;
Described voltage source is connected between feedback voltage input and the first input end of described sampling comparator; The blanking output of described feedback voltage blanking circuit is connected with the input of the second input of described sampling comparator and described sampling executive circuit;
The output output sampling control signal of described sampling comparator, described sampling control signal is controlled described sampling executive circuit the voltage signal of described feedback voltage blanking circuit output is sampled.
12. 1 kinds of feedback voltage blanking methods, comprising:
According to the voltage parameter that characterizes load condition, generate blanking time control signal, described blanking time control signal indication is interval with the blanking time of the voltage parameter variation of described sign load condition;
According to described blanking time control signal, in corresponding blanking time interval, export with synchronous the first voltage signal changing of feedback voltage, the second voltage signal that described in output delay, feedback voltage obtains outside blanking time interval.
13. 1 kinds of feedback voltage blanking methods, comprising:
According to the voltage parameter that characterizes load condition, generate the first blanking time control signal and the second blanking time control signal, described the first blanking time control signal and described the second blanking time control signal are indicated respectively with the first blanking time interval and second blanking time of the voltage parameter variation of described sign load condition interval, described the first blanking time interval and the second blanking time interval have identical initial time, and described the second blanking time interval is greater than described the first blanking time interval;
According to described blanking time control signal, in the first blanking time interval, turn-off the electrical connection between feedback voltage input and blanking output, outside the first blanking time interval, in the second blanking time interval, output is with synchronous the first voltage signal changing of feedback voltage, the second voltage signal of feedback voltage acquisition described in output delay the second blanking time interval outside.
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