JP2001327163A - Synchronously rectifying switching converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synchronously rectifying switching converter capable of keeping an on-state throughout the entire period over which a regenerative MOSFET is to pass a regenerative current, improving efficiency, and operating in parallel. SOLUTION: This converter is provided with a tertiary winding 23 of a power converting transformer 20 obtaining gate driving signals of a rectifying MOSFET 60 and a regenerative MOSFET 70, an impedance device, for example, resistors 61, 71 which are connected to the gates of the rectifying MOSFET 60 and the regenerative MOSFET 70 and control the voltage ratio of the gate driving signals, and a clamp circuit 50 which is connected to a primary winding 21 of the power transformer 20, and keeps the gate driving signal level of the regenerative MOSFET 70 constant throughout almost the entire period over which a switching MOSFET 30 is in an off-state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronous rectification type switching regulator used in a power supply circuit of a computer, a communication device, various electronic devices, an electric device and the like.

[0002]

2. Description of the Related Art FIG. 6 is a circuit diagram showing a conventional self-driving synchronous rectification type switching regulator. That is, the DC input voltage from the DC voltage source 10 is converted into a periodic rectangular wave pulse voltage by the ON / OFF operation of the main switch MOSFET 30, and the power conversion transformer 20
Is applied to the primary winding 21. This rectangular wave pulse voltage is transmitted to the secondary winding 22 of the power conversion transformer 20, rectified and smoothed by a rectifying and smoothing circuit such as a rectifying MOSFET 60, a regenerating MOSFET 70, a choke coil 80, an output capacitor 90, etc. , T2.

A synchronous rectification switching converter has a low O
ON / O of main switch for inverter with rectifier of N resistance
The rectification function is realized by driving in synchronization with the FF operation. A MOSFET is often used as the rectifying element, and there is a method of using a terminal voltage on the secondary side of a power conversion transformer as a gate drive signal of the MOSFET. This is generally called a self-driven synchronous rectification system, and is widely used because of simplicity of the circuit.

FIG. 7 is a circuit diagram showing a failure mode when a conventional self-driven synchronous rectification type switching regulator is operated in parallel. In the figure, 20 ', 2
1 ', 22', 30 ', 60', 70 ', 80', 9
0 'has the same function as that of the same number without rough. 100 is a load.

However, in this system, when the circuits are simply operated in parallel, in the case of a primary side fault of the power conversion transformer 20, the output voltage of the faulty circuit becomes zero and the output voltage from the other circuit spills. A load short circuit occurs.

As a method for remedying such a drawback, a tertiary winding 23 is provided in the power conversion transformer 20, and a rectifying MOSFET 60 and a regenerative MOSFET are provided from the tertiary winding 23.
There is a method of obtaining a gate drive signal of the ET 70. FIG. 8 shows a circuit diagram specifically implementing such a method. In the figure, diodes d1 and d2, resistors R1 and R2, and capacitors C1 and C2 constitute a gate control circuit.

FIG. 8 shows a main switch MOSFET.
30, power conversion transformer 20, rectifying MOSFET 6
0, a regenerative MOSFET 70, a choke coil 80, an output capacitor 90, a gate control circuit, and the like. The power conversion transformer 20 is structurally different from these in addition to the primary winding 21 and the secondary winding 22. And a tertiary winding 23 that is magnetically coupled.

[0008] Tertiary winding 23 of power conversion transformer 20
Are magnetically coupled to the primary winding 21, so that the main switch MOSFET 30 is
By the / OFF operation, a voltage proportional to the voltage induced on the primary side 21 is induced. That is, if the voltage value of the DC input voltage is Ei, the reset voltage value of the power conversion transformer 20 is Er, and the turn ratio of the primary winding 21 to the tertiary winding 23 is nd, the terminal voltage of the tertiary winding 23 is , MOS for main switch
When FET 30 is ON, nd · Ei, MO for main switch
When the SFET 30 is OFF, nd · Er is obtained. The reset voltage value Er differs depending on the circuit system of the converter and the configuration of the snubber circuit.

FIG. 9 is a diagram showing a terminal voltage waveform of the tertiary winding 23 of FIG. Main switch MOSFET 30 is ON
In this case, the terminal voltage waveform of the tertiary winding 23 is represented by 101, its peak value is nd · Ei, and its duration is T1. 3 when the main switch MOSFET 30 is OFF
The terminal voltage waveform of the secondary winding 23 is represented by 102, its peak value is nd · Er, and its duration is T2, which corresponds to the reset time of the power conversion transformer 20. Generally, in the case of a single-ended forward converter, the entire period during which the main switch MOSFET 30 is OFF does not become the reset time, and there is always a pause time T3. The terminal voltage waveform of the tertiary winding 23 is a diode d
1, d2, resistors R1, R2, and capacitors C1, C2
MOSFET 6 for rectification through a gate control circuit consisting of
0 and used as a gate drive signal of the regenerative MOSFET 70.

[0010]

The diodes d1 and d2 of the gate control circuit are connected to the periods T2 and T2 in FIG.
1 alternately repeats ON and OFF states,
02 is between the gate and source of the regenerative MOSFET 70,
The waveform 101 is directly applied between the gate and the source of the rectifying MOSFET 60. As a result, the regenerative MOS
The FET 70 can hold the ON state only during the period T2 when the main switch MOSFET 30 is in the OFF state. During the remaining period T3, the regenerative MOSFET 70 is turned off, so that a regenerative current flows through the body diode of the regenerative MOSFET 70, resulting in a corresponding decrease in efficiency.

The voltages of the two gate drive signals are n
It becomes approximately equal to d · Ei and nd · Er. Therefore, the voltage ratio becomes Ei / Er and cannot be changed even if the turns ratio nd of the primary winding 21 and the tertiary winding 23 of the power conversion transformer 20 is changed. Therefore, when the configuration of the snubber circuit is variously different, or when the fluctuation range of the input voltage is very wide, the rectifying MOSFET 60 and the regenerative MOSFET 70 are used.
However, there is a disadvantage that the balance of the gate drive voltages cannot be set appropriately.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and keeps the regenerative MOSFET in an ON state for the entire period in which a regenerative current should flow, and has a rectifying and regenerating MOS.
It is an object of the present invention to provide a synchronous rectification switching converter capable of improving efficiency by appropriately selecting a gate drive voltage ratio of an FET.

[0013]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a method for converting a DC input voltage to a main switch MOSFET.
And applies the pulse voltage to the primary winding of the power conversion transformer. The pulse voltage extracted to the secondary winding of the power conversion transformer is converted into a rectification MOSFET, a regenerative MOSFET, a choke coil, and an output. In a synchronous rectification switching converter that obtains a DC output voltage by rectifying and smoothing with a rectifying and smoothing circuit including a capacitor,
A tertiary winding of the power conversion transformer for obtaining a gate drive signal of the rectifying MOSFET and the regenerating MOSFET, and an impedance connected to the gates of the rectifying MOSFET and the regenerating MOSFET for controlling a voltage ratio of the gate driving signal. Element and a primary winding of the power conversion transformer, and the main switch MOSFET sets the gate drive signal level of the regenerative MOSFET to OF.
And a clamp circuit for keeping the voltage constant over substantially the entire region in the F state.

According to the present invention, the DC input voltage is converted into a rectangular wave pulse voltage by a main switch MOSFET, applied to a primary winding of a power conversion transformer, and taken out to a secondary winding of the power conversion transformer. M for pulse voltage rectification
In a synchronous rectifying switching converter for obtaining a DC output voltage by rectifying and smoothing by a rectifying and smoothing circuit including an OSFET, a regenerating MOSFET, a choke coil, and an output capacitor, the rectifying MOSFET and the regenerating MO are provided.
A tertiary winding of the power conversion transformer for obtaining a gate drive signal of the SFET, the rectifying MOSFET and a regenerative M
An impedance element connected to the gate of the OSFET for controlling the voltage ratio of the gate drive signal; and an impedance element connected between the drain and the source of the MOSFET for the main switch; Is provided with a clamp circuit that keeps constant over almost the entire area in the OFF state.

According to the present invention, the DC input voltage is converted into a rectangular wave pulse voltage by a main switch MOSFET, applied to a primary winding of a power conversion transformer, and taken out to a secondary winding of the power conversion transformer. M for pulse voltage rectification
In a synchronous rectifying switching converter for obtaining a DC output voltage by rectifying and smoothing by a rectifying and smoothing circuit including an OSFET, a regenerating MOSFET, a choke coil, and an output capacitor, the rectifying MOSFET and the regenerating MO are provided.
A tertiary winding of the power conversion transformer for obtaining a gate drive signal of the SFET, the rectifying MOSFET and a regenerative M
An impedance element connected to the gate of the OSFET to control the voltage ratio of the gate drive signal; and a quaternary winding of the power conversion transformer,
The gate drive signal level of the ET is changed to the main switch MOS.
And a clamp circuit for holding the FET constant over substantially the entire area where the FET is in the OFF state.

According to the present invention, in a synchronous rectification switching converter, a means for obtaining a gate drive signal of a rectifying element MOSFET is magnetically coupled separately from a primary winding and a secondary winding of a power conversion transformer. Adopting a circuit using a tertiary winding enables parallel operation of the circuits. By providing a clamp circuit, the regenerative MOSFET is kept in the ON state over almost the entire OFF period of the main switch MOSFET. And MO for rectification
The gate and source of each of the SFET and the regenerative MOSFET are connected by a suitable impedance element (resistance or capacitor), and the ratio of the gate drive signal level is adjusted by changing the impedance value ratio of this impedance element. Solved the problem as follows.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings, the same portions are denoted by the same reference numerals and description thereof will be omitted.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. That is, the DC voltage source 10 is connected to one of the power conversion transformers 20 through the main switch MOSFET 30.
Connected to the next winding 21 and the main switch MOSFET
The gate of 30 is connected to the control circuit 40. The drain of the main switch MOSFET 30 is an auxiliary switch M
An OSFET 51 and a clamping capacitor 52 are connected in series to the positive terminal of the DC voltage source 10, and the gate of the auxiliary switch MOSFET 51 is connected to a control circuit 40.
Connected to. The auxiliary switch MOSFET 51 and the clamp capacitor 52 constitute a clamp circuit 50. One end of the secondary winding 22 of the power conversion transformer 20 is connected to a load terminal T1 via a choke coil 80, and the other end of the secondary winding 22 is
0 is connected to the load side terminal T2. M for rectification
The gate of the OSFET 60 is connected to the power conversion transformer 20.
Is connected to one end of the tertiary winding 23. The rectifying MOS
An impedance element, for example, a resistor 61 is connected between the gate and the source of the FET 60. The rectifying MOSFET
A regeneration MOSFET 70 is connected between the source of the secondary winding 60 and one end of the secondary winding 22.
The gate of 70 is connected to the other end of the tertiary winding 23 of the power conversion transformer 20. MOSFET 70 for regeneration
An impedance element, for example, a resistor 71 is connected between the gate and the source. An output capacitor 90 is connected between the load terminals T1 and T2, and the load terminal T1 is connected to the control circuit 40. The impedance elements, for example, the resistors 61 and 71 constitute a signal level distribution circuit,
MOSFET 60 for rectification and MOSFET 70 for regeneration
The choke coil 80 and the output capacitor 90 constitute a rectifying / smoothing circuit.

The DC input voltage from the DC voltage source 10 is applied between the drain and source of the main switch MOSFET 30 via the primary winding 21 of the power conversion transformer 20. The main switch MOSFET 30 repeats the ON / OFF operation according to the gate drive signal from the control circuit 40. When the main switch MOSFET 30 is in the ON state, the voltage value Ei of the DC input voltage is applied to both ends of the primary winding 21 as it is. The winding ratio of the primary winding 21 and the secondary winding 22 of the power conversion transformer 20 is ns, and the winding ratio of the primary winding 21 and the tertiary winding 23 is nd.
Then, the terminal voltage of the secondary winding 22 when the main switch MOSFET 30 is ON is ns · Ei, and the terminal voltage of the tertiary winding 23 is nd · Ei. In this state, the terminal voltage nd · Ei of the tertiary winding 23 becomes
It is divided in proportion to the value of an impedance element such as a resistor 61 between the gate and the source of 0 and the impedance element such as a resistor 71 between the gate and the source of the regenerative MOSFET 70. Among the divided voltages, the voltage applied to both ends of the impedance element such as the resistor 61 biases the rectifying MOSFET 60 to the ON state, and the voltage applied to both ends of the impedance element such as the resistor 71 biases the regenerative MOSFET 70 to the OFF state. I do. As a result, the terminal voltage ns · Ei of the secondary winding 22 supplies a load current to the load-side terminals T1 and T2 via the output choke coil 80 and the rectifying MOSFET 60.

When the main switch MOSFET 30 is turned off, a clamp voltage Ec is generated across the primary winding 21 of the power conversion transformer 20 by the operation of the clamp circuit 50. The polarity of the clamp voltage Ec is M for the main switch.
The polarity is opposite to the voltage across the primary winding 21 when the OSFET 30 is ON. At this time, the terminal voltage of the secondary winding 22 is ns · Ec, and the terminal voltage of the tertiary winding 23 is ns · Ec.
c. The terminal voltage ns.Ec of the tertiary winding 23 is divided in proportion to the value of the impedance element, for example, the resistor 61 and the impedance element, for example, the resistor 71, as in the case where the main switch MOSFET 30 is ON. 70 is applied between the gate and source, but the polarity is reversed. As a result, the voltage across the impedance element, for example, the resistor 61, is
60 is turned off, and the current return path of the terminal voltage of the secondary winding 22 is cut off. The voltage at both ends of the impedance element, for example, the resistor 71 keeps the regenerative MOSFET 70 in the ON state and continues to flow the regenerative current to the output choke coil 80.

The clamp circuit 50 has an auxiliary switch M
The auxiliary switch MOSFET 51 is controlled by the control circuit 40 so as to operate complementarily to the main switch MOSFET 30. The capacitance of the clamping capacitor 52 is selected such that the resonance frequency determined by the excitation impedance LM of the primary winding 21 is sufficiently lower than the switching frequency of the converter. Under such conditions, the main switch MOSFET 30 is turned off.
In this state, a substantially constant clamp voltage Ec is held at both ends of the primary winding 21 over the entire time period when the main switch MOSFET 30 is OFF. Here, MO for main switch
Assuming that the duty ratio of the SFET 30 is D, the clamp voltage E
c is Ec ≒ from the relationship of the constant voltage-time product of the transformer.
It is approximated as {D / (1-D)} × Ei.

The primary-side leakage inductance of the power conversion transformer 20 is appropriately set, and the control circuit 40 controls the main switch MOSFET 30 and the auxiliary switch MOSFET.
It is also possible to operate the soft switch by delicately controlling the complementary operation of the FET 51.

FIG. 2A shows one of the power conversion transformers 20.
2B shows a terminal voltage waveform of the secondary winding 21, and FIG. 2B shows a terminal voltage waveform of the tertiary winding 23 of the power conversion transformer 20.

FIG. 2B and FIG. 9 are compared. In FIG. 9, there is a period T3 in which the reset voltage becomes zero.
In (b), the main switch MOSFET 30 is turned off.
The clamp voltage is maintained throughout the period of F,
It can be seen that the regenerative MOSFET 70 can maintain the ON state.

The terminal voltage of the tertiary winding 23 shown in FIG. 2B is applied from one terminal of the tertiary winding 23 to the other terminal of the tertiary winding 23 via impedance elements such as resistors 61 and 71. Generate a circulating current that returns to Due to this circulating current, the terminal voltage of the tertiary winding 23 is applied between the gate and source of the rectifying MOSFET 60 and the regenerating MOSFET 70 by an impedance element, for example, the impedance value Z6 of the resistor 61.
A voltage proportionally distributed between 1 and an impedance element such as an impedance value Z71 of a resistor 71 is applied. However, since the sources of the two MOSFETs 60 and 70 are common, their respective gate-source voltages are expressed with polarities opposite to each other. This situation is shown in FIGS. 3 (a) and 3 (b). Rectifying MOSFs corresponding to the impedance values Z61 and Z71, respectively.
ET60, including the gate capacitance of the regenerative MOSFET 70.

FIG. 3A shows a waveform of a voltage applied between the gate and the source of the rectifying MOSFET 60, and FIG.
(A) 201 is the gate drive voltage of the rectifying MOSFET 60, and its voltage value is Z61 / (Z61 + Z71) n
d · Ei.

FIG. 3B is a diagram showing a voltage waveform applied between the gate and the source of the regenerative MOSFET 70.
Reference numeral 302 in (b) denotes a gate drive voltage of the regenerative MOSFET 70, the voltage value of which is Z71 / (Z61 + Z71) n
d · Ec.

The ratio of the two gate drive voltages is (Z61 ·
Ei) / (Z71 · Ec), and the transformer 20
Ei / E derived from the constant voltage-time product relation
Substituting c = (1-D) / D gives (Z61 / Z71) ×
{(1-D) / D}.

This equation gives the impedance Z for the duty ratio determined by the conditions under which the switching converter is used.
It means that a balanced drive voltage can be set by appropriately selecting 61 and Z71.

Considering the basic operation principle of the clamp circuit 50, the clamp circuit 50 is
The same effect can be expected with a configuration connected between the drain and the source of the semiconductor device. FIG. 4 shows an example of this configuration.

FIG. 5 is structurally independent of the primary winding 21, the secondary winding 22, and the tertiary winding 23 of the power conversion transformer 20,
A clamp circuit 5 is provided at both ends of the magnetically coupled quaternary winding 24.
0 is connected, and this configuration has the same effect.

As described above, in the synchronous rectification switching converter, parallel operation is enabled by supplying the gate drive signal of the rectification MOSFET from another winding of the transformer, and the efficiency is improved by the clamp circuit and the signal level distribution circuit. Plan.

[0033]

As described above, according to the present invention, in a synchronous rectification switching converter capable of operating in parallel,
A regenerative MOSFET maintains an ON state for the entire period when a regenerative current is to flow, and a rectifying and regenerating MOSFE
The efficiency can be improved by appropriately selecting the gate drive voltage ratio of T.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2A shows a terminal voltage waveform of a primary winding of a power conversion transformer, and FIG. 2B shows a terminal voltage waveform of a tertiary winding of the power conversion transformer.

3A is a diagram showing a voltage waveform applied between a gate and a source of a rectifying MOSFET, and FIG.
FIG. 4 shows a diagram of a voltage waveform applied between the gate and the source of the FET.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention.

FIG. 6 is a circuit diagram showing a conventional self-driven synchronous rectification type switching regulator.

FIG. 7 is a diagram showing a failure mode when a conventional self-driven synchronous rectification type switching regulator is operated in parallel.

FIG. 8 is a circuit diagram showing a synchronous rectification type switching regulator that obtains a gate drive signal using a tertiary winding of a conventional transformer.

9 is a diagram showing a terminal voltage waveform of the tertiary winding of FIG. 8;

DESCRIPTION OF SYMBOLS 10 DC voltage source 20 Power conversion transformer 21 Primary winding 22 Secondary winding 23 Tertiary winding 24 Quaternary winding 30 MOSFET for main switch 40 Control circuit 50 Clamp circuit 51 MOSFET for auxiliary switch 52 Clamping capacitor 60 Rectifying MOSFET 61 Impedance element such as resistor 70 Regenerative MOSFET 71 Impedance element such as resistor 80 Choke coil 90 Output capacitor C1, C2 Capacitor d1, d2 Diode R1, R2 Resistance

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H006 AA01 CA02 CA12 CB03 CB07 CC02 DA04 DB01 DC05 FA01 5H730 AA01 AA14 AS01 BB23 BB84 DD04 DD26 DD32 DD41 EE02 EE08 EE13 EE72 FD01 FG01

Claims (3)

[Claims] A DC input voltage is applied to a main switch MOSFE.
T converts the pulse voltage into a rectangular wave pulse voltage, applies the pulse voltage to the primary winding of the power conversion transformer, and converts the pulse voltage extracted to the secondary winding of the power conversion transformer to a rectifying MOSFET;
In a synchronous rectification switching converter for obtaining a DC output voltage by rectifying and smoothing by a rectifying / smoothing circuit including a regenerative MOSFET, a choke coil, and an output capacitor, the power conversion for obtaining a gate drive signal of the rectifier MOSFET and the regenerative MOSFET. A tertiary winding of a transformer, an impedance element connected to the gates of the rectifier MOSFET and the regenerative MOSFET, and controlling a voltage ratio of the gate drive signal; and a tertiary winding of the power conversion transformer, A synchronous rectifying switching converter, comprising: a clamp circuit that holds a gate drive signal level of a regenerative MOSFET constant over substantially the entire region where the main switch MOSFET is in an OFF state. 2. A main switch MOSFE for DC input voltage.
T converts the pulse voltage into a rectangular wave pulse voltage, applies the pulse voltage to the primary winding of the power conversion transformer, and converts the pulse voltage extracted to the secondary winding of the power conversion transformer to a rectifying MOSFET;
In a synchronous rectification switching converter for obtaining a DC output voltage by rectifying and smoothing by a rectifying / smoothing circuit including a regenerative MOSFET, a choke coil, and an output capacitor, the power conversion for obtaining a gate drive signal of the rectifier MOSFET and the regenerative MOSFET. A tertiary winding of a transformer, an impedance element connected to the gates of the rectifying MOSFET and the regenerative MOSFET and controlling a voltage ratio of the gate drive signal, and a drain-source connected to the main switch MOSFET; A synchronous rectifying switching converter, comprising: a clamp circuit that holds a gate drive signal level of the regenerative MOSFET constant over substantially the entire region where the main switch MOSFET is OFF. 3. A DC input voltage is applied to a main switch MOSFE.
T converts the pulse voltage into a rectangular wave pulse voltage, applies the pulse voltage to the primary winding of the power conversion transformer, and converts the pulse voltage extracted to the secondary winding of the power conversion transformer to a rectifying MOSFET;
In a synchronous rectification switching converter for obtaining a DC output voltage by rectifying and smoothing by a rectifying / smoothing circuit including a regenerative MOSFET, a choke coil, and an output capacitor, the power conversion for obtaining a gate drive signal of the rectifier MOSFET and the regenerative MOSFET. A tertiary winding of a transformer, an impedance element connected to the gates of the rectifying MOSFET and the regenerative MOSFET and controlling a voltage ratio of the gate drive signal, and a tertiary winding of the power conversion transformer, A synchronous rectifying switching converter, comprising: a clamp circuit that holds a gate drive signal level of a regenerative MOSFET constant over substantially the entire region where the main switch MOSFET is in an OFF state.