JP2011151936A - Power conversion circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power conversion circuit that can prevent an on-pulse width from excessively being expanded with respect to an input voltage which is abruptly changed when the input voltage of a power conversion circuit is abruptly changed, and thereby can prevent the saturation of a transformer and an excessive rise of an output voltage. <P>SOLUTION: The power conversion circuit includes a capacitor which charges an electric charge corresponding to a voltage at the secondary side of the transformer, a second switch element which short-circuits the capacitor, a comparator which detects that both-end voltages of the capacitor have become higher than a prescribed reference voltage, a pulse-width control means which limits the pulse width of an on-pulse by turning off a first switch element when both-end voltages of the capacitor become higher than the prescribed reference voltage, and a control circuit which turns on the second switch element while the first switch element is turned off by turning off the first switch element when the comparator detects that both-end voltages of the capacitor have become higher than the prescribed reference voltage. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power conversion circuit.

  In the power conversion circuit, the peak value of the rectangular wave on the secondary side of the transformer is proportional to the value of the input voltage, the peak value of the rectangular wave on the secondary side of the transformer is detected, and the detected rectangular waveform is processed. It is known that a DC voltage proportional to the input voltage of the power conversion circuit is obtained by holding the peak value of the processed waveform with a capacitor (see, for example, Patent Documents 1 and 2).

JP 2005-245097 A JP 2003-033015 A

  However, in the above-described conventional example, a square wave on the secondary side of the transformer is detected, the waveform is processed, and the peak value is held in a capacitor to obtain a DC voltage proportional to the input voltage. Because it is used for on-pulse width limitation, when the input voltage of the power converter circuit changes suddenly, the voltage across the capacitor cannot follow this changed input voltage, and it is too wide for the input voltage. There is a problem that the on-pulse width is reached and the output voltage of the power conversion circuit becomes excessively high.

  In other words, in the conventional circuit, a rapid change in the input voltage cannot be handled unless the voltage across the capacitor is increased in a short time in response to the change in the input voltage. In order to increase the capacitor voltage in a short time, it is conceivable to reduce the time constant of the resistor and capacitor. However, if the time constant is reduced, the capacitor is charged by a surge voltage or noise, and a voltage value far from the voltage value to be detected is detected. For this reason, the time constant cannot be reduced. Further, in the above conventional circuit, since a current flows through the discharging resistor during charging, the resistance value of the discharging resistor must be increased. Therefore, when the input voltage suddenly decreases, the voltage across the capacitor does not decrease immediately, and the detected voltage becomes a value far from the actual input voltage. Therefore, when the input voltage suddenly decreases, there is a problem that the pulse width is excessively narrowed by the maximum pulse width limitation, and the output voltage is lowered.

  The present invention includes a first switch element that turns on and off an input voltage that is a voltage of a DC voltage source, a transformer that converts an AC voltage generated by turning on and off the first switch element, In a power conversion circuit comprising a drive circuit that drives the first switch element and a rectifier that rectifies the AC voltage generated on the secondary side of the transformer, if the input voltage suddenly increases, surge voltage or noise It is an object of the present invention to provide a power conversion circuit that is capable of appropriately limiting the maximum pulse width even when the input voltage suddenly decreases.

  The present invention includes a DC voltage source, a first switch element that turns on and off the voltage of the DC voltage source, and a transformer that converts an AC voltage generated by turning on and off the first switch element. A power conversion circuit comprising: a drive circuit that drives the first switch element; and a rectifier that rectifies an AC voltage generated on the secondary side of the transformer, and a charge corresponding to the voltage on the secondary side of the transformer A capacitor that charges the capacitor, a second switch element that short-circuits the capacitor, a comparator that detects that the voltage across the capacitor is higher than a predetermined reference voltage, and the voltage across the capacitor is equal to the predetermined voltage When the comparator detects that the voltage is higher than the reference voltage, the first switch element is turned off, and during the period in which the first switch element is turned off, A power conversion circuit and a control circuit for turning on the second switching element.

  According to the present invention, a first switch element that turns on and off an input voltage, which is a voltage of a DC voltage source, and a transformer that converts an AC voltage generated by turning on and off the first switch element. In a power conversion circuit comprising a drive circuit for driving the first switch element and a rectifier for rectifying an AC voltage generated on the secondary side of the transformer, if the input voltage suddenly increases, a surge voltage The maximum pulse width can be appropriately limited even when the input voltage suddenly decreases, thereby preventing transformer saturation and excessive increase of the output voltage. There is an effect that can be.

1 is a circuit diagram illustrating a power conversion circuit 100 that is Embodiment 1 of the present invention. FIG. 3 is a timing chart showing the operation of the first embodiment. It is a circuit diagram which shows the power converter circuit 200 which is Example 2 of this invention. 3 is a timing chart showing the operation of the power conversion circuit 200. It is a circuit diagram which shows the power converter circuit 300 which is Example 3 of this invention. 3 is a timing chart showing the operation of the power conversion circuit 300.

  The modes for carrying out the invention are the following examples. In addition, this invention is not limited to the Example shown below.

  FIG. 1 is a circuit diagram showing a power conversion circuit 100 that is Embodiment 1 of the present invention.

  The power conversion circuit 100 is a power conversion circuit that converts power from the DC voltage source 10 and transmits it to the load 20. The power conversion circuit 100 includes a first switch element SW1, a transformer T1, a rectifier diode D1, a smoothing capacitor C1, a freewheeling diode D2, a resistor R1, a capacitor C2, and a second switch element SW2. , A reference voltage source 30, a comparator 40, a control circuit 50, and a drive circuit 60.

  The first switch element SW1 turns on and off the voltage of the DC voltage source 10. The transformer T1 converts the alternating voltage generated by the on / off control of the first switch element SW1 into a voltage obtained by stepping up or down. The rectifier diode D1 is an example of a rectifier and rectifies an AC voltage generated on the secondary side of the transformer T1. The capacitor C1 is a smoothing capacitor.

  The capacitor C2 charges a charge corresponding to the voltage on the secondary side of the transformer T1. The second switch element SW2 is an element that short-circuits the capacitor C2, and discharges the electric charge of the capacitor C2 for each on-pulse that is a pulse for turning on the first switch element SW1.

  The reference voltage source 30 generates a reference voltage Vref. The comparator 40 is an example of a comparison circuit, and detects that the voltage across the capacitor C2 has become higher than a predetermined reference voltage.

  The drive circuit 60 is an insulating drive circuit insulated from the ground potential such as the secondary side of the transformer T1, the control circuit 50, and outputs a drive signal for turning on and off the first switch element SW1.

  The control circuit 50 outputs a control signal Vg for ON / OFF control of the first switch element SW1 to the drive circuit 60. The control signal Vg is also a signal for turning on and off the second switch element SW2.

  First, when the control signal Vg is turned on, the drive circuit 60 turns on the first switch element SW1, and maintains the first switch element SW1 in the on state while the control signal Vg is on. During the period when the control signal Vg is on, the second switch element SW2 is controlled to be off.

  Next, when the control signal Vg is turned off, the drive circuit 60 turns off the first switch element SW1 and turns on the second switch element SW2. That is, the control circuit 50 turns on the second switch element SW2 during a period in which the first switch element SW1 is turned off in one cycle in which the first switch element SW1 is turned on and off.

  Here, the second switch element SW2 is turned on during the period in which the first switch element SW1 is turned off, the electric charge charged in the capacitor C2, which will be described later, is discharged. It is only necessary to turn off the element SW2, and it is not always necessary to turn on the second switch element SW2 simultaneously with the timing at which the first switch element SW1 is turned off. In the first embodiment, the common control signal Vg is used as a signal for controlling the first switch element SW1 and the second switch element SW2, and the second switch element is turned on simultaneously with turning off the first switch element SW1. To do. Thus, the circuit configuration can be simplified by making the control signal Vg common.

  The pulse width of the first switch element SW1 is controlled by the voltage detection circuit configured by the resistor R1 and the capacitor C2, the comparator 40, the reference voltage source 30, the control circuit 50, and the drive circuit 60. When the comparator 40 detects that the voltage across the capacitor C2 has become higher than the predetermined reference voltage, the control circuit 50 and the drive circuit 60 turn off the first switch element SW1, thereby the first The pulse width when the switch element SW1 is turned on is controlled.

  Next, the operation of the first embodiment will be described.

  FIG. 2 is a timing chart illustrating the operation of the first embodiment. The “operation when the input voltage is low” shown in FIG. 2A and the “operation when the input voltage is high” shown in FIG. 2B are low in the input voltage range in which the power conversion circuit 100 can operate. Operation in the case, operation in the case of high.

  In the power conversion circuit 100, the DC voltage output from the DC voltage source 10 turns on and off the first switch element SW1, whereby an AC voltage is generated on the primary side of the transformer T1, and this AC voltage is converted by the transformer T1. The converted voltage is rectified by the rectifier diode D1 and smoothed by the capacitor C1, and the smoothed DC voltage is supplied to the load 20.

  Here, when the first switch element SW1 is turned on, a voltage Vdf proportional to the voltage of the DC voltage source 10 is applied to the freewheeling diode D2. Further, when the first switch element SW1 is turned on, the second switch element SW2 is turned off, and the voltage Vdf of the freewheeling diode D2 is applied to the voltage detection circuit constituted by the resistor R1 and the capacitor C2. The capacitor C2 is charged through the resistor R1.

  By appropriately setting the constants of the resistor R1 and the capacitor C2, the voltage V + of the capacitor C2 increases in a slope shape as shown in FIG.

  As shown in FIG. 2 (1), when the input voltage is low, the voltage Vdf of the freewheeling diode D2 is low, the slope of the voltage V + of the capacitor C2 rises with a gentle slope, and the voltage V + of the capacitor C2 becomes The first switch element SW1 continues to be turned on until a reference voltage Vref set by the reference voltage source 30 is reached, and a predetermined voltage is supplied to the load.

  When the voltage V + of the capacitor C2 reaches the reference voltage Vref set by the reference voltage source 30, the comparator 40 sends a signal Vout to the control circuit 50. When receiving the signal Vout, the control circuit 50 immediately inverts the control signal Vg for driving the first switch element SW1, and the first switch element SW1 is turned off. At the same time, the second switch element SW2 is turned on, and the charge charged in the capacitor C2 is discharged.

  Since the voltage Vdf of the freewheeling diode D2 is proportional to the voltage of the DC voltage source 10, the higher the voltage value of the DC voltage source 10, the higher the ON time of the first switch element SW1 is shown in FIG. To be shorter.

  The series of circuit operations described above is performed for each cycle of the power conversion circuit 100, and during the period in which the first switch element SW1 is turned off in one cycle in which the first switch element SW1 is turned on and off, 2 switch element SW2 is turned on and reset. Therefore, even when the voltage value of the DC voltage source 10 changes suddenly, the ON time of the first switch element SW1 is limited by the time corresponding to the voltage value of the DC voltage source 10, that is, the first switch element. The ON time of SW1 can be limited in a short time. That is, the pulse width of the on pulse can be limited.

  FIG. 3 is a circuit diagram showing a power conversion circuit 200 that is Embodiment 2 of the present invention.

  The power conversion circuit 200 is a power conversion circuit that converts the power from the DC voltage source 10 and transmits it to the load 20.

  The power conversion circuit 200 makes the voltage detection point on the secondary side of the transformer T1 different from that of the power conversion circuit 100 and detects the voltage on the secondary side of the transformer T1, that is, the secondary winding voltage Vn2 of the transformer T1. It is a circuit to detect.

  Since the secondary winding voltage Vn2 of the transformer T1 is a positive or negative voltage, a diode D3 is added to the power conversion circuit 100, and a negative voltage is applied to the series circuit (secondary voltage detection circuit) of the resistor R1 and the capacitor C2. To prevent it.

  FIG. 4 is a timing chart showing the operation of the power conversion circuit 200.

  FIG. 4 shows a voltage Va instead of the voltage Vdf in FIG.

  Other basic operations in the power conversion circuit 200 are the same as the operations in the power conversion circuit 100.

  FIG. 5 is a circuit diagram showing a power conversion circuit 300 that is Embodiment 3 of the present invention.

  The power conversion circuit 300 includes switch elements SW11, SW12, SW13, and SW14 instead of the first switch element SW1 in the power conversion circuit 100, a drive circuit 61 instead of the drive circuit 60, and a transformer T1. Instead, a transformer T2 is provided, and rectifier diodes D11 and D12 are provided instead of the rectifier diode D1. That is, the power conversion circuit 300 is an embodiment using a full bridge circuit.

  FIG. 6 is a timing chart showing the operation of the power conversion circuit 300.

  In FIG. 6, the voltage Vb is shown instead of the voltage Vdf in FIG.

  Other basic operations in the power conversion circuit 300 are the same as the operations in the power conversion circuit 100.

  According to the above embodiment, when the input voltage suddenly increases, the slope of the slope becomes steep, but since the voltage across the capacitor does not rise suddenly, it is hardly affected by surge voltage or noise.

  Further, according to the above embodiment, the capacitor voltage is reset for each cycle by the capacitor discharge switch, so that the maximum pulse width can be appropriately limited even when the input voltage suddenly decreases.

  According to the above embodiment, the maximum pulse width restriction corresponding to the input voltage that can cope with a sudden change in the input voltage can be applied, so that saturation of the transformer can be prevented and excessive increase of the output voltage can be prevented. .

  Furthermore, according to the above embodiment, since the slope voltage having a slope corresponding to the input voltage is used, the time constants of the resistor and the capacitor can be set larger.

100: power conversion circuit,
10: DC voltage source,
T1, trance,
D1: Rectifier diode,
C2: Capacitor,
SW1 is the first switch element,
SW2 ... second switch element,
30: Reference voltage source,
40 ... comparator,
50. Control circuit,
60: Drive circuit.

Claims (6)

A DC voltage source, a first switch element that turns on and off the voltage of the DC voltage source, a transformer that converts an AC voltage generated by turning on and off the first switch element, and the first A power conversion circuit comprising: a drive circuit that drives the switch element; and a rectifier that rectifies an AC voltage generated on the secondary side of the transformer.
A capacitor for charging a charge corresponding to the voltage on the secondary side of the transformer;
A second switch element for short-circuiting the capacitor;
A comparator for detecting that the voltage across the capacitor is higher than a predetermined reference voltage;
When the comparator detects that the voltage across the capacitor has become higher than the predetermined reference voltage, the first switch element is turned off, and the first switch element is turned off during the period in which the first switch element is turned off. A control circuit for turning on the second switch element;
A power conversion circuit comprising: In claim 1,
The control circuit applies a signal for turning on the second switch element to the second switch element at the same time as turning off the first switch element, and short-circuits the capacitor, whereby the first switch element is turned on. A power conversion circuit, characterized by being a circuit that discharges the electric charge charged in the capacitor until the element is next turned on. In claim 1,
A resistor connected in series with the capacitor and detecting a voltage on the secondary side of the transformer;
The comparator compares the voltage across the capacitor, which changes according to the slope determined by the time constant between the capacitor and the resistor, with the predetermined reference voltage, and the voltage across the capacitor reaches the predetermined reference voltage. And a signal for inverting the first switch element is sent to the control circuit to control a pulse width when the first switch element is turned on. In claim 1,
The power conversion circuit according to claim 1, wherein the capacitor is a capacitor that charges a charge corresponding to the voltage rectified by the rectifier. In claim 1,
The power conversion circuit, wherein the capacitor is a capacitor that charges a charge corresponding to a voltage rectified by a second rectifier different from the rectifier, on a secondary side voltage of the transformer. In claim 1,
The rectifier is composed of a rectifier diode and a freewheeling diode,
The anode of the rectifier diode is connected to one end of the secondary side of the transformer, the cathode of the rectifier diode and the cathode of the freewheeling diode are connected to each other, and the anode of the freewheeling diode is the other end of the secondary side of the transformer Connected to
The power conversion circuit, wherein the capacitor is a capacitor that charges a charge corresponding to a voltage proportional to a voltage of the DC voltage source applied to the freewheeling diode.

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