KR20160079463A - Switching mode power supply for constant current control with improved stability, and operating method thereof - Google Patents

Abstract

According to an embodiment of the present invention, a switching mode power supply for constant current control comprises: an oscillation unit to generate an oscillation signal having a predetermined switching period and a charging/discharging current; a conduction time detection unit to detect conduction time based on a first detection voltage by a current flowing through an auxiliary coil of a transformer having a primary coil, a secondary coil, and the auxiliary coil; an intermediate voltage calculation unit to calculate an intermediate voltage based on the charging/discharging current and the conduction time; a turnoff control unit to compare a second detection voltage by a current flowing through a power switch for adjusting conduction of the primary coil and the intermediate voltage to perform charging and discharging based on a comparison result to generate a turnoff signal; and a pulse width modulation (PWM) control unit to control a switching operation of the power switch based on the oscillation signal and the turnoff signal. The turnoff control unit uses a predetermined base current to perform charging, and uses the predetermined base current and a reference current to perform discharging to perform discharging faster than charging.

Description

TECHNICAL FIELD [0001] The present invention relates to a switching mode power supply for constant current control with improved stability and a method of operating the same.

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a switching mode power supply for constant current control which can be applied to an adapter of a mobile device and has improved stability and an operation method thereof.

In a compact switching mode power supply device, a primary side control technique for controlling an output voltage and an output current using voltage information of a transformer auxiliary winding without using an optocoupler is becoming mainstream. In the primary side control, the control method differs depending on whether the current waveform of the primary winding of the transformer is DCM (Discontinuous Current Mode) or CCM (Continuous Current Mode).

In general, the primary side control of the DCM is known in the most common manner, and accurate control of the output current can be realized.

On the other hand, the primary-side control of the CCM is advantageous for miniaturization, but it is disadvantageous that precision control is difficult

Therefore, the CCM method, which is advantageous for miniaturization, can be applied to the current regulator applied to a small-sized mobile device, and it is difficult to precisely control the current regulator. Therefore, it is necessary to develop a technique that can solve such shortcomings.

Patent Document 1 described in the following prior art documents relates to a switching mode power supply and a driving method, but does not provide a solution to the above-mentioned problem.

Korean Patent Publication No. 2008-0048754

An embodiment of the present invention is a switching mode power supply device for a constant current control which is applicable to an adapter of a mobile device and which is suitable for miniaturization and has improved precision control performance compared with existing products of the same size, ≪ / RTI >

According to an embodiment of the present invention, an oscillation unit generates an oscillation signal and a charge / discharge current having a preset switching period. An energization time detector for detecting an energization time based on a first detection voltage due to a current flowing through an auxiliary winding of a transformer having a primary winding, a secondary winding, and an auxiliary winding; An intermediate voltage calculation unit for calculating an intermediate voltage based on the charge / discharge current and the energization time; A turn-off control unit for comparing a second detected voltage due to a current flowing through a power switch for controlling energization of the primary winding and the intermediate voltage, and performing charging and discharging based on the comparison result to generate a turn-off signal; And a PWM (pulse width modulation) controller for controlling the switching operation of the power switch based on the oscillation signal and the turn-off signal; Wherein the turn-off control unit performs charging using the preset basic current and performs discharging using the preset basic current and the reference current, thereby switching the constant current control switching mode A power supply is proposed.

Also, according to an embodiment of the present invention, there is provided a method of generating an oscillation signal,

The energization time detecting unit detecting energization time based on a first detection voltage by a current flowing through an auxiliary winding of a transformer having a primary winding, a secondary winding, and an auxiliary winding; Calculating an intermediate voltage based on the charging / discharging current and the energizing time; The turn-off control unit compares the second detected voltage by the current flowing through the power switch for controlling the energization of the primary winding and the intermediate voltage, and performs charging and discharging based on the comparison result to generate a turn-off signal ; And a PWM (Pulse Width Modulation) control unit controlling the switching operation of the power switch based on the oscillation signal and the turn-off signal; Wherein the step of generating the turn-off signal includes the steps of: charging is performed using a predetermined basic current; discharging is performed using a preset basic current and a reference current, thereby discharging is performed faster than charging; An operation method of a switching mode power supply for constant current control is proposed.

Industrial Applicability According to the present invention, it is possible to apply to an adapter of a mobile device, which is suitable for small-sized manufacturing, and improves precision control performance and stability compared to existing products of the same size.

In addition, in generating the turn-off signal through the charging and discharging operations, charging is performed using the basic current ia, discharging is performed using the basic current ia and the reference current iramp, Discharge can be performed more quickly than in the case where the discharge is performed, so that a more stable operation becomes possible.

1 is a block diagram of a switching mode power supply apparatus according to an exemplary embodiment of the present invention.
2 is a current and voltage waveform diagram of a switching mode power supply device according to an embodiment of the present invention.
3 is a circuit diagram showing an embodiment of an intermediate voltage calculation unit according to an embodiment of the present invention.
4 is a timing chart of main current and voltage of the intermediate voltage calculation unit according to an embodiment of the present invention.
5 is a circuit diagram showing an embodiment of a turn-off control unit according to an embodiment of the present invention.
FIG. 6A is a waveform diagram of a conventional second detection voltage, a charge voltage, and a gate signal, and FIG. 6B is a waveform diagram of a second detection voltage, a charge voltage, and a gate signal according to an embodiment of the present invention.
7 is a flowchart illustrating an operation method of a switching mode power supply apparatus according to an embodiment of the present invention.

Hereinafter, the present invention is not limited to the embodiments described. In addition, in each embodiment of the present invention, the structure, shape, and numerical value described as an example are merely examples for helping understanding the technical matters of the present invention, and thus can be variously changed. All or some of each of the embodiments of the present invention may be selectively combined with each other. In the drawings referred to in the present invention, components having substantially the same configuration and function as those of the present invention will be denoted by the same reference numerals.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, in order that those skilled in the art may easily implement the present invention.

1 is a block diagram of a switching mode power supply apparatus according to an embodiment of the present invention.

1, a switching mode power supply apparatus according to an embodiment of the present invention includes a transformer 50, a power switch 60, a detection resistor RS, detection resistance circuits R11 and R12, an oscillation unit 100, An energization time detector 200, an intermediate voltage calculator 300, a turn-off controller 400, and a PWM (Pulse Width Modulation) controller 500.

The transformer 50 may include a primary winding L10, a secondary winding L20 and an auxiliary winding Laux. The transformer 50 may include a primary winding L10, a secondary winding L20, The secondary side energy can be transferred to the secondary side energy, so that the transformer 50 can convert the input voltage Vin into the output voltage Vout. Further, the energy can be transferred according to the winding ratio of the primary winding L10 and the auxiliary winding Laux.

At this time, the current flowing in the primary winding of the transformer can be controlled according to the switching operation of the power switch 60, which will be described later.

The detection resistor RS can detect the second detection voltage Vcs by the current Ipri flowing through the power switch 60 that regulates the energization of the primary winding L10 of the transformer 50 . Here, the power switch 60 may be an NMOS transistor MN.

The detection resistor circuit R11 and R12 can detect the first detection voltage Vs by the current Isec flowing through the auxiliary winding Laux of the transformer 50. [

The oscillation unit 100 can generate the oscillation signal Sosc, the charge / discharge current iosc, and the reference current iramp having the preset duty cycle Tsw with a predetermined switching period Tsw. The oscillation unit 100 may generate the reference current iramp and provide the generated reference current to the turn-off control unit 400 during a discharge operation of the turn-off control unit 400.

For example, the oscillation unit 100 may include an oscillation current source Iosc and a reference current source Iramp.

The energization time detection unit 200 can detect the energization time tson based on the first detection voltage Vs by the current Isec flowing through the auxiliary winding Laux of the transformer 50. [

For example, the energization time detecting unit 200 can detect a time at which the level of the first detection voltage Vs is maintained at the high level at the energization time tson.

The intermediate voltage calculation unit 300 can calculate the intermediate voltage Vmid based on the oscillation signal Sosc and the energization time tson.

For example, the intermediate voltage calculation unit 300 may calculate the intermediate voltage Vmid according to the following equation (1) based on the switching period Tsw of the oscillation signal Sosc and the energization time tson have.

The turn-off control unit 400 controls the turn-off control unit 400 so that the second detection voltage Vcs and the intermediate voltage Vmid due to the current Ipri flowing through the power switch 60, which controls the energization of the primary winding L10, And charging and discharging are performed based on the comparison result to generate the turn-off signal Soff. At this time, the turn-off control unit 400 may shorten the time required to discharge by using the predetermined reference current (iramp) rather than the time required for charging.

For example, the turn-off control unit 400 may control the turn-off control unit 400 such that the second detection voltage Vcs and the intermediate voltage Vmid become equal to each other at an intermediate point of time tM from the rising point t1 of the second detection voltage Vcs And discharging is performed using the basic current ia and the reference current iramp after the intermediate time point tM so as to discharge the charge The turn-off signal Soff having a turn-off level can be generated when the charge voltage due to the discharge becomes lower than a preset reference voltage.

The PWM control unit 500 can control the switching operation of the power switch 60 based on the oscillation signal Sosc and the turnoff signal Soff.

For example, the PWM control unit 500 generates a gate signal Sg having a turn-on level from the rising edge of the oscillation signal Sosc to the rising edge of the turn-off signal Soff, As shown in FIG.

2 is a current and voltage waveform diagram of a switching mode power supply device according to an embodiment of the present invention.

2 shows the waveform of the primary side current Ipri flowing through the primary winding L10 and the power switch 60 of the transformer 50 and the secondary side current Ipri flowing through the auxiliary winding Laux of the transistor 50, The waveform of the current Isec and the waveform of the first detection voltage Vs obtained by detecting the secondary side current Isec with the detection resistor circuits R11 and R12.

At this time, the output current Io is an average current of the secondary side current Isec, and can be expressed by the following equation (2).

In Equation 3, N1 is the number of turns of the primary winding L10 of the transformer, N2 is the number of turns of the secondary winding L20 of the transformer, and Vmid is the oscillation signal Sosc, Can be calculated based on the time tson, which is the intermediate voltage corresponding to the middle point of the magnitude of the primary current Ipri flowing through the power switch 60. [

Therefore, in order to keep the output voltage Io constant, the product of the intermediate voltage Vmid and the "energization time tson / switching period Tsw" Should be.

In Equation (3), when the constant const is k in Equation (1), the equations (1) and (3) can be expressed by the same equation, and the constant (k) Can be set in advance.

FIG. 3 is a circuit diagram showing an embodiment of an intermediate voltage calculation unit according to an embodiment of the present invention, and FIG. 4 is a timing chart of main current and voltage of an intermediate voltage calculation unit according to an embodiment of the present invention.

3, the intermediate voltage calculation unit 300 may include a first circuit unit 310, a second circuit unit 320, a third circuit unit 330, and a holding unit 340.

3 and 4, the first circuit unit 310 may generate the charged first voltage V1 using the charge / discharge current Iosc during the high level of the energization time tson . Here, the charging may be performed by a capacitor.

3, the first circuit unit 310 includes a first current source Iosc, a first switch Q11, and a first capacitor Ct1 in series between the driving voltage VDD and the ground. And a first discharging switch Q12 is connected in parallel to the first capacitor Ct1.

At this time, the first switch Q11 may be turned on or off according to the energization time tson signal to provide the first voltage V1 charged in the first capacitor Ct1.

Here, Iosc is the charge / discharge current, Vosc is the voltage of the capacitor, and Cosc is the charge / discharge capacitance.

The second circuit unit 320 may generate the charged second voltage V2 using the first voltage and the current based on the internal resistance R1.

3, the second circuit unit 320 includes a first operational amplifier OP1 for transferring the first voltage V1, a current mirror OP1 connected in parallel to the driving voltage VDD, And a transistor Q23 and a first resistor R1 are connected in series between one of the transistors Q21 and Q22 and the ground of the pair of transistors Q21 and Q22 . A second capacitor Ct2 is connected between the other one of the transistors Q21 and Q22 and the ground and a discharging switch Q24 is connected to the second capacitor Ct2 in parallel. .

The transistor Q23 operates according to the output of the operational amplifier OP1 and generates the first current I1 by the first voltage V1 and the first resistor R1, The current is mirrored to the second capacitor Ct2 and is supplied to the second capacitor Ct2 to charge the second capacitor Ct2 and the second voltage V2 charged in the second capacitor Ct2 ) May be provided.

When the second voltage exceeds the internal reference voltage, the third circuit unit 330 may generate the charged third voltage V3 using the current based on the predetermined basic current source Ia.

3, the third circuit unit 330 includes a first comparator comp1 for comparing a voltage charged by the second circuit unit 320 with an internal reference voltage, The second switch Q31 and the third capacitor Ct3 are connected in series between the first capacitor Ct2 and the ground and the third capacitor Ct3 is connected in parallel to the second capacitor Ct3, And a discharge switch Q32 is connected.

At this time, the second switch Q31 may be turned on or off according to the output signal of the first comparator comp1 to provide the third voltage V3 charged in the third capacitor Ct3.

The holding unit 340 may sample and hold the peak voltage of each cycle of the third voltage V3 to provide the intermediate voltage Vmid.

For example, the holding unit 340 may include an output switch SW1 for sampling a peak voltage of the third voltage charged by the third circuit unit 330, And an output capacitor Ct4 for maintaining the peak voltage of each period to provide the intermediate voltage Vmid.

In Equation (6), Ct1, Ct2, Ct3 and Cosc are capacitances, respectively.

5 is a circuit diagram showing an embodiment of a turn-off control unit according to an embodiment of the present invention.

5, the turn-off control unit 400 may include a comparison unit 410, a current mirror unit 420, a charge / discharge circuit unit 430, and an off-time detection unit 440. Referring to FIG.

The comparator 410 compares the second detection voltage Vcs with the intermediate voltage Vmid when the power switch 60 is on and provides a charge signal or a discharge signal according to the comparison result can do.

The comparator 410 includes a comparator 411 for comparing the second detection voltage Vcs input to the noninverting input terminal with the intermediate voltage Vmid input to the inverting input terminal of the comparator 411, And a NAND gate 412 for performing an NAND operation on the output signal and the gate signal Sg of the power switch 60.

The comparator 410 provides a signal for charging when the second detection voltage Vcs is lower than the intermediate voltage Vmid when the power switch 60 is on, If the second detection voltage Vcs is higher than the intermediate voltage Vmid when the power switch 60 is on, a signal for discharging can be provided. This can be referred to FIG.

The current mirror unit 420 may provide a charging current according to the basic current source Ia and provide a discharging current according to the basic current source Ia and the reference current source Iramp. Here, the reference current (iramp) of the reference current source Iramp may be provided during the discharging operation.

For example, the current mirror unit 420 includes a first transistor M21 for providing a current (ia) by the current source Ia and a current (iramp) of the reference current source Iramp, A second transistor M22 connected to the charging and discharging circuit unit 430 through a current mirror with the current mirror I21 and providing a current ia by the current source Ia to the charging and discharging circuit unit 430 as a charging current, Discharging the basic current ia of the basic current source Ia and the current iramp of the reference current source Iramp flowing through the second transistor M22 to the charging and discharging circuit unit 430, And a third transistor M23 serving as a current.

As a result, the current mirror unit 420 can supply the basic current ia of the basic current source Ia to the charge / discharge circuit unit 430 as a charging current, and the basic current ia of the basic current source Ia And the current (iramp) of the reference current source Iramp to the charge / discharge circuit unit 430 as a discharge current. Accordingly, since the discharge current flows more than the current (iramp) of the reference current source Iramp rather than the charge current, the discharge time can be shortened.

When the charging signal is input, the charging / discharging circuit unit 430 provides the charging voltage using the charging current. When the discharging signal is input, the charging voltage can be discharged using the discharging current .

For example, the charging and discharging circuit unit 430 is connected between the driving voltage and the charging and discharging capacitor Ccd, and is connected to the charging switches M31, M32 and discharge switches M33 and M34 which are connected between the charge and discharge capacitor Ccd and ground and operate to switch on and off in response to the output signal of the comparator 410. [

Accordingly, when the charging switches M31 and M32 are turned on, the charge / discharge capacitor Ccd is charged in accordance with the basic current ia of the basic current source Ia, and the discharge switches M33, The charging voltage of the charge / discharge capacitor Ccd may be discharged in accordance with the basic current ia of the basic current source Ia and the current iramp of the reference current source Iramp.

The off-time detection unit 440 compares the charging voltage of the charging / discharging circuit unit 430 with the internal reference voltage to generate an off signal Soff having an off level if the charging voltage is lower than the internal reference voltage.

At this time, the point at which the charging voltage is lower than the internal reference voltage can be further accelerated as the discharging time is shortened.

FIG. 6A is a waveform diagram of a conventional second detection voltage, a charge voltage, and a gate signal, and FIG. 6B is a waveform diagram of a second detection voltage, a charge voltage, and a gate signal according to an embodiment of the present invention.

6A and 6B are waveform diagrams of the second detection voltage, the charge voltage, and the gate signal. Referring to FIG. 6, the second detection voltage Vcs may be a trapezoidal waveform that gradually rises as the primary current Ipri gradually increases.

Referring to FIG. 6A, the basic current ia, which is the same current at the time of charging and discharging, is used, unlike the embodiment of the present invention. At this time, the gate signal Sg is undesirably large in pulse width and small in width The power switch operating in accordance with such a gate signal can be operated unstably. In order to prevent such an operation, it is necessary to adjust the width to be as small as possible when the pulse width is large.

5 and 6B, the comparator 410 compares the second detection voltage Vcs with the intermediate voltage Vmid. At this time, the second detection voltage Vcs is higher than the intermediate voltage Vss Vmid), the charging / discharging circuit unit 430 is charged using the charging current according to the output signal of the comparing unit 410. [ If the second detection voltage Vcs is higher than the intermediate voltage Vmid, the charge / discharge circuit unit 430 can discharge using the discharge current according to an output signal of the comparator 410.

5 and 6B, the comparator 410 compares the second detection voltage Vcs with the intermediate voltage Vmid. At this time, the second detection voltage Vcs is higher than the intermediate voltage Vss Vmid), the charging / discharging circuit unit 430 is charged using the charging current according to the output signal of the comparing unit 410. [ If the second detection voltage Vcs is higher than the intermediate voltage Vmid, the charge / discharge circuit unit 430 can discharge using the discharge current according to an output signal of the comparator 410.

Here, the charging current is determined by the basic current (ia), and the discharging current may be determined by the basic current (ia) and the reference current (iramp). The reference current (iramp) of the reference current source Iramp may be provided during a discharge operation after a predetermined time (tfill).

According to this operation, the charging voltage Vcd provided by the charging and discharging circuit unit 430 rises up to the intermediate time tM (charging operation) as shown in FIG. 6, (Discharging operation).

7 is a flowchart illustrating an operation method of a switching mode power supply apparatus according to an embodiment of the present invention.

A method of operating the switching mode power supply apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 to 7. FIG.

Hereinafter, the operation of the switching mode power supply according to the embodiment of the present invention will be described with reference to FIGS. 1 to 6, In the description, possible redundant descriptions may be omitted.

First, in step S100, the oscillation unit 100 may generate an oscillation signal Sosc having a preset switch period and duty ratio.

Next, in step S200, the energization time detecting unit 200 detects a current (a current) flowing through the auxiliary winding Laux of the transformer 50 having the primary winding L10, the secondary winding L20 and the auxiliary winding Laux It is possible to detect the energization time tson based on the first detection voltage Vs by Isec.

For example, in the step S200 of detecting the energization time, the energization time detector 200 detects a time at which the level of the first detection voltage Vs is maintained at the high level as the energization time tson .

Next, in step S300, the intermediate voltage calculation unit 300 can calculate the intermediate voltage Vmid based on the charge / discharge current Iosc and the energization time tson. For example, in the calculation of the intermediate voltage (S300), the intermediate voltage (Vmid) is calculated according to Equation (1) based on the switching period (Tsw) of the oscillation signal (Sosc) and the energization time Can be calculated.

Next, in step S400, the turn-off control unit 400 sets the second detection voltage Vcs by the current Ipri flowing through the power switch 60, which controls the energization of the primary winding L10, The voltage Vmid can be compared with each other and charging and discharging can be performed based on the comparison result to generate the turn-off signal Soff. At this time, in the step of generating the turn-off signal, it is possible to shorten the time required for discharging by using the preset reference current (iramp) rather than the time required for charging. The oscillation unit 100 may generate the reference current iramp and provide the generated reference current to the turn-off control unit 400 during the discharge operation of the turn-off control unit 400.

For example, in the step S400 of generating the turn-off signal Soff, the second detection voltage Vcs and the intermediate voltage Vmid are supplied from the rising point t1 of the second detection voltage Vcs, The charging is performed using the basic current ia set in advance during the period from the reference current ia to the same intermediate time tM, and after the intermediate time tM, Off signal (Soff) having a turn-off level when the charge voltage due to such charge / discharge becomes lower than a preset reference voltage.

In step S500, the PWM control unit 500 can control the switching operation of the power switch 60 based on the oscillation signal Sosc and the turn-off signal Soff.

For example, in the step S500 of generating the gate signal Sg, a gate signal Sg having a turn-on level from the rising edge of the oscillation signal Sosc to the rising edge of the turn-off signal Soff is generated To the power switch (60).

According to an embodiment of the present invention as described above, since it is a CCD type, it can be manufactured in a small size, and the on-time of the gate signal is determined based on the oscillation signal, So that more precise control is possible.

In addition, in generating the turn-off signal through the charging and discharging operations, charging is performed using the basic current ia, discharging is performed using the basic current ia and the reference current iramp, Discharge can be performed more quickly than in the case where the discharge is performed, so that a more stable operation becomes possible.

50: Transformer
60: Power switch
100:
200: energization time detecting section
300: intermediate voltage calculation unit
400: Turn-off control unit
500: Pulse Width Modulation (PWM)

Claims (14)

An oscillation unit for generating an oscillation signal and a charge / discharge current having a preset switching period;
An energization time detector for detecting an energization time based on a first detection voltage due to a current flowing through an auxiliary winding of a transformer having a primary winding, a secondary winding, and an auxiliary winding;
An intermediate voltage calculation unit for calculating an intermediate voltage based on the charge / discharge current and the energization time;
A turn-off control unit for comparing a second detected voltage due to a current flowing through a power switch for controlling energization of the primary winding and the intermediate voltage, and performing charging and discharging based on the comparison result to generate a turn-off signal; And
A PWM (pulse width modulation) controller for controlling the switching operation of the power switch based on the oscillation signal and the turn-off signal; Lt; / RTI >
The turn-off control unit performs charging using a preset basic current, performs discharging using a preset basic current and a reference current,
Switching mode power supply for constant current control.
The oscillator according to claim 1,
And generates the reference current to provide the reference current to the turn-off control unit during a discharge operation of the turn-off control unit.
The apparatus according to claim 1,
And the time when the level of the first detection voltage is maintained at the high level is detected as the energization time.
The apparatus as claimed in claim 1,
Based on the switching period of the oscillation signal and the energization time,

And the intermediate voltage is calculated in accordance with the constant voltage.
The apparatus of claim 1, wherein the turn-
Wherein charging is performed using a predetermined basic current for a period from a rise time point of the second detection voltage to an intermediate time point at which the second detection voltage and the intermediate voltage are equal to each other, Off signal when the charging voltage due to such charging / discharging becomes lower than a preset reference voltage by generating a turn-off signal having a turn-off level.
The apparatus of claim 1, wherein the PWM controller comprises:
And generates and supplies a gate signal having a turn-on level from a rising edge of the oscillation signal to a rising edge of the turn-off signal to the power switch.
The apparatus as claimed in claim 1,
A first circuit for generating a first voltage charged using the current of the oscillation signal during a high level of the energization time;
A second circuit for generating a second voltage charged by using the first voltage and the current due to the internal resistance;
A third circuit unit for generating a third voltage that is stacked by using a current based on a predetermined basic current source when the second voltage exceeds an internal reference voltage; And
A holding unit for sampling and holding a peak voltage of each cycle of the third voltage to provide the peak voltage as the intermediate voltage;
And a control unit for controlling the switching power supply.
The apparatus of claim 1, wherein the turn-
A comparator comparing the second detection voltage with the intermediate voltage when the power switch is on and providing a charging signal or a discharging signal according to the comparison result;
A current mirror unit providing a charging current according to a pre-charged basic current source and providing a discharging current according to the basic current source and the reference current source;
A charging / discharging circuit unit for supplying the charged voltage using the charging current when the charging signal is input, and discharging the charging voltage using the discharging current when the discharging signal is input; And
An off-timing detecting unit for comparing the charging voltage of the charge / discharge circuit unit with an internal reference voltage to generate an off signal having an off level if the charge voltage is lower than an internal reference voltage;
And a control unit for controlling the switching power supply.
Generating an oscillation signal by the oscillation unit;
The energization time detecting unit detecting energization time based on a first detection voltage by a current flowing through an auxiliary winding of a transformer having a primary winding, a secondary winding, and an auxiliary winding;
Calculating an intermediate voltage based on the charging / discharging current and the energizing time;
The turn-off control unit compares the second detected voltage by the current flowing through the power switch for controlling the energization of the primary winding and the intermediate voltage, and performs charging and discharging based on the comparison result to generate a turn-off signal ; And
Controlling a switching operation of the power switch based on the oscillation signal and the turn-off signal, the PWM (Pulse Width Modulation) control unit controlling the switching operation of the power switch; Lt; / RTI >
In the step of generating the turn-off signal, charging is performed using a predetermined basic current, and discharging is performed using a preset basic current and a reference current, thereby discharging is performed faster than charging
Method of operation of switching mode power supply for constant current control.
10. The method of claim 9, wherein generating the turn-
Wherein the oscillation unit generates the reference current and provides the reference current to the turn-off control unit during a discharge operation of the turn-off control unit.
10. The method according to claim 9, wherein the step of detecting the energization time comprises:
And the time when the level of the first detection voltage is maintained at the high level is detected as the energization time.
10. The method of claim 9, wherein calculating the intermediate voltage comprises:
Based on the switching period of the oscillation signal and the energization time,

Wherein the intermediate voltage is calculated according to the following equation.
10. The method of claim 9, wherein generating the turn-
Wherein charging is performed using a predetermined basic current for a period from a rise time point of the second detection voltage to an intermediate time point at which the second detection voltage and the intermediate voltage are equal to each other, Off signal when the charge voltage due to such charging / discharging becomes lower than a predetermined reference voltage by performing a discharging operation using a current to generate a turn-off signal.
10. The method of claim 9, wherein generating the gate signal comprises:
Generating a gate signal having a turn-on level from a rising edge of the oscillation signal to a rising edge of the turn-off signal and providing the gate signal to the power switch.

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