KR20150031802A - Voltage tracking circuit and buck converter with protecting function from over voltage - Google Patents

Abstract

The present invention relates to a voltage tracking circuit and to an over voltage protection buck converter having the same. According to an embodiment, the present invention tracks the variation of input voltage and outputs the voltage by generating output voltage which reflects the variation of the input voltage when the input voltage reaches within a specific range. The present invention generates the output voltage which reflects the variation of the voltage of the light source of a lighting device and controls the operation of the lighting device according to the output voltage.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a voltage follower circuit and an overvoltage protection buck converter having the voltage follower circuit,

The present invention relates to a voltage follower circuit and an overvoltage protection buck converter having the voltage follower circuit.

Recently, light emitting diodes (LEDs) have emerged as promising markets in the domestic lighting industry.

As part of efforts to save energy in developed countries, light emitting diodes are attracting attention.

Light emitting diodes (LEDs) are being introduced to the market, replacing the existing fluorescent lamp (FL) market, and adding emotional and multi-functional LED lighting products that are difficult to realize with conventional fluorescent lamps.

There is a problem that the light emitting diode is burned out due to the overvoltage of the power supply device in the lighting device in the lighting device using the conventional light emitting diode.

To solve this problem, a switching control chip having an OVP (Overvoltage Protection) pin has been developed. The switching control chip having the OVP pin blocks a switching control signal output to the switch when it is determined that an abnormal voltage or an overvoltage is applied to the OVP pin.

Such a switching control chip has to have an overvoltage protection circuit inside thereof, so that the number of parts increases, the volume increases, and the price becomes high.

In particular, when a switching control chip having an OVP pin is applied to a buck converter, the circuit becomes complicated.

The embodiment provides a voltage follower circuit that follows and outputs a variation amount of an input voltage.

Embodiments provide an overvoltage protection buck converter that controls the operation of the converter by sensing an overvoltage across the light source.

The voltage follow-up circuit includes: a first diode connected between a first node and a second node; A first resistor coupled between the first node and the third node; A second resistor coupled between the second and third nodes; A second diode connected between the third node and the ground; And a switching element connected to the first node and connected between the first node and the second node, wherein the switching element monitors the variation of the input voltage applied to the first node and outputs the output voltage to the second node Voltage follow-up circuit.

The voltage follow-up circuit according to an embodiment of the present invention is characterized in that at least one of the first and second diode units comprises a plurality of zener diodes connected in series.

The voltage follow-up circuit according to the embodiment is characterized in that the first diode portion has a first Zener voltage, the second diode portion has a second Zener voltage, and when the input voltage applied to the second node satisfies Equations 1 and 2 And outputs the output voltage following the variation amount of the input voltage.

Equation 1

Equation 2

At this time, the base voltage means 0V.

The voltage follow-up circuit according to the embodiment is such that the first zener voltage is larger than the second zener voltage.

The voltage follow-up circuit according to the embodiment may further include: a first diode connected between the second node and the output terminal of the switching element; And a second diode connected between a fourth node and a fifth node which is an output terminal of the switching device, and the output voltage is output to the fifth node.

The voltage follow-up circuit includes: a first diode connected between a first node and a second node; A first resistor coupled between the first node and the third node; A second resistor coupled between the second and third nodes; A second diode connected between the third node and the ground; And a switching element connected to the first node and connected between the first node and the second node, wherein when the input voltage applied to the first node is in a first voltage range, A voltage follower circuit in which a following output voltage is applied to the second node; And a buck converter having a driving chip for outputting a dimming signal and for stopping the follow-up voltage in a second voltage range, wherein an output voltage of the buck converter is applied to the first node of the voltage follow- Overvoltage Protection Buck Converter.

The voltage follow-up circuit according to the embodiment may further include: a first diode connected between the second node and the fourth node; A second diode coupled between the fourth node and the fifth node; Wherein the first and second diodes prevent reverse current flowing to the second node side and the follow-up voltage is applied to the fifth node.

The overvoltage protection buck converter according to an embodiment includes a plurality of zener diodes in which at least one of the first and second diode units is serially connected.

A voltage follower circuit according to an embodiment, wherein the first diode portion has a first Zener voltage and the second diode portion has a second Zener voltage, wherein the first voltage range corresponds to Equations (1) and (2).

Equation 1

Equation 2

The voltage follower circuit according to an embodiment, wherein the first zener voltage is greater than the second zener voltage.

The overvoltage protection buck converter according to the embodiment, wherein the output voltage of the voltage follower circuit corresponds to Equation (3) when the input voltage satisfies Equation (2).

Equation 3

However, the output voltage before variation has a larger value than the sum of the first zener voltage Vz1 and the second zener voltage Vz2, and the error is the difference voltage between the base terminal voltage of the switch and the source terminal voltage of the switch.

According to the embodiment, when the output voltage reaches a certain range of the input voltage, the output voltage reflecting the variation amount of the input voltage is generated and the output voltage following the variation amount of the input voltage can be outputted.

According to an embodiment, an output voltage reflecting a variation amount of a voltage applied to a light source can be generated, and the operation of the buck converter can be controlled according to the output voltage.

1 and 2 are voltage follow-up circuit diagrams according to a first embodiment of the present invention.
2 is a voltage follow-up circuit diagram according to a second embodiment of the present invention.
3 shows the operation of the voltage follower circuit.
4 is a block diagram of an overvoltage protection buck converter in accordance with an embodiment of the present invention.
5 is a circuit diagram of an overvoltage protection buck converter in accordance with an embodiment of the present invention.

Hereinafter, a voltage follower circuit and an overvoltage protection buck converter having the voltage follower circuit according to an embodiment of the present invention will be described in detail with reference to the drawings. The following embodiments are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention. Therefore, the present invention is not limited to the embodiments described below, but may be embodied in other forms. In the drawings, the size and thickness of an apparatus may be exaggerated for convenience. Like reference numerals designate like elements throughout the specification.

1 is a circuit diagram of a voltage tracking circuit according to a first embodiment of the present invention.

1, the voltage follow-up circuit 100 according to the first embodiment includes first and second diode units 110 and 120, first and second resistors R1 and R2, and a switch Q1. can do.

The first and second diode units 110 and 120 may include a plurality of Zener diodes.

When a reverse voltage is applied to a PN junction silicon diode having a high impurity concentration, the Zener diode hardly flows when the reverse voltage is low and the Zener effect in which a large amount of current flows at a specific voltage when the voltage is increased Is a diode used.

The voltage across the zener diode may increase in proportion to the voltage across the cathode until it reaches the Zener voltage. When a voltage across the Zener diode exceeds a Zener voltage, a Zener current flows to the Zener diode so that a voltage across the Zener diode can be maintained at a Zener voltage.

The first diode unit 110 may have a first zener voltage Zv1 and the second diode unit 120 may have a second zener voltage Zv2 that is lower than the first zener voltage Zvl. have.

The first and second diode units 110 and 120 may include a plurality of zener diodes connected in series in order to have a specific zener voltage.

The switch Q1 may be an N-channel transistor (MOSFET). Therefore, when a high level signal higher than the threshold voltage is applied to the base terminal of the transistor, the transistor is turned on. When the low level signal is applied to the base terminal of the transistor, a turn- .

The first diode unit 110 is connected between the first and second nodes, and the first resistor Rl is connected between the first node N1 And the second diode unit 120 is connected between the third node N2 and the third node N3 and the second resistor R2 is connected between the second and third nodes N2 and N3, And may be connected between the node N3 and the ground terminal.

The first node N1 may be a terminal to which an input voltage is applied, and the second node N2 may be a terminal to which an output voltage is applied.

The first and second diode units 110 and 120 may include a plurality of Zener diodes.

The Zener diode of the first diode unit 110 may have a cathode terminal connected to the first node N1 and an anode terminal connected to the second node N2.

The Zener diode of the second diode unit 120 may have a cathode terminal connected to the third node N3 and an anode terminal connected to the ground terminal.

The base terminal and the source terminal of the switch Q1 may be connected to the second node N2, and the drain terminal may be connected to the first node N1.

2 is a voltage follow-up circuit diagram according to a second embodiment of the present invention.

Referring to FIG. 2, the voltage follow-up circuit 100 according to the second embodiment may further include first and second diodes D1 and D2.

The cathode terminal of the first diode D1 may be connected to the second node N2, and the anode terminal may be connected to the fourth node N4.

The cathode terminal of the second diode D2 may be connected to the fifth node N5, and the anode terminal thereof may be connected to the fourth node N4.

The first and second diodes D1 and D2 may block the reverse current formed in the direction of the fifth node N5, the fourth node N4 and the second node N2.

When the voltage follower circuit 100 further includes the first and second diodes 110 and 120, the output voltage is latched at the fifth node N5.

The operation of the voltage follower circuit 100 according to the second embodiment will be described.

When the Zener voltage of the first diode section 110 of the voltage follow-up circuit 100 is the first Zener voltage Zv1 and the Zener voltage of the second diode section 120 is lower than the first Zener voltage Zv1, Zener voltage Zv2.

When the input voltage applied to the first node N1 varies with time, the voltage applied to the base terminal of the switch Q1 when the input voltage is lower than the second zener voltage Zv2 at the initial time, The voltage applied to the node N2 may be a voltage reflecting the variation of the input voltage following the input voltage.

When the input voltage increases to have a voltage corresponding to the voltage range between the first zener voltage Zv1 and the second zener voltage Zv2, the voltage across the second diode unit 120 is equal to the second zener voltage Zv2 And at the same time, the voltage applied to the base terminal of the switch Q1 can also maintain the second zener voltage Zv2.

The voltage of the first diode unit 110 may maintain the first zener voltage Zv1 when the input voltage increases and becomes higher than the first zener voltage Zv1. The voltage applied to the base terminal of the switch Q1 may be the follow-up voltage following the input voltage.

That is, when the input voltage fluctuates within a range larger than the first zener voltage Zv1, the voltage applied to the base terminal of the switch Q1 may vary by a variation amount of the input voltage. Therefore, the output voltage may have a voltage corresponding to Equation (1) below.

However, the output voltage before variation has a larger value than the sum of the first zener voltage Vz1 and the second zener voltage Vz2, and the error is the difference voltage between the base terminal voltage of the switch and the source terminal voltage of the switch.

The error in Equation (1) may be about 0.7 V, which is the voltage difference between the base terminal and the source terminal of the switching Q1.

3 is a diagram illustrating an operation of the voltage follower circuit 100 according to the embodiment.

The case where the input voltage applied to the first node N1 increases from 120V to 120V with a constant slope from 0V and drops from 120V to 0V will be described.

The first Zener voltage Zv1 was set to 80V and the second Zener voltage Zv2 was set to 20V.

Referring to FIG. 3, the input voltage applied to the first node N1 during the first time interval T1 increases from 0V to 20V.

The voltage applied to the base terminal of the second node N2, that is, the switch Q1 rises from 0V to 20V, and the voltage across the second diode section 120 also rises from 0V to 20V.

The voltage across the fifth node N5, which is an output terminal, can rise from 0V to 20V with a voltage substantially equal to the voltage applied to the base terminal of the switch Q1. However, the voltage applied to the base terminal of the switch Q1 and the voltage applied to the fifth node N5 may differ by about 0.7V.

This difference is a result of the voltage difference between the gate and source terminals of the switching element Q1.

The input voltage applied to the first node N1 during the second time period T2 increases from 20V to 100V.

Since the voltage applied to the second diode unit 120 is maintained at 20V, which is the second zener voltage Zv2, the voltage applied to the base terminal of the second node N2, that is, the switch Q1 can be maintained at 20V.

When the voltage applied to the base terminal of the switch Q1 is maintained at 20V, the voltage at the fifth node N5, which is an output terminal, can be maintained at 19.3V, which is a difference voltage between 20V and 0.7V.

A voltage across the first diode unit 110 may take a difference voltage between the voltages of the first and second nodes N1 and N2.

The input voltage applied to the first node N1 during the third time period T3 rises from 100V to 120V.

The voltage applied to the second diode unit 120 is maintained at 20V which is the second zener voltage Zv2 and the voltage applied to the first diode unit 110 is maintained at 80V which is the first zener voltage Zv1.

The voltage across the second node N2, the base terminal of the switch Q1, follows the input voltage.

In other words, a voltage added by a variation amount of the input voltage is applied at a voltage of 20V which is a voltage applied to the base terminal of the switch Q1.

For example, when the input voltage rises from 100V to 120V, the voltage applied to the base terminal of the switch Q1 may also rise from 20V to 40V. The voltage applied to the fifth node N5, which is an output terminal, may also increase from 19.3V to 20.3V to 39.3V.

The input voltage applied to the first node N1 during the fourth time period T4 drops from 120V to 100V.

The voltage applied to the second diode unit 120 is maintained at 20V which is the second zener voltage Zv2 and the voltage applied to the first diode unit 110 is maintained at 80V which is the first zener voltage Zv1.

The voltage across the second node N2, the base terminal of the switch Q1, follows the input voltage.

In other words, a voltage is subtracted from the 40V voltage applied to the base terminal of the switch Q1 by a variation amount of the input voltage.

For example, when the input voltage drops from 120V to 100V, the voltage applied to the base terminal of the switch Q1 may also drop from 40V to 20V. The voltage applied to the fifth node N5, which is an output terminal, may also take a voltage drop of 19.3 V from 39.3 V to 20 V. [

The input voltage applied to the first node N1 during the fifth time period T5 drops from 100V to 20V.

Since the voltage applied to the second diode unit 120 is maintained at 20V, which is the second zener voltage Zv2, the voltage applied to the base terminal of the second node N2, that is, the switch Q1 can be maintained at 20V.

When the voltage applied to the base terminal of the switch Q1 is maintained at 20V, the voltage at the fifth node N5, which is the output terminal, can be maintained at 19.3V, which is 20V-0.7V. A voltage across the first diode unit 110 may take a difference voltage between the voltages of the first and second nodes N1 and N2.

The input voltage applied to the first node N1 during the sixth time period T6 drops from 20V to 0V.

The voltage applied to the base terminal of the second node N2, that is, the switch Q1 drops from 20V to 0V, and the voltage across the second diode section 120 also falls from 2V to 0V.

The voltage across the fifth node N5 which is the output terminal can drop from 19.3V to 0V at a voltage substantially equal to the voltage applied to the base terminal of the switch Q1.

The voltage follow-up circuit 100 according to the embodiment is configured such that the output voltage follows the input voltage during the first and third time periods T1 and T2 when the input voltage rises and the variation amount of the input voltage is reflected on the output voltage, May fluctuate.

Since the output voltage follows the input voltage during the fourth and sixth time periods T4 and T6 during which the input voltage drops, the voltage drop of the input voltage may be reflected on the output voltage so that the output voltage may drop.

In summary, the output voltage across the fifth node N5 can follow the variation of the input voltage within a specific voltage range, and the voltage range over which the output voltage follows the input voltage is the first and second diode portions (Zv1, Zv2) of the Zener diodes included in the first, second, third,

When the Zener diode of the first diode unit 110 has the first Zener voltage Zv1 and the Zener diode of the second diode unit 120 has the second Zener voltage Zv2, Can follow the variation amount of the input voltage in the range of 0V to the second zener voltage (Zv2).

Also, the voltage of the fifth node N5 can follow the variation of the input voltage within the range of the input voltage> the first zener voltage Zv1 + the second zener voltage Zv2. That is, a voltage in a range corresponding to the following equations (2) and (3).

The voltage follower circuit 100 according to the embodiment can be used as an overvoltage protection circuit in a switching mode power supply.

The circuit type of the switching mode power supply includes a non-isolation type such as a buck type, a boost type, and a buck-boost type, and a flyback type, An isolation method such as a Forward method or a Push-pull method is available.

Hereinafter, a buck switching mode power supply which is difficult to apply the overvoltage protection circuit will be described as an embodiment, but the present invention is not limited thereto.

The detailed description of the matters which are well known to those skilled in the art will be omitted.

4 is a block diagram of an overvoltage protection buck converter 300 in accordance with an embodiment of the present invention.

Referring to FIG. 4, an overvoltage protection buck converter 300 according to an embodiment of the present invention may include a voltage follower circuit 100 and a buck converter circuit 200.

The buck converter 200 has a characteristic in which the output voltage is lower than the input voltage.

The buck converter 200 may include a rectifying unit 210, a compensating unit 220, a switching control chip 230, and an output unit 240.

The rectifying part 210 rectifies the AC voltage. For example, a bridge diode rectifying circuit, in other words, a bridge rectifier may be used for the rectifying part 210.

Bridge Diode The rectifier circuit is a bridge circuit that connects four diodes.

The bridge diode rectifier circuit can output a voltage of the same polarity regardless of whether a voltage of any polarity is inputted.

The compensation unit 220 can remove the ripple noise and can perform necessary compensation operation while the input voltage is fed back to the output voltage.

The switching control chip 230 receives a voltage rectified to the VCC terminal. The switching operation of the second switch Q1 can be controlled by repeating the switching operation of on / off at a predetermined frequency or adjusting the length of the on / off state.

The switching control chip 230 may be a PWM (Pulse-Width Modulation) IC (Integrated Circuit). When the voltage applied to the VCC terminal is higher than a specific voltage, the protection operation may be activated and not activated.

That is, if the input voltage exceeds the proper level, it can stop the driving to protect the entire circuit.

The output unit 240 may include a low-pass filter composed of an inductor L and a capacitor C, and may remove unnecessary AC components included in an output terminal of the output unit by the low-pass filter. The output voltage of the output unit 240 may be adjusted according to an on-off ratio, that is, a duty ratio of the second switch device Q2 controlled by the switching control chip 230. [

One or more LED light sources (not shown) may be connected to the output terminal of the output unit 240.

The voltage applied to the output terminal of the output unit 240, that is, the voltage applied to the LED light source, is applied to the first node N1, which is the input terminal of the voltage follow- The voltage of the fifth node N5, which is the output terminal of the voltage follower circuit 100, may be fed back to the VCC terminal of the buck converter 200. [

5 is a circuit diagram of an overvoltage protection buck converter 300 in accordance with an embodiment of the present invention.

Referring to FIG. 5, the rectifying unit 210 of the buck converter circuit unit 200 may include a full-wave rectifying circuit 210 including a diode and a first capacitor C1 connected in parallel thereto.

The full wave rectifying circuit 210 can rectify and output the input voltage, and the first capacitor C1 can remove the ripple of the rectified voltage.

The compensation unit 220 includes a second capacitor C2 connected to the Vc terminal of the switching control chip 230 to remove ripple noise of the rectified voltage, a third capacitor C3, a fourth capacitor C4, And a fourth resistor R4. The fourth capacitor (C4) and the fourth resistor (R4) connected in series with the third capacitor (C3) may be connected in parallel with each other.

They can function to compensate the output voltage.

The output unit 240 may include a fifth resistor R5, an inductor L and a fifth capacitor C5. The voltage between the fifth resistor (R5) and the inductor (L) is fed back to the SENSE terminal of the switching control chip (230).

The inductor (L) has a constant output voltage and the fifth capacitor (C5) can remove ripple noise.

The fifth resistor (R5) may measure the amount of current and feed back to the SENSE terminal.

The output voltage of the buck converter 200 may be supplied while the LED light source is connected to the input terminal of the voltage follower circuit 100.

The fifth node N5 which is the output terminal of the voltage follower circuit 100 is connected to the VCC terminal of the switching control chip 230 so that the output voltage of the voltage follower circuit 100 is connected to the VCC terminal . ≪ / RTI >

The operation of the overvoltage protection buck converter 300 will be described with a specific example.

When the driving stop voltage of the switching control chip 230 of the buck converter 200 is set to 35 V, when the voltage applied to the VCC terminal of the switching control chip 230 becomes 35 V, the switching control chip 230 Stops driving. Accordingly, when the rectified voltage becomes 35 V or more, the switching control chip 230 stops driving to protect the buck converter circuit unit 200.

On the other hand, when a voltage exceeding an appropriate level is applied to the LED light source connected to the output terminal of the buck converter 200 in the overvoltage protection buck converter 300 in which the voltage follower circuit 100 is connected to the buck converter circuit unit 200, It is necessary to protect the light source.

The overvoltage protection buck converter 300 according to the embodiment of the present invention stops driving the switching control chip 230 of the buck converter circuit unit 200 when the voltage exceeding the predetermined level is applied to the LED light source to protect the LED light source have.

For example, an appropriate voltage applied to the LED light source connected to the output terminal of the buck converter circuit part 200 is 100V.

If the voltage applied to the LED light source is over 115 V, the operation of the switching control chip 230 is stopped.

When the driving of the switching control chip 230 is stopped, power supplied to the LED light source is cut off, thereby preventing the LED light source from being burned.

The operation of the switching control chip 230 may be stopped when the voltage applied to the LED light source is 115 V or more and the switching control chip 230 may be restarted when the voltage applied to the LED light source is 115 V or less .

The first zener voltage Zv1 of the first diode section 110 of the voltage follow-up circuit 100 may be set to 80V and the second zener voltage Zv2 of the second diode section 120 may be set to 20V.

When the voltage applied to the LED light source is 100V, the voltage applied to the fifth node N5 of the voltage follower circuit 100 is 20V, so that the switching control chip 230 is in a driving state.

When the voltage applied to the LED light source rises at 100V, the voltage across the fifth node N5 also increases following the variation of the voltage at the first node N1. When the voltage applied to the LED light source is 115 V or more, the voltage variation of 15 V, which is the voltage variation of the first node N1, is reflected on the fifth node N5, and the voltage applied to the fifth node N5 is 35 V .

Since the fifth node N5 is connected to the VCC terminal, a voltage of 35 V or more is applied to the VCC terminal of the switching driver chip 230. Therefore, the switching drive chip 230 stops operating.

When the voltage applied to the LED light source is more than 115 V, which is an overvoltage, the buck converter 200 stops its operation and burn-out of the LED light source is prevented.

The switching control chip 230 has a function of stopping the drive when the input voltage becomes an overvoltage. When the voltage follower circuit 100 is connected to the switching control chip 230 and the voltage applied to the LED light source becomes an overvoltage The switching control chip 230 has a function of stopping the driving of the switching control chip 230.

According to the embodiment of the present invention, a buck converter that detects an overvoltage of a light source and operates only within an appropriate voltage range is formed by combining a switching control chip 230 having no overvoltage detection function of a light source part and a voltage follow- . Therefore, the number of parts is reduced and the circuit is simplified, thereby improving the yield and strengthening the price competition.

The voltage follow-up circuit 100 according to the embodiment is described for protecting the LED light source of the buck converter 200. However, the present invention is not limited to this, and may be applied to any circuit requiring a varying output voltage Lt; / RTI >

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

100. Voltage follower circuit
110. A semiconductor device comprising:
120. Second diode section
200. Buck converter
210. Rectifier
220. Compensation Department
230. Switching control chip
240. Output section
300. Overvoltage Protection Buck Converter

Claims (11)

A first diode connected between the first and second nodes;
A first resistor coupled between the first node and the third node;
A second resistor coupled between the second and third nodes;
A second diode connected between the third node and the ground; And
And a switching element connected to the first node and a control terminal connected between the first node and the second node,
And outputs an output voltage to the second node in response to a variation amount of an input voltage applied to the first node. The method according to claim 1,
Wherein at least one of the first and second diode units comprises a plurality of zener diodes connected in series. 3. The method of claim 2,
The first diode portion has a first Zener voltage,
The second diode portion has a second Zener voltage,
And outputs the output voltage following the variation amount of the input voltage when the input voltage applied to the second node satisfies Equations (1) and (2).
Equation 1

Equation 2

The method of claim 3,
Wherein the first zener voltage is greater than the second zener voltage. The method according to claim 1,
A first diode coupled between the second node and an output terminal of the switching device;
And a second diode connected between a fourth node and a fifth node which are output terminals of the switching element,
And the output voltage is output to the fifth node. A first diode connected between the first and second nodes; A first resistor coupled between the first node and the third node; A second resistor coupled between the second and third nodes; A second diode connected between the third node and the ground; And a switching element connected to the first node and connected between the first node and the second node, wherein when the input voltage applied to the first node is in a first voltage range, A voltage follower circuit in which a following output voltage is applied to the second node; And
And a buck converter having a driving chip for outputting a dimming signal and for stopping the operation of the tracking voltage in a second voltage range
Wherein the output voltage of the buck converter is coupled to the first node of the voltage follower circuit. The method according to claim 6,
A first diode coupled between the second node and the fourth node;
A second diode coupled between the fourth node and the fifth node;
The first and second diodes prevent reverse current flowing to the second node side,
Wherein the tracking voltage is applied to the fifth node. The method according to claim 6,
Wherein at least one of the first and second diode units comprises a plurality of zener diodes connected in series. 9. The method of claim 8,
The first diode portion has a first Zener voltage,
The second diode portion has a second Zener voltage,
Wherein the first voltage range corresponds to equations (1) and (2).
Equation 1

Equation 2

10. The method of claim 9,
Wherein the first zener voltage is greater than the second zener voltage. 11. The method of claim 10,
Wherein the output voltage of the voltage follower circuit corresponds to Equation (3) when the input voltage satisfies Equation (2).
Equation 3

However, the output voltage before variation has a larger value than the sum of the first zener voltage Vz1 and the second zener voltage Vz2, and the error is the difference voltage between the base terminal voltage of the switch and the source terminal voltage of the switch.

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