JP5644954B2 - Isolated switching power supply - Google Patents

Description

  The present invention relates to an insulating switching power supply device.

  In a converter of a hard switching topology, such as a forward converter or a flyback converter, used in a power conversion circuit of an insulating switching power supply device, a leakage inductance of a power transmission transformer is used as a primary power switching element or a secondary rectifying element. A spike voltage resulting from is applied.

  If a switching element with a high breakdown voltage is used to reduce the influence of the spike voltage, or if a snubber circuit with power loss is added, power conversion efficiency will be reduced. Also, when the voltage is applied to both ends of the primary side power switching element, the parasitic capacitance is generated when the charge accumulated in the parasitic capacitance existing in parallel with the primary side power switching element is discharged. Short circuit loss occurs.

  For example, in a converter having a topology that performs ZVS (zero voltage switching) such as a phase shift full bridge converter, the above-described parasitic capacitance short-circuit loss does not occur, but a spike voltage caused by the leakage inductance of the transformer is applied to the secondary side rectifying element. If a rectifying element having a high withstand voltage is used to reduce the influence of the spike voltage or a snubber circuit with power loss is added, the power conversion efficiency is reduced as in the case described above. In addition, the aforementioned spike voltage can cause EMI noise.

  On the other hand, not only ZVS for the primary side power switching element, but also LLC resonant converter that can perform ZCS (zero current switching) for the secondary side rectifier element (transformer primary winding, series inductor and clamp capacitor connected in series to it) Is known as a very high-efficiency power conversion circuit, which can solve the problems of spike voltage and parasitic capacitance short circuit with respect to the primary side power switch and the secondary side rectifying element described above. However, the LLC resonant converter has a drawback that the input voltage range in which a highly efficient switching operation can be maintained is narrow.

  On the other hand, an insulating DC-DC converter having a topology in which an active clamp type inverter on the primary side and a voltage doubler rectifier circuit on the secondary side is disclosed in Patent Document 1, Patent Document 2, and Patent Document 3. . In such an isolated DC-DC converter having an active clamp type inverter on the primary side and a voltage doubler rectifier circuit on the secondary side, it is known that the output voltage and the output current can be PWM controlled. In addition, it is known that a multi-resonant operation in which ZVS and ZCS are compatible is possible depending on the setting of circuit constants. Therefore, the isolated DC-DC converter having this topology can perform a switching operation with less stress on the primary side power switching element and the secondary side rectifying element constituting the power conversion circuit.

Japanese Patent No. 25661201 JP 2001-224171 A JP 2001-339948 A

  In the switching power supply devices disclosed in Patent Documents 1 to 3, the secondary side rectifying element is formed of a diode. In the voltage doubler rectifier circuit, since the output current passes through the secondary side rectifier element in two stages, the effect of conduction loss due to the secondary side rectifier element is affected when it is applied to an insulated switching power supply device having a relatively low output voltage. There is a problem that large and highly efficient power conversion is difficult. Further, Patent Documents 1 to 3 do not describe at all how the synchronous rectification elements should be controlled when the secondary rectification elements are synchronous rectification elements.

  An object of the present invention is to provide a specific configuration for controlling a synchronous rectifying element, and to provide an insulated switching power supply device that solves the above-described problems.

The insulated switching power supply device of the present invention is
DC power input (V1),
Power transmission transformer (MT),
A main switching element (Q1) that controls switching of a DC voltage applied to the primary winding (Np) of the power transmission transformer from the DC power supply input section, and a timing that is complementary to ON / OFF of the main switching element and sandwiches a dead time Sub-switching element (Q2) driven by
A series circuit connected to the sub-switching element to form a series circuit, and the series circuit is connected to one end of the primary winding of the power transmission transformer;
A series inductor (L1) connected in series with the primary winding or secondary winding (Ns) of the power transmission transformer;
First and second synchronous rectifier elements (Q4, Q3) connected to the secondary winding of the power transmission transformer;
Synchronous rectification driving circuit for driving the first and second synchronous rectification elements, and first and second smoothing capacitors (C3, C), which constitute a voltage doubler rectification / smoothing circuit together with the first and second synchronous rectification elements C2)
The first smoothing capacitor is charged via the series inductor and the first synchronous rectifier element during the conductive period of the first synchronous rectifier element that starts during the conductive period of the main switching element, and The second smoothing capacitor is charged via the series inductor and the second synchronous rectifier element during the conduction period of the second synchronous rectifier element started in the conduction period, and the output of the voltage doubler rectifier / smoothing circuit A control circuit that controls the input / output conversion ratio according to the duty ratio of the main switching element so that the voltage (Vout) or the output current (Iout) gradually approaches the target value;
It is provided with.

The isolated DC-DC converter of the present invention is
(A) PWM control of output voltage and output current is possible.

(B) The voltage stress on the primary side power switching element and the secondary side rectifying element is small.

(C) Zero voltage switching of the main switching element is possible.

(D) By using a synchronous rectifier in the topology having the above-described features, it can be applied to an insulated DC-DC converter with a relatively low voltage output of several volts to several tens of volts, and a highly efficient power conversion operation. Can be realized.

(E) Safe circuit operation can be realized by taking measures to prevent backflow and through current of the first and second synchronous rectifier elements.

(F) Since the series inductor connected in series with the primary winding or the secondary winding of the power transmission transformer can be easily formed by the leakage inductance of the power transmission transformer, a small filter inductor used for reducing input / output ripples The magnetic component can be composed of only one power transmission transformer, and the cost can be reduced.

(G) Loosely coupled transformers with large leakage inductance often require a special winding structure, and there is a problem in that the AC resistance of the winding increases. However, the series inductor has a small voltage applied to both ends and a large inductance value. Does not require a loosely coupled transformer.

FIG. 1 is a circuit diagram of an insulation type DC-DC converter 101 according to a first embodiment of the present invention. FIG. 2 is an equivalent circuit diagram of the insulation type DC-DC converter 101. FIG. 3 is a timing chart of the insulated DC-DC converter 101. 4A is an equivalent circuit diagram in mode 1, FIG. 4B is an equivalent circuit diagram in mode 2, FIG. 4C is an equivalent circuit diagram in mode 3, and FIG. 4 (E) is an equivalent circuit diagram in mode 5, FIG. 4 (F) is an equivalent circuit diagram in mode 6, FIG. 4 (G) is an equivalent circuit diagram in mode 7, and FIG. (H) is an equivalent circuit diagram in mode 8. FIG. FIG. 5 is a circuit diagram of another DC-DC converter 101B of the first embodiment. FIG. 6 is a diagram illustrating a circuit for generating a timing signal and a waveform of the timing signal in the second embodiment. FIG. 7 is a circuit diagram of a portion that transmits a pulse signal to the sub switching element Q2 and the synchronous rectification elements Q3 and Q4 shown in FIG. FIG. 8 is a circuit diagram of the insulation type DC-DC converter 102 of the second embodiment. FIG. 9 is a diagram illustrating a driving circuit for the sub switching element Q2 in the DC-DC converter according to the third embodiment. FIG. 10 is a circuit diagram of the insulation type DC-DC converter 103 of the third embodiment. FIG. 11 is a circuit diagram of another DC-DC converter 103B of the third embodiment. FIG. 12 is a diagram illustrating a voltage drop detection circuit of the secondary winding Ns11 of the power transmission transformer MT of the DC-DC converter of the fourth embodiment. FIG. 13 is a modification of the circuit that transmits the pulse signal to the sub switching element Q2 and the synchronous rectification elements Q3 and Q4 shown in FIG. FIG. 14 is a circuit diagram of the insulation type DC-DC converter 104 of the fourth embodiment. FIG. 15 shows a synchronous rectifier driving circuit unit according to the fifth embodiment. FIG. 16 is a circuit diagram of the isolated DC-DC converter 105 of the fifth embodiment. FIG. 17 is a circuit diagram of the insulation type DC-DC converter 106 of the sixth embodiment.

<< First Embodiment >>
FIG. 1 is a circuit diagram of an insulation type DC-DC converter 101 according to a first embodiment of the present invention. The insulation type DC-DC converter 101 includes an input unit of a DC input power source V1, a power transmission transformer MT, a main switching element Q1, a sub switching element Q2, a capacitor C6, and a series inductor L1. The power transmission transformer MT includes a primary winding Np11 and a secondary winding Ns11. The sub switching element Q2 is driven at a complementary timing with the main switching element Q1 across the dead time.

  A series circuit of the sub switching element Q2 and the capacitor C6 is connected to one end of the primary winding Np11 of the power transmission transformer MT to constitute an active clamp circuit. The series inductor L1 is connected in series with the primary winding Np11 of the power transmission transformer MT. This series inductor L1 is an inductor corresponding to the leakage inductance of the power transmission transformer MT. Alternatively, when an inductor is connected in series to the primary winding Np11 of the power transmission transformer MT, the inductor corresponds to a series connection of the inductor and the leakage inductance.

  A first synchronous rectifier element Q4, a second synchronous rectifier element Q3, a first smoothing capacitor C3, and a second smoothing capacitor C2 are connected to the secondary winding Ns11 of the transformer MT. This circuit constitutes a voltage doubler rectification / smoothing circuit. The first smoothing capacitor C3 is charged via the series inductor L1 and the first synchronous rectification element Q4 during the conduction period of the first synchronous rectification element Q4 started during the conduction period of the main switching element Q1. The second smoothing capacitor C2 is charged via the series inductor L1 and the second synchronous rectification element Q3 during the conduction period of the second synchronous rectification element Q3 which is started during the conduction period of the sub switching element Q2. Note that the series inductor L1 is on the primary side, but the fact that it is charged via this series inductor L1 will become apparent in the later equivalent circuit.

  A smoothing capacitor constituted by a series connection of the first smoothing capacitor C3 and the second smoothing capacitor C2, an output filter inductor L2, and a third smoothing capacitor C10 constitute a π-type filter. This π-type filter reduces the ripple of the voltage supplied to the load circuit Load.

  The main switching element Q1 and the sub switching element Q2 are connected to a primary side control circuit PCC (Primary Control Circuit), and the first synchronous rectification element Q4 and the second synchronous rectification element Q3 are secondary side control circuit SCC (Secondary Control Circuit). Circuit).

  The feedback circuit (not shown) compares the output voltage of the voltage doubler rectifier / smoothing circuit with the reference voltage, generates a feedback signal based on the error, and insulates from the secondary side to the primary side. The data is transmitted in a state and input to the primary side control circuit PCC. The primary-side control circuit PCC controls the duty ratio of the main switching element Q1 (PWM control) according to the feedback signal, and also controls the duty ratio of the sub-switching element Q2 that is driven at a complementary timing. Vout is made asymptotic to the target value, and the output voltage of the isolated DC-DC converter is stabilized.

FIG. 2 is an equivalent circuit diagram of the isolated DC-DC converter 101. The power transmission transformer MT can be expressed as an equivalent circuit in which a primary and a secondary are connected by an excitation inductance Lm and a series inductor L1. When the capacities of the first and second smoothing capacitors C3 and C2 are converted to the primary side, they are equivalent to the square of the turns ratio of the power transmission transformer MT, so these are (Ns11 / Np11) ² · C3, It can be expressed as (Ns11 / Np11) ² · C2, and the output filter inductor and load circuit can also be expressed as (Np11 / Ns11) ² · L2 and (Np11 / Ns11) · Vout in terms of the primary side.

  Next, the operation of the insulated DC-DC converter 101 will be described with reference to the timing chart of FIG. 3 and the equivalent circuit for each operation period of FIG. In FIG. 3, Vgs is a gate-source voltage, Vds is a drain-source voltage, and Id is a drain current.

[Mode 1] t0 to t1, FIG. 4 (A)
The main switching element Q1 is on. At t0, the parasitic diode of the first synchronous rectifier Q4 is turned on, and the first smoothing capacitor (Ns11 / Np11) ² · C3 is charged. Q4 is turned on during this period.

[Mode 2] t1 to t2, Fig. 4 (B)
Q1 is turned off at t1. Vds increases when Q1's output capacitance (drain-source capacitance) is charged. The first smoothing capacitor (Ns11 / Np11) ² · C3 continues to be charged.

[Mode 3] t2 to t3 (delay period after ON period), FIG. 4 (C)
At t2, the parasitic diode of the sub switching element Q2 conducts and charges C6. Q2 is turned on during this period. While (Ns11 / Np11) ² · C3 is charged, the current flowing through the first synchronous rectifier Q4 decreases and reaches 0 at t3. If the current flowing through Q4 at t2 is Ipkon and the peak voltage of Q1 is Vdspk, this delay period lasts for (L1 · Ipkon) / Vdspk. Therefore, the delay period increases as the inductance of the series inductor L1 increases, and increases as the output current increases and Ipkon increases.

[Mode 4] Near t3, Fig. 4 (D)
At t3, the first synchronous rectifier element Q4 is turned off, and both the first synchronous rectifier element Q4 and the second synchronous rectifier element Q3 are turned off. The series circuit of the capacitor C6, the series inductor L1, and the exciting inductance Lm resonates.

[Mode 5] t3 to t4, Fig. 4 (E)
The parasitic diode of the second synchronous rectifier element Q3 is turned on to charge the second smoothing capacitor (Ns11 / Np11) ² · C2. During this period, the second synchronous rectifier Q3 is turned on.

[Mode 6] t4 to t5, Fig. 4 (F)
At t4, Q2 is turned off, the output capacitance of the main switching element Q1 is discharged, and the drain voltage decreases. (Ns11 / Np11) ²・ C2 continues to be charged.

[Mode 7] t5 to t6 (delay period after off period), FIG. 4 (G)
At t5, the parasitic diode of the main switching element Q1 becomes conductive. The main switching element Q1 is turned on during this period. While (Ns11 / Np11) ² · C2 is charged, the current flowing through the second synchronous rectifier Q3 decreases, and reaches 0 at t6. If the current flowing through the series inductor L1 at t5 is Ipkoff and the peak voltage of the main switching element Q1 is Vdspk, this delay period continues for (L1 · Ipkoff) / Vdspk. Therefore, the delay period increases as the series inductor L1 increases, and increases as the output current increases and Ipkoff increases.

[Mode 8] Near t6 (same condition as t0), FIG. 4 (H)
At t6, the second synchronous rectifier element Q3 is turned off, and both the first synchronous rectifier element Q4 and the second synchronous rectifier element Q3 are turned off. The operation state at t6 is exactly the same as t0, and the periodic operation is repeated.

  As described above, there are delay periods immediately after the main switching element Q1 and the sub switching element Q2 are turned off, and currents flowing through the first synchronous rectification element Q4 and the second synchronous rectification element Q3 via the series inductor L1 respectively. Until the voltage decreases to 0, the voltage across the first synchronous rectifier element Q4 and the second synchronous rectifier element Q3 is not inverted.

  Therefore, in the first embodiment, the conduction period of the first synchronous rectifier element Q4 is formed with a phase lag behind the conduction period of the main switching element Q1. In other words, the first synchronous rectifier element Q4 starts to conduct after the start of conduction of the main switching element Q1, and the current decreases immediately after the main switching element Q1 is turned off. The conduction period of the second synchronous rectifier element Q3 is formed with a phase lag behind the conduction period of the sub-switching element Q2. That is, the second synchronous rectifying element Q3 starts to conduct after the conduction of the sub switching element Q2, and the current decreases immediately after the sub switching element Q2 is turned off. The first and second synchronous rectifier elements Q4 and Q3 are driven according to the conduction period of the first and second synchronous rectifier elements Q4 and Q3.

  FIG. 5 is a circuit diagram of another DC-DC converter 101B of the first embodiment. The position of the first smoothing capacitor C3 is different from the circuit shown in FIG. That is, in the DC-DC converter 101B shown in FIG. 5, the first smoothing capacitor C3 is connected to the position where the output voltage is applied before the π-type filter by the output filter inductor L2 and the third smoothing capacitor C10. ing. The operation is similar to that of the DC-DC converter 101 except that the voltage applied to the first smoothing capacitor C3 increases to the output voltage. However, regarding the reduction of the output ripple voltage, the connection method of the DC-DC converter 101 is more advantageous than the DC-DC converter 101B.

  According to the first embodiment, the effects (a), (b), (c), (d), (f), and (g) described above are exhibited.

<< Second Embodiment >>
In the second embodiment, the sub-switching element Q2 and the first and second synchronous rectifier elements Q4, Q3 provided in the insulation type DC-DC converter 101 of the first embodiment are more specifically driven. Shown in

  In this example, a pulse signal indicating the off timing of the sub-switching element Q2 and the first and second synchronous rectifying elements Q4 and Q3 is transmitted by a signal transmission transformer PT and driven based on the pulse signal.

  FIG. 6 is a diagram illustrating a circuit for generating a timing signal and a waveform of the timing signal in the second embodiment. The primary side control circuit (Primary Control Circuit) includes a main switching element drive terminal OutA and an overlap signal output terminal OutB. From the main switching element drive terminal OutA, a square-wave main switching element drive signal that is at the H level during the ON period of the main switching element Q1 is output. From the overlap signal output terminal OutB, in addition to the ON period of the main switching element Q1, a square wave overlap signal is output in which the preceding and following dead time periods (Td1, Td2) are also at the H level. When an overlap signal is used, there is a feature that a sub switching element drive circuit can be easily configured when a P-channel MOSFET is used as the sub switching element. Some commercially available control ICs have an overlap signal output function. A transmission winding Np21 of the signal transmission transformer PT is connected between the main switching element drive terminal OutA and the overlap signal output terminal OutB via an impedance element including a resistor R7 and a capacitor C9.

  Since the main switching element drive terminal OutA and the overlap signal output terminal OutB have the same output voltage except for the dead time period, and the potential of OutB becomes high only during the dead time period, the transmission winding of the signal transmission transformer PT during the dead time period A pulse signal is generated at Np21. The signal transmission transformer PT transmits the pulse signal from the transmission winding Np21 to the reception winding Ns21, and the drive circuit connected to the reception winding Ns21 has the sub-switching element Q2 or the first and second elements according to the timing of the pulse signal. The synchronous rectifier elements Q4 and Q3 are driven.

  FIG. 7 is a circuit diagram of a portion for transmitting a pulse signal to the sub switching element Q2 and the synchronous rectification elements Q3 and Q4 shown in FIG. In FIG. 7, the signal transmission transformer PT transmits the pulse signal shown in FIG. On the other hand, a voltage doubler rectifier circuit composed of C1, R5 and a parasitic diode of switching element Q5 is connected to the winding of power transmission transformer MT, and the output of this voltage doubler rectifier circuit is connected to the gate of sub-switching element Q2. Has been. When a pulse signal is transmitted by the signal transmission transformer PT, the switching element Q5 is turned on and the sub-switching element Q2 is immediately turned off.

  Although FIG. 7 shows the portion related to the sub switching element Q2, the same applies to the first and second synchronous rectifier elements Q4 and Q3. That is, the first and second synchronous rectifier elements Q4 and Q3 are also provided with a signal transmission transformer PT, and the output of the voltage doubler rectifier circuit is connected to the gates of the first and second synchronous rectifier elements Q4 and Q3. Has been. When the pulse signal is transmitted by the signal transmission transformer PT, the first and second synchronous rectifier elements Q4 and Q3 are turned off.

  FIG. 8 is a circuit diagram of the insulation type DC-DC converter 102 of the second embodiment. The insulated DC-DC converter 102 includes an input portion of a DC input power supply V1, a main switching element Q1, a sub switching element Q2, a capacitor C6, a power transmission transformer MT, and the like. The power transmission transformer MT includes a primary winding Np11 that transmits power, a secondary winding Ns11 that receives power, and auxiliary windings Ns12, Ns13, and Np12 that are used to drive a power switching element.

  A series inductor L1 is connected in series to the primary winding Np11 of the power transmission transformer MT. The second synchronous rectification element (on / off side synchronous rectification element) Q3 starts to conduct during the conduction period of the sub switching element Q2. The first synchronous rectifier element (on-on side synchronous rectifier element) Q4 starts to conduct during the conduction period of the main switching element Q1.

  The signal transmission transformer PT that transmits a pulse signal includes a transmission winding Np21, a reception winding Np22, Ns21, and Ns22. A signal for driving the main switching element Q1 is output from the OutA terminal, and an overlap signal is output from the OutB terminal (see FIG. 6).

  A transmission winding Np21 of the signal transmission transformer PT is connected between the OutA terminal and OutB terminal via a capacitor C9 and a resistor R7 which are impedance elements. As shown in FIG. 6, a pulse signal is generated in a period corresponding to the dead time and transmitted from the transmission winding Np21 to each of the reception windings Np22, Ns21, and Ns22.

  In the second embodiment, the same drive circuit shown in FIG. 7 is used for driving all of the sub-switching element Q2 and the first and second synchronous rectifier elements Q4 and Q3. In the first synchronous rectifying element Q4) and the on / off side (Q2 and the second synchronous rectifying element Q3), the polarity of the winding of the connected power transmission transformer MT is reversed.

  In the example of FIG. 8, the series inductor L1 is connected in series with the primary winding Np11 of the power transmission transformer MT, and is disposed in front of the power transmission transformer MT. Includes a phase delay due to the series inductor L1. Therefore, the induced voltage of the power transmission transformer MT changes at a timing delayed from the voltage across the main switching element Q1. Accordingly, the sub-switching element Q2, the first and second synchronous rectifier elements Q4, Q3 are turned on when the gate is charged at a timing delayed from the voltage across the main switching element Q1, and the pulse signal is transmitted to the terminal OutA. , Turn off at the same timing as the output transition of OutB.

  In the configuration of the second embodiment, the driving timings of the first and second synchronous rectifier elements Q4 and Q3 do not completely coincide with the conduction periods of the first and second synchronous rectifier elements Q4 and Q3. The first and second synchronous rectifier elements Q4 and Q3 are turned off in the middle of the conduction period, and then a current flows through the parasitic diodes of the first and second synchronous rectifier elements Q4 and Q3. However, if the ratio of the phase delay due to the series inductor L1 is small with respect to the entire switching period, the configuration is sufficiently practical.

<< Third Embodiment >>
FIG. 9 is a diagram illustrating a driving circuit for the sub switching element Q2 in the DC-DC converter according to the third embodiment. Here, the diode D1 and the capacitor C1 constitute a bootstrap circuit. This bootstrap circuit supplies power for driving the sub switching element Q2. Vcc is a DC voltage source for operating a primary side control circuit PCC (Primary Control Circuit). As a configuration for supplying Vcc, a configuration in which the output of the auxiliary winding provided in the power transmission transformer MT is rectified and smoothed, a configuration in which the DC input power supply V1 is supplied via a regulator, or the like can be employed.

  The capacitor C7 and the resistor R9 constitute a differentiation circuit. This differentiation circuit transmits the voltage change of terminal OutB to switching element Q12, turns on Q12 at the moment when terminal OutB changes from L level to H level, and Q12 at the moment when terminal OutB changes from H level to L level. Turn off.

  The diode D3 and the resistors R6 and R9 maintain the switching element Q12 in the on state during the period when the terminal OutB is at the H level.

  The resistor R5, the switching element Q11, and the diode D2 have a function of charging the gate capacitance of the sub switching element Q2 during the OFF period of the switching element Q12. With these, the period during which the terminal OutB is at the H level is The period during which the terminal OutB is at the L level is converted into the ON period of the sub switching element Q2. The potential change of the source of the sub switching element Q2 due to the on / off of the main switching element Q1 also acts in the direction of promoting the driving operation of the sub switching element Q2.

  FIG. 10 is a circuit diagram of the insulation type DC-DC converter 103 of the third embodiment. The insulated DC-DC converter 103 includes an input unit of a DC input power supply V1, a main switching element Q1, a sub switching element Q2, a capacitor C6, and a power transmission transformer MT. The power transmission transformer MT includes a primary winding Np11 that transmits and receives power, a secondary winding Ns11, and auxiliary windings Ns12 and Ns13 that are used to drive a power switching element.

  The series inductor L1 is connected in series with the secondary winding Ns11 of the power transmission transformer MT.

  The first synchronous rectifier element (on-on side synchronous rectifier element) Q4 starts to conduct during the conduction period of the main switching element Q1. The second synchronous rectification element (on / off side synchronous rectification element) Q3 starts to conduct during the conduction period of the sub switching element Q2.

  The control / drive circuit on the primary side has almost the same configuration as the circuit shown in FIG. 8 in the second embodiment, and the sub-switching element Q2 is driven by the circuit shown in FIG.

  In the third embodiment, a voltage generated at both ends of the series inductor L1 is detected immediately after the on period of the main switching element Q1 and immediately after the on period of the sub switching element Q2, and a voltage is generated at both ends of the series inductor L1. The first and second synchronous rectifier elements Q4 and Q3 are turned off.

  Specifically, immediately after the main switching element Q1 is turned off, a voltage having (+) on the gate side of the switching element Q9 is generated at both ends of the series inductor L1, and Q9 is turned on. When Q9 is turned on, the charge accumulated in the gate of the first synchronous rectifier element Q4 is discharged, and the first synchronous rectifier element Q4 is turned off. The induced voltage of the power transmission transformer MT is inverted, and a voltage of (+) is applied to the resistor R3 and the switching element Q7 via the auxiliary winding Ns13, capacitor C4, resistor R11, and the gate of the second synchronous rectifier element Q3 is charged. As a result, the second synchronous rectifier Q3 is turned on. On the primary side, the sub-switching element Q2 is turned on, the second synchronous rectification element Q3 is turned on, and the second smoothing capacitor C2 is charged.

  Immediately after the on-period of the sub-switching element Q2, a voltage having (+) on the gate side of the switching element Q8 is generated at both ends of the series inductor L1, and Q8 is turned on. When Q8 is turned on, the gate accumulated charge of the second synchronous rectifier element Q3 is discharged, and the second synchronous rectifier element Q3 is turned off.

  The induced voltage of the power transmission transformer MT is inverted, and a voltage (+) is applied to the resistor R8 and the switching element Q10 via the auxiliary winding Ns12, the capacitor C8, and the resistor R14, and the gate of the first synchronous rectifier element Q4 is charged. As a result, the first synchronous rectifier Q4 is turned on. On the primary side, the main switching element Q1 is turned on, Q4 is conducted, and the first smoothing capacitor C3 is charged.

  As described above, in the third embodiment, driving is performed by turning off the first and second synchronous rectifier elements Q4 and Q3 using the voltage generated at both ends of the series inductor L1 as a trigger.

  FIG. 11 is a circuit diagram of another DC-DC converter 103B of the third embodiment. In the insulated DC-DC converter 103B shown in FIG. 11, the series inductor is constituted by a transformer PT2 to which a primary winding Np31 is connected. The transformer PT2 transmits a voltage generated in the primary winding Np31 to the secondary side to turn off the first and second synchronous rectifier elements Q4 and Q3. The rest is the same as the DC-DC converter 103 shown in FIG.

<< Fourth Embodiment >>
FIG. 12 is a diagram illustrating a voltage drop detection circuit of the power transmission transformer MT of the DC-DC converter according to the fourth embodiment. This circuit includes a comparator COMP and a reference voltage generation circuit that generates a reference voltage V4. The resistor Rns represents an equivalent resistance component of the secondary winding Ns11 of the power transmission transformer MT. An induction voltage differential winding Ns14 is provided in the power transmission transformer MT.

  A voltage drop corresponding to the current flowing through the secondary winding Ns11 occurs in the equivalent resistance component Rns of the secondary winding Ns11 of the transformer MT. The induced voltage differential winding Ns14 connected in parallel to the secondary winding Ns11 has the same number of turns as the secondary winding Ns11 and is tightly coupled. Therefore, the induced voltages of the secondary winding Ns11 and the induced voltage differential winding Ns14 cancel each other. A high resistance Rd is connected in series to the induction voltage differential winding Ns14, the current is suppressed to a small level, and almost no voltage drop occurs. Accordingly, the voltage drop at the resistance component Rns can be measured by observing the voltage across the resistor Rd.

  When the current flowing through the synchronous rectifier elements Q3 and Q4 is estimated from the voltage drop of the resistance component Rns, and the voltage drop is equal to or higher than the reference voltage V4, the second synchronous rectifier element Q3 is turned on and is lower than the reference voltage Turn off. As a result, current flows only through the second synchronous rectifier element Q3 from the source to the drain.

  FIG. 13 is a modification of the circuit that transmits a pulse signal to the sub-switching element Q2 and the synchronous rectifier elements Q3 and Q4 shown in FIG. 7. In the circuit shown in FIG. 7, the charge accumulated in the capacitor C1 is discharged. In this way, the loss generated is reduced. According to the circuit shown in FIG. 13, when switching element Q6 is turned on, switching element Q7 is turned off. Therefore, even when charge remains in capacitor C1 during the on period of switching element Q6, the charge is not discharged and discharge loss occurs. Can be reduced.

  FIG. 14 is a circuit diagram of the insulation type DC-DC converter 104 of the fourth embodiment. In the primary side control circuit PCC, a drive signal for the main switching element Q1 is output from the terminal OutA, and an overlap signal is output from the terminal OutB. A capacitor C9 and a resistor R7, which are impedance elements, are connected in series with the transmission winding Np21 of the signal transmission transformer PT between the terminal OutA and the terminal OutB. Therefore, a pulse signal is generated in the signal transmission transformer PT during a period corresponding to the dead time, and is transmitted from the transmission winding Np21 to the reception windings Np22 and Ns21.

  The drive circuit shown in FIG. 7 is used for the drive circuit portion of the sub switching element Q2. The sub switching element Q2 is driven based on the voltage generated in the auxiliary winding Np12 of the power transmission transformer MT and the pulse signal received by the reception winding Np22 of the signal transmission transformer PT.

  The circuit shown in FIG. 13 is used for the drive circuit section of the first synchronous rectifier Q4. The first synchronous rectification element Q4 is driven based on the voltage generated in the auxiliary winding Ns12 of the power transmission transformer MT and the pulse signal received by the reception winding Ns21 of the signal transmission transformer PT. A switching element Q8 is connected in parallel to the switching element Q6 driven by the signal transmission transformer PT, and the gate of the switching element Q8 is commonly connected to the gate of the second synchronous rectifier element Q3. That is, during the on period of the second synchronous rectifier element Q3, the switching element Q8 is also in the on state. When Q8 is turned on, the first synchronous rectifier element Q4 is maintained in the off state. If the synchronous rectifier elements Q3 and Q4 are driven at an appropriate timing, simultaneous ON will not occur. However, even if a deviation occurs in the drive timing, the first synchronous rectifier element Q4 and the first synchronous rectifier element Q4 are The two synchronous rectifier elements Q3 are prevented from being turned on simultaneously.

  In the insulated DC-DC converter 104 of the fourth embodiment, the second synchronous rectifier element Q3 is driven by a circuit for detecting a voltage drop of the secondary winding of the transformer MT shown in FIG. That is, the voltage drop of the secondary winding Ns11 of the transformer MT is detected by the difference from the induced voltage differential winding Ns14, and the voltage drop of the secondary winding Ns11 due to the current in the direction in which the second synchronous rectifier element Q3 is conducted. When becomes greater than a certain value, the synchronous rectifier Q3 is turned on. After that, when the current in the direction of conducting the second synchronous rectifying element Q3 decreases and the voltage drop of the secondary winding Ns11 becomes less than a certain value, the second synchronous rectifying element Q3 is turned off again.

  Since the output current in the voltage doubler rectification passes through the first synchronous rectifier element Q4 and the second synchronous rectifier element Q3 once each, if any one of the synchronous rectifier elements is provided with a backflow prevention measure, an isolated DC-DC There is no reverse flow phenomenon in which power is transmitted from the output side of the converter to the input side. That is, in the fourth embodiment, since the second synchronous rectifier element Q3 is driven so that only the current flows from the source to the drain, no backflow phenomenon occurs.

  When a reverse flow phenomenon occurs, the input voltage of the isolated DC-DC converter rises and components such as switching elements and rectifier elements are destroyed, or when a parallel operation is performed for an isolated DC-DC converter, There is a problem in that the power transmitted to the output is caused by a circulating current that is regenerated from the output to the input by another converter, resulting in a decrease in system efficiency. In the fourth embodiment, such a problem can be prevented.

  FIG. 15 shows a synchronous rectifier driving circuit unit according to the fifth embodiment. This circuit includes a comparator U1, a current amplification element E2, a detection resistor R11, and the like. When a current flows through the parasitic diode of the synchronous rectifier element Q3, a forward voltage drop occurs across the parasitic diode. Since the diode D2 is a Schottky barrier diode whose forward voltage drop is smaller than that of the parasitic diode, a current flows through the diode D2 via the detection resistor R11. The current causes a voltage larger than the reference voltage V3 at both ends of the detection resistor R11, and the output voltage of the comparator U1 is inverted from the L level to the H level. After a delay by the delay circuit composed of the resistor R9 and the capacitor C11, the input voltage of the current amplifying element E2 is also inverted from the L level to the H level, and the synchronous rectifying element Q3 and the switching element Q9 are turned on.

  When a rectified current flows through the synchronous rectifier element Q3, a voltage drop occurs between the source and drain of Q3. Since the detection resistor R11 is configured with a high resistance and almost no current flows through the switching element Q9, the voltage drop at Q9 is small. Therefore, when Q9 is turned on, a voltage drop of the synchronous rectifier element Q3 is observed at both ends of the detection resistor R11. When the voltage drop of the synchronous rectifier element Q3 is observed, the output of the comparator U1 maintains the H level, and the synchronous rectifier element Q3 and the switching element Q9 maintain the on state.

  When the voltage across the detection resistor R11 decreases due to a decrease in the current of the synchronous rectifier element Q3, the output voltage of the comparator U1 is inverted from the H level to the L level, and the charge of the capacitor C11 is discharged through the diode D3. Since the input voltage of the amplifying element E2 is also inverted from the H level to the L level, the synchronous rectifying element Q3 and the switching element Q9 are turned off again. With the above-described operation, the synchronous rectifier Q3 is turned on only during the period when the rectified current flows from the source to the drain, and is turned off during the other periods.

  Since the switching element Q9 has a parasitic capacitance in parallel with the Schottky barrier diode D2, when the drain voltage of the synchronous rectifier Q3 changes, the parasitic capacitance is energized and noise is generated at both ends of the detection resistor R11. To do. In order to prevent malfunction due to this noise, the comparator U1 is provided with hysteresis by resistors R8 and R14, and the diode D3, resistor R9, and capacitor C11 delay the turn-on of the synchronous rectifier Q3 but do not delay the turn-off. A circuit is configured.

  FIG. 16 is a circuit diagram of the isolated DC-DC converter 105 of the fifth embodiment. In the primary side control circuit PCC, the drive circuit unit of the sub switching element Q2 combines the pulse signal received by the reception winding Np22 of the signal transmission transformer PT and the signal transmitted from the terminal OutB via the capacitor C12. The sub-switching element Q2 is driven based on the above.

  The transition of the overlap signal output from the terminal OutB is transmitted through the capacitor C12 and divided by the capacitors C12 and C8. Capacitors C8 and C12 and resistor R6 constitute a differentiation circuit. By the action of the differential circuit, the gate-source voltage of the switching element Q5 is maintained at the H level during the off period of the sub switching element Q2, and the off state of the sub switching element Q2 is more reliably maintained.

  The first synchronous rectifier element (on-on side) Q4 includes a circuit composed of the auxiliary winding Ns12 of the power transmission transformer MT, the capacitor C7, the resistor R3, the reception winding Ns21 of the signal transmission transformer PT, and the switching element Q6 (shown in FIG. 7). The same drive circuit as the above circuit is connected.

  In the fifth embodiment, the first synchronous rectifier element Q4 is not provided with a countermeasure against backflow, but the voltage of the first smoothing capacitor C3 is “input voltage × (transformer 2) regardless of the presence or absence of the countermeasure against backflow. Next winding number / transformer primary winding number) ”is maintained. Therefore, if a countermeasure against backflow is applied only to the second synchronous rectifying element Q3 on the on / off side, power is output from the output side to the input side of the isolated DC-DC converter 105. The reverse flow phenomenon that is transmitted can be prevented.

  In the fifth embodiment, the second synchronous rectifier element (on / off side) Q3 has the same drive circuit as that shown in FIG. That is, when the voltage drop of the second synchronous rectifier Q3 is detected, Q3 is turned on, and when the conduction current of Q3 decreases and the voltage drop becomes less than a certain value, Q3 is turned off again. In this driving method, current flows through the second synchronous rectifier element Q3 only in the direction from the source to the drain, so that the backflow current of the insulated DC-DC converter 105 is prevented. Further, the second synchronous rectifier Q3 is turned on at the same time by Q3 and the first synchronous rectifier Q4, so that the current for discharging the accumulated charges of the first and second smoothing capacitors C3 and C2 changes Q3 and Q4. Since the driving method according to the fifth embodiment is on the through current path that penetrates, the through current can be prevented.

<< Sixth Embodiment >>
FIG. 17 is a circuit diagram of the insulation type DC-DC converter 106 of the sixth embodiment. In the primary side control circuit PCC, the terminal OutA outputs a drive signal for the main switching element Q1, and the terminal OutB outputs an overlap signal. Between the terminal OutA and the terminal OutB, a capacitor C9 and a resistor R6, which are impedance elements, are connected in series with the transmission winding Np21 of the signal transmission transformer PT. Therefore, a pulse signal is generated in the signal transmission transformer PT during a period corresponding to the dead time, and is transmitted from the transmission winding Np21 to the reception windings Ns21 and Ns22.

  Switching element Q12 is driven based on the signal differentiated from the output of terminal OutB by capacitor C11 and resistor R5, and the voltage obtained by dividing the output of diode D7 by resistors R12 and R5, and this switching element Q12 is inverted. At this timing, the sub switching element Q2 is driven.

  The first synchronous rectifier element (on-on side) Q4 includes an auxiliary winding Ns12 of the power transmission transformer MT, a capacitor C7, resistors R3 and R9, a reception winding Ns21 of the signal transmission transformer PT, diodes D5 and D6, and a switching element Q10. , Q11 constitutes a drive circuit similar to that shown in FIG.

  In the sixth embodiment, the first synchronous rectifier element Q4 is not provided with a countercurrent countermeasure, but the voltage of the first smoothing capacitor C3 is “input voltage × (transformer 2) regardless of the presence or absence of the countercurrent countermeasure. Next winding number / transformer primary winding number) ”, so that if a countermeasure against backflow is applied only to the second synchronous rectifying device Q3 on the on / off side, power is output from the output side to the input side of the isolated DC-DC converter. The transmitted backflow phenomenon can be prevented.

  In the sixth embodiment, the second synchronous rectifier element (on / off side) Q3 is also configured with a drive circuit similar to FIG. That is, a drive circuit is configured by the auxiliary winding Ns13 of the power transmission transformer MT, the capacitor C8, the resistors R7 and R8, the reception winding Ns22 of the signal transmission transformer, the diodes D1 and D4, and the switching elements Q7 and Q9.

  The resistor R13 is an equivalent resistance of the output filter inductor L2. The voltage across the output filter inductor L2 is integrated by the resistor R11 and the capacitor C4 and converted to a DC voltage. The comparator U2 compares the integrated DC voltage with the reference voltage V4. When the DC voltage is less than the reference voltage, the output voltage of the comparator U2 is maintained at the L level, so that the gate of the switching element Q9 connected via the diode D8 is maintained at the L level, and the second synchronous rectifying element Charging current does not flow into the gate of Q3.

  As described above, at the time of a light load, the second synchronous rectifier element Q3 is maintained in the off state, so that no backflow current flows through the insulated DC-DC converter 106 of the sixth embodiment.

C2 ... Second smoothing capacitor
C3: First smoothing capacitor
C6… Capacitor
C10 ... Third smoothing capacitor
COMP: Comparator
D2 ... Schottky barrier diode
E2 ... Current amplification element
L1… Series inductor
L2… Output filter inductor
Lm ... Excitation inductance
Load… Load circuit
MT ... Power transmission transformer
OutA ... Main switching element drive terminal
OutB: Overlap signal output terminal
PCC ... Primary side control circuit
PT. PT2 ... Signal transmission transformer
Q1 ... Main switching element
Q2 ... Sub switching element
Q3 ... Second synchronous rectifier
Q4 ... 1st synchronous rectifier
Rd ... High resistance
Rns: Resistance component
SCC ... Secondary control circuit
U1, U2 ... Comparators 101, 101B ... DC-DC converter 102 ... DC-DC converter 103, 103B ... DC-DC converter 104-106 ... DC-DC converter

Claims (18)

DC power input section,
A power transmission transformer;
A main switching element that performs switching control of a DC voltage applied to the primary winding of the power transmission transformer from the DC power supply input unit, and a sub-switching that is driven at a timing that is complementary to ON / OFF of the main switching element and sandwiches a dead time Elements,
A series circuit connected to the sub-switching element to form a series circuit, and the series circuit is connected to one end of the primary winding of the power transmission transformer;
A series inductor connected in series to the primary winding or the secondary winding of the power transmission transformer;
First and second synchronous rectifier elements connected to a secondary winding of the power transmission transformer;
A synchronous rectification driving circuit for driving the first and second synchronous rectification elements; first and second smoothing capacitors in which a voltage doubler rectification / smoothing circuit is formed together with the first and second synchronous rectification elements;
The first smoothing capacitor is charged via the series inductor and the first synchronous rectifier element during the conductive period of the first synchronous rectifier element that starts during the conductive period of the main switching element, and The second smoothing capacitor is charged via the series inductor and the second synchronous rectifier element during the conduction period of the second synchronous rectifier element started in the conduction period, and the output of the voltage doubler rectifier / smoothing circuit A control circuit that controls the input / output conversion ratio according to the duty ratio of the main switching element so that the voltage or output current gradually approaches the target value;
An insulating switching power supply device comprising: The synchronous rectification driving circuit includes:
Turning on the first synchronous rectifier element later than the start of conduction of the main switching element to reduce the current flowing through the first synchronous rectifier element immediately after the main switching element is turned off;
2. The insulation according to claim 1, wherein the second synchronous rectifying element is turned on later than the conduction start of the sub-switching element to reduce a current flowing through the second synchronous rectifier element immediately after the sub-switching element is turned off. Type switching power supply. The synchronous rectification driving circuit drives the first synchronous rectification element to turn off at the same time as or behind the turn-off of the main switching element,
3. The insulated switching power supply device according to claim 2, wherein the second synchronous rectifying element is turned off at the same timing as or behind the turn-off of the sub switching element.   4. The synchronous rectification drive circuit according to claim 2, wherein at least one of the first synchronous rectification element and the second synchronous rectification element is turned on using a voltage excited by the power transmission transformer. 5. Isolated switching power supply.   A signal transmission transformer having a plurality of windings, wherein the synchronous rectification drive circuit receives the pulse signal transmitted from the primary side to the secondary side via the signal transmission transformer, and the first synchronous rectification The insulated switching power supply device according to any one of claims 2 to 4, wherein at least one of an element and the second synchronous rectifying element is turned off.   The synchronous rectification drive circuit includes a signal transmission transformer having a plurality of windings, the sub-switching element is turned on using a voltage excited by the power transmission transformer, and is transmitted through the signal transmission transformer. The insulated switching power supply device according to claim 2, wherein a pulse signal is received to turn off the auxiliary switching element. A square-wave main switching element driving signal that is at H level during the on period of the main switching element is output to the main switching element driving terminal, and in addition to the on period of the main switching element, the preceding and following dead time periods are also at H level. A control circuit on the primary side that outputs a square wave-shaped overlap signal to the overlap signal output terminal,
The pulse signal generated during the dead time period is connected between the main switching element driving terminal and the overlap signal output terminal, directly or via an impedance element, and the transmission winding of the signal transmission transformer. The insulated switching power supply device according to claim 5 or 6, wherein transmission is performed by a signal transmission transformer.   A synchronous inductor that is connected in series with the secondary winding of the power transmission transformer; and the synchronous rectification drive circuit detects a voltage applied to both ends of the serial inductor to detect first and second synchronous rectifications. The insulated switching power supply device according to claim 1, wherein at least one of the elements is turned off. A series inductor connected in series with the primary winding of the power transmission transformer;
The series inductor is a series inductor transformer having a secondary winding, and a voltage applied to both ends of the primary winding of the series inductor transformer is transmitted to the secondary winding to detect a voltage change of the secondary winding. The insulated switching power supply device according to claim 1, wherein at least one of the first and second synchronous rectifying elements is turned off. Current detection means for detecting the amount of current in the path from the DC power supply input unit to the output of the voltage doubler rectification / smoothing circuit;
10. The backflow prevention circuit according to claim 1, further comprising a backflow prevention circuit that maintains at least one of the first and second synchronous rectifying elements in an off state when a detection value of the current detection unit is a predetermined value or less. The insulation type switching power supply device described in 1.   In the current detection means, a series circuit of an induction voltage differential winding and a detection resistor whose winding direction and number of turns are equal to the secondary winding of the power transmission transformer are parallel to the secondary winding of the power transmission transformer. The insulated switching power supply device according to claim 10, which is a circuit connected to the circuit. A voltage drop detection circuit for detecting a voltage drop of the synchronous rectification element in at least one of the first and second synchronous rectification elements;
The insulated switching power supply device according to any one of claims 1 to 9, further comprising a backflow prevention circuit that maintains the synchronous rectifying element in an ON state only during a period in which the voltage drop detected by the voltage drop detection circuit is equal to or greater than a predetermined value. . A π-type filter including a filter inductor is provided at the subsequent stage of the voltage doubler rectifying / smoothing circuit,
A voltage drop detection circuit for integrating the voltage across the filter inductor to detect the voltage drop across the filter inductor;
10. A backflow prevention circuit that maintains at least one of the first and second synchronous rectifier elements in an off state when a voltage drop detected by the voltage drop detection circuit is a predetermined value or less. The insulation type switching power supply device according to any one of the above.   When the first and second synchronous rectifying elements are simultaneously turned on, a through current is generated in which the accumulated charge of the first and second smoothing capacitors is discharged through the first and second synchronous rectifying elements. The insulated switching power supply device according to any one of claims 1 to 13, further comprising a through-current prevention circuit for preventing the above-described problem. A path from the DC power supply input unit to the output of the voltage doubler rectification / smoothing circuit and a common path with the through current include a forward current detection circuit that detects a current amount,
The through current prevention circuit maintains at least one of the first and second synchronous rectification elements in an off state when a forward current detected by the forward current detection circuit is a predetermined value or less. Both the reverse flow phenomenon in which power is transmitted from the output section to the input side and the through current in which the accumulated charge of the first and second smoothing capacitors discharges through the first and second synchronous rectifier elements are prevented. The insulated switching power supply device according to claim 14. Among the first and second synchronous rectifying elements, a control terminal short-circuit switch whose ON period substantially coincides with the synchronous rectifying element connected to the low side,
When the control terminal short-circuit switch is turned on, the through current prevention circuit reduces the control terminal voltage of the synchronous rectifying element connected to the high side, and maintains the synchronous rectifying element connected to the high side in the off state. The insulated switching power supply device according to claim 14.   The insulated switching power supply device according to any one of claims 1 to 16, wherein the series inductor includes a leakage inductance of the power transmission transformer.   The insulated switching power supply device according to any one of claims 1 to 16, wherein the series inductor is configured by an inductor separate from a transformer.

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