KR101701290B1 - Transformer Coupled Recycle Snubber Circuit - Google Patents

Abstract

Discloses a transformer-coupled reuse snubber circuit. To a snubber circuit capable of reducing switching loss and reusing transformer leakage inductance magnetic energy.

Description

Transformer Coupled Recycle Snubber Circuit [0002]

This embodiment relates to a transformer-combined reuse snubber circuit.

The contents described in this section merely provide background information on the present embodiment and do not constitute the prior art.

LEDs are widely used in lighting applications due to their high illumination efficiency and environmental friendliness. Some considerations for offline LED drivers are isolation, power factor and efficiency.

Insulated drivers in terms of insulation are excellent at safety issues, but non-insulated structures have advantages in terms of performance and cost effectiveness. Non-isolated LED drivers are classified into two types: a current source (CS) type and a switched-mode power supply (SMPS) type.

In a current source (CS) type LED driver, as shown in Figure 1 (a), the LED string is connected to the line voltage ( _vg ) Connected in series to a current source that can be programmed between ground and ground. The LED current is defined by a direct current source. Thus, a current source (CS) type LED driver has a simple structure and an easy operation principle.

The value of the current source for correcting the power factor in the current source (CS) type of LED driver is changed with a step of changing the number of active LED through an appropriate forward voltage drop of the line voltage step-by-step change v _g. Here, the V _LED must always be slightly smaller than the v _g for the current source operating in the saturation mode. Otherwise, the LED driver's current source will not operate normally. Thus, each current source has a _Vg and V _LED ( _vg - V _LED ). The higher v _g , the lower the efficiency of the LED fixed maximum. Thus, this type of LED driver is difficult to use in a wide range of input supply voltages.

A power supply (SMPS) type LED driver is suitable for a buck type LED driver because the line voltage v _g is much higher than the forward voltage V _{LED of the} LED. Power supply (SMPS) type LED drivers require several separate components, including inductors, but maintain high efficiency over a wide input voltage range. In addition, LED voltage is properly applied to all LED is available by controlling the power switch M _1. In order to maintain the simplicity of the auxiliary circuit in the LED driver, the power switch must be operated in hard switching, and such switching may result in reduced efficiency or permanently damage the switch. On the other hand, an additional power switch connected to the control block or an additional snubber inductor (passive) is required for soft switching operation, which increases the complexity of the LED driver.

The present embodiment aims to provide a snubber circuit that can reduce the switching loss and reuse the leakage inductance magnetic energy of the transformer.

According to an aspect of this embodiment, the primary winding N ₁ ; A secondary winding (N ₂₎ and a first snubber diode connected in series with the first series circuit (D _sn1) for receiving an induced electromotive force by the primary winding (N _1); A second Snubber diode (D _sn2 ) having one end connected to one end of the primary winding (N ₁ ) and the other end connected to one end of the first series circuit; And one end thereof is connected to one end of the first series circuit and the other end of the second snubber diode (D _sn2 ), and the other end thereof is connected to the other end of the first series circuit, Wherein the connection of the snubber capacitor C _sn includes a snubber capacitor C _sn connected via the power switch M ₁ .

As described above, according to the present embodiment, it is possible to reduce the construction cost of the LED driver and to provide a transformer-combined reuse snubber circuit having a power switch for soft switching operation, thereby improving the power conversion efficiency of the LED driver .

1 is a circuit diagram showing a general non-isolated LED driver.
2 is a circuit diagram showing an LED driver using a transformer-combined reuse snubber circuit according to the present embodiment.
3A to 3E are circuit diagrams illustrating an operation mode of the LED driver according to the present embodiment.
4 is a graph showing waveforms of operation modes of the LED driver according to the present embodiment.

Hereinafter, the present embodiment will be described in detail with reference to the accompanying drawings.

In this embodiment, a highly efficient offline LED driver is proposed. A buck converter of the LED driver according to this embodiment is used to achieve high efficiency over a wide input range. In addition, a transformer-coupled recycle snubber circuit (TCR Snubber) is used for the soft-switching operation of the power switch to improve reliability as well as power efficiency.

Hereinafter, the circuit design and operation principle of the LED driver according to the present embodiment will be described.

2 is a circuit diagram showing an LED driver using a transformer-combined reuse snubber circuit according to the present embodiment.

As shown in FIG. 2, the LED driver 100 according to the present embodiment includes a transformer coupled recycle snubber (TCR snubber). Here, the transformer-coupled reuse snubber circuit replaces the inductor of a buck converter of a typical LED driver. The transformer-combined reuse snubber circuit (TCR Snubber) according to the present embodiment includes two diodes (D _sn1 and D _sn2 ), one capacitor (C _sn ) and a secondary coil (N ₂ ) of a transformer sharing the core of the main inductor . The LED driver 100 shown in FIG. 2 is according to one embodiment, and not all of the components shown in FIG. 2 are essential components, and in some embodiments, some of the components included in the LED driver 100 are additionally, Changed or deleted.

The LED driver 100 is driven in a continuous conduction mode (CCM) or a discontinuous conduction mode (DCM) in terms of the conduction mode of the LED driver 100 according to the present embodiment .

LED driver 100 has the advantage of generally having low output current ripple when driven in continuous conduction mode (CCM). However, LED driver 100 is a free-wheeling diode (Freewheeling Diode, D _o) off (Off), and the flow of large reverse recovery current from the line voltage (v _g) to ground exists to the flow of this current is a power Reducing efficiency.

On the other hand, when the LED driver 100 is driven in the discontinuous conduction mode (DCM), the current remaining in the freewheeling diode D _o is zero. That is, there is almost no reverse recovery current of the LED driver 100. Accordingly, the LED driver according to the present embodiment is desirably designed to operate in a discontinuous conduction mode (DCM).

The switching of the power switch M ₁ by Zero-Current Switching (ZCS) in the LED driver 100 operates in discontinuous conduction mode (DCM). On the other hand, it is desirable to perform zero voltage switching (ZVS) while switching off the power switch M1, since switching reduces the power switch efficiency and damages the power switch. The LED driver 100 includes two leakage inductances L _lkg1 and L _lkg2 with two windings embedded _therein and a magnetization inductance L _m .

The transformer-combined reuse snubber circuit included in the LED driver 100 includes a transformer having a primary winding N ₁ and a secondary winding N ₂ , a transformer having an anode connected to one end of the secondary winding N ₂ , snubber diode (D _sn1), a first snubber diode, and its anode is connected to the cathode of the (D _sn1), first primary winding (N ₁₎ once the second snubber diode (D _sn2), and one end is the cathode is connected to the a first snubber diode is connected to the contact point of the anode of the cathode and the second snubber diode (D _sn2) of (D _sn1), the other end is connected to end and the other of the secondary winding (N _2), a secondary winding (N ₂ ) Includes a snubber capacitor C _sn connected via the power switch M ₁ .

The LED driver 100 includes an input capacitor C _in and a snubber capacitor C _{sn that} receive the magnetic energy of the leakage inductance of the secondary winding when the second snubber diode D _sn2 is turned on, the anode is connected to the contact power supply unit and a power switch (M ₁₎ connected in parallel to being, a first one the output diode (D _o) cathode is connected to the winding. The LED driver 100 includes an output capacitor C _o connected between the contact point of the snubber capacitor C _sn and the power switch M ₁ and the other end of the primary winding and a plurality of LEDs ) Connected in series and connected in parallel at both ends of the output capacitor. Herein, the input capacitor C _in receives the magnetic energy of the leakage inductance remaining after charging the snubber capacitor C _sn . The output diode D _o is turned on when all the voltages charged in the snubber capacitor C _sn are discharged to continuously output and discharge the magnetic energy of the magnetizing inductance L _m of the primary winding.

FIGS. 3A to 3E are circuit diagrams for explaining an operation mode of the LED driver according to the present embodiment, and FIG. 4 is a graph showing a waveform for each operation mode of the LED driver according to the present embodiment.

Hereinafter, the operation mode will be described for each mode of the LED driver 100. FIG.

- Mode I (t ₀ -t ₁₎ -

Mode I of the LED driver 100 starts with the power switch M ₁ turned on. The LED driver magnetization at 100, the inductance L _m the current is initially zero and increases linearly. On the other hand, the snubber capacitor C _sn is leaking by the second reflection voltage of the secondary coil inductance L N _{2 lkg2} And the diode D _sn1 .

- Mode II [t ₁ -t ₂ ] -

When the voltage v _sn of the snubber capacitor C _sn reaches the line voltage v _g , the LED driver 100 turns on the diode D _sn2 and _transfers the remaining energy of the leakage inductance L _lkg2 to the input capacitor C _in to be recycled.

- Mode III [t ₂ -t ₃ ] -

_After the energy of the leakage inductance L _lkg2 is completely transferred to the capacitor C _in , the diodes D _sn1 and D _sn2 of the LED driver 100 are cut off and the voltage v _sn of the snubber capacitor C _sn maintains the value of the line voltage v _g . Here, LED driver magnetizing inductance L _m of the current 100 subsequently increases linearly.

- Mode IV [t ₃ -t _4] -

When the power switch M ₁ is turned off in the LED driver 100, mode IV starts. Since the voltage v _sn of the snubber capacitor C _sn is equal to the line voltage v _g , it is delivered to the diode D _sn2 and at the same time the current path is immediately switched from the power switch M ₁ to the snubber capacitor C _sn and the diode D _sn2 . Here, the current path is via C _sn , D _sn2 , L _lkg1 , L _m and the outputs (C _o and LED).

Then, the snubber capacitor C _sn of the LED driver 100 is discharged, and the discharge energy is supplied to the plurality of LEDs. The drain voltage v _d of the power switch M ₁ rises slowly due to the snubber capacitor C _sn . Thus, the LED driver 100 is subjected to zero voltage switching (ZVS).

- Mode V [t ₄ -t ₅ ] -

When the snubber capacitor C _sn in the LED driver 100 is completely discharged, the drain voltage v _d of the power switch M ₁ reaches the line voltage v _g . Therefore, the output diode D _o is the energy that is stored on and the L _m is released is continuously output. The snubber network is not active during this period. Operation in mode V is identical to that of conventional buck converters when the switch is off.

In mode II, the maximum value of v _sn is designed to be higher than v _g for perfect zero voltage switching (ZVS) operation of M ₁ . On the other hand, if the snubber capacitor C _sn is has a voltage lower than the line voltage v _g, such as at the end of the mode III, the drain voltage of the power switch M ₁ is turned off immediately after the power switch bit jumps to M _1. This means that the LED driver 100 performs partial and incomplete zero voltage switching (ZVS).

Hereinafter, a theoretical analysis of each mode of the LED driver 100 according to the present embodiment will be described. In particular, an equation for designing the LED driver according to the present embodiment is calculated. To simplify the equation, it is assumed that there is no parasitic effect on L _lkg1 , L _lkg2 and C _OSS in operating the LED driver, and the diodes are assumed to be in an idle state. It is assumed in all the equations that L _m >> L _{lkg1 , 2} and C _sn >> C _OSS .

- Mode I (t ₀ -t ₁₎ -

When the power switch M ₁ is turned on, the reflected voltage of the secondary winding N ₂ changes from negative to positive. Thus, the snubber capacitor C _sn is charged by the resonance of the leakage inductance L _lkg2 and the snubber diode D _sn1 by the reflected voltage of the secondary winding N ₂ . In this case, the initial voltage of the snubber capacitor C _sn is zero, and the voltage v _sn of the snubber capacitor C _sn is estimated as shown in equation (1).

In Equation (1), w ₀ _ ₁ is expressed by Equation (2).

The current i _Csn of the snubber capacitor C _sn from Equation (1) is calculated by Equation (3).

Therefore, the current i _M1 of the power switch M ₁ is estimated as shown in Equation (4).

The current i _Lm of the magnetizing inductance (L _m ) in mode I is relatively small. The current i _Lm for charging the snubber capacitor C _sn increases sharply and generates a current peak. This current i _Lm increases the conduction loss. However, if the time interval for charging the snubber capacitor C _sn is sufficiently short, the additional conduction loss is also small.

When the power switch M ₁ is turned off for zero voltage switching (ZVS) in the LED driver 100, the expected maximum value of the voltage v _sn of the snubber capacitor C _sn is the line voltage v _g Or more.

Based on [Equation 1], the expected maximum value of the voltage v _sn is estimated as shown in [Equation 5].

- Mode II [t ₁ -t ₂ ] -

Upon reaching the LED driver 100 snubber capacitor C _sn voltage v _sn is the line voltage v _g in, snubber diode D is turned on _sn2. When the snubber diode D _sn2 is turned on, the remaining energy of the leakage inductance L _lkg2 is transferred to the input capacitor C _in to be recycled. Here, the voltage v _sn is a constant value, and the operation in which the voltage v _sn of the snubber capacitor C _sn reaches the line voltage v _g is expressed by Equation (6).

In mode II LED driver 100 has to calculate the current in the switch in the leakage inductance L _lkg2, t ₁ In order to estimate the current i of the power switch M _{1 M1.} On the basis of Equation (6), in the fact that the voltage v _sn (t ₁ ) is equal to the line voltage v _g , t ₁ is calculated as shown in Equation (7) on the basis of Equation (1).

LED driver 100 i _Csn (t ₁₎ is i _Llkg2 in fact equal to the (t _1), [Equation 7] [Equation 3] to the leakage inductance in the t ₁ of L _lkg2 current included in the i _Llkg2 (t ₁₎ is calculated as shown in equation 8].

In mode II the leakage inductance current of _lkg2 L is the line voltage v _g is the secondary winding N ₂ decreases linearly by the voltage difference between the reflected voltage of. Therefore, the current of the leakage inductance L _lkg2 is estimated by the following equation (9).

As a result, the current of the power switch M ₁ is calculated by the following equation (10).

- Mode III [t ₂ -t ₃ ] -

In the LED driver 100 of mode III, the energy of the leakage inductance L _lkg2 is completely transferred to the capacitor C _in . That is, in the fact that the leakage inductance L ₂ at t _lkg2 is zero, equation 8], and t ₂ from equation 9, is calculated by [Equation 11].

In mode III, the snubber diodes D _sn1 and D _sn2 are turned off after the energy of the leakage inductance L _lkg2 has been completely transferred to the capacitor C _in . Therefore, the voltage v _sn of the snubber capacitor C _sn is not changed as in Equation (12).

Here, the current of the power switch M ₁ is only iLm, and the current of the power switch M ₁ is as shown in Equation (13).

- Mode IV [t ₃ -t _4] -

In mode IV the power switch M ₁ is turned off and the energy stored in the snubber capacitor C _sn is transferred to the magnetizing inductance L _m along with the outputs C _o and LED s. Here, the current paths of the energy stored in the snubber capacitor C _sn pass through C _sn , D _sn2 , L _lkg1 , L _m, and the outputs (C _o and LED). Here, the voltage v _sn of the snubber capacitor C _sn is estimated as shown in Equation (14).

In Equation (14), w _{0 _ 4} is expressed by Equation (15).

In Equation (16), D is the duty ratio, and T represents the period of one switching cycle. Based on the equation (14), the drain voltage v _d of the power switch M ₁ is calculated by the following equation (16).

(16) is not intuitive by the two trigonometric functions, and it is assumed that the magnetization inductance L _m and the time constant of the snubber capacitor C _sn in Equation (17) are larger than the time interval of the mode IV do.

Therefore, [Equation 16] can be expressed by a simple first order Taylor series as shown in [Equation 18].

As expected, the approximate result according to Equation (18) is equal to the capacitor equalization of snubber capacitor C _sn . The drain voltage v _d of the power switch M ₁ rises slowly due to the snubber capacitor C _sn , which is subjected to zero voltage switching (ZVS).

- Mode V [t ₄ -t ₅ ] -

The energy stored in the snubber capacitor C _sn from the LED driver 100 when fully discharged, the output diode D _o is turned on, the snubber network maintains the disabled state until the next switching cycle. Here, the drain voltage v of the power switch M _{1 d} is fixed by the turned-on output diode D _o, the maximum drain voltage v _d of the power switch M ₁ from the LED driver 100 according to this embodiment is [Equation 19] Is equal to v _g , as shown in Fig.

The LED driver 100 according to the present embodiment has been proposed based on a buck converter for realizing a simple and highly efficient offline non-isolated LED driver. The LED driver 100 according to the present embodiment is a simple and low-cost structure while improving power efficiency, A transformer-coupled reuse snubber circuit (TCR snubber) is used. Because snubber inductors are integrated into the core (coupling inductor) of the main inductor, the snubber network requires only one additional capacitor and two diodes.

The transformer-combined reuse snubber circuit according to the present embodiment is described as being connected to only a plurality of LED modules having a plurality of LEDs (Lighting Emitting Diodes) connected in series. However, the present invention is not limited thereto. For example, a transformer-coupled reuse snubber circuit may be coupled to a load circuit comprising a plurality of loads connected in series.

The foregoing description is merely illustrative of the technical idea of the present embodiment, and various modifications and changes may be made to those skilled in the art without departing from the essential characteristics of the embodiments. Therefore, the present embodiments are to be construed as illustrative rather than restrictive, and the scope of the technical idea of the present embodiment is not limited by these embodiments. The scope of protection of the present embodiment should be construed according to the following claims, and all technical ideas within the scope of equivalents thereof should be construed as being included in the scope of the present invention.

100: LED driver

Claims (10)

Primary winding N ₁ ;
A secondary winding (N ₂₎ and a first snubber diode connected in series with the first series circuit (D _sn1) for receiving an induced electromotive force by the primary winding (N _1);
A second Snubber diode (D _sn2 ) having one end connected to one end of the primary winding (N ₁ ) and the other end connected to one end of the first series circuit; And
One end of the first series circuit is connected to one end of the first series circuit and the other end of the second snubber diode (D _sn2 ), and the other end is connected to the other end of the first series circuit, The connection includes a snubber capacitor (C _sn ) connected via a power switch (M ₁ )
The snubber capacitor (C _sn) and the power switch and (M ₁₎ an anode is connected to a contact point connected, the transformer further comprising an output diode (D _o) cathode is connected to one end of the primary winding Coupled reuse snubber circuit. The method according to claim 1,
Further comprising an input capacitor (C _in ) receiving the magnetic energy of the leakage inductance of the secondary winding when the second snubber diode is turned on. 3. The method of claim 2,
The input capacitor (C _in )
And the magnetic energy of the leakage inductance remaining after charging the snubber capacitor (C _sn ) is input. delete The method according to claim 1,
Wherein the output diode (D _o) is
And turns on when the voltage charged in the snubber capacitor (C _sn ) is discharged to continuously output and discharge the magnetic energy of the magnetizing inductance (L _m ) of the primary winding. The transformer reuse snubber Circuit. The method according to claim 1,
It said output transformer coupled diode reuse snubber circuit further comprising a load circuit connected in parallel to both ends of the (D _o). The method according to claim 1,
Wherein the power switch M ₁ performs zero voltage switching when the power switch M ₁ is turned off. The method according to claim 1,
Wherein the power switch M ₁ performs zero-current switching when the power switch M ₁ is turned on. The method according to claim 1,
The first series circuit comprising:
And an anode of the first snubber diode (D _sn1 ) is connected in series to one end of the secondary winding (N ₂ ). The method according to claim 1,
The first series circuit comprising:
And the cathode of the first snubber diode (D _sn1 ) is connected in series to the other end of the secondary winding (N ₂ ).

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