JP2011062047A - Switching power supply - Google Patents

Abstract

A switching power supply device that detects an overcurrent state by a frequency / voltage converter and protects the load from overcurrent when the load is AC driven.
A switching element that receives a DC voltage from a DC power supply, a control unit that performs switching control of the switching element, a primary winding that is supplied with a switching output from the switching element, and an AC voltage generated by the switching output. A converter transformer having a secondary winding to be excited, a load circuit connected to the secondary winding of the converter transformer and supplied with an AC voltage, and a frequency of the AC voltage excited to the secondary winding is converted into a voltage. An overcurrent protection circuit that includes a frequency / voltage converter and controls the control unit to suppress the switching output when the output voltage of the frequency / voltage converter becomes equal to or higher than a specified voltage.
[Selection] Figure 2

Description

  The present invention relates to a variable frequency switching power supply device, and more particularly to a switching power supply device including an overcurrent protection circuit.

  Conventionally, a switching power supply device is used to drive a load such as a halogen lamp. The switching power supply device has a switching element and a converter transformer, switches the switching element at a high frequency to convert a DC voltage into a high-frequency AC voltage, and rectifies and smoothes the high-frequency AC voltage to be supplied to the load circuit. ing. When a lamp is connected as a load circuit, the lamp can be dc lit.

  By the way, in the conventional switching power supply device, the lamp is controlled to be lit at the rated current. However, the rated current may be exceeded for some reason, and the lamp will be damaged if a current exceeding the rated current flows for a predetermined time. End up. For this reason, when a current exceeding the rated current flows through the load circuit (lamp), the switching element is stopped so that the overcurrent protection operation is activated.

  Patent Document 1 discloses a switching power supply device having an overcurrent protection function. In the example of Patent Document 1, a rectifier circuit that rectifies a commercial AC power supply, a switching unit that performs switching by inputting a rectified DC voltage, a power factor correction circuit that is inserted between the rectifier circuit and the primary side ground, and An overcurrent detection resistor is inserted between the power factor correction circuit and the primary side ground, and the load level is detected based on the voltage across the overcurrent detection resistor to control the switching means to perform the overcurrent protection operation. .

  However, in the example of Patent Document 1, since current always flows through the overcurrent detection resistor during energization, power loss occurs. When a current resonance circuit is provided on the output side of the switching means and the load circuit (for example, a lamp) is AC driven, the peak value of the drive voltage is constant although the drive frequency changes. There is a problem that the overcurrent protection operation cannot be performed because the amplitude does not change.

JP-A-2005-318779

  In the conventional switching power supply device, the load level is detected based on the voltage across the overcurrent detection resistor to control the switching means, and the overcurrent protection operation is performed. Since current flows, power loss occurs. Further, in the case of a variable frequency switching power supply that drives a load (for example, a lamp) with alternating current, the amplitude of the voltage at both ends of the overcurrent detection resistor does not change, and thus there is a problem that the overcurrent protection operation cannot be performed.

  The present invention has been made in view of such circumstances. When a load (for example, a lamp) is AC driven, an overcurrent is obtained by converting a frequency into a voltage by a frequency / voltage converter (F / V converter). It is an object of the present invention to provide a switching power supply device that detects a state and achieves overcurrent protection and power loss reduction.

  According to a first aspect of the present invention, there is provided a switching power supply apparatus according to the present invention, wherein a switching element that receives a DC voltage from a DC power supply, a control unit that controls the switching of the switching element, and a switching output from the switching element are supplied. A converter transformer having a secondary winding, a secondary winding in which an AC voltage is excited by the switching output, a load circuit connected to the secondary winding of the converter transformer and supplied with the AC voltage; Including a frequency / voltage converter that converts the frequency of the alternating voltage excited in the next winding into a voltage, and controls the control unit when the output voltage of the frequency / voltage converter exceeds a specified voltage. And an overcurrent protection circuit for suppressing the switching output.

  According to a fifth aspect of the present invention, there is provided a switching power supply device according to the present invention, wherein a DC voltage from a DC power supply is input to a switching element, the switching element is subjected to switching control by a control unit, and a switching output from the switching element is supplied to a converter transformer. The secondary winding of the converter transformer is excited by the switching output, the alternating voltage is excited by the switching output, the alternating voltage excited by the secondary winding is supplied to the load circuit, and the secondary winding A frequency / voltage converter converts the frequency of the alternating voltage excited to a voltage, and when the output voltage of the frequency / voltage converter becomes equal to or higher than a specified voltage, the control unit is controlled to change the switching output. It suppresses and protects the load circuit from overcurrent.

  In the switching power supply device of the present invention, when the load circuit is AC driven, the frequency / voltage converter (F / V converter) can convert the frequency into the voltage, thereby detecting the overcurrent state. The load circuit can be protected from overcurrent. Moreover, power loss can be reduced by using an F / V converter.

1 is a circuit diagram showing a configuration of a switching power supply device according to an embodiment of the present invention. The circuit diagram which shows an example of the overcurrent protection circuit in the embodiment. The wave form diagram which shows an example of operation | movement of the F / V converter in the same embodiment. The circuit diagram which shows the modification of the switching power supply device of this invention.

  Hereinafter, an embodiment of a switching power supply device of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram showing a configuration of a switching power supply apparatus 100 of the present invention. The switching power supply device 100 includes an AC power supply 11, a full-wave rectifier circuit 12, a PFC (Power Factor Correction) circuit 13, a resonant converter 15, a load circuit 18, and an overcurrent protection circuit 20. In the following description, an example in which a lamp 18 such as a halogen lamp is connected as the load circuit 18 will be described.

  The AC power supply 11 is full-wave rectified by a full-wave rectifier circuit 12, and a DC voltage is supplied to the PFC circuit 13. The PFC circuit 13 is a power factor correction circuit that boosts the DC voltage rectified by the full-wave rectifier circuit 12. The PFC circuit 13 includes a boost converter including an inductance element L1 and a diode D1, a switching element Q1 connected to a connection point between the inductance element L1 and the diode D1, a smoothing capacitor C1, and a control IC.

  The voltage across the smoothing capacitor C1 is proportional to the output voltage of the PFC circuit 13, and this output voltage is fed back to the control IC 14. A control pulse for driving the switching element Q1 is output from the control IC 14, and the output voltage is stabilized by controlling the switching element Q1 on and off according to the feedback voltage. Such a PFC circuit 13 is also called an active filter. The PFC circuit 13 constitutes a DC voltage source for the converter 15.

  Converter 15 includes switching elements Q2 and Q3 connected in series between the output terminal of PFC circuit 13 and a reference potential point (ground). The DC voltage from the PFC circuit 13 is input to the drain of the switching element Q2, the source is connected to the drain of the switching element Q3, and the source of the switching element Q3 is connected to the reference potential point (earth). A series resonance circuit including a primary winding T1 of a converter transformer T and a capacitor C2 is connected between the connection point of the switching elements Q2 and Q3 and the ground. Further, the PWM signal from the control unit 16 is supplied to the gates of the switching elements Q2 and Q3, and the switching elements Q2 and Q3 perform a complementary switching operation at a predetermined frequency by the PWM signal.

  For example, a lamp 18 is connected to both ends of the secondary winding T2 of the transformer T as a load circuit. The tertiary winding T3 of the transformer T is connected to a rectifying / smoothing circuit composed of a diode D2 and a capacitor C3. By dividing the rectified / smoothed output voltage by a series circuit of resistors R1 and R2, a converter is obtained. A detection voltage V0 proportional to the output voltage of 15 can be obtained. The detection voltage V0 is supplied to the feedback circuit 17, and the feedback circuit 17 controls the control unit 16 according to the change of the detection voltage V0, thereby controlling the on / off cycle of the switching elements Q2 and Q3. The control unit 16 is configured by an integrated circuit (IC).

  A switching output is obtained at the connection point of the switching elements Q2 and Q3, and the series circuit of the primary winding T1 of the transformer T and the capacitor C2 is current-resonated by this switching output, and an AC voltage is applied to the secondary winding T2 of the transformer T. Is excited. Accordingly, the lamp 18 is AC lit by the AC voltage of the secondary winding T2. Thus, the converter 15 operates as a current resonance type, and the frequency of the output AC voltage of the secondary winding T2 of the transformer T is changed by controlling on / off of the switching elements Q2, Q3 by the PWM signal.

  Furthermore, in the present invention, an overcurrent protection circuit 20 is provided to prevent an overcurrent from flowing through the lamp 18. When an overcurrent flows through the lamp 18, the frequency of the alternating voltage of the secondary winding T2 of the transformer T becomes lower than a specified frequency. Therefore, the overcurrent protection circuit 20 includes an F / V converter (frequency / voltage converter) that converts the frequency of the alternating voltage generated in the secondary winding T2 of the transformer T into a voltage, and converts the change in frequency into a voltage. When the converted voltage exceeds a preset specified value, the control unit 16 is controlled to stop the switching elements Q2 and Q3 and stop the switching output. Alternatively, the switching elements Q2 and Q3 are intermittently driven alternately to alternately stop and oscillate to bring the switching output closer to the stop state.

  That is, the converter 15 controls the load circuit (lamp 18) to light at the rated current, but the rated current may be exceeded for some reason. If the rated current flows for a predetermined time or more, the lamp 18 is damaged. Invite. For this reason, the protection operation is performed when the frequency is such that a current of a predetermined value or more flows with respect to the rated current of the lamp 18.

  Details of the overcurrent protection circuit 20 will be described below with reference to FIG. As shown in FIG. 2, the overcurrent protection circuit 20 includes an F / V converter 21 and operational amplifiers A21 and A22 constituting a comparator. The F / V converter 21 converts the frequency of the output AC voltage of the secondary winding T2 of the transformer T into a voltage. For example, the AC voltage is shaped and converted into a rectangular wave, and the rectangular wave is integrated. Convert to voltage.

  FIG. 3 is a waveform diagram showing the operation of the F / V converter 21. 3A shows an AC voltage waveform of the secondary winding T2 of the transformer T. FIG. This alternating voltage (a) is shaped by a comparator and converted into a rectangular wave as shown in FIG. The rectangular wave (b) is integrated by an integrating circuit including a capacitor and converted into a sawtooth wave as shown in FIG. A predetermined voltage can be obtained by peak-holding the peak value of the sawtooth wave (c) with a sampling and holding circuit. The output voltage V1 of the F / V converter 21 increases as the frequency of the AC voltage of the secondary winding T2 of the transformer T decreases. As the configuration of the F / V converter 21, other circuit configurations can be adopted besides the one that operates as shown in FIG.

  Returning to FIG. 2, the output voltage V1 of the F / V converter 21 is supplied to the non-inverting input terminal (+) of the operational amplifier A21 and compared with the reference voltage V21 supplied to the inverting input terminal (−). When the output voltage V1 of the F / V converter 21 becomes equal to or higher than the reference voltage V21, a high-level comparison output voltage V2 is output from the operational amplifier A21.

  The comparison output voltage V2 is integrated by a time constant circuit including a resistor R21 and a capacitor C21, supplied to the non-inverting input terminal (+) of the operational amplifier A22, and compared with the reference voltage V22 supplied to the inverting input terminal (−). The When the integration output V3 becomes equal to or higher than the reference voltage V22, a high-level comparison output voltage V4 is output from the operational amplifier A22 and supplied to the control unit 16. When the output voltage V4 is supplied from the operational amplifier A22, the control unit 16 stops or intermittently drives the switching elements Q2 and Q3 to suppress the switching output. This prevents an overcurrent from flowing through the lamp 18.

  The comparison output voltage V2 is integrated by the time constant circuit of the resistor R21 and the capacitor C21. This is an overcurrent when the overcurrent continuously flows for a predetermined time (for example, several hundred mm sec.). This is to make the protective operation work. When the overcurrent is instantaneous and the influence on the lamp 18 is small, the protective operation is prevented from working excessively.

  As described above, in the present invention, when the load circuit 18 is AC-driven, the F / V converter 21 converts the frequency into a voltage, so that an overcurrent state can be detected, and the load is accurately detected from the overcurrent. The circuit 18 can be protected. Further, when an overcurrent detection resistor is used as in the prior art, a power loss due to the overcurrent detection resistor always occurs, but the power loss can be reduced by using the F / V converter 21.

  In addition, when the load circuit 18 is AC driven, the peak value of the AC voltage is constant, and the amplitude of the voltage at both ends does not change even if an overcurrent detection resistor is used. In the present invention, it is possible to reliably detect an overcurrent by using the F / V converter 21.

  Next, a modification of the present invention will be described with reference to FIG. FIG. 4 drives the load circuit 18 with a DC voltage.

  In FIG. 4, the anodes of rectifying diodes D3 and D4 are connected to both ends of the secondary winding T2 of the transformer T, and the cathodes of the diodes D3 and D4 are connected to each other and connected to the smoothing circuit 19. The intermediate terminal (ground) of the secondary winding T2 of the transformer T is connected to the smoothing circuit 19.

  The AC voltage generated in the secondary winding T2 of the transformer T is converted to DC by the diodes D3 and D4 and the smoothing circuit 19, and the load circuit 18 (lamp 18) is driven by DC voltage, and the lamp 18 is lit by DC. The AC voltage generated in the secondary winding T2 of the transformer T is supplied to the overcurrent detection circuit 20 including the F / V conversion circuit 21. The overcurrent protection operation is the same as in the example of FIG. 1, and the protection operation is activated when the frequency is such that a current exceeding a predetermined value flows with respect to the rated current of the lamp 18.

  As described above, in the switching power supply device of the present invention, when the load circuit is AC driven, the F / V converter can detect the overcurrent state by converting the frequency into the voltage. The load circuit can be protected. Moreover, power loss can be reduced by using an F / V converter.

  The embodiment of the present invention is not limited to the configuration described above. For example, although an example in which a halogen lamp is driven as a load circuit has been described, the present invention can also be applied to driving other load circuits. Various modifications can be made without departing from the scope of the claims.

DESCRIPTION OF SYMBOLS 100 ... Switching power supply device 11 ... AC power supply 12 ... Full wave rectifier circuit 13 ... PFC circuit 14 ... Control IC
DESCRIPTION OF SYMBOLS 15 ... Converter 16 ... Control part 17 ... Feedback circuit 18 ... Load circuit (lamp)
20 ... Overcurrent protection circuit 21 ... F / V converter (frequency / voltage converter)
Q2, Q3 ... switching element T ... converter transformer T1 ... primary winding T2 ... secondary winding C2 ... capacitor (for current resonance)
A21, A22 ... Operational amplifier (comparator)
R21, C21 ... Time constant circuit

Claims (5)

A switching element that receives a DC voltage from a DC power supply;
A control unit that performs switching control of the switching element;
A primary transformer to which a switching output from the switching element is supplied; a converter transformer having a secondary winding in which an alternating voltage is excited by the switching output;
A load circuit connected to the secondary winding of the converter transformer and supplied with the AC voltage;
A frequency / voltage converter that converts the frequency of the AC voltage excited in the secondary winding into a voltage, and controls the control unit when the output voltage of the frequency / voltage converter becomes equal to or higher than a specified voltage; And an overcurrent protection circuit that suppresses the switching output.   Including a capacitor connected in series with the primary winding of the converter transformer, and the switching circuit of the switching element causes current resonance in the series circuit of the primary winding of the converter transformer and the capacitor. The switching power supply device according to claim 1, wherein: The overcurrent protection circuit compares the output voltage of the frequency / voltage converter with a first reference voltage, and when the output voltage of the frequency / voltage converter becomes equal to or higher than the first reference voltage, A first comparator for generating one comparison output;
A time constant circuit for integrating the first comparison output;
A second comparison that compares the output voltage of the time constant circuit with a second reference voltage and generates a second comparison output when the output voltage of the time constant circuit becomes equal to or higher than the second reference voltage. A container,
The switching power supply device according to claim 1, wherein the control unit is controlled by the second comparison output to suppress the switching output.   2. The switching power supply device according to claim 1, wherein the load circuit is driven by a DC voltage obtained by rectifying the AC voltage excited by the secondary winding. Input the DC voltage from the DC power supply to the switching element,
The switching control of the switching element by the control unit,
A switching output from the switching element is supplied to a primary winding of the converter transformer, and an alternating voltage is excited in the secondary winding of the converter transformer by the switching output;
Supplying the AC voltage excited by the secondary winding to a load circuit;
The frequency of the AC voltage excited in the secondary winding is converted into a voltage by a frequency / voltage converter, and the control unit is controlled when the output voltage of the frequency / voltage converter exceeds a specified voltage. The switching output is suppressed to protect the load circuit from overcurrent.

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