JP6273895B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply device that converts an input voltage into a stable output voltage.

  An electronic device or the like to which DC power is supplied from a switching power supply device that converts an input voltage into a stable output voltage may require input voltage information. For example, when the input voltage is supplied from a battery, the state of charge of the battery can be monitored based on information on the input voltage. Also, when the AC power supply is rectified and smoothed to obtain the input voltage, it is possible to detect that the AC power supply has been shut off based on the input voltage information.

  As a switching power supply with a function to detect the input voltage input to the primary side on the secondary side, the flyback voltage is peak-charged using a diode and a capacitor, and the input voltage is synthesized by combining the output voltage and resistance. A technique for generating a voltage corresponding to the above has been proposed (see, for example, Patent Document 1).

JP 2007-49833 A

  However, in the prior art, since the input voltage is detected by the voltage between the terminals of the capacitor peak-charged with the flyback voltage, the output voltage, and the resistance combined voltage, the DC power supply has an output voltage adjustment function, When the output voltage fluctuates due to a sudden load fluctuation or the like, the input voltage cannot be detected correctly. In order to correctly detect the input voltage, a means for correcting fluctuations in the output voltage is required, which complicates and increases the circuit.

  An object of the present invention is to solve the above-described problems of the prior art in view of the above-described problems, and to provide a switching power supply device that can correctly detect an input voltage on the secondary side even if the output voltage fluctuates. .

A switching power supply device according to the present invention includes a switching circuit connected in parallel to a DC power supply, a series circuit including a transformer primary winding and a capacitor, a rectifier diode connected to the transformer secondary winding, and a smoothing capacitor. a rectifier smoothing circuit consisting of, in response to the inter-terminal voltage before Kiko capacitor and a control circuit for controlling on and off of the switching element, a switching power supply unit for supplying to a load an output voltage from the smoothing capacitor, A clamping diode connected in parallel to both ends of a series circuit composed of the primary winding and the capacitor, a voltage generated in the secondary winding when the switch element is turned on, and the switch element is turned off And an input voltage detection circuit for detecting an input voltage of the DC power supply with a voltage obtained by adding a voltage generated in the secondary winding to It is characterized in.
Furthermore, in the switching power supply of the present invention, the input voltage detection circuit includes a first detection capacitor and a first detection diode connected in parallel to both ends of the secondary winding, and the switch element is turned on. A first detection circuit for detecting a voltage generated in the secondary winding, a second detection diode connected in parallel to the first detection diode, and a second detection capacitor. A second detection circuit for detecting a voltage obtained by adding a voltage detected by the detection circuit and a voltage generated in the secondary winding when the switch element is turned off; and a voltage across the terminals of the second detection capacitor. Thus, the input voltage of the DC power supply may be detected.
Furthermore, the switching power supply device of the present invention includes a voltage dividing circuit for detecting the voltage across the capacitor, and transmits information to the secondary side by changing the output voltage by changing the ratio of the voltage dividing circuit. You may make it do.

  According to the present invention, since the input voltage can be detected based on a voltage corresponding to the input voltage and unrelated to the output voltage, the input voltage can be correctly detected even if the output voltage fluctuates. There is an effect.

It is a circuit block diagram which shows the circuit structure of 1st Embodiment of the switching power supply device which concerns on this invention. It is a wave form diagram which shows the signal waveform and operation | movement waveform of each part of FIG. It is a wave form diagram which shows the signal waveform and operation | movement waveform of each part of FIG. It is a circuit block diagram which shows the circuit structure of 2nd Embodiment of the switching power supply device which concerns on this invention. FIG. 5 is a circuit configuration diagram illustrating a configuration example of a voltage detection circuit illustrated in FIG. 4.

(First embodiment)
In the switching power supply according to the first embodiment, referring to FIG. 1, a series circuit including a switch element Q1, a primary winding Np of a transformer T, and a capacitor C1 is connected to a DC power supply E (input voltage VE). Has been. The cathode of the diode D1 is connected to the connection point between the switch element Q1 and the primary winding Np of the transformer T, and the anode of the diode D1 is connected to the connection point between the capacitor C1 and the DC power supply E, respectively. A diode D1 is connected in parallel to both ends of a series circuit composed of Np and a capacitor C1.

  A voltage dividing circuit including a resistor R1 and a resistor R2 is connected between both ends of the capacitor C1. The divided voltage at the connection point between the resistor R1 and the resistor R2 is input to the control circuit 10. The control circuit 10 detects the inter-terminal voltage VC1 of the capacitor C1 based on the divided voltage at the connection point between the resistor R1 and the resistor R2, and controls the switch element Q1 via the driver circuit 11 based on the inter-terminal voltage VC1 of the capacitor C1. Turn on and off.

  A diode D2 that is a rectifier and a smoothing capacitor C2 are connected in series to the secondary winding Ns of the transformer T, and the voltage across the terminals of the smoothing capacitor C2 is supplied to the load as the output voltage Vo. The diode D2 and the smoothing capacitor C2 constitute a rectifying / smoothing circuit that rectifies and smoothes the voltage generated in the secondary winding Ns of the transformer T.

  When the switch element Q1 is on, a voltage VE-VC1 obtained by subtracting the voltage VC1 between terminals of the capacitor C1 from the input voltage VE is applied to the primary winding Np of the transformer T, and energy is stored in the transformer T. Capacitor C1 is charged. At this time, a voltage for turning off the diode D2 is generated in the secondary winding Ns of the transformer T. When the switch element Q1 is turned off, the diode D1 is turned on to enter a freewheel period, and the primary winding Np of the transformer T is clamped to the voltage VC1 between terminals of the capacitor C1. Therefore, since (VE−VC1) × Ton = VC1 × Toff, the voltage VC1 between the terminals of the capacitor C1 is VC1 = VE * Ton / (Ton + Toff), and is determined by the on / off duty ratio of the switch element Q1. During this freewheel period, a voltage is generated in the secondary winding Ns so that the diode D2 is turned on, and the energy accumulated in the transformer T is transmitted to the secondary side to charge the smoothing capacitor C2. For this reason, a voltage of VC1 * Ns / Np is generated in the secondary winding Ns. That is, the output voltage Vo can be stabilized by controlling the inter-terminal voltage VC1 of the capacitor C1.

  Further, an input voltage detection circuit 20 for detecting the input voltage VE is connected between both ends of the secondary winding Ns of the transformer T. The input voltage detection circuit 20 includes a capacitor C3, a diode D3, a diode D4, a capacitor C4, a resistor R3, and a resistor R4. A series circuit including a capacitor C3 and a diode D3 is connected as a first detection circuit between a connection point between one end of the secondary winding Ns and the diode D2 and the other end of the secondary winding Ns. ing. The diode D3 is connected in a direction to conduct when a negative voltage (voltage that turns off the diode D2) is generated in the secondary winding Ns. A series circuit including a diode D4 and a capacitor C4 is connected in parallel with the diode D3 as a second detection circuit. The diode D4 is connected in a direction to conduct when a positive voltage (voltage that turns on the diode D2) is generated in the secondary winding Ns. Further, a voltage dividing circuit including a resistor R3 and a resistor R4 is connected between both ends of the capacitor C4.

Hereinafter, the operation of the input voltage detection circuit 20 will be described in detail.
When the switch element Q1 is turned on, a negative voltage (a voltage for turning off the diode D2) is generated in the secondary winding Ns, so that the diode D3 conducts, and if the voltage drop of the diode D3 is ignored, the capacitor C3 The inter-terminal voltage VC3 is charged at (VE-VC1) * Ns / Np. When the switch element Q1 is turned off, a positive voltage (voltage that turns on the diode D2) is generated in the secondary winding Ns, so that the diode D4 conducts, and if the voltage drop of the diode D4 is ignored, the capacitor C4 The inter-terminal voltage VC4 is VC3 + VC1 * Ns / Np. Since the inter-terminal voltage VC3 of the capacitor C3 is charged at (VE-VC1) * Ns / Np, the inter-terminal voltage VC4 of the capacitor C4 becomes VE * Ns / Np, which is a voltage proportional to the input voltage VE. It becomes. Therefore, the input voltage VE can be detected on the secondary side of the DC power supply by detecting the voltage VC4 between the terminals of the capacitor C4. Furthermore, since the voltage VC4 between the terminals of the capacitor C4 is irrelevant to the output voltage Vo and the voltage VC1 between the terminals of the primary side capacitor C1, the detected voltage does not change even when the output voltage Vo varies.

  The divided voltage at the connection point between the resistor R3 and the resistor R4 is input to the microcomputer 30 via the analog / digital converter (ADC) 21. The microcomputer 30 recognizes the inter-terminal voltage VC4 of the capacitor C4 based on the divided voltage at the connection point between the resistors R3 and R4, and detects the input voltage VE. Even if the output voltage Vo fluctuates, the voltage VC4 between terminals of the capacitor C4 (the divided voltage at the connection point between the resistor R3 and the resistor R4) does not change. Can be detected with high accuracy. In the first embodiment, the output voltage Vo is supplied as a power source for the microcomputer 30 via the regulator (REG) 31. Thereby, even if the output voltage Vo fluctuates due to fluctuations in the load on the secondary side or fluctuations in the input voltage VE on the primary side, the voltage supplied to the microcomputer 30 can be stabilized.

  FIGS. 2 and 3 show the waveforms of the respective parts when the setting of the output voltage Vo is low and when it is high. 2 and 3, (a) is a drive voltage Q1G applied to the gate of the switch element Q1, (b) is a voltage VD1 between terminals of the diode D1, and (c) is generated in the secondary winding Ns. Voltages VNs and (d) show the output voltage Vo, and (e) shows the voltage VC4 between the terminals of the capacitor C4. 2 and 3, it can be seen that the inter-terminal voltage VC4 of the capacitor C4 is constant regardless of the setting of the output voltage Vo.

As described above, according to the first embodiment, the series circuit including the switching element Q1, the primary winding Np of the transformer T, and the capacitor C1, which are connected in parallel to the DC power source E, and the transformer T A rectifying / smoothing circuit comprising a rectifying diode D2 connected to the next winding Ns and a smoothing capacitor C2, and a control circuit 10 for controlling on / off of the switch element Q1 in accordance with the voltage VC1 between terminals of the capacitor C1; A switching power supply that supplies an output voltage Vo from C2 to a load, and a voltage ((VE-VC1) * Ns / N) generated in the secondary winding Ns when the switch element Q1 is on, and the switch element Q1 The voltage (VE * Ns / Np) obtained by adding the voltage (VC1 * Ns / Np) generated in the secondary winding Ns when is turned off to the input voltage VE of the DC power source E. And an input voltage detecting circuit 20 to output.
With this configuration, the input voltage VE is detected by the input voltage detection circuit 20 on the secondary side based on the voltage corresponding to the input voltage VE and unrelated to the output voltage Vo and the voltage VC1 between the terminals of the primary side capacitor C1. Therefore, even if the output voltage Vo varies, the input voltage VE can be detected correctly.

Furthermore, according to the first embodiment, the input voltage detection circuit 20 includes a first detection capacitor (capacitor C3) and a first detection diode (diode D3) connected in parallel to both ends of the secondary winding Ns. ), And a second detection diode (diode D4) connected in parallel to the first detection diode and a first detection circuit for detecting a voltage generated in the secondary winding Ns when the switch element Q1 is on. ) And a second detection capacitor (capacitor C4), and detects a voltage obtained by adding the voltage detected by the first detection circuit and the voltage generated in the secondary winding Ns when the switch element Q1 is turned off. And a detection circuit, and configured to detect the input voltage VE of the DC power supply E with the voltage across the terminals of the second detection capacitor.
With this configuration, without providing a special circuit for canceling the fluctuation of the output voltage Vo, the output voltage Vo and the inter-terminal voltage VC1 of the primary-side capacitor C1 are compatible with the input voltage VE with a simple circuit configuration. Irrelevant voltages can be detected.

(Second Embodiment)
Referring to FIG. 4, the switching power supply apparatus according to the second embodiment includes a resistor R5, a switch SW1, and a voltage detection circuit 40 in addition to the configuration of the first embodiment. The resistor R5 is connected in series with the resistor R2 used for voltage feedback of the capacitor C1, and the switch SW1 is connected in parallel with the resistor R5. As a result, the divided voltage at the connection point between the resistor R1 and the resistor R2 input to the control circuit 10 changes according to the on / off state of the switch SW1. That is, when the switch SW1 is turned on, the resistor R5 is short-circuited, and the inter-terminal voltage VC1 and the output voltage Vo of the capacitor C1 rise. When the switch SW1 is turned off, the inter-terminal voltage VC1 and the output voltage Vo of the capacitor C1 are changed to the resistor R1. And the voltage set by the resistors R2 and R5. Since the inter-terminal voltage VC4 of the capacitor C4 is irrelevant to the output voltage Vo and the inter-terminal voltage VC1 of the primary side capacitor C1, the inter-terminal voltage of the capacitor C4 even if the output voltage Vo is changed by turning on / off the switch SW1. VC4 does not fluctuate.

  On the secondary side, a voltage detection circuit 40 for detecting the output voltage Vo is provided. As the voltage detection circuit 40, a comparator COMP shown in FIG. 5A, a Zener diode ZD1 shown in FIG. 5B, or an analog / digital converter (ADC) 41 shown in FIG. 5C can be used. . The output of the voltage detection circuit 40 is input to the microcomputer 30, and the microcomputer 30 can detect a change in the output voltage Vo that occurs when the switch SW <b> 1 is turned on / off. Therefore, by turning on / off the switch SW1 according to the digital signal input to the primary side, the digital signal input to the primary side is transmitted to the secondary side as the fluctuation of the output voltage Vo.

As described above, according to the second embodiment, the voltage dividing circuit (resistors R1, R2, R5) for detecting the voltage VC1 between the terminals of the capacitor C1 is provided, and the ratio of the voltage dividing circuit is changed by the switch SW1. By changing the output voltage Vo, information is transmitted to the secondary side.
With this configuration, a digital signal can be transmitted from the primary side to the secondary side without using a special element such as a photocoupler by utilizing the fact that the fluctuation of the output voltage Vo does not affect the input voltage detection circuit 20. Can do.

  As mentioned above, although this invention was demonstrated by specific embodiment, the said embodiment is an example and it cannot be overemphasized that it can change and implement in the range which does not deviate from the meaning of this invention.

10 Control Circuit 11 Driver 20 Input Voltage Detection Circuit 21 Analog / Digital Converter (ADC)
30 Microcomputer 31 Regulator (REG)
40 Voltage Detection Circuit 41 Analog / Digital Converter (ADC)
C1, C3, C4 Capacitor C2 Smoothing capacitor COMP Comparator D1, D2, D3, D4 Diode E DC power supply Q1 Switch element R1, R2, R3, R4, R5 Resistor SW1 Switch T Transformer Np Primary winding Ns Secondary winding ZD1 Zener diode

Claims (3)

A series circuit composed of a switching element connected in parallel to a DC power source, a primary winding of the transformer, and a capacitor; a rectifying smoothing circuit composed of a rectifying diode and a smoothing capacitor connected to the secondary winding of the transformer; depending on the terminal voltage of Kiko capacitor and a control circuit for controlling on and off of the switching element, a switching power supply apparatus for supplying an output voltage to a load from the smoothing capacitor,
A clamping diode connected in parallel to both ends of a series circuit composed of the primary winding and the capacitor ;
The input voltage of the DC power supply is detected by a voltage obtained by adding the voltage generated in the secondary winding when the switch element is on and the voltage generated in the secondary winding when the switch element is off. And an input voltage detection circuit. The input voltage detection circuit is
A first detection capacitor and a first detection diode connected in parallel to both ends of the secondary winding, and detecting a voltage generated in the secondary winding when the switch element is on. A detection circuit;
A second detection diode and a second detection capacitor connected in parallel to the first detection diode. The voltage detected by the first detection circuit and the secondary winding when the switch element is turned off. A second detection circuit for detecting a voltage obtained by adding the generated voltage,
2. The switching power supply device according to claim 1, wherein an input voltage of the DC power supply is detected by a voltage between terminals of the second detection capacitor. A voltage dividing circuit for detecting a voltage between terminals of the capacitor;
3. The switching power supply device according to claim 1, wherein information is transmitted to the secondary side by changing the output voltage by changing the ratio of the voltage dividing circuit.

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