JPH11220880A - Power-supply apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a power-supply apparatus in which the frequency of a switching frequency is made high and whose conversion efficiency is enhanced. SOLUTION: A power-supply apparatus is provided with a first switch means S1 which switches an input DC current via a primary winding; with a second switch means S2 which turns on and off the connection of a secondary winding to a load circuit; and with a control means 6 wherein a first switching operation which outputs an output current, based on the induced voltage of the secondary winding, in such a way that the first switch means S1 is controlled once to an on-state, that the first switch means S1 is controlled to an off-state, and that the second switch means S2 is controlled to an on-state and a second switching operation, which sets the second switch means S2 to an off-state when a reverse current flows to the side of the secondary winding for a prescribed time, and which sets the first switch means S1 to the on-state at a prescribed timing are executed alternately. The power-supply apparatus is provided with current detecting means 12, 13 which detect the value of a current flowing in the secondary winding. The control means 6 controls the first switch means S1 to the on-state at a timing based on the detected value of the current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply for generating DC power by switching, and more particularly to a so-called resonance type power supply.

[0002]

2. Description of the Related Art As a resonance type power supply of this type, a flyback type power supply 21 shown in FIG. 5 is conventionally known. The power supply device 21 includes a switching transformer 2, and a capacitor 3 for smoothing the input DC of the voltage E <b> 1 and a switching control (not shown) on the primary winding 2 a side of the transformer 2. S1 controlled on / off by integrated circuit
And a capacitor 4 for series resonance, and a diode 5 connected in parallel to the switch S1. The capacitor 4 is constituted by a parasitic capacitance of the FET as the switch S1, or a capacitor connected in parallel to the switch S1 separately from the parasitic capacitance. The diode 5 is constituted by a diode called a so-called body diode or a parasitic diode existing inside the FET as the switch S1, or an independent diode connected in parallel to the switch S1 separately from the body diode. Further, the power supply device 21 includes a rectifying diode 22 and a smoothing capacitor 11 on the secondary winding 2b side.

In this power supply device 21, when the switch S1 is turned on, a current I1 flows in the primary winding 2a in the direction shown in FIG. In this case, the secondary winding 2b has
The current I2 in the direction shown in FIG. On the other hand, when the switch S1 is controlled to be in the off state, the secondary winding 2b has the state shown in FIG.
As shown in (1), a current I4 based on the flyback voltage generated in the secondary winding 2b flows. Thus, an output voltage rectified by the diode 22 and smoothed by the capacitor 11 and stabilized at the voltage E2 is output to the outside of the device. At this time, both ends of the capacitor 4
As shown in FIG. 5B, a voltage EC expressed by the following equation and in the direction shown in FIG. 5 is generated. EC = E1 + E3 where the primary winding 2a and the secondary winding 2b of the transformer 2
Are N1 and N2, respectively.
If the forward voltage is ignored, the voltage E3 is approximately expressed by the following equation, and the voltage EC is expressed by the following equation. E3 = (N1 / N2) · E2 ... Equation EC = E1 + (N1 / N2) · E2 ... Equation

Therefore, in this state, the switch S
If 1 is immediately turned on, both ends of the capacitor 4 are short-circuited, so that the energy stored in the capacitor 4 is consumed as heat loss in a short-circuit circuit by the switch S1. In this case, the energy stored in the capacitor 4 is proportional to the square of the voltage EC across the capacitor 4. Therefore, the higher the voltage EC is, the larger the energy loss due to the short circuit becomes. Further, when the switch S1 is switched at a high switching frequency of several hundred KHz to reduce the size of the power supply device,
Loss occurs at each switching. Therefore, if the control method of immediately turning on the switch S1 while the capacitor 4 is being charged is employed, the conversion efficiency of the power supply device is reduced, and noise is generated when the capacitor 4 is short-circuited. There's a problem.

For this reason, in the power supply device 21, the switch S1 is controlled to be on by a so-called zero volt switch system. Specifically, in the power supply device 21, a series resonance phenomenon is generated on the primary circuit side of the transformer 2 by the energy stored in the capacitor 4, and the switch S1 is turned on when the voltage EC across the capacitor 4 is 0V. Control. That is, if the switch S2 is turned off when the stored energy of the transformer 2 has been released to the capacitor 11 side by outputting the current I4 from the secondary winding 2b, both ends of the capacitor 4
As shown in (b), a voltage EC higher than the voltage E1 across the capacitor 3 is generated. Therefore, the energy stored in the capacitor 4 is discharged to the capacitor 3 via the primary winding 2a. On the other hand, when the energy of the capacitor 4 has been released, the energy is released from the capacitor 3 toward the capacitor 4. By repeating these, a series resonance phenomenon occurs as shown by a broken line in FIG. In this case, the series resonance frequency f in the series resonance phenomenon does not affect the series resonance phenomenon since the capacitor 3 has a sufficiently large capacitance value as compared with the capacitance value of the capacitor 4, so that the inductance of the primary winding 2a is reduced. Assuming that the value is L and the capacitance value of the capacitor 4 is C, the following expression is used. Therefore, in the power supply device 21, by controlling the switch S1 to be on when the voltage EC across the capacitor 4 is near 0V,
An attempt is made to reduce energy loss when the capacitor 4 is short-circuited. f = 1 / (2 × π × (L × C) ^0.5 ) formula

In this case, the voltage E3 is, as described above,
Turn ratio (N1 / N2) of transformer 2 and output voltage E2
Is determined uniquely. For this reason, considering the fluctuation of the input DC voltage E1, when the voltage E1 is higher than the voltage E3, the voltage EC across the capacitor 4 does not reach 0 V during the series resonance. Therefore, even if the zero volt switch is performed, the switch S1 is controlled to be turned on at the time t1 when the energy is stored in the capacitor 4 as shown in FIGS. Therefore, there is a problem that power loss occurs at the time of switching of the switch S1.

For this reason, a so-called active clamp type power supply device 31 shown in FIG. 7 has been proposed in order to ensure a zero volt switch. This power supply 31
Is different from the power supply device 21, as shown in the figure, in place of the diode 22, a switch S2 configured by, for example, an FET to turn on / off the connection between the secondary winding 2b and the load circuit, and the diode 10 It has. Here, the diode 10 is configured by a diode called a so-called body diode or a parasitic diode existing inside the FET as the switch S2, or an independent diode connected in parallel to the switch S2 separately from the body diode.

In the power supply device 31, when the switch S1 is controlled to the on state while the switch S2 is maintained in the off state, a current I1 flows in the primary winding 2a in the direction shown in FIG. In this case, the current I2 in the direction shown in FIG. 5 is going to flow through the secondary winding 2b, but is blocked by the switch S2 and the diode 10. On the other hand, when the switches S1 and S2 are turned off and on, respectively, the flyback voltage generated in the secondary winding 2b is applied to the secondary winding 2b as shown in FIG. Flows based on the current I4. Thereby, the capacitor 11
The output voltage which is smoothed and stabilized at the voltage E2 is output to the outside of the device. In this case, unlike the power supply device 21, the power supply device 31 is kept on for a predetermined period of time even after the release of energy from the secondary winding 2b of the transformer 2 to the capacitor 11 is completed. in this case,
The current I4 stops flowing when the flyback voltage and the voltage E2 across the capacitor 11 become equal to each other.
If the switch S2 is further kept on in this state, the current I5 flows in the opposite direction from the current I4 from the capacitor 11 to the secondary winding 2b. Is done. Next, when the switch S2 is turned off after the current I5 flows for a predetermined time, the induced voltage in the primary winding 2a of the reversely excited transformer 2 becomes opposite to the voltage E3.
Is stored in the capacitor 3 via the primary winding 2a. In this case, compared to the case of free resonance in which the reverse current I5 does not flow through the secondary winding 2b,
Since the release of energy from the capacitor 4 to the capacitor 3 is enhanced, the amplitude value of the series resonance waveform in the primary circuit increases. Therefore, even when the voltage E1 fluctuates, as shown in FIG.
Can be controlled to 0V. The diode 5 is connected to the switch S at the time of series resonance.
1 functions to maintain the voltage between both ends at a positive voltage.

Next, after the switch S2 is turned off, the switch S1 is turned on as shown in FIG. In this case, the switch S1 is, for example,
On / off control is performed by a switching control signal output from an integrated circuit for switching control. On the other hand, the timing at which the switching control integrated circuit outputs the switching control signal is at the time t2 shown in FIGS. 3B and 3C, that is, the terminal voltage of the capacitor 4 starts to decrease in this power supply device. Or when the voltage of the primary winding 2a starts to decrease. In this case, a certain response delay occurs inside the integrated circuit until the switching control signal is output, and a certain response delay occurs before the switch S1 actually operates (hereinafter, both response delay times are collectively referred to as “the two response delay times”). As a result, the switch S1 is actually turned on at time t3, which is later than time t2. Thereby, in the power supply device 31, a zero volt switch is made possible.

[0010]

However, the conventional power supply device 31 has the following problems. That is, in the conventional power supply device 31, when the switch S1 is controlled to be in the ON state, as described above, after the switching control integrated circuit attempts to output the switching control signal and before the switch S1 actually operates, 500ns ~ 6
A response delay time of about 00 nS occurs. On the other hand, when the switching frequency of the switch S1 is set to about 400 KHz in order to achieve the miniaturization of the power supply device, the voltage EC across the capacitor 4 becomes zero after the voltage of the primary winding 2a decreases.
The time to reach V is, according to the above equation, 20
The time is as short as about 0 nS to 300 nS. Therefore, when the voltage EC of the capacitor 4 reaches 0 V, the switch S
It becomes impossible to control 1 to the ON state. Therefore, the power supply device 31 can perform the zero volt switch only when the switching frequency is low, and cannot perform the zero volt switch when the switching frequency is high, or causes power loss due to switching. There is a problem.

On the other hand, even if there is some response delay before the switching control signal is output by the integrated circuit, the zero volt switch can be reliably performed by lowering the resonance frequency. However, in order to reduce the resonance frequency, it is necessary to increase the inductance of the primary winding 2a. As a result, the size of the transformer 2 is increased. As a result, the switching frequency is increased to reduce the size and weight of the power supply device. Would be contrary.

The present invention has been made to solve such a problem, and has as its main object to provide a power supply device capable of increasing the switching frequency and improving the conversion efficiency. And

[0013]

According to a first aspect of the present invention, there is provided a power supply apparatus comprising: a switching transformer having a primary winding and a secondary winding; and an input direct current switching via the primary winding. First switch means for:
Second to turn on / off the connection between the secondary winding and the load circuit
Switch means and control means, and the control means controls the first switch means to an on state once, and thereafter, the first switch means
A first switching operation of outputting an output current based on an induced voltage induced in the secondary winding to the load circuit side by controlling the switch means to an off state and controlling the second switch means to an on state; A second switch means for controlling the second switch means to be in an off state when a reverse current flows from the load circuit toward the secondary winding for a predetermined time, and controlling the first switch means to be in an on state at a predetermined timing; Power supply device that alternately performs the switching operation of
A current detecting means for detecting a value of a current flowing through the secondary winding, wherein the control means comprises:
As a predetermined timing, the first switch means is controlled to be turned on at a timing based on the detected current value detected by the current detection means. The control means for controlling on / off of the first switch means and the control means for controlling on / off of the second switch means are separated from each other so that the primary winding side of the switching transformer is provided. And on the secondary winding side.

In this power supply device, the first means is controlled by the control means.
Is controlled to the ON state, the input DC flows through the primary winding of the transformer, whereby energy is accumulated in the transformer. Then, by the control means,
When the second switch is controlled to the on state after the first switch is controlled to the off state, the output current based on the induced voltage of the secondary winding is completely discharged to the load circuit, and then the load is controlled. Reverse current starts flowing from the circuit side to the secondary winding side. Next, when the second switch is turned off after a reverse current flows for a predetermined period of time, the primary winding is determined by at least the capacitance including the parasitic capacitance of the first switch and the inductance of the primary winding. A series resonance phenomenon occurs due to the frequency to be performed. On the other hand, the current detecting means detects the value of the current flowing through the secondary winding, and the control means performs the first switching at a predetermined timing based on the detected current value detected by the current detecting means during the second switching operation. Control the means to the ON state. Therefore, the control means can control the first switch means to be in an on state before the current has been passed through the secondary winding. At this time, even when, for example, an integrated circuit for switching control is used as the control means, the response delay time inside the integrated circuit and in the first switch means and the series resonance frequency represented by the above equation are taken into consideration. After doing
By controlling the first switch means to the ON state,
The zero volt switch can be reliably performed.

According to a second aspect of the present invention, in the power supply unit of the first aspect, the control means determines the predetermined timing at a timing based on a time when a direction of a current flowing through the secondary winding is reversed. One switch means is controlled to an on state.

The predetermined timing for controlling the first switch means to be in the ON state may be before the end of the reverse current flowing through the secondary winding, and the detected current value can be appropriately determined. In this case, if the direction of flow from the secondary winding to the load circuit is positive, the response delay time is controlled to a certain extent by controlling the first switch means to be in the ON state when the detected current value is positive. Even if a long switching control integrated circuit is used, the first switch means can be appropriately controlled. On the other hand, the time during which the output current flows through the secondary winding changes according to the load condition of the load circuit. Therefore, if the detected current value for controlling the first switch means to be in the ON state is set to a very large positive value, the current flowing through the secondary winding may not reach the value, and the first switch Sometimes the means cannot be properly controlled. In this power supply device, when the direction of the current flowing through the secondary winding is reversed, the first switch is controlled to be in the ON state. In this case, even if the load condition of the load circuit changes, the direction of the current flowing through the secondary winding is always reversed. For this reason, it is possible to reliably control the first switch unit to the ON state.

According to a third aspect of the present invention, there is provided the power supply device according to the first aspect, wherein the control means sets the predetermined timing between a voltage corresponding to the detected current value and a predetermined offset voltage which is a positive constant voltage. The first switch means is controlled to be in an ON state at a timing based on when the added voltage reaches zero volt or a voltage near the zero volt.

For example, it is assumed that a voltage corresponding to the detected current value becomes a positive voltage when flowing in the direction from the secondary winding to the load circuit side, becomes a negative voltage when flowing in the reverse direction, and a positive voltage power supply. When only the control means is driven, the control means can normally control the first switch means to be in the ON state only when the voltage corresponding to the detected current value is in the range of zero volt or positive voltage, When the voltage corresponding to the detected current value is a negative voltage, it is difficult to control the first switch means to be on. Therefore, in such a case,
When a switching control integrated circuit having a short response time is used, if the first switch means is controlled to be on before the direction of the current flowing through the secondary winding is reversed,
In some cases, the timing at which the integrated circuit is turned on is too early. On the other hand, in this power supply device, the control means controls the first switch means to an on state when an addition voltage obtained by adding a voltage corresponding to the detected current value and a predetermined offset voltage reaches a predetermined voltage. . In this case, by setting the offset voltage to a positive voltage, the range of the added voltage can be arbitrarily determined within the range of the positive voltage. Therefore, by setting the offset voltage to a voltage value most suitable for the response delay time of the switching control integrated circuit to be used, even if the detected current value is in either the positive or negative range, the first voltage is set at an appropriate timing. The switch means can be controlled to be turned on.

According to a fourth aspect of the present invention, in the power supply device of the third aspect, the control means controls the first switch means at a timing based on when the added voltage reaches zero volt or a voltage near the zero volt. It is characterized in that it is turned on.

In the power supply according to the third aspect, the first switch means can be controlled to be turned on when the added voltage is an arbitrary positive voltage. For example, the arbitrary positive voltage and the added voltage can be controlled. A comparator or the like is required for comparison. In this power supply device, in a state where the offset voltage suitable for the response delay time of the control unit or the like is set, the control unit sets the first voltage when the added voltage reaches, for example, zero volt.
Are turned on. Therefore, the control means can easily and easily control the first switch means to the ON state at a timing most suitable for the response delay time without using a comparator or the like.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a power supply according to the present invention will be described below with reference to the accompanying drawings. The same components as those of the power supply devices 21 and 31 are denoted by the same reference numerals, and redundant description will be omitted.

First, the configuration of a flyback type power supply 1 to which a power supply according to the present invention is applied will be described with reference to FIG. The power supply device 1 is a so-called synchronous rectification type switching power supply device, and includes a transformer 2 having a primary winding 2a and a secondary winding 2b. Also, on the primary winding 2a side, a capacitor 3, a switch S1 corresponding to first switch means in the present invention, and a switch S1
Are provided with a capacitor 4 and a diode 5 connected in parallel to each other, and a switching control unit 6 which forms a part of the control means of the present invention and controls on / off of the switch S1. On the other hand, on the secondary winding 2b side, a switch S2, a diode 10, a current transformer 12 and a discharge current detection unit 13 as current detection means in the present invention, and a capacitor 11 are provided. In addition,
The switching control unit 6 controls the switching duty ratio of the switch S1 to perform feedback control so that the DC voltage smoothed by the capacitor 11 is stabilized at the voltage E2. The switch S2 corresponds to a second switch unit in the present invention, and is turned on / off by a second switching control unit (not shown) which constitutes a control unit in the present invention together with the switching control unit 6. Further, the discharge current detector 13 detects the directions and current values of the currents I4 and I5 flowing through the current transformer 12, and when the direction changes from the current I4 to the current I5,
The detection signal SD is output to the switching control unit 6.

Next, the overall operation of the power supply device 1 will be described with reference to FIG.

At the initial stage of power-on, when the switch S2 is in the off state, the switching control unit 6
1 is turned on. At this time, the current I1 in the direction shown in FIG.
Energy is stored in the transformer 2. Next, the switching control unit 6 controls the switch S1 to be turned off, and the second switching control unit controls the switch S2 to be turned on. Thereby, the secondary winding 2b is
As shown in (a), a current I4 based on the flyback voltage generated in the secondary winding 2b flows to the capacitor 11 via the current transformer 12. At this time, the discharge current detector 13 detects the value of the current flowing through the current transformer 12. On the other hand, the capacitor 11 smoothes the voltage based on the current I4. As a result, the output voltage smoothed and stabilized at the voltage E2 is output to the outside of the device.

Next, when the energy stored in the transformer 2 is completely released by the current I4 flowing to the capacitor 11, the current I5 starts flowing from the capacitor 11 to the secondary winding 2b. At this time, the discharge current detector 13 outputs the detection signal SD to the switching controller 6 at time t4 shown in FIG. As a result, the switching control unit 6 controls the switch S1 to be turned on at time t4 when the input of the detection signal SD is detected. The switch S1 is controlled to be turned on with a delay of the response delay time td of the switching control unit 6 and the switch S1, as shown in FIG. Next, the second switching control unit controls the switch S2 to be turned off at time t5 when the current I5 flows for a predetermined time. In this state, a series resonance phenomenon that resonates on the primary winding 2a side by a waveform W1 having a frequency determined by the capacitance of the capacitor 4 and the inductance of the primary winding 2a as shown by a broken line in FIG. Occur. At this time,
The diode 5 prevents the voltage EC across the capacitor 4 from becoming a negative voltage, as shown in FIG.

Next, at time t6 when the response delay time td of the switching control section 6 and the switch S1 has elapsed from time t4, as shown in FIG.
Is actually turned on. In this case, the inductance of the primary winding 2a or the capacitance of the capacitor 4 in the transformer 2 is set in advance so that the switch S1 is controlled to be turned on when the voltage value of the series resonance waveform W1 first reaches 0V. Have been. Therefore, the switch S
1 is reliably turned on when the charging voltage of the capacitor 4 first reaches 0V.

FIG. 3D shows a conventional power supply device 31.
5 shows the operation state of the switch S1. According to this, as shown in FIGS.
1 is controlled to an on state at a time t7 delayed by a response delay time td from a time t5 when the switch S2 is turned off. Therefore, the timing at which the switch S1 is controlled to the on state is determined by the switch S1 in the power supply device 1.
Compared with the timing at which the current
Is delayed by the period (time t5 to time t4). Therefore, the conventional power supply device 31 is replaced by the switching frequency of the switch S1 and the transformer 2 of the power supply device 1.
In the conventional power supply device 31, when the charging voltage of the capacitor 4 is 0 V, the switch S1 is set to the same value as the inductance of the primary winding 2a in FIG. Obviously, it cannot be controlled to the ON state, causing power loss.

As described above, according to the power supply device 1, the switching control unit 6 can control the switch S1 to the on state before the current I5 flows through the secondary winding 2b. When the voltage EC between both ends of the capacitor 4 reaches 0 V, the switch S1 can be surely controlled to the ON state, thereby preventing power loss due to the switch S1. As a result, the power supply 1
Conversion efficiency can be improved. At the same time,
Since the switch S1 can be controlled to be turned on when the voltage EC across the capacitor 4 first reaches 0 V, it is possible to limit the generation period of the series resonance phenomenon on the primary winding 2a side to the minimum time. it can. As a result, the power loss due to the resonance current during the resonance phenomenon can be minimized, so that the conversion efficiency of the power supply device 1 can be further improved.

Next, a power supply device 41 according to another embodiment will be described with reference to FIGS. The same components as those of the power supply device 1 are denoted by the same reference numerals, and the description thereof will not be repeated. The description of the same operation will be omitted.

As shown in FIG. 3, this power supply 41
In place of the transformer 2 in the power supply device 1, a primary winding 42
a, a transformer 42 having a secondary winding 42b and an auxiliary winding 42c, and a switching control unit 43 in place of the switching control unit 6. Also, the secondary winding 42b
On the side, a volume 45 for changing a voltage value corresponding to a current flowing through the secondary winding 42b and generated at both ends of the secondary winding 12b of the current transformer 12 is provided. In this case, since one end of the secondary winding of the current transformer 12 and one end of the auxiliary winding 42c of the transformer 42 are connected to each other, the voltage E5 generated at both ends of the secondary winding 12b of the current transformer 12, The auxiliary winding 4 of the transformer 42 corresponds to the offset voltage in the present invention.
The voltage E4 induced at both ends of 2c is added, and the added voltage E6 is input to the switching control unit 43.

In the power supply device 41, as shown in FIG. 4A, when currents I4 and I5 flow through the secondary winding 42b,
The current I is applied to the secondary winding 12 b of the current transformer 12.
4, a voltage E5 corresponding to the positive / negative and current values of I5 and the resistance value of the volume 45 is generated. Therefore, a positive voltage is generated in the secondary winding 12b when the current I4 flows, and a negative voltage is generated in the secondary winding 12b when the current I5 flows. On the other hand, the voltage E4 induced in the auxiliary winding 42c of the transformer 42
Are the secondary winding 42b and the auxiliary winding 42 of the transformer 42.
c is N2 and N3, respectively.
If the forward voltage of 0 is ignored, it is approximately expressed by the following equation. E4 = (N3 / N2) .E2

In this case, by appropriately determining the number of turns N3, the added voltage E6 of the voltage E4 and the voltage E5 becomes zero volt time t12 as shown in FIG.
The current value (I
4, I5), the voltage E is longer than the time t11 when the sign is inverted.
4 is delayed by an amount corresponding to the voltage value of 4. Therefore, in the power supply device 41, when an integrated circuit for switching control having a shorter response time is used as the switching controller 43, the switch S1 can be controlled to be turned on at a timing most suitable for the response delay time td. , The number of turns N3 of the auxiliary winding 42c is appropriately set. In such a case, the switch S1 is controlled to the ON state by the switching control unit 43 at the time t12 when the voltage E6 reaches zero volt, so that the switch S1 is delayed from the time t12 by the response time td (for example, FIG.
At time t6 shown in (b) and (c)), it is actually turned on.

As described above, according to the power supply device 41,
By appropriately setting the voltage value of the voltage E4 or the voltage E5, the switching control unit 43 can determine whether the current flowing through the secondary winding 42b is positive or negative regardless of the response delay time t.
The switch S1 can be turned on at the timing most suitable for d.

In the power supply device 41, an example has been described in which the switching control section 43 controls the switch S1 to be in the ON state when the voltage E6 reaches zero volt.
Not limited to this, a predetermined comparator or the like for comparing with a variable reference voltage is built in the switching control unit 43,
The switch S1 may be turned on when the voltage E6 falls below the reference voltage. Also, an example has been described in which the voltage value of the voltage E6 is changed by changing the voltage value of the voltage E4. However, the voltage value (that is, the slope) of the voltage E5 is changed by changing the resistance value of the volume 45. Thereby, the voltage value of the voltage E6 and the timing at which the voltage of the voltage E6 crosses zero volt can be appropriately changed. Furthermore, although an example has been described in which the auxiliary winding 42c of the transformer 42 is used to generate the voltage E4 corresponding to the offset voltage in the present invention, a stabilized DC constant voltage or the like can be used as the offset voltage. In this case, the switching control unit 43 can control the switch S1 to be on based on the algebraic sum of the DC constant voltage and the voltage E5. By varying the voltage values of the voltages E4 and E5, the voltage value of the voltage E6 can of course be set to an arbitrary voltage range as shown in FIG.

In the power supply devices 1 and 41 according to the embodiment of the present invention, an example in which FETs are used as the switches S1 and S2 has been described. However, the present invention is not limited to this. An element can be used. In addition, the current detection means in the present invention,
The present invention is not limited to the current transformer 12 and the discharge current detecting unit 13 shown in the embodiment of the present invention, and the configuration can be changed as appropriate.

[0036]

As described above, according to the power supply device of the first aspect, the control means controls the first switch means to be in the ON state at a timing based on the current value detected by the current detection means. A zero volt switch can be reliably performed on the first switch means, whereby
It is possible to increase the switching frequency and improve the conversion efficiency in the power supply device, and to prevent the generation of unnecessary noise.

According to the power supply device of the second aspect,
Even when the load condition of the load circuit changes, the control means controls the first switch means to be in the ON state at a timing based on the time when the direction of the current flowing through the secondary winding is reversed. The zero volt switch can be reliably performed on the first switch means.

Further, according to the power supply device of the third aspect, the control means determines that the addition voltage of the voltage according to the detected current value and the predetermined offset voltage that is a positive constant voltage is the predetermined timing as the predetermined timing. By controlling the first switch means to be in an ON state at a timing based on when the voltage reaches the voltage, the first switch means can be controlled at an appropriate timing regardless of whether the current value detected by the current detection means is in either the positive or negative range. The means can be controlled to the on state.

According to the power supply device of the fourth aspect,
The control means controls the first switch means to be in the ON state at a timing based on the time when the added voltage reaches zero volt or a voltage in the vicinity thereof. The first switch can be easily turned on at the timing most suitable for the delay time.

[Brief description of the drawings]

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

2A is a current waveform diagram showing a current waveform flowing through a secondary winding 2b of a transformer 2, FIG. 2B is a voltage waveform diagram of a voltage across a capacitor 4, and FIG. 2C is an operation state of a switch S1. FIG. 4D is an operating state diagram showing the switch S1 in the conventional active clamp type power supply 31 when it is assumed that the switching frequency of the power supply 1 and the inductance of the primary winding 2a in the transformer 2 are the same. It is an operation state diagram showing an operation state.

FIG. 3 is a circuit diagram of a power supply device 41 according to the embodiment of the present invention.

4A is a voltage waveform diagram of a voltage E5 corresponding to the current values of currents I4 and I5 flowing through a secondary winding 42b of a transformer 42, and FIG. 4B is a diagram induced at both ends of an auxiliary winding 42c of the transformer 42. FIG. 9C is a voltage waveform diagram of the voltage E4, FIG. 9C is a voltage waveform diagram of the voltage E6 input to the switching control unit 43, and FIG. 9D is another voltage waveform diagram of the voltage E6.

FIG. 5 is a circuit diagram of a conventional power supply device 21.

6A and 6B are current waveform diagrams and the like of respective parts in the conventional power supply device 21, wherein FIG. 6A is a current waveform diagram showing a current waveform flowing through the secondary winding 2b, and FIG. The waveform diagram, (c) is an operation state diagram showing the operation state of the switch S1.

FIG. 7 is a circuit diagram of a conventional power supply device 31.

8A and 8B are current waveform diagrams and the like of respective parts in a conventional power supply device 31, wherein FIG. 8A is a current waveform diagram showing a current waveform flowing through a secondary winding 2b, and FIG. The waveform diagram, (c) is an operation state diagram showing the operation state of the switch S1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply device 2 Transformer 2a Primary winding 2b Secondary winding 6 Switching control unit 12 Current transformer 13 Discharge current detection unit 41 Power supply device 42 Transformer 42a Primary winding 42b Secondary winding 42c Auxiliary winding 43 Switching control unit S1 switch S2 switch

Claims (4)

[Claims] 1. A switching transformer having a primary winding and a secondary winding, first switching means for switching an input direct current through the primary winding, and a switch between the secondary winding and a load circuit. A second switch unit for turning on / off the connection of the control unit, and a control unit.
The first switch means is once turned on, and thereafter the first switch means is turned off and the second switch means is turned on, so that the secondary winding is induced. A first switching operation for outputting an output current based on the induced voltage to the load circuit, and a second switch when a reverse current flows from the load circuit toward the secondary winding for a predetermined time. And a second switching operation for controlling the first switch means to be turned on at a predetermined timing by alternately controlling the means to be turned off, and detecting a current value flowing through the secondary winding. Current control means, wherein the control means detects the current detected by the current detection means as the predetermined timing during the second switching operation. Power supply and controls the first switching means in the ON state at a timing based on the current values. 2. The method according to claim 1, wherein the control unit controls the first switch unit to be turned on at a timing based on a time when a direction of a current flowing through the secondary winding reverses, as the predetermined timing. The power supply device according to claim 1, wherein: 3. The control device according to claim 2, wherein the predetermined timing is based on a time when an addition voltage of a voltage corresponding to the detected current value and a predetermined offset voltage that is a positive constant voltage reaches a predetermined voltage. 2. The power supply device according to claim 1, wherein the first switch means is controlled to be turned on at a timing when the first switch means is turned on. 4. The control means according to claim 3, wherein said control means controls said first switch means to be in an on state at a timing based on when said additional voltage reaches zero volt or a voltage close thereto. The power supply as described.