JP5082693B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply apparatus that controls an output voltage with a voltage of a control winding of a transformer.

  Conventionally, a ringing choke converter or the like that outputs a voltage to the secondary side of the transformer by applying / blocking the voltage to the primary side of the transformer by a switching element using a transformer having different polarities on the primary side and the secondary side There is a switching power supply.

  In such a switching power supply device, in order to stabilize the output voltage, the output voltage is detected via a photocoupler or the like, and the ON period of the switching element is increased or decreased based on this detection. It is normal. However, in the case of using a photocoupler, since the output voltage is directly detected, it is possible to control the output voltage relatively stably, but there is a problem that the cost increases and the circuit area increases.

On the other hand, in order to stabilize the output voltage, a control winding is provided in the transformer, and the ON period of the switching element is increased / decreased based on the voltage of the control winding, thereby reducing the cost by omitting the photocoupler and the like. A power supply device that is miniaturized has also been proposed (for example, Patent Documents 1 to 3). In such a power supply circuit, basically, a constant voltage circuit such as a Zener diode or a shunt regulator is used, and when the voltage of the control winding increases, the current flows through the constant voltage circuit and the switching element is turned off. Control is performed to speed up the output, thereby stabilizing the output voltage.
JP 2001-251855 A JP 2004-320856 A JP-A-5-304778

  For example, a circuit as shown in FIG. 4 can be cited as a switching power supply device in which a control winding is provided in a transformer to stabilize the output voltage. In the switching power supply device 80, for example, an AC voltage generated in the control winding N3 is supplied to the base terminal of the switching transistor Tr1 via the capacitor Cr. As a result, the switching transistor Tr1 is turned on / off, a voltage is applied to or interrupted from the primary winding N1, and power is transmitted to the secondary winding N2. In addition, a voltage proportional to the voltage output to the secondary winding N2 is also generated in the control winding N3, and this voltage is rectified by the rectifier diode D3 and stored in the smoothing capacitor C3. When the voltage of the smoothing capacitor C3 increases and exceeds the Zener voltage of the Zener diode Z81, the Zener diode Z81 is turned on to reduce the voltage at the base terminal of the switching transistor Tr1, thereby switching the switching transistor Tr1. The output voltage is stabilized by advancing the timing of turning off.

  However, in the above-described power supply device that controls the output voltage based on the voltage of the control winding, there is a problem that the output voltage decreases relatively greatly as the output current increases. This decrease in output voltage is, for example, that the voltage of the secondary winding (N2) becomes higher than the output voltage Vout due to the voltage drop of the rectifier diode (D2) connected in series to the secondary winding (N2) of the transformer. In addition, since the current of the secondary winding (N2) is increased, the degree of coupling between the transformer secondary winding (N2) and the control winding (N3) is reduced, and the voltage of the secondary winding (N2) is reduced. The reason is that the voltage of the control winding (N3) becomes high.

  An object of the present invention is to provide a switching power supply device that can alleviate a decrease in output voltage accompanying an increase in output current in a switching power supply device that controls an output voltage based on the voltage of a control winding.

  In order to achieve the above object, the present invention applies / shuts down the voltage to the primary winding (N1) of the transformer (2) by the switching element (Tr1), and also connects the primary winding (N1) of the transformer and the secondary winding. In the switching power supply (1) that alternately turns on and off the current flow with the line (N2) and outputs the voltage to the secondary winding (N2) side, the feedback winding (N3) of the transformer A self-excited oscillation circuit section (Cr, Rr) for generating an oscillation voltage for turning on and off the switching element by the generated AC voltage, a first control winding (N3) provided in the transformer, and the first control winding A control circuit unit (5) for changing the ON period of the switching element by comparing a voltage generated in the line with a set voltage, a second control winding (N4) provided in the transformer, and the second control Electricity generated in the winding And a configuration in which a set voltage correcting circuit for correcting (6) the size of the set voltage according to the magnitude.

  According to such a means, when the output current increases and the output voltage decreases, the set voltage correction circuit corrects the magnitude of the set voltage to alleviate the amount of decrease in the output voltage. I can do it. In addition, since the output current itself is not detected, but the amount of change in the voltage generated in the control winding as the output current increases is detected for correction processing, the above correction processing is realized with a simple circuit configuration. I can do it.

  Specifically, the control circuit unit (5) includes a first smoothing capacitor (C3) that smoothes and accumulates a voltage generated in the first control winding, and a constant current that flows when a set voltage is exceeded. A voltage circuit (Z1, R1, R2), and when the voltage of the first smoothing capacitor exceeds the set voltage, a current flows through the constant voltage circuit to turn off the control terminal of the switching element (Tr1). It can be configured to output a voltage.

  More specifically, the constant voltage circuit includes a dividing resistor (R1, R2) for dividing a predetermined voltage and a Zener diode (Z1) connected to a dividing point (A) of the dividing resistor, The set voltage correction circuit (6) includes a second smoothing capacitor (C4) that smoothes and accumulates a voltage generated in the second control winding (N4), and the voltage according to the magnitude of the voltage of the second smoothing capacitor. A transistor (Tr3) that allows current to flow through the dividing point of the dividing resistor can be used.

  With such a configuration, it is possible to appropriately reduce a decrease in output voltage due to an increase in output current, and also to determine the size of the dividing resistor, the collector resistance, emitter resistance, etc. of the transistor that passes current to the dividing point. By appropriately adjusting, the correction amount of the set voltage can be easily adjusted.

  More specifically, the constant voltage circuit includes a shunt regulator (Z6: FIG. 3) that generates a constant voltage according to a reference voltage, and a dividing resistor (Z6) that generates a reference voltage for the shunt regulator by dividing a predetermined voltage. R7, R8), and the set voltage correction circuit (6b) smoothes and accumulates the voltage generated in the second control winding, and the voltage of the second smoothing capacitor. The transistor (Tr3) that allows current to flow through the dividing point (C) of the dividing resistor according to the size of the dividing resistor.

  Even with such a configuration, it is possible to moderate the decrease in the output voltage accompanying the increase in the output current as well as the size of the dividing resistor, the collector resistance, the emitter resistance, etc. The amount of correction of the set voltage can be easily adjusted by appropriately adjusting the magnitude.

  Specifically, the dividing resistor (R1, R2 or R7, R8) may be configured to resistively divide the voltage across the first smoothing capacitor (C3).

  Specifically, the feedback winding and the first control winding can be shared by a single winding (N3).

  With such a configuration, the switching power supply device can be manufactured at a low cost as a whole.

  In addition, in this item, although the code | symbol showing the corresponding relationship with embodiment was described in the parenthesis, this invention is not restrict | limited to this.

  According to the present invention, in a switching power supply device that applies / cuts voltage to a primary winding of a transformer by a switching element and outputs a voltage to the secondary winding side, the circuit area can be reduced without using a photocoupler. There is an effect that the power supply device can be configured without increasing and the amount of decrease in the output voltage accompanying the increase in the output current can be moderated appropriately.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram showing a configuration of a switching power supply apparatus according to an embodiment of the present invention.

  The switching power supply device 1 of this embodiment is a circuit that generates a DC output voltage Vout from an AC input voltage Vin, for example, and a discrete component is disposed on a circuit board without using an integrated circuit for switching control. It is constituted as follows. The switching power supply 1 includes a diode bridge D1 that rectifies an AC input voltage Vin, a filter circuit 4 (capacitors C11 and C12, a choke coil L1) that smoothes the rectified voltage and removes noise, and a primary winding. A transformer 2 whose polarity is reversed between N1 and the secondary winding N2, a first control winding N3 and a second control winding N4 that are provided secondary to the transformer 2, and a primary winding N1 in series. The switching transistor (switching element) Tr1 connected to the capacitor, the capacitor Cr and the resistor Rr that perform self-excited oscillation by charging and discharging with the AC voltage generated in the first control winding N3, and the base terminal of the switching transistor Tr1 are connected. The resistors R11 and R12 that supply a minute current to the node B and the secondary winding N2 are connected in series to turn on and off the secondary current. A diode D2, a protective resistor for R21 which is connected between the output terminal, and a zener diode Z21 and a smoothing capacitor C2 and the like.

  Further, the switching power supply device 1 includes a rectifier diode D3 connected in series with the first control winding N3, a smoothing capacitor C3 for smoothing and storing the voltage of the first control winding N3, and a second control winding N4. The rectifier diode D4 connected in series, the smoothing capacitor C4 for smoothing and storing the voltage of the second control winding N4, and the voltage at the base terminal of the switching transistor Tr1 when the voltage of the smoothing capacitor C3 increases. The control circuit 5 to be driven, the set voltage correction circuit 6 that raises the voltage of the node A by causing a current to flow through the divided node A of the dividing resistors R1 and R2 when the voltage of the smoothing capacitor C4 rises, and the output current becomes excessive. In this case, an overcurrent protection circuit 3 is provided for stopping the output of the self-excited oscillation voltage.

  One end of the capacitor Cr is connected to the node B, charges and discharges the AC voltage generated in the first control winding N3 to generate a self-excited oscillation voltage, and supplies the oscillation voltage to the node B. It is like that. Thereby, an oscillation voltage is applied to the base terminal of the switching transistor Tr1, the switching transistor Tr1 is turned on / off, and a voltage is applied / cut off to the primary winding N1.

  The control circuit 5 includes a constant voltage circuit (dividing resistors R1 and R2 and a Zener diode Z1) that supplies current when a set voltage is exceeded, and a base terminal of the switching transistor Tr1 that is turned on when current flows through the constant voltage circuit. And a transistor Tr2 that draws current from.

  The constant voltage circuit has a configuration in which the voltage across the smoothing capacitor C3 is divided by the dividing resistors R1 and R2, and the anode of the Zener diode Z1 is connected to the dividing node A. Then, using the cathode potential of the smoothing capacitor C3 as a reference, the voltage obtained by adding the voltage drop of the resistor R2 and the Zener voltage of the Zener diode Z1 is set as a set voltage, and the cathode voltage of the Zener diode Z1 exceeds the set voltage. In such a case, a current is passed.

  With such a configuration, when the voltage across the smoothing capacitor C3 exceeds the set voltage, the base current of the transistor Tr2 flows, thereby turning on the transistor Tr2 and connecting the base terminal of the switching transistor Tr1. Reduce the voltage of B. As a result, the switching transistor Tr1 is turned off, and the output voltage is stabilized.

  The set voltage correction circuit 6 is a circuit that varies the voltage of the divided node A of the divided resistors R1 and R2 based on the voltage of the smoothing capacitor C4. Specifically, the set voltage correction circuit 6 receives the divided resistors R4 and R5 that divide the combined voltage of the smoothing capacitors C4 and C3, and the divided voltage of the divided resistors R4 and R5 as a base and supplies the divided node A to the divided node A. It is composed of a transistor Tr3 and the like for passing current. A base resistor R6 and a collector resistor R3 are connected to the transistor Tr3, and a collector terminal is connected to one end side of the dividing resistor R1 via the resistor R3.

  With such a configuration, when the voltage of the smoothing capacitor C4 increases, a current flows through the transistor Tr3 according to the voltage value, and the voltage of the divided node A is increased. Due to this voltage fluctuation, the magnitude of the set voltage of the constant voltage circuit is corrected, and the set voltage at which current flows through the Zener diode Z1 is pushed up.

  Next, the overall operation of the switching power supply device 1 will be described.

When the input power source Vin is input and a current flows through the starting resistors R11 and R12, a base current is supplied to turn on the switching transistor Tr1, and a voltage is applied to the primary winding N1. As a result, the current of the primary winding N1 increases, but when the collector current of the switching transistor Tr1 is saturated, the current increase of the primary winding N1 is stopped, and the secondary winding N2 and the first control winding N3 are stopped. The voltage of is reversed. Then, the voltage of the first control winding N3 at this time is output to the base terminal of the switching transistor Tr1 via the capacitor Cr, and the switching transistor Tr1 is turned off. In this way, the switching transistor Tr1 is turned on / off by self-excited oscillation, and the voltage is applied / cut off to the primary winding N1.

  When a voltage is applied to the primary winding N1 and a current flows through the primary winding N1, magnetic energy is accumulated in the core of the transformer 2, and when the switching transistor Tr1 is next turned off, this magnetic energy is transferred to the secondary winding. N2 is transmitted, current flows to the secondary side, and the output voltage Vout smoothed by the smoothing capacitor C2 is generated.

  At this time, a voltage proportional to the voltage of the secondary winding N2 is output to the first control winding N3 and the second control winding N4, and this voltage is rectified by the rectifier diodes D3 and D4 to be smoothed capacitors C3 and C4. Accumulated in. When the voltage of the smoothing capacitor C3 increases and exceeds the sum of the voltage of the dividing resistor R2 and the Zener voltage, the Zener diode Z1 is turned on, and a current flows from the node B to the transistor Tr2 of the control circuit 5. As a result, the switching transistor Tr1 is turned off earlier. Thereby, the current flowing through the primary winding N1 is suppressed and the output voltage Vout is stabilized.

  On the other hand, when the output current increases and the output voltage decreases, the voltage generated in the second control winding N4 increases. As a result of this voltage increase, the base voltage of the transistor Tr3 of the set voltage correction circuit 6 increases, and the current flowing through the resistor R2 via the transistor Tr3 is increased. As a result, the voltage at the divided node A to which the Zener diode Z1 is connected rises, making it difficult to turn on the transistor Tr2. Thereby, the ON period of the switching transistor Tr1 is lengthened, and the decrease in the output voltage Vout is alleviated.

  FIG. 2 is a VI characteristic diagram showing improvement in characteristics by the switching power supply device 1. In the figure, the characteristic line “after improvement” is that of the switching power supply device 1 of FIG. 1, and the characteristic line “before improvement” is that of the switching power supply device 80 of FIG.

  As shown in FIG. 2, according to the switching power supply device 1 of this embodiment, the setting voltage of the constant voltage circuit is increased by the action of the setting voltage correction circuit 6 so that the output voltage increases when the output current increases. Thus, it is possible to obtain characteristics in which the amount of decrease in output voltage is reduced.

  As described above, according to the switching power supply device 1 of this embodiment, the potential of the reference potential point A of the Zener diode Z1 is set by the set voltage correction circuit 6 when the output voltage Vout decreases as the output current increases. And the amount of decrease in output voltage can be mitigated. In addition, since the correction process is performed by detecting the voltage change of the control winding N4 accompanying the increase in the output current, instead of detecting the output current itself, the above correction process can be realized with a simple circuit configuration. I can do it.

  Further, since the set voltage correction circuit 6 is configured to increase or decrease the current flowing through the dividing resistor R2 by the transistor Tr3, the size of the dividing resistors R1 and R2 and the size of the collector resistor R3 and the base resistor R6 of the transistor Tr3 are appropriately adjusted. By doing so, the correction amount of the set voltage can be easily adjusted. Further, the correction amount can be adjusted by the number of windings of the second control winding N4.

  Further, according to the switching power supply device 1 of this embodiment, since it is configured only by discrete components without using a photocoupler or a control IC, the switching power supply device can be manufactured at a low cost as a whole.

[Modification]
FIG. 3 is a circuit diagram showing a modification of the switching power supply device according to the embodiment of the present invention.

  In the switching power supply device 1 of FIG. 1 described above, the Zener diode Z1 is applied as the constant voltage circuit of the control circuit 5, and the Zener diode Z1 is connected in order to change the set voltage flowing in the Zener diode Z1. The configuration for raising and lowering the voltage at the reference point A is shown. On the other hand, in the switching power supply device 1B of this modification, the shunt regulator Z6 is applied as the constant voltage circuit of the control circuit 5b, and the reference voltage of the shunt regulator Z6 is changed in order to change the set voltage in which current flows through the shunt regulator Z6. This is a structure that moves up and down. The other configuration is the same as that of FIG.

  That is, in the switching power supply device 1, as the control circuit 5b for stabilizing the output voltage Vout, the dividing resistors R7 and R8 for dividing the voltage across the smoothing capacitor C3 to generate the reference voltage, and the setting corresponding to the reference voltage A shunt regulator Z6 that flows current when the voltage is exceeded, a transistor Tr2 that draws current from the base terminal of the switching transistor Tr1 when current flows through the shunt regulator Z6, and the like are provided. The shunt regulator Z6 has an anode terminal connected to the cathode potential point of the smoothing capacitor C3 and a cathode terminal connected to the base terminal of the transistor Tr2.

  With such a configuration, when the voltage across the smoothing capacitor C3 exceeds the set voltage of the shunt regulator Z6, the base current of the transistor Tr2 flows, thereby turning on the transistor Tr2 and connecting the base terminal of the switching transistor Tr1. The voltage at the node B is reduced. As a result, the switching transistor Tr1 is turned off, and the output voltage is stabilized.

  The set voltage correction circuit 6b that raises and lowers the reference voltage of the shunt regulator Z6 generates a reference voltage by receiving the divided resistors R4 and R5 that divide the combined voltage of the smoothing capacitors C4 and C3 and the divided voltage as a base. And a transistor Tr3 for supplying current to the dividing resistor R7. The transistor Tr3 has a collector terminal connected to the divided node C of the divided resistors R7 and R8 that generate the reference voltage via the resistor R9, and an emitter terminal connected to the potential point of the cathode of the smoothing capacitor C3. .

  With such a configuration, when the voltage of the smoothing capacitor C4 rises, a current flows through the transistor Tr3 according to the voltage value, the voltage of the divided node C of the dividing resistors R7 and R8 is lowered, and the current flows to the shunt regulator Z6. The set voltage that flows is reduced.

  Even in such a configuration, the amount of reduction in the output voltage accompanying the increase in the output current can be mitigated by the same action as that of the switching power supply device 1 of FIG.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, in the above embodiment, in order to generate the voltage at the reference point A of the Zener diode Z1 of FIG. 1 or the reference voltage of the shunt regulator Z6 of FIG. Although it is generated, the voltage of the reference point A and the reference voltage may be generated from any voltage as long as a relatively stable voltage is obtained. Further, the transistor Tr2 in FIGS. 1 and 3 may be omitted, and the current may be directly drawn from the base terminal of the switching transistor Tr1 by the Zener diode Z1 or the shunt regulator Z6.

  In addition, it is possible to obtain the same effect by operating the set voltage correction circuits 6 and 6b by the voltage fluctuation of the first control winding N3 without using the second control winding N4.

  Further, in the above embodiment, a constant voltage circuit in which a current flows at a set voltage or higher is used, and the circuit operation when the voltage of the first control winding exceeds the set voltage is caused by flowing a current through the constant voltage circuit. When a set voltage is actually generated by a constant voltage circuit, this voltage is compared with the voltage of the first control winding by a voltage comparator, and the set voltage is exceeded based on the comparison result. You may comprise so that circuit operation may be caused. In addition, the details specifically shown in the above embodiment can be changed as appropriate without departing from the spirit of the invention.

It is a circuit diagram which shows the structure of the switching power supply device of embodiment of this invention. It is a VI characteristic figure which compared the characteristic of the switching power supply of embodiment. It is a circuit diagram which shows the modification of the switching power supply device of embodiment of this invention. It is a circuit diagram which shows an example of the switching power supply device which does not have a reference voltage correction circuit.

Explanation of symbols

1,1B Switching power supply 2 Transformer N1 Primary winding N2 Secondary winding D2 Rectifier diode N3 First control winding C3 Smoothing capacitor (first smoothing capacitor)
D3 Rectifier diode N4 Second control winding C4 Smoothing capacitor (second smoothing capacitor)
D4 Rectifier diode Tr1 Switching transistor (switching element)
Cr Capacitor for self-excited oscillation Rr Resistor for self-excited oscillation 5, 5b Control circuit R1, R2 Dividing resistor Z1 Zener diode R7, R8 Dividing resistor Z6 Shunt regulator 6, 6b Setting voltage correction circuit Tr3 transistor

Claims (4)

A voltage is applied to or interrupted from the primary winding of the transformer by the switching element, and the current flow is alternately turned on and off between the primary winding and the secondary winding of the transformer, and the voltage is applied to the secondary winding side. In a switching power supply that performs output,
A self-excited oscillation circuit section for generating an oscillation voltage for turning on and off the switching element by an AC voltage generated in a feedback winding of the transformer;
A first control winding provided in the transformer;
A control circuit unit that compares a voltage generated in the first control winding with a set voltage to change an ON period of the switching element;
A second control winding provided in the transformer;
A set voltage correction circuit for correcting the magnitude of the set voltage according to the magnitude of the voltage generated in the second control winding;
Equipped with a,
The control circuit section includes:
A first smoothing capacitor for smoothing and accumulating a voltage generated in the first control winding;
With a constant voltage circuit that allows current to flow when the set voltage is exceeded,
When the voltage of the first smoothing capacitor exceeds the set voltage, a current flows through the constant voltage circuit and a voltage for turning off the control terminal of the switching element is output.
The constant voltage circuit is:
A dividing resistor for dividing a predetermined voltage;
A Zener diode connected to a dividing point of the dividing resistor;
Consisting of
The set voltage correction circuit includes:
A second smoothing capacitor for smoothing and storing a voltage generated in the second control winding;
A transistor for passing a current to a dividing point of the dividing resistor in accordance with a voltage level of the second smoothing capacitor;
Switching power supply unit, characterized in that composed. A voltage is applied to or interrupted from the primary winding of the transformer by the switching element, and the current flow is alternately turned on and off between the primary winding and the secondary winding of the transformer, and the voltage is applied to the secondary winding side. In a switching power supply that performs output,
A self-excited oscillation circuit section for generating an oscillation voltage for turning on and off the switching element by an AC voltage generated in a feedback winding of the transformer;
A first control winding provided in the transformer;
A control circuit unit that compares a voltage generated in the first control winding with a set voltage to change an ON period of the switching element;
A second control winding provided in the transformer;
A set voltage correction circuit for correcting the magnitude of the set voltage according to the magnitude of the voltage generated in the second control winding;
Equipped with a,
The control circuit section includes:
A first smoothing capacitor for smoothing and accumulating a voltage generated in the first control winding;
With a constant voltage circuit that allows current to flow when the set voltage is exceeded,
When the voltage of the first smoothing capacitor exceeds the set voltage, a current flows through the constant voltage circuit and a voltage for turning off the control terminal of the switching element is output.
The constant voltage circuit is:
A shunt regulator that generates a constant voltage according to the reference voltage;
A dividing resistor that divides a predetermined voltage to generate a reference voltage of the shunt regulator;
Consisting of
The set voltage correction circuit includes:
A second smoothing capacitor for smoothing and storing a voltage generated in the second control winding;
A transistor for passing a current to a dividing point of the dividing resistor in accordance with a voltage level of the second smoothing capacitor;
Switching power supply unit, characterized in that composed. The dividing resistor switching power supply device according to claim 1 or 2, characterized in that it is configured to resist dividing the voltage across the first smoothing capacitor. The switching power supply device according to any one of claim 1 to 3, and the feedback winding and the first control winding is characterized in that it is shared by one of the windings.

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