CN2884681Y - Power limited circuit for PWM power source control chip - Google Patents

Abstract

The utility model discloses a power limit circuit for PWM power supply control chip, comprising a startup resistor (R startup) placed outside the PWM power supply control chip (A1) and a compensation circuit placed inside the PWM power supply control chip (A1), wherein the compensation circuit comprises a current switch (X0), current multiplier (X1), reference current source (X3) and current adder (X2), and the startup resistor is connected between the input voltage and current switch, and the maximum output power of the power limit circuit is adjustable. The purpose of the utility model is to provide a power limit circuit for PWM power supply control chip, a compensation circuit is integrated inside the power limit circuit, without any additional compensation components, and the maximum output power of Flyback converter can be guaranteed not to change as the input voltage varies based on only a resistor.

Description

The Power Limitation circuit that is used for the PWM power supply control chip

Technical field

The utility model relates to protective circuit, more particularly, relates to a kind of Power Limitation circuit of the PWM of being used for power supply control chip.

Background technology

Generally speaking, be integrated with the kinds of protect function in the power supply control chip, exempt from permanent damages with protection system and load thereof.The power output limitation function is primarily aimed at the protection of power-supply system under overload and the short-circuit conditions.Described circuit just is mainly used in the PWM power supply control chip.

The circuit diagram of common PWM switch power supply system based on the Flyback topological structure comprises a control chip (A0), a starting resistance (R as shown in Figure 1 _Startup), a switching tube (M0) starts electric capacity (C _Startup) and auxiliary electric elements, wherein start electric capacity (C _Startup) and switching tube (M0) between adopt one group of coil (T1) to be coupled.Analyze PWM power-supply system output Power Calculation.ENERGY E of storing in the inductance and the peak current I that flows through _pSuc as formula shown in (1) and (2), output power of power supply P can be represented by (3) formula as can be known, wherein L respectively _pBe former limit inductance value, T is a switch periods, t _OnBe the power tube ON time, V _INBe inlet highway voltage, η is the conversion efficiency of former limit to secondary.

$E=\frac{1}{2}\×L_p\×I_p^2=P\×T---\left(1\right)$

$I_p=\frac{V_{\mathrm{IN}}}{L_p}\×t_{\mathrm{ON}}\·---\left(2\right)$

$P=\frac{V_{\mathrm{IN}}^2\×{t_{\mathrm{ON}}}^2}{2\×T\×L_p}\×\mathrm{\η}---\left(3\right)$

Under the constant situation of load, for different input voltage V _IN, feedback control loop can be to t _OnAutomatically adjust, adjustment process satisfies formula (4), (5), thereby makes system's power output keep constant, and wherein N is the turn ratio of former limit to secondary.

$V_{\mathrm{in}}=\frac{N\×(1-D)}{D}{V}_{\mathrm{out}}---\left(4\right)$

$D=\frac{t_{\mathrm{ON}}}{T}---\left(5\right)$

Yet when system reached peak power output, situation was really not so.At this moment, t _OnFor by input voltage V _INThe certain value of decision, as the formula (6), V wherein _LimitBe the Power Limitation threshold voltage, L _pBe former limit inductance value, R _sIt is current sampling resistor.

$t_{\mathrm{ON}}=\frac{V_{\mathrm{limit}}\×L_p}{V_{\mathrm{in}}\×R_s}---\left(6\right)$

At this moment, peak power output also is subjected to PWM controller response time t _DInfluence.At t time of delay _DWith internal power pipe still conducting, promptly continue through-put power, so the actual Maximum Power Output P of system _MaxAs the formula (7).

$P_{\max }=\frac{V_{\mathrm{IN}}^2\×{(t_{\mathrm{ON}}+t_D)}^2}{2\×L_P\×T}---\left(7\right)$

Though, t _DUsually less (greatly about about 150-200ns), still, along with the continuous lifting of PWM controller operating frequency, t _DImproving t with respect to the period T proportion _DInfluence increasing.Generally speaking, t _DIt is a constant that is determined by self speed of controller.Obvious, at t _On, t _DBe under the situation of definite value the peak power output P of system _MaxCan change with the variation of input voltage.When input voltage changed in the 90VAC-264VAC scope, system's peak power output will be several times of system's peak power outputs under the low input under the high input voltage, shown in Fig. 2 (a).In order to address this problem, just need design input voltage compensation circuit.

So make system's peak power output can not change along with the variation of input voltage with regard to a kind of voltage compensating circuit of needs.

The utility model content

The purpose of this utility model provides a kind of Power Limitation circuit of the PWM of being used for power supply control chip, it is integrated compensating circuit in inside, sheet need not to add any compensating device outward, only uses a resistance just can guarantee that the peak power output of Flyback transducer does not change with the difference of input voltage.

According to one side of the present utility model, a kind of Power Limitation circuit of the PWM of being used for power supply control chip is provided, comprise be positioned over the outer starting resistance of PWM power supply control chip and be positioned in the PWM power supply control chip compensating circuit, wherein compensating circuit comprises current switch, electric current multiplier, reference current source and current adder, described starting resistance is connected between input voltage and the described current switch, and the power output maximum of described Power Limitation circuit is adjustable.

According to an embodiment of the present utility model, described current switch comprises that one starts diode and switching tube, and described starting resistance is connected between input voltage and the current switch, flows through the input current I of starting resistance _INVariation be proportional to the variation of input voltage; Before the chip enable, switching tube is closed, and starting current starts the electric capacity charging by starting diode to one, starts threshold value when the voltage that starts electric capacity surpasses, and switching tube is opened, and starts diode reverse and ends input current I _INAll the inflow current multipliers and by the electric current multiplier with input current I _INLinear transformations is I _Os, the reference current I that current adder produces reference current source _RefWith I _OsSubtract each other and obtain I _SumAnd finish the current-voltage conversion, produce Power Limitation threshold voltage V _LimitI _INBe to be proportional to input voltage V _INFunction, Power Limitation threshold voltage V _LimitVariation and input voltage V _INBe varied to direct ratio, opposite in sign; By selecting the power output maximum of resistance Adjustment System under high input voltage and low input of starting resistance.

According to one side of the present utility model, in the described PWM of the being positioned over power supply control chip compensating circuit comprise: current switch, electric current multiplier, current adder, reference current source, buffer, oscillator, trigger, first comparator, second comparator, NAND gate and under-voltage locking device; Wherein said current switch comprises switching tube and starts diode that the switching tube drain electrode links to each other as the input of current switch with the startup diode cathode, starts diode cathode and V _CCLink to each other, the switching tube grid links to each other with the output of under-voltage locking device, and the switching tube source electrode links to each other with the electric current multiplier input, and the output of electric current multiplier links to each other with the current adder negative input end; Reference current source links to each other with the positive input terminal of current adder; The current signal of current adder output is a voltage signal by electric resistance changing, after buffer is isolated, as Power Limitation threshold voltage V _LimitLink to each other with the positive input terminal of second comparator, the negative input end of first comparator and second comparator links to each other with the source end of power tube; Primary current I _LPressure drop on sampling resistor is sampled voltage V _s

According to an embodiment of the present utility model, in system's power up, the under-voltage locking device is closed switching tube, by the input current I of starting resistance _INThe inflow current switch is given the charging of startup electric capacity by starting diode; Work as V _CCWhen surpassing the actuation threshold threshold voltage, the under-voltage locking device is opened switching tube, starts diode reverse and ends input current I _INAll flow to the electric current multiplier; The PWM power supply control chip will be by the auxiliary winding power supply of a coil; Input current I _INBe proportional to busbar voltage V _INVariation, input current I _INProcessing output current I through the overcurrent multiplier _Os, I _OsLink to each other with the negative input end of current adder; The positive input terminal of current adder links to each other with reference current source, reference current source output reference current I _RefCurrent adder output current I _SumResistance is converted to voltage signal with current signal, isolates through buffer, produces Power Limitation threshold voltage V _LimitV _LimitDetermine the maximum input current in former limit, and then determined system's peak power output.

According to an embodiment of the present utility model, Power Limitation threshold voltage V _LimitBe sampled voltage V _sThe ceiling voltage that can reach; The electric current I that in power tube, flows through _LDuring increase, the sampled voltage V on the sampling resistor _sTo increase simultaneously; Second comparator is sampled voltage V relatively _sWith Power Limitation threshold voltage V _LimitWhen sampled voltage Vs greater than Power Limitation threshold voltage V _LimitThe time, the second comparator output logic low level is to NAND gate; NAND gate output logic high level, with trigger reset, the switch-off power pipe.

According to an embodiment of the present utility model, it is constant that peak power output keeps in input voltage range 90VAC-264VAC.

According to an embodiment of the present utility model, adopt the method for resistors match to determine circuit parameter.

Adopt the technical solution of the utility model, the restriction electricity circuit that this kind is used for the PWM power supply control chip has the compensating circuit that is integrated in PWM power supply control chip inside, sheet need not to add any compensating device outward, only needs a resistance just can guarantee that the peak power output of Flyback transducer does not change with the difference of input voltage.Comprise the current switch that constitutes by diode and NMOS pipe in the compensating circuit, utilize the outer resistance monitoring input voltage V of sheet _InVariation, take into account system start-up simultaneously.Owing to only use an off chip resistor (saving the outer compensating network of sheet), reduced system power dissipation, and be convenient to the PCB layout.Be integrated with the electric current multiplier in the compensating circuit, in order to weaken the influence of integrated resistor absolute value and temperature coefficient to precision.

Description of drawings

The above and other feature of the utility model, character and advantage will be by becoming more obvious below in conjunction with accompanying drawing to the description of embodiment, and Reference numeral identical in the accompanying drawing is represented identical feature all the time, wherein:

Fig. 1 is the circuit diagram of the PWM switch power supply system based on the Flyback topological structure of the prior art.

Fig. 2 (a) is if be explanation V _LimitConstant, peak power output P _MaxThe schematic diagram that can change with the variation of input voltage;

Fig. 2 (b) is if be explanation V _LimitIncrease with input voltage reduces, peak power output P _MaxCan keep constant schematic diagram.

Fig. 3 is the circuit block diagram according to the restricting circuits of an embodiment of the present utility model.

Fig. 4 is the concrete line map according to the restricting circuits of an embodiment of the present utility model.

Embodiment

The purpose of this utility model provides a kind of Power Limitation circuit of the PWM of being used for power supply control chip, it is integrated compensating circuit in inside, sheet need not to add any compensating device outward, only uses a resistance just can guarantee that the peak power output of Flyback transducer does not change with the difference of input voltage.Power Limitation circuit of the present utility model uses a resistance outside sheet, both help system started, and plays monitoring input voltage V again _INEffect.Owing to only using a starting resistance to save the outer compensating network of sheet, reduced system power dissipation, be convenient to the PCB layout.The compensating circuit of PWM controller inside comprises current switch, the electric current multiplier, and reference current source and current adder when not influencing chip enable, can be adjusted the power output maximum according to input voltage.

According to design philosophy of the present utility model, a kind of Power Limitation circuit of the PWM of being used for power supply control chip is provided, comprise being positioned over the outer starting resistance R of PWM power supply control chip A1 _StartupBe positioned in the PWM power supply control chip A1 compensating circuit, wherein compensating circuit comprises current switch X0, electric current multiplier X1, reference current source X3 and current adder X2, starting resistance is connected between input voltage and the described current switch, and the power output maximum of Power Limitation circuit is adjustable.

Below with reference to a specific embodiment of the present utility model.

With reference to figure 3, Fig. 3 is the circuit block diagram according to the restricting circuits of an embodiment of the present utility model.Starting resistance R _StartupBe connected between input voltage and the current switch, flow through starting resistance R _StartupInput current I _INVariation be proportional to the variation of input voltage.Current switch is formed by starting diode D0 and switching tube M1.Before the chip enable, under-voltage locking device (UVLO) X10 closes switching tube M1, and starting current is given the startup capacitor C by starting diode D0 _StartupCharging.When starting capacitor C _StartupVoltage V _CCSurpass the startup threshold value, UVLO X10 opens switching tube M1, starts diode D0 and oppositely ends input current I _INWhole inflow current multiplier X1.Electric current multiplier X1 is with input current I _INLinear transformations is I _Os, current adder X2 is with reference current I _RefWith I _OsSubtract each other and obtain I _Sum, utilize the interior resistance R 4 of sheet to finish the current-voltage conversion again, produce Power Limitation threshold voltage V _LimitBecause I _INBe to be proportional to input voltage V _INFunction, so Power Limitation threshold voltage V _LimitVariation and input voltage V _INBe varied to direct ratio, opposite in sign.By selecting suitable starting resistance, system's peak power output is remained unchanged, under high input voltage and low input shown in Fig. 2 (b).Fig. 2 (b) is if illustrated V _LimitIncrease with input voltage reduces, peak power output P _MaxCan keep constant.

Because, in the transfer process of voltage, used chip integration to become resistance R 4 at electric current, and the resistance absolute value is difficult to accurate control in the integrated circuit, and certain temperature coefficient is arranged, therefore, design current multiplier X1 is to weaken the influence to the circuit precision of resistance absolute value and temperature coefficient.

Continuation is with reference to figure 3, and pwm chip A1 includes current switch X0, electric current multiplier X1, current adder X2, reference current source X3, buffer X4, oscillator X5, trigger X6, the first comparator X7, the second comparator X8, NAND gate X9 and UVLO X10.Open pipe closes M1 drain electrode and anodal linking to each other as the input of current switch X0 of startup diode D0, starts diode D0 negative pole and V _CCLink to each other, switching tube M1 grid links to each other with UVLO X10 output, and switching tube M1 source electrode links to each other with electric current multiplier X1 input.Electric current multiplier X1 output links to each other with current adder X2 negative input end.Reference current source X3 links to each other with the positive input terminal of current adder X2.The current signal of current adder X2 output changes voltage into by resistance R 4, after buffer X4 isolates, as Power Limitation threshold voltage V _LimitLink to each other with the positive input terminal of the second comparator X8.The negative input end of the first comparator X7 and the second comparator X8 links to each other with the source end of power tube M2.Primary current I _LAt sampling resistor R _sOn pressure drop be sampled voltage V _s

In system's power up, UVLO X10 closes switching tube M1, by starting resistance R _StartupInput current I _INInflow current switch X0 gives the startup capacitor C by starting diode D0 _StartupCharging.Work as V _CCWhen surpassing the actuation threshold threshold voltage, UVLO X10 opens switching tube M1, starts diode D0 and oppositely ends input current I _INAll flow to electric current multiplier X1.Pwm power limited chip A1 will be by the auxiliary winding power supply of coil T1.Yi Zhi, input current I _INBe proportional to busbar voltage V _INVariation, satisfy formula (8).

$I_{\mathrm{IN}}=\frac{V_{\mathrm{IN}}-V_{\mathrm{gs}}-V_{\mathrm{ds}}}{R_{\mathrm{startup}}}\≈\frac{V_{\mathrm{IN}}}{R_{\mathrm{startup}}}---\left(8\right)$

Input current I _INThrough the processing of overcurrent multiplier X1, output current Ios satisfies formula (9),

Ios＝K×I _IN (9)

Wherein K is the constant by the line design decision.Ios links to each other with the negative input end of current adder X2; The positive input terminal of current adder X2 links to each other with reference current source X3, reference current source X3 output reference current I _RefThe output current I of current adder X2 _SumSatisfy formula (10).Resistance R 4 is converted to voltage signal with current signal, isolates through buffer X4, produces Power Limitation threshold voltage V _Limit, satisfy formula (11).V _LimitDetermine the maximum input current in former limit, and then determined system's peak power output.

Isum＝Iref-Ios＝Iref-K×I _IN (10)

$\mathrm{Vlimit}=R_4\×\mathrm{Isum}=R_4\×\mathrm{Iref}-\mathrm{\α}\×K\×R_4\×\frac{V_{\mathrm{IN}}}{R_{\mathrm{startup}}}---\left(11\right)$

V _LimitBe V _sThe ceiling voltage that end can reach, the resistance R that links to each other with power tube M2 source end _sBe current sampling resistor, sample rate current is converted to voltage signal.The electric current I that in power tube M2, flows through _LDuring increase, sampling resistor R _sOn voltage Vs will increase simultaneously.The second comparator X8 is V relatively _sAnd V _LimitWork as V _sGreater than V _LimitThe time, the second comparator X8 output logic low level is to NAND gate X9.NAND gate X9 output logic high level, with trigger reset, switch-off power pipe M2 reaches the purpose of power output restriction with this.

Easily know by formula (11), if the influence of resistance is left in the basket V _LimitBe input voltage V _INFunction, V _LimitVariation and input voltage V _INBe varied to direct ratio, opposite in sign.Select suitable starting resistance R _Startup, can make peak power output 90VAC～264VAC in wide input voltage range keep constant.

With reference to figure 4, Fig. 4 is the concrete line map according to the restricting circuits of an embodiment of the present utility model.Because the resistance absolute value is difficult to the influence of accurately control and temperature coefficient in the integrated circuit, the design of circuit parameter depends on resistance R 4 absolute values and improper.Adopt the method for resistors match among the design, got rid of the influence of resistance absolute value and temperature coefficient.Design I _RefSatisfy formula (12), wherein V _RefBe reference voltage.If resistance R 4 and resistance R 31 couplings, then preceding paragraph is a constant in the formula (11), and its precision is by resistors match and V _RefPrecision decision.By transistor N ₁, N ₂, N ₃, N ₄

$\mathrm{Iref}=\frac{\mathrm{Vref}}{R_{31}}---\left(12\right)$

Linear annexation, know that easily formula (13) sets up.Design transistor N ₁, N ₂, N ₃, N ₄Coupling fully, but then push type (14), wherein I ₁, I ₂, I ₃, I ₄Be respectively transistor N ₁, N ₂, N ₃, N ₄Collector current.By Kirchhoff's current law (KCL), easily know formula (15), (16) establishment, wherein I _ConBe reference current.Suppose that transistor β is enough big, ignore the N3 base current, can get formula (17).Can release Iout by formula (14)～(17) and satisfy formula (18), wherein a, b, c are respectively corresponding current mirror image multiplication factor, formula (19) shows that then the consequent coefficient of formula (11) is only relevant with the metal-oxide-semiconductor matching with resistors match if resistance R 4 is mated with resistance R 31.

Vbe1-Vbe2＝Vbe4-Vbe3 (13)

$\frac{I_1+I_4}{I_4}=\frac{I_2+I_3}{I_3}---\left(14\right)$

I ₁+I ₄＝Icon (15)

I ₂+I ₃＝a·I _IN (16)

$I_4=b\·\frac{V_{\mathrm{ref}}}{R_{31}}---\left(17\right)$

$\mathrm{Ios}=$ $c\·$ $I_3=c\·\frac{a\·I_{\mathrm{IN}}\×b\·\frac{V_{\mathrm{ref}}}{R_{31}}}{\mathrm{Icon}}=K\·I_{\mathrm{IN}}$ $\left(18\right)$

$K=a\·b\·c\·\frac{\mathrm{Vref}}{\mathrm{Icon}}\·\frac{1}{R_{31}}---\left(19\right)$

Adopt the technical solution of the utility model, the restriction electricity circuit that this kind is used for the PWM power supply control chip has the compensating circuit that is integrated in PWM power supply control chip inside, sheet need not to add any compensating device outward, only needs a resistance just can guarantee that the peak power output of Flyback transducer does not change with the difference of input voltage.Comprise the current switch that constitutes by diode and NMOS pipe in the compensating circuit, utilize the outer resistance monitoring input voltage V of sheet _InVariation, take into account system start-up simultaneously.Owing to only use an off chip resistor (saving the outer compensating network of sheet), reduced system power dissipation, and be convenient to the PCB layout.Be integrated with the electric current multiplier in the compensating circuit, in order to weaken the influence of integrated resistor absolute value and temperature coefficient to precision.

The foregoing description provides to being familiar with the person in the art and realizes or use the present invention/utility model; those skilled in the art can be under the situation of the invention thought that does not break away from the present invention/utility model; the foregoing description is made various modifications or variation; thereby the protection range of the present invention/utility model do not limit by the foregoing description, and should be the maximum magnitude that meets the inventive features that claims mention.

Claims (5)

1. a Power Limitation circuit that is used for the PWM power supply control chip is characterized in that, comprises being positioned over the outer starting resistance (R of PWM power supply control chip (A1) _StartuD) and be positioned in the PWM power supply control chip (A1) compensating circuit, wherein said compensating circuit comprises current switch (X0), electric current multiplier (X1), reference current source (X3) and current adder (X2), described starting resistance is connected between input voltage and the described current switch, and the power output maximum of described Power Limitation circuit is adjustable.

2. the Power Limitation circuit that is used for the PWM power supply control chip as claimed in claim 1 is characterized in that, described current switch comprises that one starts diode (D0) and switching tube (M1), described starting resistance (R _Startup) be connected between input voltage and the current switch, flow through starting resistance (R _Startup) input current I _INVariation be proportional to the variation of input voltage;

Before the chip enable, switching tube (M1) is closed, and starting current starts electric capacity (C by starting diode (D0) to one _Startup) charging, when starting electric capacity (C _Startup) voltage (V _Cc) surpassing the startup threshold value, switching tube (M1) is opened, and starts diode (D0) and oppositely ends input current I _INWhole inflow current multipliers (X1) and be I with input current IIN linear transformations by electric current multiplier (X1) _OsThe reference current I that current adder (X2) produces reference current source (X3) _RefWith I _OsSubtract each other and obtain I _SumAnd finish the current-voltage conversion, produce Power Limitation threshold voltage V _LimitI _INBe to be proportional to input voltage V _INFunction, Power Limitation threshold voltage V _LimitVariation and input voltage V _INBe varied to direct ratio, opposite in sign; By selecting starting resistance (R _Startup) the power output maximum of resistance Adjustment System under high input voltage and low input.

3. the Power Limitation circuit that is used for the PWM power supply control chip as claimed in claim 2 is characterized in that, in the described PWM of the being positioned over power supply control chip compensating circuit comprise:

Current switch (X0), electric current multiplier (X1), current adder (X2), reference current source (X3), buffer (X4), oscillator (X5), trigger (X6), first comparator (X7), second comparator (X8), NAND gate (X9) and under-voltage locking device (X10); Wherein said current switch (X0) comprises switching tube (M1) and starts diode (D0), switching tube (M1) drain electrode links to each other as the input of current switch (X0) with startup diode (D0) is anodal, starting diode (D0) negative pole links to each other with Vcc, switching tube (M1) grid links to each other with under-voltage locking device (X10) output, switching tube (M1) source electrode links to each other with electric current multiplier (X1) input, and electric current multiplier (X1) output links to each other with current adder (X2) negative input end; Reference current source (X3) links to each other with the positive input terminal of current adder (X2); The current signal of current adder (X2) output changes voltage signal into by resistance (R4), after buffer (X4) is isolated, as Power Limitation threshold voltage V _LimitLink to each other with the positive input terminal of second comparator (X8), the negative input end of first comparator (X7) and second comparator (X8) links to each other with the source end of power tube (M2); Primary current IL is at sampling resistor (R _s) on pressure drop be sampled voltage V _s

4. the Power Limitation circuit that is used for the PWM power supply control chip as claimed in claim 3 is characterized in that, in system's power up, under-voltage locking device (X10) is closed switching tube (M1), by starting resistance (R _Startup) input current I _INInflow current switch (X0) is given startup electric capacity (C by starting diode (D0) _Startup) charging; Work as V _CcWhen surpassing the actuation threshold threshold voltage, under-voltage locking device (X10) is opened switching tube (M1), starts diode (D0) and oppositely ends input current I _INAll flow to electric current multiplier (X1); PWM power supply control chip (A1) will be by the auxiliary winding power supply of a coil (T1); Input current I _INBe proportional to busbar voltage V _INVariation, input current I _INProcessing output current I through overcurrent multiplier (X1) _Os, I _OsLink to each other with the negative input end of current adder (X2); The positive input terminal of current adder (X2) links to each other with reference current source (X3), reference current source (X3) output reference current I _RefCurrent adder (X2) output current I _SumResistance (R4) is converted to voltage signal with current signal, isolates through buffer (X4), produces Power Limitation threshold voltage V _LimitV _LimitDetermine the maximum input current in former limit, and then determined system's peak power output.

5. the Power Limitation circuit that is used for the PWM power supply control chip as claimed in claim 3 is characterized in that sampled voltage V _sPeak be Power Limitation threshold voltage V _LimitSampling resistor (R _s) on sampled voltage V _sWith the electric current I that flows through in the power tube (M2) _LIncrease and increase; Second comparator (X8) is sampled voltage V relatively _sWith Power Limitation threshold voltage V _LimitAs sampled voltage V _sGreater than Power Limitation threshold voltage V _LimitThe time, second comparator (X8) output logic low level is to NAND gate (X9); NAND gate (X9) output logic high level, with trigger reset, switch-off power pipe (M2).

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