JP3073433U - Switching power supply - Google Patents

Abstract

(57) [PROBLEMS] To prevent a voltage drop in a path in which a DC output supply source switches to a regulator and a rectifying / smoothing circuit by a small-capacity capacitor. A first regulator (21) to which an output of a first rectifying / smoothing circuit (11) is led through a switch circuit (5), and a normal current to guide an output of a second rectifying / smoothing circuit (12) to a non-voltage drop path (35). When the path unit 6 and the standby mode are set,
In a configuration in which the output voltages of the first and second rectifying / smoothing circuits 11 and 12 are lower than those in the normal operation mode, when the standby mode is set, the connection of the switch circuit 5 is closed,
A switch control unit 7 that opens the connection of the switch circuit 5 at a timing that is later than the timing of the transition when the transition from the standby mode to the normal operation mode is provided.

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention relates to a switching power supply that can be switched between two modes, a normal operation mode and a standby mode in which the output voltage is lower than the normal operation mode.

[0002]

[Prior art]

 As a prior art of a switching power supply capable of switching between two modes, a normal operation mode and a standby mode in which the output voltage is lower than the normal operation mode, there is a technique proposed as Japanese Patent Application Laid-Open No. 2-142354. In other words, in this technology, when the switching element that switches the current flowing through the primary coil is in an on state, a forward output unit that takes out the output from the secondary coil, and when the switching element is in an off state, the output from the secondary coil And a flyback output unit for extracting an output. Further, a regulator circuit for stabilizing the output of the forward output section to 5 V is provided. Then, a voltage divider circuit is provided in which the rectified output of the secondary coil for the flyback output unit and the rectified output of the secondary coil for the forward output unit are provided. The output of the voltage divider circuit is output to the secondary side. The voltage is led to a voltage comparator for detecting a voltage error. Also, the voltage dividing ratio in the voltage dividing circuit can be changed. Therefore, when the voltage dividing ratio in the voltage dividing circuit increases, the voltage is stabilized based on the rectified output of the flyback output unit, and the output voltage of the flyback output unit is stabilized at a high voltage. Further, when the voltage dividing ratio in the voltage dividing circuit becomes small, the voltage is stabilized based on the rectified output of the forward output section, and the output voltage of the flyback output section is almost stabilized at a low voltage.

[0005] However, the above-described configuration has a configuration in which a secondary coil and a rectifying / smoothing circuit are separately provided in order to generate a DC output to be supplied to the regulator circuit, so that the circuit configuration is complicated. Have been. For this reason, when the voltage obtained by rectifying and smoothing the output of a predetermined secondary coil among the plurality of secondary coils is the same as the output voltage of the regulator circuit, the configuration is simplified to avoid complication of the configuration. The configuration shown in FIG.

[0006] The DC output 52 in FIG. 1 has a voltage of about 38 V in the normal operation mode and about 7 V in the standby mode. In addition, since the DC output 53 is an operating power supply for digital circuits except the microcomputer 43, the DC output 53 is set to 5. in the normal operation mode. 6V, which is about 1V in the standby mode. In addition, the regulator 42 includes: Sends DC output stabilized at 6V. When the operation mode is the normal operation mode, the connection of the switch 41 is opened. Therefore, in the normal operation mode, the microcomputer 43 is supplied with the DC output 53 via the diode D12. On the other hand, when the standby mode is set, the connection of the switch 41 is closed. Therefore, when the standby mode is set, the DC output stabilized at 5.6 V by the regulator 42 is supplied to the microcomputer 43 via the diode D11.

[0005]

[Problems to be solved by the invention]

 However, when the above configuration is used, the following problems have occurred. This problem will be described with reference to FIG. Time T5 indicates the time when the mode shifts from the standby mode to the normal operation mode. In the standby mode, since the power consumption on the secondary side is extremely small, the primary side (not shown) performs an intermittent switching operation. Therefore, at time T5, the DC output 52 goes from 7V to 38V, and starts to gradually increase. At time T5, the DC output 53 goes from 1V to 5.6V and starts to increase gradually. The switch 41 is opened at time T5. Therefore, the voltage of the path 54 (the voltage supplied to the microcomputer 43) shows a voltage change equal to a voltage obtained by subtracting the forward voltage of the diode D12 from the voltage of the DC output 53 after time T5. . That is, after the voltage of the path 54 greatly decreases at the time T5, it gradually increases toward 5V. Therefore, in order to maintain the voltage supplied to the microcomputer 43 at 5 V immediately after the time T5, it is necessary to connect a large-capacity capacitor having a large element price and a large shape to the path 54. there were. Further, when the configuration is such that the value of the current flowing through the diode D13 exceeds 1 A, the loss due to the diode D13 is a value that cannot be ignored.

The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to change a timing of opening a connection of a switch circuit provided in a path for supplying operating power to a regulator from a standby mode. By setting the timing later than the transition to the normal operation mode, a small-capacity capacitor can prevent a voltage drop in the path where the DC output supply source switches to the regulator and the rectifying and smoothing circuit. Is to provide.

[0007] In addition to the above object, when the standby mode shifts to the normal operation mode, when the voltage of the DC output on the secondary side rises to a preset voltage, the connection of the switch circuit is opened to open the first switch. It is an object of the present invention to provide a switching power supply capable of suppressing an increase in the amount of heat generated by the first regulator by shortening a period during which the input voltage supplied to the regulator is high.

Further, in addition to the above object, by detecting the switching timing of the switch circuit based on the voltage change of the DC output on the higher voltage side, the timing of opening the connection of the switch circuit can be easily optimized. It is an object of the present invention to provide a switching power supply that can be set at an appropriate timing.

Further, in addition to the above object, by using a PNP transistor as a switching element of a path for leading the DC output of the second rectifying / smoothing circuit to a non-voltage drop path, the voltage drop of the switching element can be reduced. By eliminating the need for a voltage shifting diode inserted in the output path of the second rectifying / smoothing circuit, it is possible to prevent an increase in loss even when the output current value of the second rectifying / smoothing circuit is large. Switching power supply.

In addition to the above object, by changing the DC output to be subjected to the error detection between the standby mode and the normal operation mode, the voltage non-drop path can be changed in both the standby mode and the normal operation mode. It is an object of the present invention to provide a switching power supply capable of accurately stabilizing the voltage at a predetermined voltage.

Another object of the present invention is to provide a switching power supply capable of accurately stabilizing a DC output voltage, which is not an object of error detection, to a predetermined voltage in a normal operation mode.

Another object of the present invention is to provide a switching power supply capable of achieving the above object in a set-top box.

[0013]

[Means for Solving the Problems]

 In order to solve the above-mentioned problem, a switching power supply according to the present invention includes a transformer having at least first and second secondary coils wound thereon when the first voltage is higher than the second voltage; A switching circuit for switching the current flowing through the primary coil wound around the first coil, a first rectifying and smoothing circuit for rectifying and smoothing the output of the first secondary coil, and a rectifying and smoothing output for the second secondary coil. A DC output sent from the first rectifying / smoothing circuit is guided through the second rectifying / smoothing circuit and the switch circuit, and the voltage of the DC output sent to the non-voltage drop path is stabilized to a value close to the second voltage. And a normal current path section for guiding the DC output sent by the second rectifying / smoothing circuit to the non-voltage drop path when the first regulator does not send the DC output to the non-voltage drop path. When the normal operation mode is set, the output voltage of the first rectifying and smoothing circuit is set to the first voltage, and the output voltage of the second rectifying and smoothing circuit is set to the second voltage. And a switching power supply in which the output voltage of the second rectifying and smoothing circuit is lower than that in the normal operation mode. When the standby mode is set, the connection of the switch circuit is closed, and when the mode shifts from the standby mode to the normal operation mode, A switch control unit is provided for opening the connection of the switch circuit at a timing later than the transition timing.

That is, when the mode shifts from the standby mode to the normal operation mode, the voltage of the DC output sent from the second rectifying / smoothing circuit starts to increase toward the second voltage. Therefore, when the connection of the switch circuit is opened, the voltage of the DC output of the second rectifying / smoothing circuit rises to a value close to the second voltage. Therefore, when the connection of the switch circuit is opened, the DC output that has risen to a value near the second voltage is guided to the non-voltage drop path. Therefore, when the connection of the switch circuit is opened, the voltage drop generated in the non-voltage drop path becomes very small.

[0015] In addition to the above configuration, when the switch control unit shifts from the standby mode to the normal operation mode, the switch control unit waits until the voltage of the DC output on the secondary side rises to a preset voltage, When the standby is completed, the connection of the switch circuit is opened.

That is, when the voltage supplied to the first regulator becomes a high voltage, the connection of the switch circuit is quickly opened. Therefore, the period during which a high voltage is supplied to the first regulator is shortened.

In addition, in addition to the above configuration, the switch control unit opens the connection of the switch circuit based on a DC output voltage sent from the first rectifying / smoothing circuit.

That is, the voltage of the DC output sent from the first rectifying and smoothing circuit is the first voltage and has a high voltage value. Therefore, even after the switch control unit opens the connection of the switch circuit, a sufficient margin can be expected for the rise in the voltage of the DC output sent from the first rectifying / smoothing circuit.

Further, in addition to the above configuration, the normal current path section includes a PNP transistor having a collector connected to an output of the second rectifying / smoothing circuit and a collector connected to a non-voltage drop path. The control unit turns off the PNP transistor when opening the connection of the switch circuit, and turns on the PNP transistor when closing the connection of the switch circuit.

That is, the amount of voltage drop generated by the PNP transistor is very small. Therefore, the difference between the voltage passing through the PNP transistor and the voltage not passing through the PNP transistor becomes very small.

Further, in addition to the above configuration, the non-voltage drop path is applied to a switching power supply serving as a supply path of an operation power supply to the microcomputer, and the error detection circuit is configured to perform the first rectification when the standby mode is set. An error in the output voltage of the smoothing circuit is detected, and when in the normal operation mode, an error in the output voltage of the second rectifying and smoothing circuit is detected.

That is, when the DC output of the first rectifying / smoothing circuit is supplied to the first regulator in the standby mode, the voltage of the DC output of the first rectifying / smoothing circuit is stabilized. The voltage of the non-voltage drop path is accurately stabilized. Further, when the normal operation mode is set, the output of the second rectifying / smoothing circuit is stabilized, so that the voltage of the non-voltage drop path is accurately stabilized.

Further, in addition to the above configuration, a second regulator is provided to guide the DC output sent from the first rectifying / smoothing circuit and to stabilize the output voltage to a predetermined voltage.

That is, the output voltage of the second regulator is stabilized even when the voltage of the DC output sent from the first rectifying and smoothing circuit fluctuates.

Further, in addition to the above configuration, the operation of the analog circuit section for performing predetermined processing of the guided signal, the digital circuit section for processing the output of the analog circuit section, and the operations of the analog circuit section and the digital circuit section are described. The present invention is applied to a switching power supply provided in a set-top box having a microcomputer to be controlled, a DC output sent from a second regulator is guided to an analog circuit section, and the non-voltage drop path is guided to the microcomputer. The DC output from the second rectifying / smoothing circuit is guided to the digital circuit.

That is, the above-described operation occurs in the set-top box.

[0027]

[Embodiment of the invention]

 Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an electrical configuration of a set-top box using an embodiment of the switching power supply according to the present invention.

In the figure, a primary coil L1, an auxiliary coil L2, a first secondary coil L11, and a second secondary coil L12 are wound around a transformer 2. Further, the switching circuit 1 to which the primary coil L1 and the auxiliary coil L2 are connected is a block for switching the current flowing through the primary coil L1 based on the voltage error fed back via the photocoupler 4.

The first rectifying / smoothing circuit 11 rectifies and smoothes the output of the first secondary coil L 11, and becomes a block that sends out a DC output 31 having a voltage of 38 V (first voltage). ing. The second rectifying / smoothing circuit 12 is a block that rectifies and smoothes the output of the second secondary coil L12 to send out a DC output 32 having a voltage of 5 V (second voltage). .

A transistor Q 2 having a collector connected to the DC output 31 and an emitter connected to the first regulator 21, and a resistor connected between the base and the collector of the transistor Q 2 for raising the base potential to the collector potential The block 5 including R3 is a switch circuit that opens and closes the connection between the DC output 31 and the first regulator 21.

The first regulator 21 is a block for stabilizing the DC output 31 guided through the switch circuit 5 to 5 V (near the value of the second voltage). Then, the DC output stabilized at 5 V is sent to a non-voltage drop path 35 which is a path of an operation power supply to the microcomputer 15.

A PNP transistor (hereinafter simply referred to as a transistor) Q3 having an emitter connected to the DC output 32 and a collector connected to the non-voltage drop path 35, and a connection between the emitter and the base of the transistor Q3. The block 6 composed of a resistor R4 for raising the base potential to the emitter potential and a resistor R5 for limiting the base current forms a normal current path. Then, the normal current path section 6 guides the DC output 32 to the non-voltage drop path 35 when the first regulator 21 does not send the DC output to the non-voltage drop path 35.

The error detection circuit 3 is a block that stabilizes the voltage on the secondary side by feeding back the voltage error on the secondary side to the switching circuit 1 via the photocoupler 4. Specifically, when the normal operation mode is set, the voltage of the DC output 32 is stabilized to 5 V (second voltage) by detecting the voltage error of the DC output 32, and the voltage of the DC output 31 is set to 38V (second voltage). 1 voltage). When the standby mode is set, the voltage of the DC output 31 is stabilized at 7V by detecting the voltage error of the DC output 31, and the voltage of the DC output 32 is set to about 1V.

The switch control unit 7 closes the connection of the switch circuit 5 when the standby mode is set, and opens the connection of the switch circuit 5 at a timing later than the shift timing when the mode shifts from the standby mode to the normal operation mode. It is a block. That is, when shifting from the standby mode to the normal operation mode, the controller waits until the voltage of the DC output 31 increases to a preset voltage (for example, 35 V), and opens the connection of the switch circuit 5 when the standby is completed. . In addition, it controls the opening and closing of the current path section 6 at normal time.

To this end, the switch control unit 7 includes a resistor R6 having one terminal connected to the DC output 31, and a Zener diode D4 having a cathode connected to the other terminal of the resistor R6. Also, a transistor Q4 whose base is connected to the anode of the Zener diode D4, a diode D3 whose anode is connected to the base of the transistor Q2 of the switch circuit 5, and a cathode connected to the collector of the transistor Q4, and a base of the transistor Q4 And a resistor R7 connected between the power supply and the ground level. The emitter of the transistor Q4 is grounded, and the collector is connected to the resistor R5 of the normal current path section 6.

Accordingly, the switch control section 7 turns on the transistor Q4 when the voltage of the DC output 31 exceeds 35V. As a result, the base potential of the transistor Q2 becomes close to 0, and the switch circuit 5 is turned off. Also, a base current flows through the transistor Q3, turning on the transistor Q3, and the normal current path section 6 guides the DC output 32 to the non-voltage drop path 35.

On the other hand, when the voltage of the DC output 31 is lower than 35 V, the transistor Q4 is turned off. As a result, the base potential of the transistor Q2 becomes equal to the collector potential, and the switch circuit 5 is turned on. In addition, since the transistor Q3 is turned off, the normal current path unit 6 stops guiding the DC output 32 to the non-voltage drop path 35.

The other elements will be described. An emitter is connected to the DC output 31, a collector is connected to the transistor Q1 connected to the second regulator 22, and a resistor R1 is connected between the base and the emitter of the transistor Q1. The resistor R2 connected between the base of the transistor Q1 and the collector of the transistor Q5 forms a switch circuit for opening and closing the connection between the DC output 31 and the second regulator 22. .

The transistor Q5 has a collector connected to the error detection circuit 3 and the resistor R2, and has an emitter grounded; a resistor R9 connected between the base of the transistor Q5 and the ground level; The resistor R8 connected between the base and the microcomputer 15 forms a circuit for switching between the standby mode and the normal operation mode.

That is, when the output 33 of the microcomputer 15 becomes L level, the transistor Q 1 is turned off and the connection between the DC output 31 and the second regulator 22 is opened to set the standby mode. The error detection circuit 3 detects a voltage error of the DC output 31. On the other hand, when the output 33 goes to the H level, the transistor Q1 is turned on and the connection between the DC output 31 and the second regulator 22 is closed in order to set the normal operation mode. The error detection circuit 3 detects a voltage error of the DC output 32.

The second regulator 22 is a block for generating a stabilized 35 V DC output from the 38 V DC output 31, and sends out the generated DC output to the tuner 13. The tuner (analog circuit unit) 13 is a block for receiving a digital broadcast, and performs a predetermined process on the received signal. The decoder (digital circuit unit) 14 is a block for decoding a signal that has been subjected to predetermined processing by the tuner 13, and converts a signal obtained by decoding into a signal of the NTSC system. Output. The voltage of the operation power supply of the decoder 14 is 5 V, which is the same as the voltage of the operation power supply of the microcomputer 15. The current consumption of the decoder 14 is about 1.5A.

The microcomputer 15 is a block for controlling main operations as a digital satellite broadcast receiver. Therefore, the operation of the tuner 13 and the operation of the decoder 14 are controlled.

FIG. 2 is an explanatory diagram showing a change in voltage at a main point in the embodiment. The operation of the embodiment will be described with reference to FIG.

When the standby mode is set, the microcomputer 15 sets the output 33 to the L level. Therefore, the error detection circuit 3 detects a voltage error so that the voltage of the DC output 31 becomes 7V. Then, the detection result is fed back to the switching circuit 1 via the photocoupler 4. For this reason, the voltage of the DC output 31 is stabilized at 7V. Further, since the transistor Q1 is turned off, the output voltage of the second regulator 22 becomes 0 V, and the tuner 13 stops operating. Further, since the voltage of the DC output 32 becomes about 1 V, the operation of the decoder 14 stops.

Further, since the transistor Q 4 in the switch control section 7 is turned off, the switch circuit 5 is turned on, and a voltage of about 7 V is supplied to the first regulator 21. For this reason, the first regulator 21 supplies a DC output stabilized at 5 V to the microcomputer 15 via the voltage non-drop path 35. Also, the transistor Q3 of the normal current path section 6 is turned off, and the connection between the DC output 32 and the non-voltage drop path 35 is opened.

In the above state, when an instruction to start the operation is input, the microcomputer 15 changes the output 33 from the L level to the H level (time T1). Therefore, the error detection circuit 3 detects a voltage error so that the voltage of the DC output 32 becomes 5 V, and feeds back the detected voltage error to the switching circuit 1. As a result, the voltage of the DC output 32 starts to increase from 1V to 5V. Further, the voltage of the DC output 31 starts increasing from 7V toward 38V.

When the voltage of DC output 31 rises to 35 V (time T 2) (after a delay of period t 1), transistor Q 4 shifts from off to on. As a result, the transistor Q2 turns off and the transistor Q3 turns on. That is, instead of the DC output from the first regulator 21, the DC output 32 is led to the non-voltage drop path 35.

Further, the second regulator 22 sends out a voltage near 35 V to the tuner 13, so that the tuner 13 starts operating. At time T2, the DC output 32 of about 4.5 V is supplied to the decoder 14, so that a normal operation is started when a short time has elapsed from time T2.

As described above, the voltage of the non-voltage drop path 35 is 5 V before the time T 2 and becomes about 4.5 V at the time T 2. Then, the voltage rises to a value close to 5V. That is, the amount of voltage drop that occurs in the voltage non-drop path 35 is very small (see 351). Therefore, the short-term voltage drop shown in 351 can be absorbed only by connecting the small-capacity capacitor C3 to the non-voltage drop path 35.

Although the case where the DC output 31 is guided to the switch control unit 7 as a detection target has been described, a configuration in which the DC output 32 is guided to the switch control unit 7 may be employed. In the case of this configuration, the Zener voltage of the Zener diode D4 is set so that the transistor Q4 shifts from off to on when the voltage of the DC output 32 becomes 4.5V.

As described above, the voltage of the DC output 31 when the transistor Q 4 shifts from the OFF state to the ON state is 35 V, as described above. Therefore, there is a margin that 3V can be expected to rise even after the transistor Q4 is turned on. Such a margin has a small value of about 0.5 V when the DC output 32 is led to the switch control unit 7. Therefore, the configuration in which the DC output 31 is guided to the switch control unit 7 increases the margin and facilitates the setting of the switching timing. Further, the input voltage higher than 7 V is merely introduced into the first regulator 21 only during the period t1, so that the amount of heat generated by the first regulator 21 is very small.

[0052]

[Effect of the invention]

 As described above, in the switching power supply according to the present invention, the DC output sent from the first rectifying and smoothing circuit is guided through the switch circuit, and the DC output voltage sent to the non-voltage drop path is converted to the second voltage. A first regulator that stabilizes to a value close to the above, and a normal time when the first regulator does not send a DC output to the non-voltage drop path, and directs the DC output sent by the second rectifying / smoothing circuit to the non-voltage drop path. A current path section; when the normal operation mode is set, the output voltage of the first rectifying / smoothing circuit is set to the first voltage; the output voltage of the second rectifying / smoothing circuit is set to the second voltage; The present invention is applied to a switching power supply in which the output voltage of the first and second rectifying / smoothing circuits is lower than that in the normal operation mode. When a transition from mode to the normal operation mode, a switch control unit that opens the connection of the switching circuit at a timing later than timing of the transition. Therefore, when the connection of the switch circuit is opened, the DC output that has increased to a value near the second voltage is guided to the non-voltage drop path. For this reason, when the connection of the switch circuit is opened, the voltage drop that occurs in the non-voltage drop path becomes very small, and the DC output source is switched between the regulator and the rectifying / smoothing circuit by a small capacitor. It is possible to prevent a voltage drop in the alternative path.

Further, when the switch control section shifts from the standby mode to the normal operation mode, the switch control section waits until the voltage of the DC output on the secondary side rises to a preset voltage, and ends the standby. Then, the connection of the switch circuit is opened. Therefore, when the voltage supplied to the first regulator becomes a high voltage, the connection of the switch circuit is promptly opened, and the period during which the high voltage is supplied to the first regulator is short. This can suppress an increase in the calorific value of the battery.

Further, the switch control section opens the connection of the switch circuit based on the DC output voltage sent from the first rectifying / smoothing circuit. Therefore, even after the switch control unit opens the connection of the switch circuit, a sufficient margin can be provided for the rise in the DC output voltage sent out by the first rectifying / smoothing circuit. The timing for opening the file can be easily set to the optimal timing.

Further, the normal current path section further includes a PNP transistor having a collector connected to an output of the second rectifying / smoothing circuit and a collector connected to a non-voltage drop path, and the switch control section. Is configured to turn off the PNP transistor when opening the connection of the switch circuit and turn on the PNP transistor when closing the connection of the switch circuit. That is, the amount of voltage drop generated by the PNP transistor is very small, and the difference between the voltage via the PNP transistor and the voltage not via the PNP transistor is very small. This eliminates the need for a voltage shifting diode inserted in the output path of the second rectifying and smoothing circuit, thereby preventing an increase in loss even when the output current value of the second rectifying and smoothing circuit is large. be able to.

Further, the error detection circuit detects an error in the output voltage of the first rectification smoothing circuit when the operation mode is the standby mode, and outputs the output voltage of the second rectification smoothing circuit when the operation mode is the normal operation mode. Is detected. Accordingly, in the standby mode, the voltage of the DC output of the first rectifying / smoothing circuit is stabilized, so that the voltage of the non-voltage drop path is accurately stabilized. In the normal operation mode, the output of the second rectifying / smoothing circuit is stabilized, so that the voltage of the voltage non-drop path can be accurately stabilized at a predetermined voltage.

Further, a second regulator is provided which guides a DC output sent from the first rectifying / smoothing circuit and stabilizes an output voltage to a predetermined voltage. Therefore, the output voltage of the second regulator is stabilized even when the voltage of the DC output sent from the first rectifying and smoothing circuit fluctuates. It is possible to accurately stabilize the DC output voltage to a predetermined voltage.

Further, an analog circuit unit for performing predetermined processing of the guided signal, a digital circuit unit for processing the output of the analog circuit unit, and a microcomputer for controlling operations of the analog circuit unit and the digital circuit unit The DC power output from the second regulator is guided to an analog circuit section, the non-voltage drop path is guided to the microcomputer, DC output from the rectifying / smoothing circuit is guided to the digital circuit section. Therefore, the above object can be achieved in a set-top box.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of a set-top box using an embodiment of a switching power supply according to the present invention.

FIG. 2 is an explanatory diagram showing a change in voltage at a main point of the embodiment.

FIG. 3 is a circuit diagram showing a conventional electrical connection.

FIG. 4 is an explanatory diagram showing a change in voltage at a main point in the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Switching circuit 2 Transformer 3 Error detection circuit 5 Switch circuit 6 Current path part at normal time 7 Switch control part 11 First rectification smoothing circuit 12 Second rectification smoothing circuit 13 Tuner 14 Decoder 15 Microcomputer 21 First regulator 22 First 2 Regulator 35 Non-voltage drop path L11 First secondary coil L12 Second secondary coil Q3 PNP transistor

Claims (7)

[Utility model registration claims] When the first voltage is higher than the second voltage, the current flows through at least a transformer around which the first and second secondary coils are wound and a primary coil around the transformer. A switching circuit for switching a current; a first rectifying and smoothing circuit for rectifying and smoothing the output of the first secondary coil; a second rectifying and smoothing circuit for rectifying and smoothing the output of the second secondary coil; A first regulator for guiding a DC output sent from the first rectifying / smoothing circuit via the first regulator, and for stabilizing the voltage of the DC output sent to the non-voltage drop path to a value close to the second voltage; A normal current path section for guiding the DC output sent by the second rectifying / smoothing circuit to the non-voltage drop path when the regulator does not send the DC output to the non-voltage drop path; When the normal operation mode is set by returning to the path, the output voltage of the first rectifying / smoothing circuit is set to the first voltage and the output voltage of the second rectifying / smoothing circuit is set to the second voltage. When the standby mode is set, the connection of the switch circuit is closed when the standby mode is set, and the mode shifts from the standby mode to the normal operation mode. A switching control unit that opens a connection of the switch circuit at a timing later than the transition timing. 2. The switch control section waits until the voltage of the DC output on the secondary side rises to a preset voltage when shifting from the standby mode to the normal operation mode. The switching power supply according to claim 1, wherein a connection of the switch circuit is opened. 3. The switching power supply according to claim 2, wherein the switch control unit opens a connection of the switch circuit based on a voltage of a DC output sent from the first rectifying / smoothing circuit. 4. The normal current path section includes a PNP transistor having a collector connected to an output of a second rectifying and smoothing circuit and a collector connected to a non-voltage drop path. 4. The PNP transistor is turned off when the connection of the circuit is opened, and the PNP transistor is turned on when the connection of the switch circuit is closed.
The switching power supply according to any of the above. 5. The error detection circuit detects an error in the output voltage of the first rectifying / smoothing circuit when in a standby mode, and detects an error in the output voltage of the second rectifying / smoothing circuit in a normal operation mode. 2. The method according to claim 1, wherein
The switching power supply according to any one of claims 1 to 4. 6. The switching power supply according to claim 5, further comprising a second regulator for guiding a DC output sent from the first rectifying / smoothing circuit and for stabilizing an output voltage to a predetermined voltage. 7. An analog circuit unit for performing predetermined processing of a guided signal, a digital circuit unit for processing an output of the analog circuit unit, and a microcomputer for controlling operations of the analog circuit unit and the digital circuit unit. In the switching power supply provided in the set-top box, the DC output from the second regulator is guided to an analog circuit, the non-voltage drop path is guided to the microcomputer, and the second rectifying and smoothing circuit sends the DC output. 7. The switching power supply according to claim 6, wherein the DC output is guided to a digital circuit unit.