KR102427269B1 - Active clamp buck converter - Google Patents

Abstract

An embodiment relates to an active clamp buck converter.
Specifically, this buck converter is a step in which zero voltage switching of the first and second switches is possible by adding a first capacitor, a second switch, a first inductor, a second inductor, and a second diode to the existing buck converter as shown below. It is a step down converter structure.
The buck converter according to this embodiment is divided into a total of four structures, and this structure is characterized in that it consists of a square wave generator, a resonator, a rectifier, and an output filter.
Therefore, when power is converted through the buck converter through this, the switching loss from the switching element is reduced, and the driving reliability and the lifespan of the entire system are increased through high-speed switching.

Description

Active clamp buck converter

The present disclosure relates to the field of buck converter technology, and more particularly, to a technology for increasing the lifespan of an entire system through high-speed switching by reducing switching loss from a switching device when power is converted through a buck converter. .

Unless otherwise indicated herein, the material described in this section is not prior art to the claims of this application, and inclusion in this section is not an admission that it is prior art.

In general, voltage regulation is applied in various micro devices such as digital ICs, semiconductor memories, display modules, hard disk drives, RF circuits, microprocessors, digital signal processors and analog ICs, especially in cellular phones, notebook computers and consumer products. In battery-powered applications, it is often required to avoid variations in supply voltage.

Because the product's battery or DC input voltage often must be boosted to a higher DC voltage or stepped down to a lower DC voltage, these regulators are called DC-DC converters. A step-up converter, commonly referred to as a boost converter, is needed when the battery voltage is lower than the voltage required to power the load. The step-up converter may include an inductive switching regulator or a capacitive charge pump. In contrast, a step-down converter, often called a buck converter, is used when the battery voltage is higher than the desired load voltage. A step-down converter may include an inductive switching regulator, a capacitive charge pump, and a linear regulator.

The problems of such a conventional buck converter are as follows (see FIG. 1).

1. Switching loss occurs due to hard-switching of SW, reducing the efficiency of the circuit.

2. The switching loss due to the reverse recovery current of the diode increases.

3. Since this switching loss increases in proportion to the switch driving frequency, there is a limitation of high-speed switching to reduce the size and volume of the circuit.

4. When the input-output voltage conversion ratio (Vout = D x Vin) is large, the SW duty ratio (D) is too small, making it difficult to secure the SW on time in the high-speed switching frequency drive of SW.

ex) In case of Buck converter operating with input voltage 12V, output voltage 1.2V, switching frequency 500kHz, CCM, duty ratio D = 0.1. At this time, on time (DTs) of SW needs 0.2us. As the switching frequency increases, it becomes difficult to secure on time.

Prior art documents in this background are the following patent documents and the like.

(Patent Document 0001) KR1020110019 B1

For reference, the technique of Patent Document 1 above proposes a zero-current switching pseudo-resonant pulse width modulated buck converter including a snubber network having a characteristic that is halved in relation to the proposed technique. However, unlike the proposed technology, this converter is implemented by combining the previously introduced pseudo-resonant type with a folding snubber network composed of only passive elements.

The present disclosure aims to provide an active clamp buck converter capable of increasing driving reliability and overall system lifespan through high-speed switching by reducing switching loss from a switching element when power is converted through a buck converter.

Active clamp buck converter according to the embodiment,

A step down converter capable of zero voltage switching of the first and second switches by adding a first capacitor, a second switch, a first inductor, a second inductor, and a second diode to the existing buck converter as shown below is the structure

The buck converter according to this embodiment is divided into a total of four structures, and this structure is characterized in that it consists of a square wave generator, a resonator, a rectifier, and an output filter.

More specifically, this active clamp buck converter comprises:

a first switch for switching the input AC power to a buck mode according to a control signal from the controller; and

a first diode that operates in a snubber configuration with respect to the power output generated by the first switch to be provided to the load side; contains,

a second switch that performs turn-on and turn-off complementary to the first switch;

a capacitor installed between the first switch and the second switch;

a first inductor installed between one end of the first switch and the capacitor and the first diode;

a second inductor installed between the first inductor and the first diode; and

a second diode connected to the first diode to form a rectifying unit; including,

a) when operating in the buck mode, generating a square wave by the input AC power supply, the first switch, the capacitor, and the second switch,

b) the first switch, the capacitor, the second switch, the first inductor, and the second inductor perform resonance, so that the first switch and the second switch are complementarily turned on and turned on - When performing off, zero voltage switching (ZVS) is performed using the current flow of the first inductor,

c) rectifying the generated square wave and the asymmetric AC waveform generated by the resonance by controlling the current gradient by the first diode and the second diode with the current flow of the first inductor; is characterized by

According to embodiments, when power conversion is performed through a buck converter, a switching loss from a switching device is reduced to increase driving reliability and lifespan of the entire system through high-speed switching.

1 is a circuit diagram showing the configuration of a general buck converter
2 is a circuit diagram illustrating the configuration of an active clamp buck converter according to an embodiment;
3 to 5 are diagrams for explaining an operation mode of a buck converter according to an embodiment
6 and 7 are views showing simulation results of a buck converter according to an embodiment;

2 is a circuit diagram illustrating a configuration of an active clamp buck converter according to an embodiment.

As shown in FIG. 2, the buck converter of one embodiment includes a first capacitor 112, a second switch 111, a first inductor 113, a second inductor 114, and a second diode in the conventional buck converter. By adding 115, it is a step down converter structure in which zero voltage switching of the first and second switches 101 and 111 is possible.

The buck converter according to this embodiment is divided into a total of four structures, and this structure includes a square wave generator, a resonator, a rectifier, and an output filter.

Specifically, such a buck converter consists of the following configuration.

That is, the buck converter is

Like the conventional buck converter, basically a first switch 101 for switching the input AC power to the buck mode according to the control signal of the control unit; and

a first diode (102) configured to operate in a snubber configuration with respect to the power output generated by the first switch (101) so as to be provided to the load side; contains

In this state, a second switch 111 that performs turn-on and turn-off complementary to the first switch 101;

a capacitor 112 installed between the first switch 101 and the second switch 111;

a first inductor 113 installed between one end of the first switch 101 and the capacitor 112 and the first diode;

a second inductor (114) installed between the first inductor (113) and the first diode (102); and

a second diode (115) connected to the first diode (102) to form a rectifier; includes

And, in this case, the following operation is performed.

a) That is, when operating in the buck mode, a square wave is generated by the input AC power supply, the first switch 102 , the capacitor 112 , and the second switch 111 .

b) And, by performing resonance by the first switch 102, the capacitor 112, the second switch 111, the first inductor 113, and the second inductor 114, When the first switch 101 and the second switch 111 complementarily turn-on and turn-off, zero voltage switching is performed using the current flow of the first inductor 113 .

c) In addition, as the generated square wave and the asymmetric AC waveform generated by the resonance are the current flow of the first inductor 113, the current gradient by the first diode 102 and the second diode 105 is controlled and rectified.

The operation of the buck converter according to this embodiment will be described as the four structures described above.

1. A square wave generator composed of Vin - SW1 - C1 - SW2.

- SW1 of the square wave generator is turned on for a time of D (Duty ratio) x Ts in one cycle (Ts).

- SW2 turns on for (1 - D) x Ts during Ts.

- C1 uses a capacitor large enough that VC1 (voltage across C1) voltage ripple is negligible.

의 전압을 유지한다.If we ignore the voltage ripple of VC1 in steady state

maintain the voltage of

- At this time, in Va, the voltage of VIN for the time of DTs and -VC1 for the time of (1 - D)Ts

A square wave of voltage is generated during the period of Ts.

2. Resonant part consisting of SW1 - C1 - SW2 - Lr - Lm (ZVS part)

- Design is required as Lr<<Lm.

- It is the same as the structure in which the transformer is removed from the LLC half-bridge structure composed of transformers.

- However, by using a sufficiently large value for C1, the switch voltage and current waveforms do not appear as sine waveforms.

- In the process of alternately turning on/off SW1 and SW2, the current flow of Lr is used to cause SW1 and SW2 to perform ZVS operation.

3. Rectification part composed of DO - Df

- Square wave - Converts an asymmetric AC waveform that has passed through the resonator to DC.

- Since the current slope of DO and Df is controlled by Lr, there is no switching loss due to the reverse recovery current.

4. L-C filter part composed of LO - CO

- It is the same as the existing buck converter structure, and the LO current waveform of the proposed circuit is the same as the inductor current waveform of the buck converter with the same input-output conditions.

In more detail, the operation mode of the buck converter according to this embodiment will be described below.

3 to 5 are diagrams for explaining an operation mode of a buck converter according to an embodiment.

Specifically, FIG. 3 is a view showing a total of six modes of a buck converter according to an embodiment. And, Figure 4 is a timing diagram of such a buck converter. In addition, FIG. 5 is a diagram for explaining the operation mode of the buck converter in more detail.

3 to 5, the buck converter according to an embodiment is divided into a total of six operation modes according to one cycle of alternating the first switch and the second switch.

1. Mode 1: t ₀ <t<t ₁

- As SW1's body diode turns on, SW1's ZVS starts.

- DO and Df maintain on state and SW2 maintains off state.

이므로, SW1의 전류는 V_IN/L_r의 기울기로 증가한다.-

Therefore, the current of SW1 increases with the slope of V _IN /L _r .

- Mode 1 is terminated as soon as the current of SW1 reaches 0.

2. Mode 2: t ₁ < t < t ₂

- The section where SW1 is fully turned on, the equivalent circuit is the same as in Mode1.

이므로, SW1의 전류는 V_IN/L_r의 기울기로 증가한다.-

Therefore, the current of SW1 increases with the slope of V _IN /L _r .

- Mode 2 is terminated as soon as the current (iDf) of Df reaches zero.

3. Mode 3: t ₂ < t < t ₃

- Df turns off, SW1, DO keep on, SW2 keeps off.

가 되므로, SW1의 전류는 (V_IN-v_Lm)/L_r의 기울기로 증가한다.-

Therefore, the current of SW1 increases with a slope of (V _IN -v _Lm )/L _r .

- Mode 3 ends when SW1 turns off.

4. Mode 4: t ₃ < t < t ₄

- SW1 is turn-off, Df is turn-on, and SW2's body diode turns on and SW2's ZVS turn-on starts. DO remains on.

가 되므로, SW2의 전류는 (V_C)/L_r의 기울기로 증가한다.-

Since , the current of SW2 increases with a slope of (V _C )/L _r .

- Mode 4 is terminated as soon as the current of SW2 reaches zero.

5. Mode 5: t ₄ < t < t ₅

- SW2 is fully turned on. Since it is the same as the equivalent circuit of mode 4, the current of SW2 increases with a slope of (V _C )/L _r .

- Mode 5 is terminated as soon as the current of DO reaches zero.

6. Mode 6: t ₅ < t < t ₆

- DO is turned off, SW1 is off, SW2, and Df remain on.

가 되므로, SW2의 전류는

의 기울기로 증가한다.-

, so the current in SW2 is

increases with the slope of

- Mode 6 ends the moment SW1 turns on.

6 and 7 are diagrams showing simulation results of a buck converter according to an embodiment.

Specifically, FIG. 6 is a diagram comparing the switch voltage and current waveforms of a buck converter and a conventional buck according to an embodiment. And, FIG. 7 is a diagram comparing diode current waveforms of a buck converter and a conventional buck according to an embodiment.

First, before describing the simulation of the buck converter according to an embodiment, the following case is first assumed.

1. Using the PSIM simulator, compare the switch voltage current and diode current of the proposed circuit and the basic buck converter.

The simulation conditions are as follows.

- Input voltage V _IN =12V, output voltage V _O =1.8V, switching frequency f _sw =350kHz, output resistance 1Ω, diodes are modeled with reverse recovery current, and all devices other than diodes are ideal.

- Device values of the proposed circuit: Lr = 3uH, Lm = 80uH, Lo = 10uH, C1 = 10uF, Co = 50uF

- conventionalbuck device value: Lo = 10uH, Co = 50uF

* Comparison of switch voltage and current waveforms of the proposed circuit and conventional buck (see Fig. 6)

1. - Securing Duty Ratio: Under the same switching frequency and input/output conditions, the duty ratio of the proposed circuit is 0.34 and that of the conventional buck converter is 0.16. Therefore, it can be seen that the proposed circuit is advantageous for securing switching on-time when the input-output conversion ratio is large in high-speed switching operation.

- Reverse recovery current characteristics of diode: In the case of conventional buck converter, peak 5.61A current (reverse recovery current) generated from the diode flows into SW the moment SW is turned on. This drive has the problem of increasing the switching turn-on loss. Also, a voltage peak (77.5V) occurs when the switch turns off due to the parasitic inductance of the diode. To improve this voltage peak, a separate snubber circuit must be added to the switch or diode. In the case of the proposed circuit, the reverse recovery current peak generated by the diode is limited by Lr, and the switching turn-on loss does not occur due to the diode reverse recovery current because it does not flow into the switch the moment each switch is turned on.

-ZVS characteristics: Switching turn-on loss does not occur in SW1 and SW2 of the proposed circuit while performing zero voltage switching, whereas in the conventional buck converter, switching turn-on loss occurs due to hard switching.

* Comparison of the diode current waveform between the proposed circuit and the conventional buck (see Fig. 7)

- Improved diode reverse recovery current characteristics: at the same switching frequency and input-output conditions

In the diode of the conventional buck converter, a reverse recovery peak current of 4.04A occurs.

This current flows into the switch at the moment the switch SW is turned on and causes switching turn-on damage.

Increase the thread sharply. On the other hand, in the proposed circuit, until DO and Df turn-off

As the slope of the current decreased by Lr, the reverse recovery peak current was 0.28A, respectively.

improved to 0.54A. In addition, the reverse recovery current generated in the proposed circuit is

Because it flows into the switch at the moment it is fully turned on, not the moment when it is turned on, the diode

Switching turn-on loss does not occur due to the generated reverse recovery current.

On the other hand, when the buck converter according to this embodiment additionally performs the switching as described above, by stabilizing the switching output voltage from the configuration according to the embodiment below, the effect of increasing the power density of a more improved circuit, etc. get

To this end, the configuration is made as follows.

That is, in the above configuration, sub-diodes having different numbers of negative characteristics (-) according to the target temperature are connected to the input side of the first switch to stabilize the output voltage for each target temperature.

In other words, this configuration implements improved voltage stability by implementing voltage stability from the means for temperature compensation in which the resistance value decreases as the temperature increases when switching for power conversion.

In addition, when stabilizing the output voltage in this way, a resistor is additionally connected to the sub-diode to achieve improved stabilization of the output voltage.

In addition, in this case, a plurality of the resistors are connected in series, and the plurality of resistors have the same resistance value, thereby achieving more improved output voltage stabilization.

101: first switch 102: first diode
111: second switch 112: capacitor
113: first inductor 114: second inductor
115: second diode

Claims (5)

a first switch 101 for switching the input AC power to the buck mode according to the control signal of the controller; and
a first diode (102) configured to operate in a snubber configuration with respect to the power output generated by the first switch (101) so as to be provided to the load side; contains,

a second switch 111 performing turn-on and turn-off complementary to the first switch 101;
a capacitor 112 installed between the first switch 101 and the second switch 111;
a first inductor (113) installed between one end of the first switch (101) and the capacitor (112) and the first diode (102);
a second inductor (114) installed between the first inductor (113) and the first diode (102); and
a second diode (105) connected to the first diode (102) to form a rectifier; including,

a) when operating in the buck mode, generating a square wave by the input AC power supply, the first switch 101, the capacitor 112, and the second switch 111,
b) Resonance is performed by the first switch 101, the capacitor 112, the second switch 111, the first inductor 113, and the second inductor 114, so that the first When the switch 101 and the second switch 111 complementarily perform turn-on and turn-off, zero voltage switching (ZVS) using the current flow of the first inductor 113 is used. ) and
c) the generated square wave and the asymmetric AC waveform generated by the resonance to the current flow of the first inductor 113, the current slope by the first diode 102 and the second diode 105 is controlled, rectifying; Active clamp buck converter featuring a. delete delete delete delete

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