JPH09312972A - Rectifying circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the breakage of a field effect transistor for rectification without dropping rectification efficiency by equipping a rectifying circuit with a field effect transistor which is connected in parallel with a diode for rectifying AC and besides rectifies the input voltage, based on the control signal proportionate to the rectified DC current value. SOLUTION: The current transformer 21 of a rectifying circuit 11 generates a control current I11 of a current value 27 roughly proportionate to the current value of the current I11 rectified with an inner parasitic diode 27, and outputs the generated control current I12 thereby operating a transistor(Tr) 22. For example, if the current I11 ceases to flow, the control current I12 ceases to flow, so the voltage ceases to be applied to the gate of Tr22. In this case, the charge accumulated in the gate is discharged to the ground through a diode 24 and the secondary winding 21b of the current transformer 21, and Tr22 stops.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectifier circuit that can be arranged on the output winding side of a switching transformer of a switching power supply device, and more specifically, it is synchronized with the alternating current output from the output winding of the switching transformer. The present invention relates to a rectifying circuit suitable for rectifying the alternating current.

[0002]

2. Description of the Related Art In a switching power supply device, etc.,
A rectification method is used in which an alternating current output from the output winding of a switching transformer is rectified by a diode and a capacitor arranged on the output winding side. On the other hand, in recent years, in order to reduce the power loss due to the diode at the time of rectification, development of a rectification circuit using an FET as a rectification element has become active. As such a rectifier circuit, for example, the one described in Japanese Utility Model Laid-Open No. 4-58087 is known.

Rectifier circuit 71 described in the above publication.
Is a so-called synchronous rectification circuit, and is arranged on the secondary winding 4b side of the switching transformer 4 in the forward type switching power supply device, as shown in FIG. The rectifier circuit 71 includes a main winding 72a and a driving winding 72.
choke coil 72 having b and 72c, and transformer 4
Between the MOS type FET (field effect transistor) 22 connected between the positive voltage side terminal of the secondary winding 4b and the main winding 72a of the choke coil 72, and the drain of the FET 22 and the ground terminal 13. The connected FET 73 and the smoothing capacitor 26 connected between the positive voltage output terminal 12 and the ground terminal 13 are provided. The rectifier circuit 71 also includes a resistor 74 connected between one end of the drive winding 72b of the choke coil 72 and the gate of the FET 22, and a resistor 75 connected between one end of the drive winding 72c and the gate of the FET 73. ing.

In this rectifying circuit 71, a switching means (not shown) switches the direct current input to the primary winding 4a of the transformer 4 to cause the secondary winding 4b of the transformer 4 to have a voltage V _{S1 in the} direction shown in the figure. Exchange occurs. In this case, the alternating current is rectified by the internal parasitic diode 27 of the FET 22, and the rectified direct current voltage passes through the main winding 72a of the choke coil 72 and the capacitor 2
Smoothed by 6. In this case, the choke coil 72
At both ends of the main winding 72a of the capacitor from the voltage V _S1 2
A voltage approximately equal to the value obtained by subtracting the voltage across 6 is generated,
Along with this, a voltage having a value corresponding to the turn ratio of each winding is generated in the voltage across the main winding 72a at both ends of the drive windings 72b and 72c. The voltage generated in the drive winding 72b is the FET
22 is applied to the gate of FET 22, which causes FET 22 to operate and the alternating current is rectified primarily by FET 22.

On the other hand, the voltage V is applied to the secondary winding 4b of the transformer 4.
_When an alternating current having a voltage V _S2 opposite to that of _S1 is generated, the internal parasitic diode 27 does not rectify the alternating current and a reverse voltage is generated in the drive winding 72b, so that the FET 22 is in an operation stop state. At the same time, the current flowing through the main winding 72a of the choke coil 72 continues to flow through a parasitic diode (not shown) between the drain and source of the FET 73. In this state, the back electromotive force generated in the drive winding 72c is applied to the gate of the FET 73, which causes the FE
Since T73 operates, the low-loss rectification operation is continued. As described above, the rectifier circuit 71 half-wave rectifies the alternating current by operating the FET 22 in synchronization with the alternating current generated in the secondary winding 4b. As a result, the power loss at the time of rectification becomes the power of the value obtained by multiplying the square of the rectification current by the ON resistance of the FET 22, and the power loss in the conventional diode rectification method (power obtained by multiplying the ON voltage of the diode by the rectification current). It is extremely reduced compared with.

[0006]

However, the conventional rectifier circuit 71 has the following problems. That is, generally, the maximum rated voltage that can be applied between the gate and the source of the FET is a low value of about ± 30V. Therefore, the rectifier circuit 71 has a problem that the FET 22 may be destroyed even when the voltage value of the generated DC power is less than or equal to the maximum rated voltage. In particular,
For example, in a forward type switching power supply device that generates direct current from alternating current, as shown in FIG. 6, the voltage V _S1 and the voltage V _S1 output from the secondary winding 4b of the transformer are
_S2 is not necessarily equal, and energy (proportional to the area of the hatched portion indicated by reference numeral 61 in the figure) output during the period T _ON during which the switching element arranged on the primary side of the transformer 4 is on, The energy (proportional to the area of the hatched portion indicated by reference numeral 62 in the figure) output during the period T _OFF during which the switching element is off is substantially equal.
Therefore, in the conventional rectifier circuit 71, the choke coil 7
The gate voltage proportional to the voltage across the second main winding 72a is F
Since it is applied to the gate of the ET22, the DC voltage input to the primary winding 4a side of the transformer 4 rises and the switching signal turns on even when the gate voltage is below the maximum rated voltage in normal times. When the time T _ON is shortened or the like, the voltage V _S1 rises, and accordingly the gate voltage also rises. In some cases, a gate voltage higher than the maximum rated voltage is applied between the gate and the source of the FET 22. There is a problem that the FET 22 may be destroyed by being applied to the.

On the other hand, by connecting a Zener diode or the like between the gate and source of the FET 72, the F
It is also possible to prevent breakdown of the ET 22 by pressure. However, when configuring a so-called all-range power supply device that can output a predetermined voltage to commercial power supplies around the world, if the voltage value of the commercial power supply is high, the Zener diode always loses power, resulting in the entire rectifier circuit. However, there is a problem that the rectification efficiency of is extremely reduced.

Further, in general, the FET has several hundred pF
Since the conventional rectifier circuit 71 has a gate capacitance of several thousand pF, it does not operate immediately even if a DC voltage is applied to the gate of the FET 22 via the resistor 74.
2 turn-on time is longer. On the contrary, even when the application of the DC voltage is stopped, the turn-off time of the FET 22 becomes long due to the electric charge accumulated in the gate, and as a result, the rise and fall of the switching operation of the FET 22 become long. Therefore, various problems have occurred. Specifically, if the switching operation of the FET 22 rises slowly, the internal parasitic diode 2
There is a problem that the power loss cannot be reduced because the rectification time by 7 becomes long. On the other hand, if the fall of the switching operation is slow, the FET 22 may be turned on even when the voltage V _S2 is generated in the secondary winding 4b of the transformer 4, and in such a case, the FE
There is a problem that a reverse voltage is applied across the capacitor 26 by T22 and a reverse current flows through the secondary winding 4b side of the transformer 4.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a rectifying circuit capable of preventing the breakdown of the field effect transistor for rectification without lowering the rectification efficiency. And Another object is to provide a rectifier circuit that can prevent the generation of reverse current in the rectifier circuit.

[0010]

In order to achieve the above object, a rectifier circuit according to a first aspect of the present invention comprises a diode for rectifying an input AC input and a current value or a voltage value in the current value of the rectified DC current. It is characterized in that it is provided with a control signal generating means for generating a control signal which is substantially proportional, and a field effect transistor which is equivalently connected in parallel with the diode and operates based on the control signal to rectify the input alternating current. In this case, the direct current refers to all other currents that do not include alternating current, which is a current whose direction is periodically changed and whose average value over one period is zero, and pulsating current. Or
It includes a direct current in which a pulsating current is superimposed on a direct current having a constant voltage value. The control signal may be a current signal or a voltage signal. When the control signal, which is a current signal that is substantially proportional to the current value of the rectified direct current, functions as a voltage signal, the control signal A resistor may be connected to the path through which the voltage flows and the voltage generated across the resistor may be used as the control signal.

In this rectifying circuit, the control signal generating means is
A field-effect transistor is operated by generating a control signal whose current value or voltage value is substantially proportional to the current value of the direct current rectified by the diode, and outputting the generated control signal. Thereby, the field effect transistor operates only while the diode is about to conduct, that is, when the positive voltage direct current power is generated, only when the positive polarity part of the alternating current is input. As a result, the alternating current is rectified by the field effect transistor by passing from the source to the drain of the field effect transistor having a small on-resistance. Thus, in this rectifier circuit, for example, when applied to a switching power supply device, the voltage output from the secondary winding of the switching transformer even when the AC voltage input to the switching power supply device is high. The switching of the field effect transistor is controlled by a control signal whose current value or voltage value is substantially proportional to the current value of the rectified direct current regardless of the level of the DC voltage. Therefore, the breakdown of the field effect transistor can be reliably prevented, and the field effect transistor can be applied to a rectifier circuit in a so-called all-range switching power supply device.

A rectifier circuit according to a second aspect is the rectifier circuit according to the first aspect, wherein the diode is an internal parasitic diode of a field effect transistor.

In this rectifier circuit, the internal parasitic diode existing inside the field effect transistor generates a direct current for generating a control signal by rectifying the input alternating current. As a result, it is not necessary to use a separate diode, so that the circuit can be easily configured.

The rectifier circuit according to a third aspect is the rectifier circuit according to the first or second aspect, wherein the rectifier circuit is connected between the gate of the field effect transistor and the low potential line, and when the output of the control signal is stopped, the gate is connected to the gate. It is characterized in that it is provided with a charge discharging means for discharging the accumulated charges.

Generally, a field effect transistor has several hundred p
It has a gate capacitance of F to several thousand pF. Therefore,
Even after the output of the control signal is stopped, the turn-off time of the field effect transistor becomes long due to the charges accumulated in the gate. As a result, for example, when this rectifier circuit is arranged on the secondary winding side of a switching transformer or a smoothing capacitor is connected to the output side of the rectifier circuit, the field effect transistor is turned off. If it is turned on at the time that should be, the reverse voltage induced in the secondary winding, that is, the current based on the voltage V _S2 in FIG. 6 flows in the reverse direction, or the energy stored in the smoothing condensate reverses. The reverse current flows due to the current flowing in. In this rectifier circuit, the charge discharging means connected between the low potential line such as the ground and the gate discharges the charge accumulated in the gate when the output of the control signal is stopped. Therefore, the turn-off time of the field effect transistor is shortened, so that the reverse current is reliably prevented from occurring.

A rectifier circuit according to a fourth aspect is the rectifier circuit according to any one of the first to third aspects, wherein the control signal generating means is a primary winding disposed between output lines of the rectified direct current. And a secondary winding capable of outputting a control signal whose current value or voltage value is approximately proportional to the direct current flowing through the primary winding, and either a current transformer or an autotransformer. And

In this rectifier circuit, when rectified direct current flows through the primary winding of a current transformer or a so-called autotransformer, which is a so-called autotransformer, a secondary winding which is a current detection side winding of the current transformer, or A control signal whose current value or voltage value is approximately proportional to the rectified current is generated in the secondary winding of the autotransformer. Thus, according to this rectifier circuit, the control signal generating means can be easily configured.

A rectifier circuit according to a fifth aspect of the present invention is the rectifier circuit according to the fourth aspect, further comprising current amplifying means for current amplifying the control signal and outputting the current amplified control signal to the gate of the field effect transistor. Is characterized by.

As described above, the field effect transistor has a gate capacitance of several hundred pF to several thousand pF. Therefore, in order to shorten the turn-on time of the field effect transistor, it is necessary to quickly charge the gate capacitance. In this rectifier circuit, the control signal output from the current transformer or the autotransformer is current-amplified, and the current-amplified control signal is output to the gate of the field effect transistor. As a result, the gate capacitance of the field effect transistor is quickly charged, so that the turn-on time can be extremely shortened.

A rectifier circuit according to a sixth aspect is the rectifier circuit according to the fourth or fifth aspect, wherein the control signal is output to the field effect transistor when the output voltage at the output portion of the control signal generating means is equal to or lower than a predetermined value. A control signal output control means for stopping is provided.

In this rectifier circuit, the control signal output control means outputs the control signal to the field effect transistor when the output voltage output from the control signal generation means that is the generation source of the control signal is equal to or lower than a predetermined value. Stop. Therefore, the field effect transistor starts to turn off before the rectified direct current has finished flowing through the primary winding of the current transformer or the autotransformer. As a result, it is possible to surely stop the operation of the field effect transistor before the output of the control signal is stopped, so that it is possible to reliably prevent the generation of the reverse current.

A rectifier circuit according to a seventh aspect is the rectifier circuit according to the sixth aspect, wherein the control signal output control means is a Zener diode connected between the output section of the control signal generation means and the gate of the field effect transistor. It is characterized by

Normally, the control signal flows at a current value corresponding to the difference voltage between the gate voltage of the field effect transistor and the output voltage of the control signal generating means. In this rectifier circuit, the Zener diode substantially lowers the difference voltage between the control signal generating means and the gate by the Zener voltage. Therefore, when the output voltage of the control signal generating means becomes equal to the voltage obtained by adding the Zener voltage to the gate voltage,
Since there is no voltage difference between the two, a control signal does not flow, and the gate voltage is not supplied to the gate. As described above, this rectifier circuit can be simply configured by using the Zener diode as the control signal output control means.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a rectifier circuit according to the present invention is applied to a flyback type switching power supply device (hereinafter referred to as "power supply device") will be described below with reference to the accompanying drawings. The same components as those of the conventional power supply device 71 are designated by the same reference numerals, and the description thereof will be omitted.

A power supply device 1 shown in FIG. 1 includes a diode bridge 3 for rectifying an alternating current output from an alternating current power supply 2, a switching transformer 4, and a switching MOS field effect transistor (hereinafter referred to as "FET") 5. , A switching signal output circuit 6 for outputting a switching signal
And a rectifying circuit 11 and the like.

The rectifying circuit 11 constitutes a part of the power supply device 1 and includes a current transformer (control signal generating means) 2
1, FET (field effect transistor) 22, resistor 23,
24, a diode 25 and a capacitor 26.

The current transformer 21 is connected between the positive voltage output terminal 12 for outputting rectified direct current to the outside and the primary voltage side terminal of the secondary winding 4b of the transformer 4 connected to the primary line. It is provided with a winding 21a and a secondary winding 21b having a winding ratio of n times that of the primary winding 21a and functioning as a current pickup winding, and with respect to a DC current value I ₁₁ flowing through the primary winding 21a. Control current having a current value which is the reciprocal of the winding ratio (1 / n) (corresponding to the control signal in the present invention)
I ₁₂ is output from the secondary winding 421b.

The FET 22 has an internal parasitic diode 27 therein, and when the alternating current generated in the secondary winding 4b of the transformer 4 is in the direction of the voltage V _S11 , the positive polarity of the alternating current is passed through the internal parasitic diode 27. Let the parts pass and vice versa,
When the alternating current generated in the secondary winding 4b is in the direction of the voltage V _S12 , the passage of the alternating current is blocked. As a result, the FET 22
Rectifies alternating current.

The resistor 23 functions as a terminating resistor on the secondary winding 21a side of the current transformer 21, and also as a current-voltage converter for converting the control signal I ₁₂ output from the current transformer 21 into a voltage signal. Further, the resistance 23 is F when the output of the control current I ₁₂ is stopped.
It also functions as a charge discharging unit that discharges the charges accumulated in the gate of the ET 22 to the ground, which is a low potential line.

The resistor 24 functions as a current limiter when the control current I ₁₂ is supplied. The diode 25 functions as a charge discharging unit that discharges the charge accumulated in the gate of the FET 22 to the ground via the secondary winding 21b of the current transformer 21 when the output of the control current I ₁₂ is stopped.

Next, the operation of the rectifier circuit 11 will be described with reference to FIG.

When alternating current is output from the alternating current power source 2, the alternating current is rectified into a pulsating current by the diode bridge 3. The pulsating current is switched by the FET 5 under the control of the switching signal output circuit 6, so that the current I _D flows to the primary winding 4a of the transformer 4 (see FIG. 7A).
When the current flows, energy is stored in the transformer 4. Next, when the switching by the FET 5 is turned off, the current I _{11 is} supplied from the secondary winding 4b of the transformer 4 based on the energy stored in the transformer 4 (see FIG. 7B).
Is output. In this case, since the current I ₁₁ tries to flow in the direction shown in FIG. 1, the current I ₁₁ flows through the closed loop including the internal parasitic diode 27, the secondary winding 4b, the primary winding 21a of the current transformer 21 and the capacitor 26, and Smoothed by 26. At this time, when the current I ₁₁ passes through the primary winding 21a, the control current I ₁₂ is output from the secondary winding 21b. This control current I ₁₂ is
It flows into the gate of 22 to charge the gate capacitance. After charging, the control current I ₁₁ flows in a closed loop composed of the secondary winding 21b and the resistors 24 and 23, and the voltage V _G (see FIG. 7C) generated across the resistor 23 as a gate voltage. It is applied to the gate of the FET 22. Although the minimum value of the voltage V _G is actually a negative voltage, the minimum value is 0 V here.

The voltage V _G applied to the gate is the FET 22
When the ON voltage is higher than the ON voltage V _ON of the FET 22, the FET 22 is turned on and the current ₁₁ passes between the source and the drain of the FET 22, as shown in FIG. As a result, the secondary winding 4
The alternating current generated in b is rectified mainly by the FET 22. In this case, the power loss at the time of rectification is the power of a value obtained by multiplying the square of the rectification current by the ON resistance of the FET 22, and is extremely reduced as compared with the power loss in the diode rectification method.

Next, when the current I ₁₁ stops flowing, the control current I ₁₂ also stops flowing, so that no voltage is applied to the gate of the FET 22. In this case, the charge stored in the gate is the diode 24 and the current transformer 21.
Since it is emitted to the ground through the secondary winding 21b of
The gate voltage V _G immediately goes to 0V, which causes the FET 22 to stop operating with a very short turn-off time.
As a result, when the current I _D flows through the primary winding 4a next time, the FET 22 is maintained in a completely stopped state, and at that time, the direction of the current which tends to flow through the secondary winding 4b is set. Since the forward direction of the internal parasitic diode 27 is opposite to each other, no current flows in the secondary winding 4b,
Generation of reverse current is reliably prevented.

As described above, according to the rectifier circuit 11,
The current transformer 21 generates the control current I ₁₂ having a current value substantially proportional to the current value of the current I ₁₁ rectified by the internal parasitic diode 27, and outputs the generated control current I ₁₂ to operate the FET 22. Therefore, when applied to a rectifying circuit of a so-called all-range type switching power supply device, the rectifying operation of the FET 22 is performed regardless of the input AC voltage value, that is, the voltage output from the secondary winding 4b of the transformer 4. Can be controlled.
As a result, the FET 22 does not decrease in rectification efficiency.
It is possible to reliably prevent the destruction of the.

Next, a power supply device 31 to which a rectifying circuit 32 according to another embodiment is applied will be described with reference to FIG. It should be noted that FIG. 1 mainly shows the rectifier circuit 32, which is the configuration of the transformer 4 in the power supply device 1 on the secondary winding 4b side. Further, in this embodiment, of the constituent elements of the power supply device 31, the same constituent elements as those of the power supply apparatus 1 are designated by the same reference numerals, and description thereof will be omitted.

As shown in the figure, in the rectifier circuit 32, the primary winding 41a is connected between the ground terminal 13 and the source of the FET 22, and the other end of the secondary winding 41b is a zener diode (control signal output control). Means) 42 and an autotransformer 41 connected to the cathode. The autotransformer 41 is an autotransformer, and the primary winding 41a and the secondary winding 41b having a winding ratio of n times that of the primary winding 41a are not separated and insulated from each other, and The winding portion of 41a is configured as a part of the secondary winding 41b.
Further, the autotransformer 41 outputs a control current I ₂₂ of the current value of the reciprocal of the turns ratio (1 / n) from the secondary winding 41b relative to the DC current value I ₂₁ flowing through the primary winding 41a. In this auto transformer 41, the transformer 4 together with the FET 22
Since it is arranged on the ground side of the secondary winding 4b, it is not necessary to insulate the primary winding 41a from the secondary winding 41b. As a result, by configuring both windings 41a and 41b in common, The coupling between the windings 41a and 41b is strengthened.

In the rectifier circuit 32, in addition to the Zener diode 42 described above, an npn-type transistor (current amplifying means) 43 whose base is connected to the anode of the Zener diode 42 and its emitter is connected to the emitter of the transistor 43. A pnp type transistor (charge discharging means) 44 and resistors 45, 46 and 47 are provided.

The transistor 43 is the autotransformer 41.
The control current I ₂₂ output from the secondary winding 41 b of the above is amplified, and the amplified current is output to the gate of the FET ₂₂ as a new control current I ₂₃ . In this case, since the rectified DC voltage V _D is applied to the collector of the transistor 43, a voltage higher than the on-voltage (about 5 V) between the source and the gate of the FET 22 (approximately equal to the DC output voltage) is applied during operation. ) Can be applied. Therefore, FET22
Can be operated in the fully saturated region. As a result, the source-drain voltage of the FET 22 becomes smaller, and the power loss due to the FET 22 is further reduced.

The transistor 44 functions as a charge discharging means for discharging the charge accumulated in the gate of the FET 22 to the ground. Specifically, the transistor 44 is
When the transistor 43 stops outputting the control current I _23, the base current based on the electric charge accumulated in the gate is caused to flow to the ground through the resistor 45 to start the operation. The turn-off time of the FET 22 is shortened by discharging the stored charge from the emitter to the ground via the collector.

Next, the operation of the rectifier circuit 32 will be described with reference to FIG. Note that duplicated description of the same points as the operation of the rectifier circuit 11 is omitted.

When a current I _D (see FIG. 7A) flows through the primary winding 4a of the transformer 4, the current I ₂₁ flows from the secondary winding 4b.
Is output. In this case, since the current I ₂₁ tends to flow in the direction shown in the figure, a closed loop composed of the primary winding 41a of the autotransformer 41, the internal parasitic diode 27, the secondary winding 4b of the transformer 4, and the capacitor 26 is formed. By flowing, it is smoothed by the capacitor 26. At this time, when the current I ₂₁ passes through the primary winding 41a, the control current I ₂₂ is output from the secondary winding 41b. This control current I
₂₂ is a transistor 4 via a Zener diode 42
3 is input to the base of the transistor 3, amplified by the transistor 43, and flows into the gate of the FET 22 as the control current I ₂₃ to charge the gate capacitance and operate the FET 22.

On the other hand, after charging, the control current I ₂₃ flows to the ground via the resistor 46, so that the voltage V _G generated across the resistor 46 is applied to the gate of the FET 22 as the gate voltage, so that the FET 22 Keeps on. As a result, the alternating current generated in the secondary winding 4b is rectified by the FET 22. In this case, the power loss at the time of rectification is the same as the rectification circuit 11 and is the power of a value obtained by multiplying the square of the rectification current by the ON resistance of the FET 22, which is extremely reduced as compared with the power loss in the diode rectification method. It Further, in this case, the control current I ₂₂ is the secondary winding 41b, the Zener diode 42, the resistor 45,
It flows in a closed loop composed of the internal parasitic diode 27, the secondary winding 4b of the transformer 4, and the capacitor 26, whereby the transistor 44 is maintained in the off state by the voltage generated across the resistor 45.

Next, when the current I ₂₁ stops flowing, the control current I ₂₂ also stops flowing, so that the transistor 43 stops operating, and as a result, the voltage V _G is not applied to the gate of the FET ₂₂ . In this case, since the voltage across the resistor 45 decreases, the charge accumulated in the gate of the FET 22 becomes
The base current of the transistor 44 is discharged to the ground via the emitter, the base and the resistor 45. Therefore, when the transistor 44 operates, the electric charge accumulated in the gate is discharged to the ground through the emitter and the collector of the transistor 44. Also,
The electric charge accumulated in the gate is also discharged to the ground through the resistor 46. Therefore, the gate voltage immediately becomes 0.
Since it becomes V, the FET22 can be turned off with an extremely short turn-off time.
Stops working.

Further, the voltage V _G applied to the gate of the FET 22 is dropped from the voltage V _O output from the secondary winding 41b of the autotransformer 41 by the Zener voltage of the Zener diode 42. Therefore, the voltage input to the base of the transistor 43 becomes 0 V when the voltage V _O is equal to or lower than the Zener voltage. Therefore, FET
22 indicates that the voltage V _O is the FET as shown in FIG.
When the voltage V _OFF , which is a voltage higher by the Zener voltage than the threshold voltage V _S at which 22 is turned off, is turned off (see FIG. 7C). As a result, when the current I _D flows through the primary winding 4a next time, the FET 22 is maintained in a completely stopped state, and at that time, the direction of the current which tends to flow through the secondary winding 4b is set. Since the forward direction of the internal parasitic diode 27 is opposite to that of the forward direction, no current flows through the secondary winding 4b, and the reverse current is reliably prevented from occurring. The resistor 47 terminates the impedance on the secondary winding 41b side of the autotransformer 41, in other words, the primary side impedance, to a predetermined value when no current flows through the Zener diode 42.

As described above, according to this embodiment, by operating the FET ₂₂ with the control current I _{23 obtained} by amplifying the control current I ₂₂ , the FET ₂₂ can be turned on in an extremely short turn-on time. As a result, the rectification operation of the internal parasitic diode 27 can be switched to the rectification operation by the FET 22 in a short time, and as a result, the rectification efficiency can be further improved.

In the above embodiment, an example in which the FET 22 is connected to the ground side of the secondary winding 4b of the transformer 4 has been described. However, the present invention is not limited to this, and as shown in FIG. Of course may be connected to the DC output line side. The rectifier circuit 51 shown in FIG.
The same reference numerals as those of the corresponding constituent elements of the power supply device 1 in FIG. 1 are given to the respective constituent elements, and the description thereof will be omitted. Further, in the rectifier circuit 11, a transistor or FET that current-amplifies the control signal may be connected to the output side of the current transformer 21.

Further, the rectifier circuit according to the present invention can be applied not only to the flyback type power supply device but also to the forward type power supply device. Further, the present invention can be applied to a ringing choke type switching power supply device, and in such a case, the current _ID flows to the primary winding 4a after the energy is completely output from the secondary winding 4b of the transformer 4. Therefore, even if the charge discharging means (for example, the transistor 44) for discharging the gate charge of the FET 22 is not provided,
The reverse current can be surely blocked within the period in which the FET 22 is on.

In this embodiment, the example in which the internal parasitic diode 27 of the FET 22 is used has been described.
The present invention is not limited to this, and it goes without saying that a separate diode may be used.

[0050]

As described above, according to the rectifier circuit of the first aspect, the voltage value of the input alternating current fluctuates, for example, when the rectifier circuit is configured as a synchronous rectifier circuit of an all-range type switching power supply device. Even if the voltage output from the secondary winding of the switching transformer is high or low, the control signal whose current value or voltage value is approximately proportional to the current value of the rectified DC current causes Since the switching is controlled, the breakdown of the rectifying field effect transistor can be reliably prevented. Further, since the gate voltage of the field effect transistor is limited to a predetermined value or less, no power is lost, so that the rectification efficiency is not reduced.

According to the rectifier circuit of the second aspect,
As a result of the internal parasitic diode of the field effect transistor generating a direct current for generating the control signal, the circuit can be simply configured.

According to the rectifier circuit of the third aspect,
When the field effect transistor is turned off, the charge discharging means discharges the charge accumulated in the gate, so that the turn-off time of the field effect transistor is shortened.
It is possible to reliably prevent the generation of reverse current.

According to the rectifier circuit of the fourth aspect,
The control signal generating means can be simply configured by the current transformer or the autotransformer.

Further, according to the rectifier circuit of the fifth aspect, since the amplified control signal is output to the gate of the field effect transistor, the turn-on time of the field effect transistor can be extremely shortened, resulting in improvement of rectification efficiency. Can be made.

According to the rectifier circuit of the sixth aspect,
Since the control signal output control means can stop the operation of the field effect transistor before the output of the control signal is stopped, it is possible to more reliably prevent the generation of the reverse current.

Further, according to the rectifier circuit of the seventh aspect, the control signal output control means can be easily constituted by the Zener diode.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a power supply device according to an embodiment of the present invention.

FIG. 2A is a signal waveform diagram showing a waveform of a current flowing through a primary winding of a transformer, FIG. 2B is a signal waveform diagram showing a DC current waveform generated by a rectifier circuit, and FIG.
FIG. 4A is a signal waveform diagram showing a gate voltage applied to the gate of the FET, and FIG. 7D is a diagram showing an operating state of the FET.

FIG. 3 is a circuit diagram of a rectifier circuit according to another embodiment of the present invention.

FIG. 4A is a signal waveform diagram showing a current waveform flowing in a primary winding of a transformer according to another embodiment, and FIG.
[Fig. 6] is a signal waveform diagram showing an output voltage waveform of an auto transformer in another embodiment, and (c) is a diagram showing an operating state of an FET in another embodiment.

5 is a circuit diagram of a rectifier circuit which is a modified example of the rectifier circuit in FIG.

FIG. 6 is a signal waveform diagram showing an output voltage of a switching transformer in the switching power supply device.

FIG. 7 is a circuit diagram of a conventional rectifier circuit.

[Explanation of symbols]

 11 Rectifier circuit 21 Current transformer 22 FET 23 Resistance 27 Internal parasitic diode 32 Rectifier circuit 41 Autotransformer 42 Zener diode 43 Transistor 44 Transistor 46 Resistor

Claims (7)

[Claims] 1. A diode for rectifying an input AC input, control signal generating means for generating a control signal whose current value or voltage value is substantially proportional to the current value of the rectified DC current, and equivalent to the diode. And a field-effect transistor that is connected in parallel and that operates according to the control signal to rectify the input alternating current. 2. The rectifier circuit according to claim 1, wherein the diode is an internal parasitic diode of the field effect transistor. 3. A charge discharging means connected between the gate of the field effect transistor and a low potential line and discharging the charge accumulated in the gate when the output of the control signal is stopped. Claim 1 characterized by the above.
Alternatively, the rectifier circuit according to item 2. 4. The control signal generating means has a primary winding arranged between output lines of the rectified DC current, and a current value or a voltage value is substantially proportional to the DC current flowing through the primary winding. The rectifier circuit according to any one of claims 1 to 3, wherein the rectifier circuit is one of a current transformer and an autotransformer having a secondary winding capable of outputting a control signal. 5. The rectifier circuit according to claim 4, further comprising a current amplifying unit that current-amplifies the control signal and outputs the current-amplified control signal to the gate of the field-effect transistor. 6. A control signal output control means for stopping the output of the control signal to the field effect transistor when the output voltage at the output part of the control signal generation means is below a predetermined value. Claim 4 or 5
Rectifier circuit described. 7. The rectifier circuit according to claim 6, wherein the control signal output control means is a Zener diode connected between the output section of the control signal generation means and the gate of the field effect transistor.