JP2017034793A - Active clamp dc-dc converter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active clamp DC-DC converter circuit, capable of reducing a switching loss in a switching device disposed on the primary side of a transformer of an active clamp DC-DC converter circuit.SOLUTION: An active clamp DC-DC converter circuit includes: a transformer T1; a semiconductor switching device Qm on a primary side of the transformer T1; a first capacitor Cm connected in parallel with the semiconductor switching device Qm; and a rectifier circuit on a secondary side of the transformer T1. The rectifier circuit includes a coupling inductor which, when the first capacitor Cm is being discharged, blocks a discharge current flow from the first capacitor Cm to the rectifier circuit through the transformer T1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an active clamp type DC-DC converter circuit.

  On the primary side of the transformer of the active clamp type DC-DC converter circuit, a switch element, a capacitor connected in parallel to the switch element, and a transformer reset circuit for resetting the transformer are provided. The transformer reset circuit includes a switch element and a capacitor. For example, a diode is provided as a rectifier circuit on the secondary side of the transformer.

As a related technique, an active clamp type DC-DC converter circuit disclosed in Patent Document 1 is known.
However, the switching loss of the switch element provided on the primary side of the transformer operating at high frequency depends on the input voltage and output current. For example, depending on the input voltage, zero volt switching (ZVS) operation cannot be performed. Loss increases.

Japanese Patent No. 2743869

  The objective which concerns on one side of this invention is to provide the active clamp type DC-DC converter circuit which can reduce the switching loss of the switch element provided in the primary side of the transformer of an active clamp type DC-DC converter circuit.

  An active clamp type DC-DC converter circuit according to one embodiment of the present invention includes a transformer, a switching semiconductor element on the primary side of the transformer, a first capacitor connected in parallel to the switching semiconductor element, and two transformers. And a rectifier circuit on the next side.

  The rectifier circuit includes a coupled inductor that prevents a current discharging the first capacitor from flowing through the transformer through the transformer when the first capacitor is discharging.

The coupled inductor has a first coil provided on one of the taps and a second coil provided on the other of the taps.
In addition, a reset circuit is provided on the primary side of the transformer to release energy stored in the transformer when the switching semiconductor element is in an off state.

  In the rectifier circuit, for example, one terminal of the secondary winding of the transformer is connected to one terminal of the first coil connected to the tap of the coupled inductor and one terminal of the second coil. The other terminal of the secondary winding of the transformer is connected to one terminal of the first semiconductor element, and the other terminal of the second coil is connected to one terminal of the second semiconductor element. Yes. Then, the other terminal of the first coil and one terminal of the second capacitor are connected, and the other terminal of the first semiconductor element is connected to the other terminal of the second semiconductor element and the second terminal. And the other terminal of the capacitor.

  In addition, the rectifier circuit includes, for example, one terminal of the first semiconductor element, one terminal of the first coil connected to the tap of the coupled inductor, and one terminal of the second coil. One terminal of the secondary winding of the transformer is connected to the other terminal of the first semiconductor element. The other terminal of the first coil is connected to one terminal of the second capacitor, the other terminal of the second coil is connected to one terminal of the second semiconductor element, and the transformer The other terminal of the secondary winding is connected to the other terminal of the second semiconductor element and the other terminal of the second capacitor.

  The switching loss of the switch element provided on the primary side of the transformer of the active clamp type DC-DC converter circuit can be reduced.

It is a figure which shows one Example of an active clamp type DC-DC converter circuit. It is a figure which shows one Example of an active clamp type DC-DC converter circuit. It is a figure which shows one Example of a transformer reset circuit. It is a figure which shows the equivalent circuit of the active clamp type DC-DC converter circuit in period T8. It is a figure for demonstrating operation | movement of an active clamp type DC-DC converter circuit.

Hereinafter, embodiments will be described in detail with reference to the drawings.
1 and 2 are diagrams showing an embodiment of an active clamp type DC-DC converter circuit. The active clamp type DC-DC converter circuit of FIG. 1 includes a transformer T1, a switch element Qm (a switching semiconductor element, a main switch element), a switch element Qr (an auxiliary switch element, a switching semiconductor element used for transformer reset), and a capacitor Cm. (First capacitor), capacitor Cr (capacitor used for transformer reset), and rectifier circuit. The rectifier circuit is provided on the secondary side of the transformer T1, and is coupled inductor T2 (inductor composed of coil L1 (first coil) and coil L2 (second coil)), diode D1 (first semiconductor element). ), A diode D2 (second semiconductor element), and a capacitor C1 (second capacitor). For example, a transformer or a tap inductor may be used as the coupling inductor T2. 1 and 2, the active clamp type DC-DC converter circuit is supplied with power of the input voltage Vin from the power source E, and a desired output voltage Vout (= output current Iout × load Rout) is applied to both ends of the load Rout. Is output. 1 and 2 show the leakage inductance Ls and the excitation inductance Lp of the transformer T1.

  The connection of the active clamp type DC-DC converter circuit of FIGS. One terminal of the power source E is connected to one terminal of the capacitor Cr and one terminal of the primary winding of the transformer T1. One terminal (drain) of the switch element Qr is connected to the other terminal of the capacitor Cr. The other terminal (source) of the switching element Qr, one terminal (drain) of the switching element Qm, and one terminal of the capacitor Cm are connected to the other terminal of the primary winding of the transformer T1. ing. The other terminal (source) of the switch element Qm and the other terminal of the capacitor Cm are connected to the other terminal of the power source E. That is, the capacitor Cm is connected in parallel to the switch element Qm. For example, switching semiconductor elements such as MOSFET (Metal Oxide Semiconductor Field Effect Transistor) may be used as the switching elements Qr and Qm. Further, the switch elements Qr and Qm are PWM (Pulse Width Modulation) controlled by a control circuit (not shown). That is, on / off signals are alternately input from the control circuit to the gates of the switch elements Qr and Qm, and a desired output voltage Vout is output from the active clamp type DC-DC converter circuit.

  Capacitor Cm indicates the parasitic capacitance of switch element Qm or the combined capacitance of the parasitic capacitance of switch element Qm and the capacitance of capacitor Cm when there is a capacitor Cm connected in parallel to switch element Qm. The capacitor Cm is a capacitor used for ZVS.

  A circuit in which the switch element Qr and the capacitor Cr are connected in series is a transformer reset circuit, and releases energy stored in the transformer T1 when the switching element Qm is in an off state and the switch element Qr is in an on state. The transformer reset circuit is not limited to those shown in FIGS. 1 and 2, and a capacitor Cr may be connected in parallel to the switch elements Qr and Qm connected in series as shown in FIG. FIG. 3 is a diagram showing an embodiment of the transformer reset circuit.

A rectifier circuit will be described.
The rectifier circuit includes a coupling inductor T2 that prevents the current discharging the capacitor Cm from flowing through the rectifier circuit via the transformer T1 when the capacitor Cm is discharging. The coupled inductor T2 has a tap to which one terminal of the coil L1, the coil L2, and the coil L1 and one terminal of the coil L2 are connected. In the rectifier circuit of FIG. 1, one terminal of the secondary winding of the transformer T1, one terminal of the coil L1 connected to the tap of the coupling inductor T2, and one terminal of the coil L2 are connected. The other terminal of the secondary winding of the transformer T1 is connected to one terminal (cathode) of the diode D1, and the other terminal of the coil L2 is connected to one terminal (cathode) of the diode D2. The other terminal of the coil L1 is connected to one terminal of the capacitor C1, and the other terminal (anode) of the diode D1 is connected to the other terminal (anode) of the diode D2 and the other terminal of the capacitor C1. And are connected.

  In the rectifier circuit of FIG. 2, for example, one terminal of the diode D1, one terminal of the coil L1 connected to the tap of the coupling inductor T2, and one terminal of the coil L2 are connected, and the transformer T1 One terminal of the secondary winding is connected to the other terminal of the diode D1. The other terminal of the coil L1 and one terminal of the capacitor C1 are connected, the other terminal of the coil L2 is connected to one terminal of the diode D2, and the other of the secondary windings of the transformer T1. , The other terminal of the diode D2, and the other terminal of the capacitor C1 are connected.

The diodes D1 and D2 in FIGS. 1 and 2 may be switching semiconductor elements such as MOSFETs.
The winding ratio NL between the coil L1 and the coil L2 of the coupled inductor T2 is such that the diode D1 is not turned on during the period when the switch element Qm is turned off, the switch element Qr is turned off, and the capacitor Cm is discharged. Set as follows.

The operation of the active clamp type DC-DC converter circuit will be described.
In a period T1 (a period in which the switch element Qm is on and the switch element Qr is off), when a current flows from the primary winding of the transformer T1 to the source from the drain of the switch element Qm, the secondary winding of the transformer T1 Is rectified by the diode D1 and flows to the load Rout through the coil L1.

  In the period T2 (period in which the switch element Qr is off and the switch element Qm is turned off), the capacitor Cm is charged to increase the voltage, and the voltage of the switch element Qr (drain-source voltage) decreases. When the diode D2 is turned on as the voltage Vds (drain-source voltage) of the switch element Qm increases, the period shifts to a period T3.

  In the period T3 (period in which the switch element Qm is off and the switch element Qr is off), when both the diodes D1 and D2 are on, the voltage Vds of the switch element Qm rises and the voltage of the switch element Qr is substantially reduced. It becomes 0 [V], and it shifts to the period T4.

  In a period T4 (a period in which the switch element Qm is off and the switch element Qr is turned on and turned on), the energy of the leakage inductance Ls on the primary side of the transformer T1 is transferred to the capacitor Cr via the body diode of the switch element Qr. Charge. When the diode D1 is turned off, the period shifts to a period T5.

  In a period T5 (a period in which the switch element Qm is off and the switch element Qr is on), the capacitor Cr is charged using the exciting current of the transformer T1. When the current charged in the capacitor Cr becomes approximately 0 [A], the period shifts to a period T6.

  In the period T6 (the period in which the switch element Qm is in the off state and the switch element Qr is in the on state and the energy of the capacitor Cr is released), the current flowing through the switch element Qr is reversed and flows in the forward direction. That is, energy moves from the charged capacitor Cr to the primary side of the transformer T1.

  In a period T7 (a period in which the switch element Qm is in the off state and the switch element Qr is turned off and in the off state), when the capacitor Cm is discharged, the voltage Vds of the switch element Qm drops to near Vin [V].

  In a period T8 (a period in which the switch element Qm is in an off state and the switch element Qr is in an off state), the voltage Vds of the switch element Qm is lowered to around 0 [V]. When the capacitor Cm is discharged, the current Im discharged from the capacitor Cm to the rectifier circuit via the transformer T1 is prevented from flowing to the secondary side of the transformer T1. That is, the voltage Vtap is generated in the coil L2 using the coupled inductor T2, so that the diode D1 is not turned on even when the voltage Vds of the switch element Qm decreases. The voltage of the switch element Qr rises, the diode D2 is turned on, and the period shifts to the period T9. As described above, by reducing the voltage Vds of the switch element Qm to near 0 [V], ZVS can be performed, and the switching loss of the switch element Qm is reduced.

  In a period T9 (a period in which the switch element Qr is turned off and the switch element Qm is turned on), the voltage Vds of the switch element Qm is close to 0 [V], and a current flows through the body diode of the switch element Qm. When the current flowing through the body diode of the switch element Qm becomes approximately 0 [A], the period shifts to a period T10.

  In a period T10 (a period in which the switch element Qm is on and the switch element Qr is off), the current of the switch element Qm is in the forward direction, energy is supplied from the power source E, and the current flowing through the diode D2 is approximately 0 [A ], The period shifts to the period T1.

The effect will be described.
When only the coil is used as in the conventional active clamp type DC-DC converter circuit without using the coupled inductor T2 (one terminal of the coil is connected and one terminal of the capacitor C1 is connected to the other terminal of the coil. In the case of a circuit in which terminals are connected), since the voltage Vds of the switch element Qm does not drop to near 0 [V] in the period T7 (because the voltage drops only to around the input voltage Vin of the power supply E), the switch element A large switching loss occurs in Qm, and the efficiency of the active clamp type DC-DC converter circuit decreases. In addition, the heat generated by the switch element Qm increases, and noise may be generated.

  Further, in the period T6 in the conventional active clamp type DC-DC converter circuit, the switch element Qr is turned off when a current flows in the forward direction in the switch element Qr. In the period T7, the switch element Qm and the switch element Qr are turned off. When both are turned off, resonance occurs due to the leakage inductance Ls of the transformer T1 and the capacitor Cm. When the diode D1 is turned on, the period shifts to a period T8. When both the diodes D1 and D2 are turned on in the period T8, the exciting inductance Lp is short-circuited, and resonance occurs due to the leakage inductance Ls and the capacitor Cm. Further, since the energy is reduced due to the short-circuit of the excitation inductance Lp, the voltage of the switch element Qm does not drop to near 0 [V], and resonance occurs around the input voltage Vin until the switch element Qm is turned on. to continue.

  Further, instead of using the coupled inductor T2 shown in FIG. 2 as in the prior art, one terminal of the coil (cathode) of the diode D2 in FIG. 2 is connected, and a capacitor is connected to the other terminal of the coil. Even when one terminal of C1 is connected, in the period T8, the voltage does not drop to near 0 [V], and the resonance continues until the switch element Qm is turned on.

  However, when the coupled inductor T2 is used, the diode D1 can be maintained in the OFF state by the coupled inductor T2 in the period T8, so that the voltage of the switch element Qm can be lowered to around 0 [V]. it can.

  This will be described with reference to FIGS. FIG. 4 is a diagram showing an equivalent circuit of the active clamp type DC-DC converter circuit in the period T8. In the equivalent circuit of FIG. 4, the transformer T1 has a winding ratio of 1: 1, the transformer T1 is regarded as the current source Ip1, the exciting inductance of the transformer T1 is Lm (= Lp + Ls), and the coil L1 of the coupled inductor T2 is the current source. Assuming Ip2 (Iout / Ntr), the voltage of the voltage source generated by the coils L1 and L2 of the coupled inductor T2 is expressed as Vtap. FIG. 5 is a diagram for explaining the operation of the active clamp type DC-DC converter circuit. The vertical axis in FIG. 5 indicates the voltage Vtap and the voltage Vds, and the horizontal axis indicates time. The voltage Vtap is the curve 501 in FIG. 5, and the voltage Vds is the curve 502 in FIG.

  When the switch element Qr is turned off, the voltage Vtap changes from Vout / (NL1 + NL2) / NL2 [V] to 0 [V] from time t0 to time t1 (period T7). Here, NL1 is the number of turns of the coil L1, and NL2 is the number of turns of the coil L2.

  Subsequently, from time t1 to time t2 (period T8), the voltage Vtap increases from 0 [V] to {(Vin / Ntr) −Vout} / NL−Ls * di / dt [V]. Here, * indicates multiplication. Ntr is a winding ratio of the primary winding and the secondary winding of the transformer T1. di / dt represents the slope of the current i flowing through the switch element Qm.

  Subsequently, from time t2 to time t3 (period T9) and from time t3 to t4 (period T10), the process continues to be {(Vin / Ntr) −Vout} / NL−Ls * di / dt [V]. Further, after time t4 (period T1), the voltage Vtap increases to {(Vin / Ntr) −Vout} / NL [V].

  As shown in FIG. 5, the voltage Vtap 503 (shaded portion) is generated at time t1. That is, when the voltage Vtap is 0 [V] or more, the diode D1 can be prevented from being turned on, so that the current Im discharged from the capacitor Cm does not flow to the rectifier circuit via the transformer T1. it can. As shown in FIG. 4, the current Im can be recirculated on the primary side of the transformer T1 without recirculating the current Im to the secondary side of the transformer T1, so that the capacitor Cm is discharged and the voltage Vds of the switch element Qm is discharged. Can be lowered to around 0 [V]. The diode D1 is turned on at a voltage Vtap + 0.6 [V] (junction saturation voltage) or higher.

  In the equivalent circuit of FIG. 4, the relationship between the voltage applied to the diode D2 and the switching loss of the switch element Qm is such that the switching of the switch element Qm increases as the voltage applied to the diode D2 increases (the voltage Vtap increases). Since the loss is reduced (voltage Vds is reduced), the winding ratio NL is set in consideration of the above relationship, the switch element Qm is turned off, the switch element Qr is turned off, and the capacitor Cm is discharged. It is set so that the diode D1 is not turned on during the period.

  As described above, the voltage Vds of the switch element Qm is lowered to near 0 [V] so that ZVS can be performed, and the switching loss of the switch element Qm provided on the primary side of the transformer of the active clamp type DC-DC converter circuit. Reduce.

  The present invention is not limited to the above-described embodiment, and various improvements and modifications can be made without departing from the gist of the present invention.

Cm, Cr, C1 Capacitor D1, D2 Diode E Power supply Ip1, Ip2 Current source L1, L2 Coil Lp, Ls, Lm Inductance Qm, Qr Switch element Rout Load T1 Transformer T2 Coupled inductor

Claims (5)

With a transformer,
A switching semiconductor element on the primary side of the transformer;
A first capacitor connected in parallel to the switching semiconductor element;
An active clamp type DC-DC converter circuit comprising a rectifier circuit on the secondary side of the transformer,
The rectifier circuit includes a coupled inductor that prevents the current discharging the first capacitor from flowing through the transformer to the rectifier circuit when the first capacitor is discharging.
An active clamp type DC-DC converter circuit. An active clamp type DC-DC converter circuit according to claim 1,
The coupled inductor has a first coil provided on one of the taps and a second coil provided on the other of the taps,
An active clamp type DC-DC converter circuit. An active clamp type DC-DC converter circuit according to claim 1 or 2,
When the switching semiconductor element is in an off state, a reset circuit that releases energy stored in the transformer is provided on the primary side of the transformer.
An active clamp type DC-DC converter circuit. An active clamp type DC-DC converter circuit according to claim 2,
The rectifier circuit is
One terminal of the secondary winding of the transformer is connected to one terminal of the first coil connected to the tap of the coupled inductor and one terminal of the second coil. ,
The other terminal of the secondary winding of the transformer is connected to one terminal of the first semiconductor element,
The other terminal of the second coil and one terminal of the second semiconductor element are connected,
The other terminal of the first coil and one terminal of the second capacitor are connected;
The other terminal of the first semiconductor element, the other terminal of the second semiconductor element, and the other terminal of the second capacitor are connected.
An active clamp type DC-DC converter circuit. An active clamp type DC-DC converter circuit according to claim 2,
The rectifier circuit is
One terminal of the first semiconductor element, one terminal of the first coil connected to the tap of the coupled inductor, and one terminal of the second coil are connected,
One terminal of the secondary winding of the transformer and the other terminal of the first semiconductor element are connected,
The other terminal of the first coil and one terminal of the second capacitor are connected;
The other terminal of the second coil and one terminal of the second semiconductor element are connected,
The other terminal of the secondary winding of the transformer, the other terminal of the second semiconductor element, and the other terminal of the second capacitor are connected.
An active clamp type DC-DC converter circuit.

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