JPH0591196U - DC power supply - Google Patents

Abstract

(57) [Abstract] [Purpose] Stable to a first load circuit that selectively operates at a first voltage and a second load circuit that continuously operates at a second voltage lower than the first voltage. To reduce the cost and improve the safety of the DC power supply device for supplying the converted voltage. [Configuration] A switching element is connected to the primary winding of the transformer. First and second rectifying and smoothing circuits 25 and 28 are connected to the secondary and tertiary windings 8 and 9 of the transformer. A TV circuit 32 is connected to the first rectifying / smoothing circuit 25, and a remote control receiving circuit 35 is connected to the second rectifying / smoothing circuit 28. First
Between the output terminal 29 of the rectifying / smoothing circuit 25 and the output terminal 30 of the second rectifying / smoothing circuit 28.
Connect. While the TV circuit 32 is not operating, the first transistor Q1 is turned on and the first rectifying / smoothing circuit 25 is turned on.
Lower the output voltage of.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a DC power supply device suitable for a power supply circuit of a TV receiver having a remote control reception circuit.

[0002]

[Prior Art]

 The TV receiver includes a main circuit requiring a voltage of about 120V and a remote control receiving circuit requesting a voltage of about 20V. In a conventional TV power supply device, a switching element for voltage control is connected in series to the primary winding of the transformer, the TV main circuit is connected to the secondary winding via the first rectifying and smoothing circuit, and the tertiary winding is connected. A remote control receiving circuit is connected to the second via a second rectifying / smoothing circuit. The switching elements are controlled so that the voltage of the TV main circuit is detected and kept constant. Since the remote control receiver circuit is lightly loaded, if the voltage of the heavy load TV main circuit is controlled to be constant, the voltage of the remote controller receiver circuit will also be almost constant.

[0003]

[Problems to be solved by the device]

 By the way, even in the standby state in which only the remote control reception circuit is kept operable, a normal voltage such as 120 V is generated in the secondary winding connected to the TV main circuit. It is not preferable for safety that the voltage of the secondary winding is continuously supplied to the smoothing capacitor via the rectifying diode. Therefore, a switch may be provided in front of the smoothing capacitor, and when the TV main circuit is off, this switch may disconnect the smoothing capacitor from the secondary winding side. If a switch is provided and the capacitor is disconnected as described above, safety is certainly improved. However, it is necessary to provide a switch having a capacity capable of turning on / off the current flowing in the TV main circuit, which inevitably increases the cost. Even if the smoothing capacitor is disconnected from the secondary winding, a voltage of about 120V continues to be generated in the secondary winding, so the safety of the transformer cannot be improved. Although the TV power supply device is described above, another power supply device having a plurality of loads has the same problem.

Therefore, an object of the present invention is to provide a direct current power supply device capable of reducing cost and improving safety.

[0005]

[Means for Solving the Problems]

 The present invention for achieving the above object provides a first load selectively driven by a voltage of a first value and a second load driven by a voltage of a second value lower than the first value. A DC power supply device for a load, comprising a switching element connected between one end and the other end of a DC power supply circuit via a primary winding of a transformer and electromagnetically coupled to the primary winding. A secondary winding, a tertiary winding electromagnetically coupled to the primary winding with a smaller number of turns than the secondary winding, and a first load connected to the secondary winding. A first rectifying / smoothing circuit having a first output terminal connected to and a second output terminal connected to the tertiary winding and connected to the second load. Second rectifying and smoothing circuit, and a selective connection circuit for selectively connecting the first output terminal to the second output terminal A voltage of the second value via the first control signal and the selective connection circuit used when controlling the output voltage of the first rectifying and smoothing circuit to the first value. A constant voltage control signal generation circuit that selectively generates a second control signal used when supplying to a load; and a voltage having the first value from the first rectifying and smoothing circuit to the first load. At the same time, when the second value or a voltage close to the second value is supplied from the second rectifying / smoothing circuit to the second load, the selective connection circuit is controlled to be turned off and the first control signal is generated. When the first load is in the non-driving state but the second load is in the driving state, the constant voltage control signal generating circuit is controlled to turn on the selective connection circuit and The constant voltage control so that the second control signal is generated. Switching control means for controlling the signal generation circuit, and controlling the switching element so as to obtain the voltage of the first value in response to the first control signal and responding to the second control signal. And a switching element control circuit for controlling the switching element so that the voltage having the second value can be obtained. In addition, in order to simplify the circuit configuration and improve reliability, the selective connection circuit is configured by the first transistor, and the second transistor for generating the second control signal in the constant voltage control signal generation circuit. Including the above, a third transistor is provided as switching control means, the first and second transistors are turned off by turning on the third transistor, and the first and second transistors are turned on by turning off the third transistor. It is desirable to do. Further, in order to achieve the operation of the switching element control circuit in the period in which power is supplied only to the second load with a simple configuration, the transformer is provided with a quaternary winding, and the quaternary winding is connected via a diode. Connect the capacitor, connect the capacitor to the DC power supply circuit via the charging resistor (starting resistor), and turn on when the voltage between the capacitor and the switching element control circuit exceeds the specified value. It is desirable to provide a start circuit that activates the switching element control circuit and turns off when the value is below a predetermined value or a value slightly lower than this value.

[0006]

[Action and effect]

 In the invention of each claim, when the power is supplied only to the second load, the voltage of the secondary winding decreases so as to adapt to the second load. Therefore, the high voltage is prevented from being continuously generated in the secondary winding, and the safety is improved. Further, by lowering the voltage of the secondary winding, it is not necessary to provide a switch to disconnect the smoothing capacitor, and it is possible to reduce the cost.

[0007]

【Example】

 Next, a DC power supply device for a TV according to an embodiment of the present invention will be described with reference to FIGS. In the DC power supply device of FIG. 1, a rectifying circuit 2 functioning as a DC power supply is connected to an AC power supply terminal 1. The rectifier circuit 2 comprises a rectifier and a smoothing capacitor. Although not shown, a power switch is provided between the power terminal 1 and the rectifier circuit 2. A switching element 7 composed of a field effect transistor is connected between a pair of DC terminals 3 and 4 of the rectifier circuit 2 via a primary winding 6 of a transformer 5. The transformer 5 has a secondary winding 8, a tertiary winding 9, and a quaternary winding 10 electromagnetically coupled to the primary winding 6. The quaternary winding 10 constitutes a control power supply circuit 11, to which a capacitor 13 is connected in parallel via a diode 12. Further, one end of the capacitor 13 is connected to the DC terminal 3 via the starting resistor 14.

A start circuit 15 and a control circuit 16 are sequentially connected between the control power supply circuit 11 and the gate (control terminal) of the switching element 7. The start circuit 15 has an input terminal 17, an output terminal 18, and a ground terminal 19, and when the voltage of the input terminal 17 and the voltage of the capacitor 13 are below a predetermined value, the connection between the input terminal 17 and the output terminal 18 is off. And is turned on when the value becomes a little higher than the predetermined value.

The control circuit 16 has an input terminal 20, an output terminal 21, and a ground terminal 22, and turns on / off the switching element 7 so as to keep the output voltage constant by the optical control of the phototransistor contained therein. To control. The input terminal 20 of the control circuit 16 is connected to the output terminal 18 of the start circuit 15, and the output terminal 21 of the control circuit 16 is connected to the gate of the switching element 7.

A first rectifying / smoothing circuit 25 including a first rectifying diode 23 and a first smoothing capacitor 24 is connected to the secondary winding. A second rectifying / smoothing circuit 28 including a second rectifying diode 26 and a second smoothing capacitor 27 is connected to the tertiary winding 9. Since the number of turns of the secondary winding 8 is larger than that of the tertiary winding 9, the first output voltage V1 obtained from the first output terminal 29 of the first rectifying / smoothing circuit 25 is equal to the second winding 9 during the normal operation. 2 is higher than the second output voltage V2 obtained from the second output terminal 30 of the rectifying / smoothing circuit 28. In this embodiment, the first output voltage V1 is 120V and the second output voltage V2 is 20V.

A constant voltage control and output circuit 31 is connected to the output terminals 29 and 30 of the first and second rectifying and smoothing circuits 25. This constant voltage control and output circuit 31 is driven by a second output voltage V2 and a TV circuit 32 as a main load (first load) driven by a first output voltage V1 as shown in FIG. It includes a BS (satellite broadcast) tuner 33, a VTR 34, and a remote control receiver circuit 35 as a sub load (second load), a selective connection circuit 31a, a constant voltage control signal generation circuit 31b, and a switching transistor Q3. ..

In FIG. 2, the TV circuit 32 as a main load (first load) is connected to the first output terminal 29. A sub load (second load) such as the BS (satellite broadcast) tuner 33, the VTR 34, and the remote control receiving circuit 35 is connected to the second output terminal 30.

The constant voltage control signal generation circuit 31b includes an error signal forming circuit 36 for obtaining a first control signal, a transistor Q2 and a Zener diode (constant voltage diode) for obtaining a second control signal. , A light emitting diode 43 and a resistor 42. The error signal forming circuit 36 is connected between the first output terminal 29 and the ground in order to detect the first output voltage and perform constant voltage control. This circuit 36 includes a voltage detection circuit including resistors 37 and 38 connected between an output terminal 29 and the ground, an error amplification transistor 39, and a Zener diode (constant voltage diode) 40 as a reference voltage source. And a resistor 41. The base of the transistor 39 is connected to the voltage dividing point of the two resistors 37 and 38, the zener diode 40 is connected to the emitter of the transistor 39, and the resistor 41 is connected between the output terminal 29 and the cathode of the zener diode 40. Has been done. As a result, a collector current corresponding to the difference between the voltage at the output terminal 29 and the reference voltage provided by the Zener diode 40 flows.

The light emitting diode 43 connected between the second output terminal 30 and the collector of the transistor 39 via the resistor 42 emits light corresponding to the collector current of the transistor 39, and includes a first and an optical signal. Generate a second control signal.

The selective connection circuit 31 a has a first transistor Q 1 having a Darlington structure connected between the first output terminal 29 and the second output terminal 30 via a resistor 44 and a diode 45. The first transistor Q1 has a function of supplying the voltage of the first output terminal 29 to the remote control receiving circuit 35. A second transistor Q2 is connected between the connection midpoint 46 of the error signal forming circuit 36 and the light emitting diode 43 and the ground. This second transistor Q2 functions as an error amplifier for voltage control when supplying power only to the sub-load, and its collector is connected to the cathode of the light emitting diode 43, its emitter is connected to the ground, and its base is It is connected to the first output terminal 29 via a Zener diode (constant voltage diode) 47 and a resistor 48. The base of the first transistor Q1 is also connected to the first output terminal 29 via the resistor 48.

The third transistor Q3 functions as a changeover switch, and this collector is connected to the base of the first transistor Q1 and the base of the second transistor Q2 via the Zener diode 47. , The emitter is connected to the ground, and the base is connected to the remote control receiving circuit 35. The remote control receiving circuit 35 is also connected to the TV circuit 32. The TV circuit 32 includes various circuits such as a horizontal oscillation circuit 32a, and also includes a switch means that responds to the high level output of the remote control receiving circuit 35. The high level output causes the driving state and the low level output causes the non-driving state. Is configured to be.

The control circuit 16 of FIG. 1 is configured as shown in FIG. The control circuit 16 roughly includes a voltage comparator 49, an OFF width control circuit 50, an ON width control circuit 51, and a reference voltage source 52, and is as shown in FIGS. 6 and 7C. The control pulse is supplied to the switching element 7 via the output terminal 21. Note that FIG. 6 shows the state of each part under heavy load, and FIG. 7 shows the state of each part under light load.

The off-width control circuit 50 includes a first capacitor C1, first, second and third resistors R1, R2 and R3, a transistor Q11 as a first control element, and two diodes D1. , D2. The first capacitor C1 is connected between the power supply terminal 20 and the ground via the first transistor Q11 and the diode D1. The first resistor R1 is connected in parallel with the first capacitor C1 to form a discharge circuit. The upper end of the first capacitor C1 is connected to the negative input terminal of the comparator 49. The base (control terminal) of the first transistor Q11 is connected to the reference voltage source 52 via the resistor R3, and the comparator via the charge stop control circuit of the capacitor C1 including the resistor R2 and the diode D2. It is connected to the output terminal of 49. The positive input terminal of the comparator 49 is connected to the reference voltage source 52 via the resistor R3, and is also connected to the output terminal of the comparator 49 via the resistor R2 and the diode D2.

The ON-width control circuit 51 includes a second capacitor C2, a transistor Q12 as a second control element, a transistor Q13 as a third control element, a NOT circuit (inverter) 53, and a charge control. And a phototransistor 54 as an element.

The upper end of the second capacitor C2 is connected to the power supply terminal 20 via the phototransistor 54 optically coupled to the light emitting diode 43 of FIG. 2, and the lower end is connected to the ground. In order to relate the voltage Vc2 of the second capacitor C2 to the comparator 49, a transistor Q12 is connected between the positive input terminal of the comparator 49 and the ground, and the base (control terminal) of the transistor Q12 is connected to the first terminal. It is connected to the upper end of the second capacitor C2. Further, in order to relate the discharge of the second capacitor C2 to the output of the comparator 49, a transistor Q13 as a discharge control element is connected in parallel to the second capacitor C2 and the output terminal of the comparator 49 is connected. Is connected to the base (control terminal) of the transistor Q13 via the NOT circuit 53.

[0021]

[Start circuit]

 As shown in FIG. 4, the start circuit 15 of FIG. 1 includes three transistors 55, 56 and 57, two Zener diodes (constant voltage diodes) 58 and 59, and a resistor 60. The emitter of the transistor 55 is connected to the input terminal 17, and its collector is connected to the output terminal 18. Therefore, the input voltage Vin is sent to the output terminal 18 only while the transistor 55 is on. The emitter of the transistor 56 is connected to the input terminal 17, its collector is connected to the base of the transistor 57 via the Zener diode 59, and this base is connected to the collector of the transistor 57 via the resistor 60. The collector of the transistor 57 is connected to the base of the transistor 55 via the resistor 60, the emitter is connected to the ground terminal 19, and the base is connected to the input terminal 17 via the Zener diode 58.

When the input voltage Vin of the start circuit 15 becomes the sum value Va = Vz1 + VBE of the zener breakdown voltage Vz1 of the zener diode 58 and the threshold voltage VBE of the transistor 57, these are turned on and the base of the transistor 56 is turned on. Since the current flows through the resistor 60 and the transistor 57, the transistor 56 is turned on, the Zener diode 59 is also turned on, and the transistor 55 is also turned on. As a result, as shown in FIG. 5, when the input voltage Vin becomes Va, the output voltage V0 is obtained at the output terminal 18. On the contrary, when the voltage of the control power supply circuit 11 of FIG. 1 drops from a state of Va or higher to a value lower than Va, the Zener diode 58 is turned off. However, while the Zener diode 59 is kept on, the base current of the transistor 59 is supplied therethrough, so that the transistors 57 and 55 are not turned off immediately. When the input voltage Vin becomes equal to or less than the sum value Vb of the breakdown voltage Vz2 of the Zener diode 59 and the base-emitter voltage VBE of the transistor 57, the transistors 57 and 55 are turned off. Therefore, the start circuit 15 has a hysteresis characteristic and supplies the control power supply voltage to the control circuit 16. When the TV circuit 32, which is the main load, is operating, the switching regulator operates so as to output 120 V as the first output voltage V1. Therefore, a sufficiently high voltage can be obtained in the quaternary winding 10. Since the voltage of the capacitor 13, that is, the input voltage Vin of the start circuit 15 is always higher than Vb, the transistor 55 of the start circuit 15 is kept on. On the other hand, when the TV circuit 32 as the main load is controlled to be off and only the remote control receiving circuit 35 as the sub load is on, both the first and second output voltages drop to about 20 V, so The voltage on line 10 is also low, and this voltage cannot charge capacitor 13 above Vb in FIG. Therefore, the capacitor 13 is charged with the output voltage of the rectifier circuit 2 via the resistor 14. When the transistor 55 of the start circuit 15 is turned on, the charge of the capacitor 13 is consumed by the start circuit 15 and the control circuit 16, so that the input voltage Vin of the start circuit 15 drops below Vb in FIG. When the transistor 55 is turned off, the charging of the capacitor 13 is started again, and after a predetermined time determined by the time constant, it becomes Va or more again, and the transistor 55 of the start circuit 15 is turned on. As a result, intermittent operation of the start circuit 15 occurs when power is supplied only to the sub load. Since the start circuit 15 operates intermittently, the control circuit 16 also operates intermittently, and the switching element 7 also operates intermittently, and the primary side of the transformer 5 supplies the secondary side and the tertiary side. It consumes less energy and enables stable supply of a low voltage (about 20 V) to the sub load.

[0023]

[Voltage control operation]

 Next, the voltage control operation will be described. When a power switch (not shown) is turned on to start power supply from the rectifier circuit 2, a charging current for the capacitor 13 flows through the starting resistor 14. When the voltage of the capacitor 13 becomes equal to or higher than Va in FIG. 5, the start circuit 15 is turned on, the control circuit 16 starts the operation, and the on / off operation of the switching element 7 is started.

The on / off control by the control circuit 16 is performed as shown in FIG. 6 when the load is heavy, and as shown in FIG. 7 when the load is light. Next, this will be described in detail. When the start circuit 15 is turned on, a reference voltage Vr (about 6.3 V) is obtained from the reference voltage source 52 composed of a Zener diode or the like in FIG. 3, and this is supplied to the positive input terminal of the comparator 49. At the same time, the transistor Q11 is also turned on, and the first capacitor C1 is charged with the voltage + V at the input terminal 20. This first capacitor C1 has a short rise time (0. 5V) to a value (about 5V) obtained by subtracting the sum (VBE-Vf) of the base-emitter voltage VBE of the transistor Q11 and the voltage Vf of the diode D1 from the reference voltage Vr. It is charged in 5 μs). On the other hand, the voltage Vr (6.3 V) of the reference voltage source 52 is applied to the positive input terminal of the comparator 49. Since the voltage V10 at the positive input terminal shown by the solid line in FIG. 6A of the comparator 49 is about 6.3V and the voltage V20 at the negative input terminal shown by the broken line is about 5V, The output goes high (H). Since the difference between the two input voltages V10 and V20 is about 1.3V, malfunction due to noise can be sufficiently prevented.

On the other hand, since the charging time constant of the second capacitor C2 is set sufficiently larger than the charging time constant of the first capacitor C1, this voltage Vc2 is as shown in FIG. 6B. The on period Ton has a slope and rises slowly. Since the output of the comparator 49 is at a high level, the output of the NOT circuit 53 is at a low level, and the transistor Q13 is off during the on period Ton, the discharge circuit of the second capacitor C2 is not formed. When the voltage Vc2 of the second capacitor C2 becomes about 0.7 to 0.8V, the transistor Q12 is turned on, the voltage V10 at the positive input terminal of the comparator 49 decreases, and the voltage V20 at the negative input terminal becomes lower than the voltage V20 at the negative input terminal. Becomes low, and the output of the comparator 49 is converted to a low level (L). As a result, the second diode D2 is turned on, and the voltage V10 at the positive input terminal of the comparator 49 becomes {(Vr-Vf) (R2) / (R2 + R3)} + Vf during the off period Toff, which is about It is fixed at 3V. Note that Vf represents the forward voltage of each of the diodes D1 and D2. Further, since the output of the NOT circuit 53 is at a high level and the transistor Q13 is turned on, the electric charge of the second capacitor C2 is abruptly released, and the voltage Vc2 abruptly drops.

During the off period Toff, since the voltage V10 at the positive input terminal is lower than the voltage V20 at the negative input terminal, the transistor Q11 and the first diode D1 are in a reverse bias state, and the first capacitor C1 is charged. When stopped, the charge of the first capacitor C1 is discharged with a discharge time constant of C1 R1, and this voltage, that is, the voltage V20 at the negative input terminal, decreases with a slope. Since the voltage V10 at the positive input terminal during the off period is fixed and the discharge time constant of the first capacitor C1 is constant, the time width until the voltage V20 at the negative input terminal crosses the voltage V10 at the positive input terminal, that is, The width of the off period Toff is constant.

When the voltage V20 at the negative input terminal of the comparator 49 becomes lower than the voltage 10 at the positive input terminal, the output of the comparator 49 becomes high level again, and the same operation is repeated. Since the output Vout of the comparator 49 is given to the switching element 7, the switching element 7 is turned on / off corresponding to the output Vout shown in FIG. 6 (C). In FIG. 2, when the TV circuit 32 is operating, the third transistor Q3 is on-controlled based on the control signal of the remote control receiving circuit 35. Therefore, they are kept off because the bases of the first and second transistors Q1, Q2 are connected to ground via the third transistor Q3. As a result, the light emitting diode 43 responds only to the output of the error signal forming circuit 36. Since the voltage of the Zener diode 40 as the reference voltage source in the error signal forming circuit 36 is set lower than the voltage V2 of the second output terminal 30, the light emitting diode 43 has the second output terminal 30 and the resistor 42. A current flows in the circuit of the light emitting diode 43, the transistor 39, and the Zener diode 40, and this current value changes according to the error signal. As a result, a constant voltage control operation of the switching element 7 by the control circuit 16 of FIG. 3 occurs, and the first output voltage V1 is made constant. If the first output voltage V1 on the heavy load side is controlled to be constant, the second output voltage V2 on the light load side also becomes substantially constant. Further, since the current of the light emitting diode 43 changes following the change of the second voltage V2, it means that both the first and second output voltages V1 and V2 are controlled at the same time.

When the TV circuit 32 is controlled to be off by the low level output of the remote control receiving circuit 35, the third transistor Q3 is also controlled to be off. As a result, the base current flows into the first transistor Q1 through the resistor 48 and is turned on, and the first transistor Q1 and the resistor 44 and the reverse current flow between the first output terminal 29 and the second output terminal 30. It is connected via the blocking diode 45. As a result, the output voltage of the first rectifying / smoothing circuit 25 is supplied to the remote control receiving circuit 35. At the same time, the light emitting diode 43 is connected to the ground via the second transistor Q2 instead of the error signal forming circuit 36. A circuit including the second transistor Q2, the Zener diode 47, and the resistor 48 functions as a second constant voltage control circuit, that is, a second error signal forming circuit, and the voltage V1 at the first output terminal 29 is approximately 20V. A current for controlling to a certain degree is passed through the light emitting diode 43. At this time, since the transistor 39 and the Zener diode 40 of the error signal forming circuit 36 are turned off, the error signal forming circuit 36 is substantially separated from the light emitting diode 43. The current of the light emitting diode 43 is small when the TV circuit 32 is operating and is large when the TV circuit 32 is not operating. As a result, when only the remote control receiving circuit 35 is driven, the resistance value of the phototransistor 54 of FIG. 3 becomes small, and the control circuit 16 operates as shown in FIG. That is, the charging time constant of the second capacitor C2 in FIG. 3 decreases, the charging speed of the voltage Vc2 of the second capacitor C2 increases as shown in FIG. 7B, and the output V out of the comparator 49 increases. The transistor Q2 turns on within a short period from the time when the voltage turns to a high level, and the on period Ton becomes short. As a result, the voltage V1 at the first output terminal 29 in FIGS. 1 and 2 drops from 120V to approximately 20V, and this is supplied to the remote control receiving circuit 35 through the first transistor Q1 in FIG. At this time, the voltage of the tertiary winding 9 becomes lower than before, so that the diode 26 is kept off. Therefore, the current in the light emitting diode 43 is supplied through the first transistor Q1.

As is apparent from the above, according to the power supply device of this embodiment, it is possible to easily achieve the constant voltage of the first and second output voltages V1 and V2.

[0030]

[Modification]

 The present invention is not limited to the above-mentioned embodiment, and the following modifications are possible, for example. (1) The primary side circuit and the voltage control circuit of the transformer 5 of the switching regulator can be variously modified. For example, the switching element 7 of FIG. 1 can be replaced with a bipolar transistor 7a as shown in FIG. Further, the control circuit 16 of the switching element 7 of FIG. 1 can be changed to a self-excited control circuit 16a as shown in FIG. In FIG. 8, the quaternary winding 10 is connected to the base of the transistor 7a via the parallel circuit of the resistor 61 and the capacitor 62. The phototransistor 54 is connected between the base and emitter of the transistor 7a. Note that the phototransistor 54 is not directly connected between the base and the emitter of the transistor 7a, but a control transistor is connected between the base and the emitter, and the phototransistor 54 is connected to the base of the control transistor. It is also possible to change the resistance of the control transistor in accordance with the change in the resistance of 54 to control the bypass amount of the base current to generate the constant voltage operation. In FIG. 8, the fourth winding 10 operates as a positive feedback winding, and the transistor 7a is turned on / off by a known method. The starting resistor 14a is connected between the power supply terminal 3 and the base of the transistor 7a. In FIG. 8, parts other than the control circuit 16a are configured substantially the same as in FIG. The present invention can also be applied to the case where the transistor 7a in FIG. 8 is replaced with an FET to form a self-excited oscillation circuit. (2) Instead of the transistor 39 of the error signal forming circuit 36 of FIG. 2, an error amplifier having a pair of input terminals can be connected. In this case, one of the input terminals of the error amplifier is connected to the midpoint of the resistors 37 and 38, and the other input terminal is connected to a reference voltage source such as a Zener diode 40. (3) A resistor can be connected in series or in parallel with the phototransistor 54 to form a charging circuit for the second capacitor C2. (4) The transistors Q11, Q12, Q13 as the first, second and third control elements in FIG. 3 and the transistors Q1, Q2, Q3 in FIG. 2 can be replaced with FETs or the like. Further, a voltage control transistor can be used instead of the phototransistor 54 and the light emitting diode 43. (5) Two NOT circuits (inverters) are sequentially connected to the output stage of the comparator 49, the output of the NOT circuit of the first stage is given to the base of the transistor Q13, and the cathode of the diode D2 is connected to the output terminal of the NOT circuit of the latter stage. Can be connected.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing in detail the constant voltage control and output circuit of FIG.

FIG. 3 is a circuit diagram showing the control circuit of FIG. 1 in detail.

FIG. 4 is a circuit diagram showing a start circuit of FIG.

5 is a diagram showing a relationship between an input voltage and an output voltage of the start circuit of FIG.

6 is a waveform diagram showing a state of each part of the control circuit of FIG. 3 under heavy load.

7 is a waveform diagram showing a state of each part of the control circuit of FIG. 3 under a light load.

FIG. 8 is a circuit diagram showing a part of a DC power supply device of a modified example.

[Explanation of symbols]

 31a selection connection circuit 31b constant voltage control signal generation circuit Q3 switching transistor

Claims (3)

[Scope of utility model registration request] 1. A direct current for a first load selectively driven by a voltage of a first value and a second load driven by a voltage of a second value lower than the first value. A power supply device comprising: a switching element connected between one end and the other end of a DC power supply circuit via a primary winding of a transformer; and a secondary winding electromagnetically coupled to the primary winding. A tertiary winding having a smaller number of turns than the secondary winding and electromagnetically coupled to the primary winding; and a first winding connected to the secondary winding and connected to the first load. A first rectifying / smoothing circuit having an output terminal; and a second rectifying / smoothing circuit having a second output terminal connected to the tertiary winding and to which the second load is connected. A selective connection circuit for selectively connecting the first output terminal to the second output terminal, and the first rectifying and smoothing circuit. A first control signal used to control the output voltage of the path to the first value, and a second control signal used to supply the second value voltage to the second load via the selective connection circuit. A constant voltage control signal generation circuit that selectively generates the control signal of the first load, and the first load from the first rectifying and smoothing circuit to the first load.
Supply a voltage of the value of
When the second value or a voltage close to the second value is supplied from the rectifying / smoothing circuit, the constant voltage control signal generation circuit is controlled so that the selective connection circuit is turned off and the first control signal is generated. When the first load is in the non-driving state but the second load is in the driving state, the constant voltage is controlled so that the selective connection circuit is turned on and the second control signal is generated. Switching control means for controlling a control signal generating circuit; controlling the switching element so as to obtain the voltage of the first value in response to the first control signal;
And a switching element control circuit that controls the switching element so that the voltage having the second value is obtained in response to the control signal. 2. The selective connection circuit is a first transistor connected between an output terminal of the first rectifying and smoothing circuit and an output terminal of the second rectifying and smoothing circuit, and the constant voltage control signal. The generator circuit detects a first output voltage obtained between an output terminal of the first rectifying and smoothing circuit and a common terminal (ground), and obtains the first output voltage of the first value to obtain the first output voltage. Of an error signal forming circuit that outputs an error signal corresponding to the difference between the detected value of the output voltage and the reference value, and an output terminal of the second rectifying and smoothing circuit and an output terminal of the first error signal forming circuit. A light emitting diode connected between the two; a second transistor connected between a terminal of the light emitting diode on the error signal forming circuit side and a ground to obtain an output voltage of the second value; The output terminal of the rectifying and smoothing circuit 1 and the above A constant voltage diode connected to the base of the second transistor via a resistor, and the switching control means is connected to the base of the first transistor and via the constant voltage diode. A third transistor connected to the base of the second transistor, wherein turning on the third transistor controls the first and second transistors to be off;
The direct current according to claim 1, wherein the switching element control circuit is a circuit including a light receiving element responding to the light emitting element, the circuit being a circuit for controlling the first and second transistors to be turned on by turning off the third transistor. Power supply. 3. The primary winding, the secondary winding and the 3
A quaternary winding electromagnetically coupled to the secondary winding, a capacitor connected in parallel to the quaternary winding via a diode, and a charging capacitor connected between one end of the DC power supply circuit and the capacitor. A resistor is connected between the capacitor and the switching element control circuit, the capacitor is connected to the switching element control circuit when the voltage of the capacitor is higher than a predetermined value, and the voltage of the capacitor is the predetermined value or The DC power supply device according to claim 1 or 2, further comprising a start circuit that disconnects the capacitor from the switching element control circuit when the value becomes slightly lower than the value.