JPH08331843A - Output voltage detecting circuit in switching power supply - Google Patents

Abstract

PURPOSE: To provide a stable DC voltage detecting circuit having good responsibility and suitable for use at low DC output voltage. CONSTITUTION: When a first EFT 34 is turned on, a voltage induced at a secondary winding 32b is fed to a serial circuit 18 through a first voltage supplying circuit 52. When the first FET 34 is turned off, a voltage induced at a secondary winding 33b is fed to a serial circuit 18 through a second voltage supplying circuit 53. Then, a bias voltage VBIAS higher than a DC output voltage Vo can be obtained and stability is ensured even when an abrupt change in DC input voltage Vi takes place. In addition, a variation factor in DC output voltage Vo is applied to the series circuit 18, and good responsibility is ensured at the same time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output voltage detection circuit of a switching power supply device having a shunt regulator and a photo coupler as a feedback circuit for stabilizing a DC output voltage.

[0002]

2. Description of the Related Art Generally, in a switching power supply device, an output voltage detection circuit in which a series circuit of a shunt regulator and a light emitting element of a photocoupler is connected between output terminals is used as a feedback circuit for stabilizing a DC output voltage. Used. However, when the DC output voltage is a low voltage of, for example, 2 V or 3.3 V, the value obtained by adding the reference voltage of the shunt regulator (for example, 1.25 V) and the voltage drop of the light emitting element forming the photo coupler is DC. Since the output voltage exceeds the minimum value, current does not flow into the light emitting element, and stable control cannot be performed by the output voltage detection circuit.

FIG. 6 and FIG. 7 show respective conventional examples of a switching power supply device applied to avoid such a situation. First, referring to FIG. 6, 1 is a main transformer that insulates the primary side and the secondary side from each other, and 2 is a main switching element that constitutes a main inverter section 3 that is a power conversion section together with the main transformer 1. The DC input voltage Vi is intermittently applied to the primary winding 1a of the main transformer 1 from the DC power supply E connected between the input terminals + Vin and -Vin by switching the input voltage + Vin. The voltage induced in the secondary winding 1b of the main transformer 1 is rectified by the rectifying diodes 7 and 8 which form the rectifying and smoothing circuit 6, and then,
The DC output voltage Vo is smoothed by the choke coil 9 and the smoothing capacitor 10 between the output terminals + Vout and -Vout.
Is output as

As a feedback circuit for stabilizing the DC output voltage Vo, an output voltage detection circuit 11 for detecting fluctuations in the DC output voltage Vo and a control circuit for controlling a pulse conduction width to the main switching element 2 are controlled. Each IC 12 is provided. The output voltage detection circuit 11 winds the auxiliary winding 13 around the main transformer 1, rectifies and smoothes the voltage induced in the auxiliary winding 13 by the diode 14 and the capacitor 15, and then
This bias voltage VBIAS is applied to a series circuit 18 of a light emitting diode 16a, which is a light emitting element of a photocoupler 16 in which a resistor R3 is connected in series, and a shunt regulator 17, and a DC output voltage Vo is used as a reference for the shunt regulator 17 and a resistor R1. , R2 to divide and apply. The phototransistor 16b, which is a light receiving element of the photocoupler 16 that outputs a voltage detection signal, is connected to the feedback terminal, that is, the input terminal of the control IC 12. Incidentally, C1 is a capacitor for correcting the fluctuation of the amplification factor of the photocoupler 16.

On the other hand, FIG. 7 was previously proposed by the same applicant, and in this circuit, the voltage generated at one end of the secondary winding 1b of the main transformer 1 is peak rectified by the diode 21 and the capacitor C2. 6 is different in that the bias voltage VBIAS is obtained in accordance with FIG. Note that R4 is a current limiting resistor. Other configurations are exactly the same as those of another conventional example shown in FIG.

In each of the above conventional examples, the DC output voltage V
o is divided by the resistors R1 and R2 and applied to the reference of the shunt regulator 17, and the current value flowing into the cathode of the shunt regulator 17 changes according to the difference between the applied voltage and the reference voltage of the shunt regulator 17. However, the amount of light emitted from the light emitting diode 16a also changes.
The control IC 12 inputs as the voltage detection signal the change in the current flowing into the phototransistor 16b in accordance with the change in the light emission amount of the light emitting diode 16a, and outputs the DC output voltage Vo according to the voltage detection signal from the output voltage detection circuit 11. The pulse conduction width of the main switching element 2 is controlled so as to keep it constant. In this case, since the bias voltage VBIAS higher than the output voltage Vo is applied between the resistor R3 and the series circuit 18, the output voltage detection circuit 11 outputs the DC output voltage VBIAS.
Stable control can be performed without being affected by o.

[0007]

Each of the above-mentioned conventional circuits has the following problems. First, FIG. 6 and FIG.
In the above circuit, the bias voltage VBIAS is obtained from the voltage induced in the auxiliary winding 13 or the secondary winding 1b of the main transformer 1 when the switching element 2 is turned on. The DC input voltage Vi is connected to the line 1b in proportion to the winding ratio with the primary winding 1a of the main transformer 1.
Only the voltage that depends on can be taken out. Therefore, when the DC input voltage Vi fluctuates rapidly, the bias voltage VBIAS also fluctuates, and there is a problem that the stability of the output voltage detection circuit 11 is lost. On the contrary, in the steady state, the bias voltage V
Since BIAS is substantially stable, the current flowing into the cathode of the shunt regulator 17 changes only by the voltage applied from the connection point of the resistors R1 and R2, and the DC output voltage V
There is also a drawback that the responsiveness of the output voltage detection circuit 11 to the fluctuation of o is deteriorated.

In order to solve the above problems, the present invention can reduce the DC output voltage, and
Stability is not lost even when the input voltage fluctuates rapidly, and moreover,
An object is to obtain a DC voltage detection circuit of a switching power supply device with good responsiveness.

[0009]

In order to achieve the above object, an output voltage detection circuit of a switching power supply device according to a first aspect of the present invention uses a primary switching element to switch a DC input voltage to a primary winding of a main transformer. A series circuit of a light emitting element of a photocoupler and a shunt regulator as a feedback circuit for intermittently applying and stabilizing a DC output voltage supplied from the secondary winding of the main transformer through a rectifying and smoothing circuit. In a switching power supply device having an output voltage detection circuit that outputs a voltage detection signal from the light receiving element of the photocoupler by applying the DC output voltage divided by a resistor to the reference of the shunt regulator, When the main switching element is turned on, the voltage induced in the first winding element on the secondary side of the main transformer is A first voltage supply circuit for supplying to the column circuit, and a second voltage for supplying to the series circuit a voltage induced in the second winding element on the secondary side of the main transformer when the main switching element is off. It is provided with a supply circuit and a third voltage supply circuit for supplying the variation of the DC output voltage to the series circuit.

According to a second aspect of the present invention, in the output voltage detection circuit of the switching power supply device, in addition to the configuration of the first aspect, the first winding element or the second winding element is the main transformer. It is characterized in that it is an auxiliary winding wound around.

According to a third aspect of the present invention, in the output voltage detection circuit of the switching power supply device, in addition to the configuration of the first aspect, the first winding element or the second winding element is the rectifying / smoothing element. The auxiliary winding is wound around a choke coil that constitutes a circuit.

[0012]

According to the structure of claim 1, when the main switching element is turned on, the voltage induced in the first winding element is supplied to the series circuit by the first voltage supply circuit, and when the main switching element is turned off, With the second voltage supply circuit, the second
Since the voltage induced in the winding element is supplied to the series circuit, the voltage applied to the series circuit can be easily set higher than the DC output voltage. Moreover, since the voltage is supplied to the series circuit not only when the main switching element is turned on but also when it is turned off, the voltage applied to the series circuit is not significantly affected even when the DC input voltage changes rapidly. Improves stability. Furthermore, since the fluctuation of the DC output voltage is constantly reflected in the voltage applied to the series circuit by the third voltage supply circuit, the responsiveness of the output voltage detection circuit to the fluctuation of the DC output voltage is improved.

Further, according to the structure of claim 2, even when it is difficult to supply the voltage from the secondary winding of the main transformer, the auxiliary winding of the main transformer is simply wound around the auxiliary winding. The voltage induced in the winding can be supplied to the series circuit.

Further, according to the third aspect of the present invention, the voltage induced in the auxiliary winding of the choke coil can be converted into a series circuit by redesigning the choke coil of the rectifying and smoothing circuit without redesigning the main transformer. Can be supplied to.

[0015]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In each of the following embodiments, the same parts as those in FIGS. 6 and 7 shown in the conventional example are designated by the same reference numerals, and detailed description of the common parts will be omitted.

FIG. 1 shows a first embodiment of the present invention. The first embodiment is applied to a two-transformer partial resonance type converter. That is, the main inverter unit 31 has a first main transformer 32 and a second main transformer 33 which are main transformers, and their primary windings 32a and 33a have an input terminal + Vin, along with a first MOS type FET 34 which is a main switching element. -Vin is connected in series. Also,
Between the primary windings 32a, 33a of the first main transformer 32 and the second main transformer 33, in order to clamp the flyback voltage of these primary windings 32a, 33a, a voltage clamping capacitor 35 and auxiliary switching are provided. Second MOS that is an element
A series circuit with the type FET 36 is connected. Then, by switching the first FET 34, the DC input voltage Vi is intermittently applied to the primary windings 32a and 33a of the first main transformer 32 and the second main transformer 33. Further, the drive signal from the control IC 12 which is a pulse width control circuit is applied to the gates of the first FET 34 and the second FET 36 at an appropriate dead time, that is, the first FET 34 and the second FET 36.
The FETs 36 are alternately supplied while they have time to be turned off from each other. As a result, the loss of the first FET 34 and the second FET 36 at turn-on and turn-off can be significantly reduced.

In the first main transformer 32 and the second main transformer 33, the secondary windings 32b and 33b are also connected in series with each other, and one end of the secondary winding 32b, that is, the dot side terminal,
The cathodes of the rectifying diodes 41 and 42 forming the rectifying / smoothing circuit 6 are connected to one end of the secondary winding 33b, that is, the non-dot side terminal. The anodes of the rectifying diodes 41 and 42 are commonly connected to the other output terminal -Vout, and the secondary winding 32
The connection point of b and 33b is connected to one connection terminal + Vout via the choke coil 9. In addition to the rectifying diodes 41 and 42, the rectifying / smoothing circuit 6 includes smoothing capacitors 43 connected between the input side of the choke coil 9 and the output terminal -Vout, and between the output side of the choke coil 9 and the output terminal -Vout. , 10 are equipped.

The output voltage detection circuit 51, which forms a feedback circuit together with the control IC 12, connects the series circuit 18 of the light emitting diode 16a of the photocoupler 16 and the shunt regulator 17 in series with the resistor R3, and the phototransistor of the photocoupler 16. Connect 16b to the input terminal of the control IC 12,
Further, the DC output voltage Vo is divided by the resistors R1 and R2 and applied to the reference of the shunt regulator 17, and in this respect, it has the same configuration as that of FIGS. 6 and 7 shown in the conventional example. . However, in this embodiment, when the first FET 34 is turned on, the voltage induced in the secondary winding 32b on the secondary side of the first main transformer 32 is supplied to the first voltage supply circuit 52 for supplying to the series circuit 18. , A first voltage supply circuit that supplies the voltage induced in the secondary winding 33b on the secondary side of the second main transformer 33 to the series circuit 18 when the first FET 34 is off.
It is noted that it is provided with 53 and the third voltage supply circuit 54 which supplies the variation of the DC output voltage Vo to the series circuit 18. That is, in this embodiment, the secondary winding 32b corresponds to the first winding element, and the secondary winding 33b corresponds to the second winding element.

Specifically, in the first voltage supply circuit 52, the anode of the diode D1 is connected to the dot side terminal of the secondary winding 32b constituting the first main transformer 32, and the diode D1 is connected.
The cathode of No. 1 is connected to one end of the resistor R4, and the other end of the resistor R4 is connected to the anode which is one end of the light emitting diode 16a of the photocoupler 16 via the resistor R3. In addition, the second voltage supply circuit 53 has a diode D2 at the non-dot side terminal of the secondary winding 33b that constitutes the second main transformer 33.
Is connected to the anode of the resistor D5, the cathode of the diode D2 is connected to one end of the resistor R5, and the other end of the resistor R5 is connected to the light emitting diode.
It is connected to the anode of 16a through a resistor R3. Further, the third voltage supply circuit 54 has a DC output voltage V
A resistor R6 is connected via a resistor R3 between the high voltage line of o and the anode of the light emitting diode 16a.
A capacitor C2 that smoothes the voltage rectified by the diodes D1 and D2 of the first voltage supply circuit 52 and the second voltage supply circuit 53 is connected to the resistor R6.

Next, the operation of the above structure will be described with reference to the waveform chart of FIG. In the waveform diagram of FIG. 2, the gate drive signal applied from the control IC 12 to the first FET 34 in the steady state, the supply voltage Vfor from the first voltage supply circuit 52, and the second voltage supply circuit 53. Supply voltage from
fly and are shown in order.

By switching the first FET 34, the DC input voltage Vi between the input terminals + Vin and -Vin is intermittently applied to the primary windings 32a and 33a of the first main transformer 32 and the second main transformer 33, respectively. Applied to. Then, when the first FET 34 is turned on, a positive polarity voltage is generated at the dot side terminals of the secondary windings 32b and 33b, so that the rectifying diode 41
Is in a non-conducting state, the rectifying diode 42 is in a conducting state, and the voltage induced in the secondary winding 33b is rectified and smoothed by the rectifying and smoothing circuit 6. On the other hand, when the first FET 34 is turned off, a positive voltage is generated at the non-dot side terminals of the secondary windings 32b and 33b this time, so that the rectifying diode 42 becomes non-conductive, but the rectifying diode 41 becomes conductive. Then, the voltage induced in the secondary winding 32b becomes the rectifying and smoothing circuit 6
The rectification is smoothed by. As a result, the output terminal + Vout
, -Vout, a DC output voltage Vo is generated.

On the other hand, as shown in FIG. 2, in the output voltage detection circuit 51, when the first FET 34 is turned on, the diode D1 of the first voltage supply circuit 52 becomes conductive, so that the first main transformer 32 has The voltage induced in the secondary winding 32b is smoothed by the capacitor C2 via the resistor R4, and this supply voltage Vfo
r is applied to resistor R3 and series circuit 18. Further, when the first FET 34 is turned off, the diode D2 of the second voltage supply circuit 53 becomes conductive this time, so that the voltage induced in the secondary winding 33b of the second main transformer 33 passes through the resistor R5. Smoothed by the capacitor C2, this supply voltage Vfly is applied to the resistor R3 and the series circuit 18. At this time, the voltage reflecting the fluctuation of the DC output voltage Vo is constantly applied to the resistor R3 and the series circuit 18 from the high voltage line of the DC output voltage Vo via the resistor R6.

Here, for convenience, the winding ratio of the primary winding 32a and the secondary winding 32b of the first main transformer 32, and the primary winding 33a and the secondary winding 33b of the second main transformer 33 is Assuming that both are n: 1, the average value of the supply voltage Vfor from the first voltage supply circuit 52 is expressed by the following formula 1.

[0024]

[Equation 1]

However, D is the duty of the first FET 34 (ratio of ON time to one cycle). Also, the second
The average value of the supply voltage Vfly from the voltage supply circuit 53 of FIG.

[0026]

[Equation 2]

The bias voltage VBIAS generated between the resistor R3 and the series circuit 18 is the sum of the voltage generated between the resistor R6 and the DC output voltage Vo, but the current flowing through the resistor R6 is the current flowing through the resistor R4. Is equal to the current flowing through the resistor R5 minus the current IR3 flowing through the resistor R3.

[0028]

(Equation 3)

Therefore, if the resistors R4, R5 and R6 are properly selected, the DC output voltage Vo is, for example, 2
It is possible to easily obtain the bias voltage VBIAS higher than the DC output voltage Vo even when the voltage is about V or 3.3V. Further, the first voltage supply circuit 52 and the second voltage supply circuit 53 allow the light emitting diode of the photocoupler 16 to operate.
Since the voltage is supplied to the series circuit 18 of the 16a and the shunt regulator 17 not only when the first FET 34 is turned on but also when the first FET 34 is turned off, the voltage is applied to the series circuit 18 even if the DC input voltage Vi fluctuates rapidly. The applied bias voltage VBIAS is not so affected. Therefore, the output voltage detection circuit 11 can continue stable control without depending on the fluctuation of the DC input voltage Vi. Further, in the present embodiment, the variation of the DC output voltage Vo is always reflected in the bias voltage VBIAS applied to the series circuit 18 by the resistor R6 of the third voltage supply circuit 54, so that the shunt regulator 17 has a cathode. The inflowing current changes not only with the voltage applied from the connection point of the resistors R1 and R2 but also with the bias voltage VBIAS applied to the series circuit 18, and the responsiveness of the output voltage detection circuit 51 with respect to the variation of the DC output voltage Vo. Be improved.

As described above, the output voltage detection circuit 51 in this embodiment supplies the voltage induced in the secondary winding 32b of the first main transformer 32 to the series circuit 18 when the first FET 34 is turned on. A first voltage supply circuit 52, a second voltage supply circuit 53 which supplies the voltage induced in the secondary winding 33b of the second main transformer 33 to the series circuit 18 when the first FET 34 is off,
Third supply of variation of DC output voltage Vo to series circuit 18
Since the voltage supply circuit 54 of FIG.
It is possible to obtain the output voltage detection circuit 51 which can cope with the reduction of the voltage of i, does not lose the stability even when the DC input voltage Vi fluctuates rapidly, and has a good responsiveness.

In the present embodiment, the main transformer is composed of the first main transformer 32 and the second main transformer 33, but it is of course possible to construct it with a single main transformer. Further, instead of supplying the voltage induced in the secondary winding 32b or the secondary winding 33b to the series circuit 18, the auxiliary winding is wound around the first main transformer 32 or the second main transformer 33, The voltage induced in this auxiliary winding may be supplied to the series circuit 18. A specific example thereof will be described in detail in the second embodiment below. The point is that at least when the main switching element is on and off, the voltage induced from the winding element on the secondary side of the main transformer is When the voltage supply circuit 52 and the second voltage supply circuit 53 supply the voltage to the series circuit 18, the output voltage detection circuit 51 operates even if the DC output voltage Vo is low, and stable control can be continued.

Further, the first voltage supply circuit 52 and the second voltage supply circuit 52
It is preferable that the voltage supply circuit 53 of FIG. 3 is composed of a series circuit of diodes D1 and D2 and resistors R4 and R5, and the third voltage supply circuit 54 is composed of a resistor R6. In this case, the circuit configuration of the output voltage detection circuit 51 can be simplified, and the resistors R4, R5, and R6 can be appropriately selected.
A bias voltage VBIAS higher than the DC output voltage Vo can be easily obtained based on the equation (3).

Next, a second embodiment of the present invention applied to a flyback converter will be described in detail with reference to FIG. The same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description of the common parts will be omitted.

In this embodiment, the primary winding 32 of the main transformer 32 is
The main inverter section 31 is constituted by a and the MOS type FET 34 as the main switching element, and the rectifying diode 41 constituting the rectifying / smoothing circuit 6 is connected to one end of the secondary winding 32b of the main transformer 32, that is, the non-dot side terminal. . When the FET 34 is turned on, the secondary winding 32 of the main transformer 32
Energy is stored in b, and when the FET 34 is off, the energy stored in the secondary winding 32b is output terminal + Vout,
It is sent to the −Vout side to obtain the DC output voltage Vo.

On the other hand, in the output voltage detection circuit 51, the second voltage supply circuit 53 connects the anode of the diode D2 to the non-dot side terminal of the secondary winding 32b of the main transformer 32, and the first voltage supply circuit 53. The voltage supply circuit 52 includes an auxiliary winding 32c wound around the main transformer 32, and one end of the auxiliary winding 32c, that is, the non-dot side terminal is connected to the dot side terminal of the secondary winding 32b, and the auxiliary winding 32c is connected. It differs from the configuration of the first embodiment in that the other end of the winding 32c, that is, the dot side terminal is connected to the anode of the diode D1. That is, in this embodiment, the main transformer 32
The secondary winding 32c on the secondary side corresponds to the first winding element, and the secondary winding 32b on the secondary side of the main transformer 32 also corresponds to the second winding element. The other configuration of the output voltage detection circuit 51 is exactly the same as that of the first embodiment.

In this embodiment, when the FET 34 is turned on,
A positive voltage is induced at the dot side terminals of the secondary winding 32b and the auxiliary winding 32c of the main transformer 32. Therefore, in the output voltage detection circuit 51, since the diode D1 of the first voltage supply circuit 52 conducts, the voltage induced in the auxiliary winding 32c is smoothed by the capacitor C2 via the resistor R4, and this supply voltage Vfor is Applied to R3 and series circuit 18. On the other hand, when the FET 34 is turned off, a positive voltage is induced at the non-dot side terminals of the secondary winding 32b and the auxiliary winding 32c of the main transformer 32. Therefore, since the diode D2 of the second voltage supply circuit 53 is turned on this time,
The voltage induced in the secondary winding 33b of the second main transformer 33 is smoothed by the capacitor C2 via the resistor R5, and this supply voltage Vfly is applied to the resistor R3 and the series circuit 18. Further, the voltage reflecting the fluctuation of the DC output voltage Vo is constantly applied to the resistor R3 and the series circuit 18 from the high voltage line of the DC output voltage Vo via the resistor R6.

As described above, in the output voltage detecting circuit 51 of this embodiment, the first winding element is the auxiliary winding 32c wound around the main transformer 32, and when the FET 34 is turned on, this auxiliary winding 32c is turned on.
to supply the voltage induced in c to the series circuit 18
Since the voltage supply circuit 52 of is configured, even if it is difficult to supply the voltage from the secondary winding 32b of the main transformer 32,
Just by winding the auxiliary winding 32c around the main transformer 32, the DC output voltage Vi can be lowered as in the first embodiment, and the stability can be maintained even when the DC input voltage Vi changes rapidly. It is possible to obtain the output voltage detection circuit 51 which is not lost and has good response. In particular, the auxiliary winding 32 as in the present embodiment
The configuration using c is suitable for a flyback converter or the like in which the rectifying / smoothing circuit 6 does not have a choke coil.

Although the first winding element is the auxiliary winding 32c in this embodiment, the second winding element is supplemented depending on the configurations of the main inverter section 31 and the rectifying / smoothing circuit 6. The winding 32c may be used. In this case, the second voltage supply circuit 53 may be configured to supply the voltage induced in the auxiliary winding 32c to the series circuit 18 when the FET 34 is off.

Next, a third embodiment of the present invention will be described in detail with reference to FIG. The same parts as those in FIGS. 1 and 2 are designated by the same reference numerals, and detailed description of the common parts will be omitted to avoid duplication.

This embodiment is applied to a forward converter, and the rectifying / smoothing circuit 6 is composed of a rectifying diode 41, a flywheel diode 44, a choke coil 9 around which an auxiliary winding 9b is wound, and a smoothing capacitor 10. It
In this case, when the FET 34 is turned on, a positive voltage is induced at the dot side terminal of the secondary winding 32b of the main transformer 32 and the rectifying diode 41 becomes conductive, so that the energy from the secondary winding 32b is transferred to the rectifying diode 41. It is stored in the choke coil 9 more. On the other hand, when the FET 34 is turned off, a positive voltage is induced at the non-dot side terminal of the secondary winding 32b of the main transformer 32.
44 becomes conductive, and the choke coil 9 leads to the smoothing capacitor 10
Energy is sent to the side. For the sake of convenience, the winding ratio between the winding 9a of the choke coil 9 itself and the auxiliary winding 9b is n: 1, which is the same as the winding ratio between the primary winding 32a and the secondary winding 32b of the transformer 32.

In the output voltage detection circuit 51, the second voltage supply circuit 53 is provided with the auxiliary winding 9b of the choke coil 9, and one end of this auxiliary winding 9b, that is, the dot side terminal is connected to the low voltage line of the DC output voltage Vo. Is different from the first embodiment in that the non-dot side terminal of the auxiliary winding 9b is connected to the anode of the diode D2. That is, in this embodiment, the secondary winding 32b on the secondary side of the main transformer 32 corresponds to the first winding element, and the auxiliary winding 9b on the secondary side of the main transformer 32 also serves as the second winding element.
Corresponding to the winding element. The other configuration of the output voltage detection circuit 51 is exactly the same as that of the first embodiment.

In this embodiment, when the FET 34 is turned on,
A positive voltage is induced at the dot side terminal of the secondary winding 32b of the main transformer 32. Therefore, the output voltage detection circuit 51
Since the diode D1 of the first voltage supply circuit 52 conducts, the voltage induced in the secondary winding 32b is smoothed by the capacitor C2 via the resistor R4, and this supply voltage Vfor is applied to the resistor R3 and the series circuit 18. Is applied. On the other hand, when the FET 34 is turned off, the flywheel diode 44 becomes conductive and the energy of the choke coil 9 is sent to the smoothing capacitor 10 side. At this time, a positive voltage is induced at the non-dot side terminal of the auxiliary winding 9b forming the choke coil 9 and the diode D2 of the second voltage supply circuit 53 becomes conductive, so that the auxiliary winding 9b of the choke coil 9 is made conductive.
The voltage induced in the circuit is smoothed by the capacitor C2 via the resistor R5, and this supply voltage Vfly is applied to the resistor R3 and the series circuit 18. Further, the resistor R3 and the series circuit
In 18, the voltage reflecting the fluctuation of the DC output voltage Vo is
The DC output voltage Vo is constantly applied from the high voltage line via the resistor R6.

As described above, in the output voltage detection circuit 51 of this embodiment, the second winding element is the auxiliary winding 9b of the choke coil 9 which constitutes the rectifying and smoothing circuit 6, and the auxiliary winding is provided when the FET 34 is off. Since the second voltage supply circuit 53 is configured to supply the voltage induced on the line 9b to the series circuit 18,
Even if the main transformer 32 is not redesigned, just by changing the design of the choke coil 9 of the rectifying / smoothing circuit 6, the DC output voltage Vi can be reduced as in the first embodiment, and the DC input voltage can be reduced. It is possible to obtain the output voltage detection circuit 51 which does not lose stability even when Vi changes abruptly and has good responsiveness. In particular, the configuration using the auxiliary winding 9b as in the present embodiment is suitable for a forward type converter having a choke coil in the rectifying / smoothing circuit 6.

In this embodiment, the second winding element is the auxiliary winding 9b of the choke coil 9, but depending on the configuration of the main inverter section 31 and the rectifying / smoothing circuit 6,
The first winding element may be the auxiliary winding 9b of the choke coil 9. In this case, the auxiliary winding 9b is turned on when the FET 34 is turned on.
The first voltage supply circuit 52 may be configured to supply the voltage induced in the series circuit 18 to the series circuit 18.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the gist of the present invention. For example, as shown in FIG. 5, even if the smoothing capacitor C2 in FIG. 1 is connected between the resistor R3 and the series circuit 18, the same action and drop are obtained. Further, as the main switching element, a transistor may be used instead of the MOS type FET.

[0046]

According to the output voltage detection circuit of the switching power supply device of the present invention, the DC input voltage is intermittently applied to the primary winding of the main transformer by the switching of the main switching element, and the secondary voltage of the main transformer is increased. As a feedback circuit for stabilizing the DC output voltage supplied from the next winding through the rectifying and smoothing circuit, it has a series circuit of a light emitting element of a photocoupler and a shunt regulator, and the DC of the shunt regulator is used as a reference. In a switching power supply device including an output voltage detection circuit that outputs a voltage detection signal from a light receiving element of the photocoupler by dividing the output voltage with a resistor and applying the divided voltage, a voltage of the main transformer is turned on when the main switching element is turned on. A first voltage supply circuit for supplying the voltage induced in the first winding element on the next side to the series circuit; A second voltage supply circuit that supplies a voltage induced in the second winding element on the secondary side of the main transformer to the series circuit when the main switching element is off, and a variation of the DC output voltage. Third supply to series circuit
Since it is equipped with the voltage supply circuit of No. 1, it is possible to cope with lowering of the DC output voltage, stability is not lost even if the input voltage fluctuates rapidly, and responsiveness can be improved. .

According to a second aspect of the present invention, in the output voltage detection circuit of the switching power supply device, in addition to the configuration of the first aspect, the first winding element or the second winding element is the main transformer. It is characterized in that it is an auxiliary winding that is wound around the main transformer, and even if it is difficult to supply voltage from the secondary winding of the main transformer, simply winding the auxiliary winding around the main transformer Thus, it is possible to cope with the lowering of the DC output voltage, the stability is not lost even when the input voltage fluctuates rapidly, and the responsiveness can be improved.

In the output voltage detection circuit of the switching power supply device according to a third aspect of the present invention, in addition to the configuration of the first aspect, the first winding element or the second winding element has the rectifying and smoothing element. It is an auxiliary winding that is wound around the choke coil that constitutes the circuit, and without changing the design of the main transformer, simply changing the design of the choke coil of the rectifying / smoothing circuit will produce a DC output. It is possible to cope with lowering of the voltage, stability is not lost even when the input voltage fluctuates rapidly, and the responsiveness can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a switching power supply device showing a first embodiment of the present invention.

FIG. 2 is a waveform diagram of a main part of the same.

FIG. 3 is a circuit diagram of a switching power supply device showing a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a switching power supply device showing a third embodiment of the present invention.

FIG. 5 is a circuit diagram of an output voltage detection circuit showing another modification of the present invention.

FIG. 6 is a circuit diagram of a switching power supply device showing a conventional example.

FIG. 7 is a circuit diagram of a switching power supply device showing another conventional example.

[Explanation of symbols]

 6 Rectifying and smoothing circuit 9 Choke coil 9b Auxiliary winding (second winding element) 16 Photocoupler 16a Light emitting diode (light emitting element) 16b Phototransistor (light receiving element) 17 Shunt regulator 18 Series circuit 32 First main transformer (main) Transformer) 32a primary winding 32b secondary winding (first winding element, second winding element) 32c auxiliary winding (first winding element) 33 second main transformer (main transformer) 33a primary Winding 33b Secondary winding (second winding element) 34 First FET (main switching element) 51 Output voltage detection circuit 52 First voltage supply circuit 53 Second voltage supply circuit 54 Third voltage supply Circuit R1, R2 resistance

Claims (3)

[Claims] 1. A DC output voltage supplied from a secondary winding of the main transformer through a rectifying / smoothing circuit while intermittently applying a DC input voltage to a primary winding of the main transformer by switching of a main switching element. As a feedback circuit for stabilizing the photocoupler, it has a series circuit of a light emitting element of a photocoupler and a shunt regulator, and by applying the DC output voltage divided by a resistor to a reference of the shunt regulator, the photocoupler In a switching power supply device including an output voltage detection circuit that outputs a voltage detection signal from the light receiving element of, the voltage induced in the first winding element on the secondary side of the main transformer is turned on when the main switching element is turned on. A first voltage supply circuit for supplying to a series circuit, and a second side of the secondary side of the main transformer when the main switching element is off. A second voltage supply circuit for supplying the voltage induced in the winding element to the series circuit, and a third voltage supply circuit for supplying the variation of the DC output voltage to the series circuit. An output voltage detection circuit for a switching power supply device characterized. 2. The output of the switching power supply device according to claim 1, wherein the first winding element or the second winding element is an auxiliary winding wound around the main transformer. Voltage detection circuit. 3. The first winding element or the second winding element is an auxiliary winding wound around a choke coil forming the rectifying and smoothing circuit. Output voltage detection circuit of the switching power supply device.