CN203301373U - Switching power supply and switching power supply controller for realizing constant output current - Google Patents

Abstract

The utility model provides a switching power supply and a switching power supply controller for realizing constant output current. The controller comprises: a turn-off time control circuit for determining the turn-off time; a comparator whose first input terminal receives a first reference Voltage, the second input terminal of which receives the sampling voltage of external input; the logic and driving circuit generates a driving signal according to the output signal of the off-time control circuit and the comparator, and the driving signal is used to control the on and off of the power switch off; the loop control module, its input terminal receives the sampling voltage, its output terminal is connected to the input terminal of the off-time control circuit, and is used to adjust the off-time so that the power switch is turned on during The average value of the sampling voltage is equal to the second reference voltage, wherein the first reference voltage is less than twice the second reference voltage. The utility model can precisely control the output current, so that the output current is not affected by parameters such as output voltage and input voltage.

Description

Switching power supply and switching power supply controller for realizing constant output current

technical field

The utility model relates to switching power supply technology, in particular to a switching power supply and a switching power supply controller for realizing constant output current.

Background technique

Referring to Fig. 1, in the traditional step-down LED drive circuit, when the power switch M1 is turned on, the on-time is Ton, and the input current flows through the power switch M1, the sampling resistor Rcs, the inductor L1 and the output load capacitor C1, and the inductor L1 The current on the capacitor increases, and the inductor L1 stores energy. At this time, the current flowing through the output load capacitor C1 and the output terminal is the same as the current flowing through the sampling resistor Rcs. When the current reaches the set value Vr1/Rcs, the output signal of the comparator 113 is reversed, and a corresponding trigger signal Reset is generated through the logic and driving circuit 112, so that the power switch M1 is turned off. The off-time Toff is determined by the off-time control circuit 111, and the off-time Toff is adjusted by an external resistor R1. After the power switch M1 is turned off, the current on the inductor L1 continues to flow through the freewheeling diode D1, flows through the freewheeling diode D1, the output load capacitor C1, and the output terminal, the current on the inductor L1 decreases, and the inductor L1 releases energy to the output load capacitor C1 and the output.

As shown in Figure 2, when the power switch M1 is turned on, it is assumed that the average current value flowing through the output load capacitor C1 and the output terminal is Iout1; when the upper power switch M1 is turned off, it is assumed that the average current value flowing through the output load capacitor C1 and the output terminal is Iout2 , when the circuit is in the inductor current continuous mode, Iout1 and Iout2 are the same. When the output voltage is fixed, since the peak current is fixed at Vr1/Rcs, and the off-time Toff is fixed, the drop value of the inductor current within the Toff time is fixed, so the current ripple is determined, and the output current can be fixed.

The switching power supply in Figure 1 realizes the output current control, the circuit is simple and the cost is low, but it also has disadvantages. When the output voltage changes, the off-time Toff remains unchanged, and the drop value of the inductor current within the same off-time Toff changes, so that the average output current changes, resulting in poor load regulation of the output current. And in the circuit of FIG. 1, due to unavoidable circuit delay, there is a turn-off delay time from the output signal of the comparator 113 to the turn-off of the power switch M1, and the peak current will continue to increase during the turn-off delay time, thus When the input voltage changes, the output current will also change, that is, the constant current characteristics of the circuit are not good enough, and the precision of constant current control is not enough.

Utility model content

The technical problem to be solved by the utility model is to provide a switching power supply and a switching power supply controller that realizes a constant output current, which can precisely control the output current, so that the output current is not affected by parameters such as output voltage and input voltage.

In order to solve the above technical problems, the utility model provides a switching power supply controller for realizing constant output current, including:

A turn-off time control circuit for determining the turn-off time of the power switch in the switching power supply;

a comparator whose first input terminal receives a first reference voltage, and whose second input terminal receives an externally input sampling voltage;

A logic and driving circuit, generating a driving signal according to the output signal of the off-time control circuit and the comparator, and the driving signal is used to control the turn-on and turn-off of the power switch;

A loop control module, whose input terminal receives the sampling voltage, and whose output terminal is connected to the input terminal of the off-time control circuit, and is used to adjust the off-time to make the sampling voltage during the turn-on period of the power switch The average value of the voltage is equal to the second reference voltage, wherein the first reference voltage is less than twice the second reference voltage.

According to an embodiment of the present invention, the loop control module includes: a transconductance amplifier whose output current is proportional to the difference between the second reference voltage and the sampling voltage during the conduction period of the power switch, and The output current is used to charge and discharge the compensation circuit. During the shutdown period of the power switch, the output current of the transconductance amplifier stops charging and discharging to the compensation circuit, and the voltage on the compensation circuit is used to adjust the The off-time generated by the off-time control circuit described above.

According to an embodiment of the present utility model, the first input terminal of the transconductance amplifier receives the sampling voltage, the second input terminal of the transconductance amplifier receives the second reference voltage, and the output of the transconductance amplifier terminal is connected to the first terminal of the first switch, the second terminal of the first switch is connected to the input terminal of the compensation circuit and the off-time control circuit, the control terminal of the first switch receives the driving signal, When the power switch is turned on, the first switch is turned on, and when the power switch is turned off, the first switch is turned off.

According to an embodiment of the present invention, the first input end of the transconductance amplifier is connected to the first end of the second switch and the first end of the third switch, and the second input end of the transconductance amplifier receives the first Two reference voltages, the output terminal of the transconductance amplifier is connected to the input terminal of the compensation circuit and the off-time control circuit, the second terminal of the second switch receives the sampling voltage, and the second switch of the second switch receives the sampling voltage. The control terminal receives the drive signal, the second terminal of the third switch receives the second reference voltage, the control terminal of the third switch receives the inverse signal of the drive signal, and the power switch is turned on During this period, the second switch is turned on and the third switch is turned off, and during the period when the power switch is turned off, the second switch is turned off and the third switch is turned on.

According to an embodiment of the present invention, when the sampling voltage reaches the first reference voltage, the output signal of the comparator causes the driving signal generated by the logic and driving circuit to turn off the power switch.

According to an embodiment of the present invention, after the time when the power switch is turned off reaches the off time, the output signal of the off time control circuit makes the driving signal generated by the logic and driving circuit turn on the power switch. power switch.

The utility model also provides a switching power supply, comprising:

The switching power supply controller described in any one of the above;

A freewheeling diode, the cathode of which receives the input voltage;

an output capacitor and an inductor connected in series, connected in parallel with the freewheeling diode;

A power switch whose first end is connected to the anode of the freewheeling diode, whose second end outputs the sampling voltage to the switching power supply controller, and whose control end receives the driving signal output by the switching power supply controller;

A sampling resistor, the first end of which is connected to the second end of the power switch, and the second end of which is grounded.

Compared with the prior art, the utility model has the following advantages:

The switching power supply controller of the embodiment of the utility model acquires the sampling voltage on the sampling resistor by sampling the power switch conduction device of the switching power supply, and performs loop adjustment on the off time through the loop control module to control the average value of the sampling voltage Keeping unchanged, using the characteristics of the switching power supply with a step-down structure in the continuous mode of the inductor current to achieve the purpose of constant output current.

Further, the loop control module of the embodiment of the utility model mainly includes a transconductance amplifier, which amplifies the error of the sampling voltage on the sampling resistor and the second reference voltage, and its output terminal is connected to the compensation circuit, and the voltage transmission on the compensation circuit The turn-off time control circuit is used to determine the turn-off time. After the loop is stable, the average value of the sampling voltage on the sampling resistor during the turn-on period of the power switch is the same as the second reference voltage, and the output current is determined by the second reference voltage and The resistance value of the sampling resistor is determined.

The switching power supply and the controller circuit of the embodiment of the utility model are simple, and the output current has no relationship with parameters such as input voltage, output voltage, inductance, etc., and can realize accurate constant current characteristics.

Description of drawings

Fig. 1 is a structural schematic diagram of a switching power supply in a step-down structure continuous working mode in the prior art;

Fig. 2 is a signal sequence diagram of the switching power supply shown in Fig. 1;

Fig. 3 is a schematic structural diagram of a switching power supply according to the first embodiment of the present invention;

4 is a schematic structural diagram of a switching power supply according to a second embodiment of the present invention;

Fig. 5 is a signal timing diagram of the switching power supply shown in Fig. 3 and Fig. 4;

Fig. 6 is a schematic diagram of the circuit structure of the transconductance amplifier in the switching power supply controller of the embodiment of the present invention.

Detailed ways

The utility model will be further described below in conjunction with specific embodiments and accompanying drawings, but the protection scope of the utility model should not be limited thereby.

Referring to FIG. 3 , the switching power supply in the first embodiment mainly includes: a power switch M1 , an inductor L1 , a sampling resistor Rcs, a freewheeling diode D1 , an output capacitor C1 and a switching power supply controller 300 .

Wherein, the negative pole of the freewheeling diode D1 receives the input voltage Vin, the first terminal of the output capacitor C1 is connected to the negative pole of the freewheeling diode D1, the first terminal of the inductor L1 is connected to the positive pole of the freewheeling diode D1, and the second terminal of the inductor L1 is connected to the output The second terminal of the capacitor C1, the first terminal of the power switch M1 is connected to the anode of the freewheeling diode D1, the second terminal of the power switch M1 is connected to the first terminal of the sampling resistor Rcs, and the control terminal of the power switch M1 receives the switching power supply controller 300 For the output driving signal GT, the first end of the sampling resistor Rcs is connected to the second end of the power switch M1, and the second end of the sampling resistor Rcs is grounded. The switching power supply controller 300 receives the sampling voltage on the sampling resistor Rcs and outputs the driving signal GT to The control terminal of the power switch M1 is used to control the turn-on and turn-off of the power switch M1.

Furthermore, the output capacitor C1 mainly plays the role of filtering the output current, reducing the ripple of the output current and the output voltage. The inductor L1 and the output capacitor C1 are connected in series, the connection positions of the two can be interchanged, and the output capacitor C1 is configured to be connected in parallel with the load.

When the power switch M1 is turned on, the inductor L1 stores energy. At this time, the current flowing through the inductor L1 is the same as the current flowing through the output capacitor C1 and the output terminal Vout, and the output current is the same as the current flowing through the sampling resistor Rcs. When the power switch M1 is turned off, the current flowing through the inductor L1 continues to flow through the freewheeling diode D1 to the output capacitor C1 and the output terminal Vout, and continues to transfer energy to the load. When the current of the inductor L1 is always greater than zero, the average current flowing through the inductor L1 when the power switch M1 is turned on is the same as the average current flowing through the inductor L1 when the power switch M1 is turned off, and is also the same as that flowing through the output capacitor C1 and the output terminal Vout same current.

The switching power supply controller 300 mainly includes: an off-time control circuit 311 , a logic and driving circuit 312 , a comparator 313 and a loop control module 310 .

Further, the first input terminal of the comparator circuit 313 receives the first reference voltage Vr1, the second input terminal is connected to the first terminal of the sampling resistor Rcs, when the sampling voltage on the sampling resistor Rcs is higher than the preset first reference voltage When Vr1 is reached, the output signal of the comparator 313 is reversed, and the shutdown signal Reset is output to the logic sum driving circuit 312 . The turn-off time control circuit 311 determines the turn-off time according to the control voltage Vc output by the loop control module 310, starts timing when the power switch M1 is turned off, and outputs the turn-on signal Set to the logic and driving circuit when the timing reaches the turn-off time 312. The logic and driving circuit 312 generates the driving signal GT according to the off-signal Reset and the on-signal Set output by the off-time control circuit 311 and the comparator 313, and is used to switch the on and off states of the power switch M1. When the on-signal Set arrives , the drive signal GT turns on the power switch M1 , and when the shutdown signal Reset arrives, the drive signal GT turns off the power switch M1 . The input end of the loop control module 310 receives the sampling voltage on the sampling resistor Rcs, and its output end generates the control voltage Vc, which is used to adjust the off time determined by the off time control circuit 311, so that the power switch M1 conducts The average value of the sampling voltage during the on period is equal to the second reference voltage Vr2, wherein the first reference voltage Vr1 is less than twice the second reference voltage Vr2.

It should be noted that, due to the off-time delay in the actual circuit, the sampling voltage when the actual power switch M1 is turned off is slightly higher than the first reference voltage Vr1 .

In the first embodiment, the loop control module 310 includes a transconductance amplifier 314 and a first switch S1. Wherein, the first input end of the transconductance amplifier 314 receives the sampling voltage, the second input end of the transconductance amplifier 314 receives the second reference voltage Vr2, the output end of the transconductance amplifier is connected to the first end of the first switch S1, and the first switch The second terminal of S1 is connected to the first terminal of the compensation capacitor C2 and the input terminal of the off-time control circuit 311 , the control terminal of the first switch S1 receives the driving signal GT, and the second terminal of the compensation capacitor C2 is grounded. When the power switch M1 is turned on, the first switch S1 is turned on, and when the power switch M1 is turned off, the first switch S1 is turned off.

Furthermore, the transconductance amplifier 314 works normally during the conduction period of the power switch M1, and the output current Igm of the transconductance amplifier 314 is a current proportional to the input voltage difference of the transconductance amplifier 314, that is, it is proportional to (Vr2-Vcs) The proportional value is specifically expressed as Igm=Gm*(Vr2-Vcs), where Gm is the transconductance of the transconductance amplifier 314, which is a constant value for a certain circuit, and Vr2 is the voltage value of the second reference voltage Vr2 , Vcs is the voltage value of the sampling voltage. When the power switch M1 is turned off, the connection between the transconductance amplifier 314 and the compensation capacitor C2 is disconnected. The output current Igm of the transconductance amplifier 314 is used to charge and discharge the compensation capacitor C2 to generate a control voltage Vc for adjusting the off time.

It can be seen from the negative feedback characteristics of the loop that when the output current is too large, the output current of the transconductance amplifier 314 is too small and the control voltage Vc is reduced, thereby making the off-time determined by the off-time control circuit 311 longer, so that regulation reduces the output current. The compensation capacitor C2 integrates the output current of the transconductance amplifier 314 to finally realize that the average values of the two input terminals of the transconductance amplifier 314 are equal. After the loop is stabilized, the control voltage Vc on the compensation capacitor C2 is stable, and the turn-off time is determined. .

In addition, those skilled in the art should understand that the compensation capacitor C2 can be replaced by other forms of compensation circuits such as series and parallel connections of resistors and capacitors, so as to adjust the stability and dynamic characteristics of the circuit.

The working principle of the switching power supply is as follows: during the conduction period of the power switch M1, there is a sampling voltage Vcs on the sampling resistor Rcs, and the sampling voltage Vcs is input to one input terminal of the transconductance amplifier 314, and the other input terminal of the transconductance amplifier 314 is connected to the second The reference voltage Vr2, the transconductance amplifier has the following characteristics: the output current Igm of the transconductance amplifier is proportional to the input difference voltage (Vr2-Vcs) of the transconductance amplifier 314, that is, Igm=Gm*(Vr2-Vcs), Gm is the transconductance The transconductance of the transconductance amplifier 314 is a constant value for a certain circuit, and the output terminal of the transconductance amplifier 314 is connected to the compensation circuit; The path of the power switch is disconnected; the voltage on the compensation circuit determines the turn-off time of the power switch M1; when the sampling voltage reaches the set first reference voltage Vr1, the power switch M1 is turned off; in order to ensure that the switching power supply is in the continuous mode of the inductor current, it is required The first reference voltage Vr1 is less than 2 times the second reference voltage Vr2. After the loop is stable, the average value of the output current Igm of the transconductance amplifier 314 is zero, and the constant output current of the entire switching power supply is the second reference voltage Vr2 and the sampling resistor. Ratio of Rcs.

Fig. 4 shows the structure of the switching power supply of the second embodiment, which is similar to the switching power supply shown in Fig. 3, only the specific structure of the loop control module is adjusted. As shown in FIG. 4 , the loop control module in the second embodiment includes a transconductance amplifier 314 , a second switch S2 and a third switch S3 . Wherein, the first input end of the transconductance amplifier 314 is connected to the first end of the second switch S2 and the first end of the third switch S3, the second input end of the transconductance amplifier 314 receives the second reference voltage Vr2, and the transconductance amplifier 314 The output terminal of the second switch S2 is connected to the input terminal of the compensation circuit and the off-time control circuit 311, the second terminal of the second switch S2 receives the sampling voltage, the control terminal of the second switch S2 receives the driving signal GT, and the second terminal of the third switch S3 receives The second reference voltage Vr2, the control terminal of the third switch receives the inverse signal of the driving signal GT, during the conduction period of the power switch M1, the second switch S2 is conducted and the third switch S3 is turned off, and during the period when the power switch M1 is turned off , the second switch S2 is turned off and the third switch S3 is turned on. More specifically, the inverted signal of the driving signal GT is generated by the inverter 315 .

In effect, during the conduction period of the power switch M1 , the negative input terminal of the transconductance amplifier 314 is connected to the sampling resistor Rcs, and the positive input terminal of the transconductance amplifier 314 receives the second reference voltage Vr2 . When the power switch M1 is turned off, both the positive input terminal and the negative input terminal of the transconductance amplifier 314 receive the second reference voltage Vr2 (of course, this potential can also be any other potential), as can be known from the characteristics of the transconductance amplifier 314, At this time, the output current of the transconductance amplifier 314 is zero, which is equivalent to disconnecting the connection between the transconductance amplifier 314 and the compensation capacitor C2, so its circuit function is equivalent to that of the loop control module in the first embodiment.

It should be noted that the figures shown in Fig. 3 and Fig. 4 are only examples. In fact, as long as the transconductance amplifier can charge and discharge to the compensation circuit when the power switch M1 is turned on, stop charging and discharging to the compensation circuit when the power switch M1 is turned off. Just charge and discharge.

Referring to FIG. 5 , FIG. 5 shows a working signal waveform diagram of the switching power supply shown in FIG. 3 and FIG. 4 . When the power switch M1 is turned on, it is assumed that the average current value flowing through the output capacitor C1 and the output terminal Vout is Iout1; when the power switch M1 is turned off, it is assumed that the average current value flowing through the output capacitor C1 and the output terminal Vout is Iout2. When the circuit is in the continuous mode of the inductor current, Iout1 and Iout2 should be the same, so in the present invention, by controlling Iout1, the output current of the entire switching cycle is correspondingly controlled.

When the inductor current is in continuous mode, assume that the current ripple of the output current Iout is Ib-Ia, where Ib is the peak current, Ia is the minimum current, some Ib is greater than Vr1/Rcs, and Vr2/Rcs=(Ib+Ia) /2, obviously Vr2/Rcs=(Ib+Ia)/2>Ib/2>Vr1/(2*Rcs), that is, Vr2>1/2*Vr1 can be obtained. Therefore, the first reference voltage Vr1 used as the peak current comparison point in this embodiment is smaller than twice the second reference voltage Vr2 used as the average current control point to ensure that the circuit works in the current continuous mode.

6 shows the specific circuit structure of the transconductance amplifier used in this embodiment, mainly including: current mirror 61, current mirror 62, current mirror 63, transistor Q1, transistor Q2, resistor R1, resistor R2 and current source I0.

Wherein, the current mirror 61 includes MOS transistors M3 and MOS transistors M7 , the current mirror 62 includes MOS transistors M2 and MOS transistors M4 , and the current mirror 63 includes MOS transistors M5 and M6 . The sampling voltage Vcs is input to the base of the transistor Q1, and the second reference voltage Vr2 is input to the base of the transistor Q2. Assuming that the mirror current ratio of MOS transistor M2 to MOS transistor M4 is K2, and the mirror ratio of MOS transistor M7 to MOS transistor M6 via MOS transistors M3 and M5 is K1, then the current I4 flowing through MOS transistor M4 is: I ₄ =K ₂ ·I ₂ , the current I6 flowing through the MOS transistor M6 is: I ₆ =K ₁ ·I ₁ . The output current Icomp of the entire transconductance amplifier is:

I _comp =I ₄ -I ₆ =K ₂ ·I ₂ -K ₁ ·I ₁

It is generally required that K1=K2=K, R1=R2=R, and the current I ₀ provided by the current source I ₀ is large enough to ensure that both I1 and I2 are greater than zero, then the following relationship is established:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; comp</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; K</span>}\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; rl</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; cs</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}}$

That is, the transconductance Gm is:

$\mathrm{<span\; class="notranslate">\; G\; m</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; comp</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; refl</span>}}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; K</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}$

After the circuit stabilizes, the current average value Icompavg of the output current Icomp is zero, that is

I _compavg =0

Therefore, the average value of the input sampling voltage Vcs is the same as the average value of the second reference voltage Vr2, and the average value of the sampling voltage Vcs divided by the resistance value of the sampling resistor Rcs is the average value of the output current of the switching power supply, thus the output of the switching power supply The current value of the current is Vr2/Rcs.

What is shown in FIG. 6 is only an example, and those skilled in the art should understand that the transconductance amplifier can also adopt any other suitable structure.

The above descriptions are only preferred embodiments of the present utility model, and are not intended to limit the present utility model in any form. Therefore, any simple modifications and equivalent transformations made to the above embodiments according to the technical essence of the present invention that do not deviate from the technical solution of the present utility model still belong to the protection scope of the technical solution of the present utility model.

Claims (7)

1. switch power controller of realizing constant output current comprises:

The turn-off time control circuit, for determining the turn-off time of Switching Power Supply power switch;

Comparator, its first input end receives the first reference voltage, and its second input receives the sampled voltage of outside input;

Logic and driver circuitry, produce the driving signal according to the output signal of described turn-off time control circuit and comparator, and this driving signal is for controlling the turn-on and turn-off of described power switch;

It is characterized in that,

The loop control module, its input receives described sampled voltage, its output is connected with the input of described turn-off time control circuit, for regulating the described turn-off time so that the mean value of described power switch described sampled voltage of conduction period equates with the second reference voltage, wherein, described the first reference voltage is less than 2 times of described the second reference voltage.

2. switch power controller according to claim 1, it is characterized in that, described loop control module comprises: trsanscondutance amplifier, in described power switch conduction period, its output current is directly proportional to the difference of described the second reference voltage and sampled voltage, and this output current is for discharging and recharging to compensating circuit, at described power switch blocking interval, the output current of described trsanscondutance amplifier stops discharging and recharging to described compensating circuit, the turn-off time that the voltage on described compensating circuit produces for regulating described turn-off time control circuit.

3. switch power controller according to claim 2, it is characterized in that, the first input end of described trsanscondutance amplifier receives described sampled voltage, the second input of described trsanscondutance amplifier receives described the second reference voltage, the output of described trsanscondutance amplifier connects the first end of the first switch, the second end of described the first switch connects the input of described compensating circuit and described turn-off time control circuit, the control end of described the first switch receives described driving signal, at described power switch described the first switch conduction of conduction period, at described the first switch of described power switch blocking interval, turn-off.

4. switch power controller according to claim 2, it is characterized in that, the first input end of described trsanscondutance amplifier connects the first end of second switch and the first end of the 3rd switch, the second input of described trsanscondutance amplifier receives described the second reference voltage, the output of described trsanscondutance amplifier connects the input of described compensating circuit and described turn-off time control circuit, the second termination of described second switch is received described sampled voltage, the control end of described second switch receives described driving signal, the second termination of described the 3rd switch is received described the second reference voltage, the control end of described the 3rd switch receives the inversion signal of described driving signal, in described power switch conduction period, described second switch conducting and described the 3rd switch turn-off, at described power switch blocking interval, described second switch turn-offs and described the 3rd switch conduction.

5. switch power controller according to claim 1, is characterized in that, when described sampled voltage reached described the first reference voltage, the driving signal that the output signal of described comparator makes described logic and driver circuitry produce turn-offed this power switch.

6. switch power controller according to claim 5, it is characterized in that, after the time that described power switch is turned off reaches the described turn-off time, this power switch of driving signal conduction that the output signal of described turn-off time control circuit makes described logic and driver circuitry produce.

7. a Switching Power Supply, is characterized in that, comprising:

The described switch power controller of any one in claim 1 to 6;

Fly-wheel diode, its negative pole receives input voltage;

Output capacitance and the inductance of series connection, in parallel with described fly-wheel diode;

Power switch, its first end connects the positive pole of described fly-wheel diode, and the described sampled voltage of its second end output is to described switch power controller, and its control end receives the driving signal of described switch power controller output;

Sampling resistor, its first end connects the second end of described power switch, its second end ground connection.

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