JP4260931B2 - Power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply device such as a flyback converter circuit.
[0002]
[Prior art]
An example of a flyback converter circuit used in a conventional information processing apparatus or the like is shown in FIG. 5, and an example of operation waveforms of the flyback circuit shown in FIG. 5 is shown in FIG.
[0003]
The flyback converter circuit shown in FIG. 5 switches a DC voltage from a power source E (input voltage Vin) at a predetermined timing by a switching element Q11 using a MOSFET to a primary winding N1 (number of turns np) of a transformer T. The pulsed voltage induced in the secondary winding N2 (number of turns ns) of the transformer T is rectified by the rectifier diode Do, smoothed by the smoothing capacitor CO, and supplied to the load R as the output voltage V0. It has become.
[0004]
The output voltage V0 is fed back to the control circuit, and the control circuit 10 controls the gate signal (gate voltage) Q11G supplied to the gate of the switching element Q11 according to the level of the output voltage V0. The output voltage V0 is stabilized by changing the switching timing of the switching element Q11. In FIG. 5, C11 is a parallel capacitor connected between the drain and source of the switching element Q11.
[0005]
FIG. 6 shows waveforms of the gate signal Q11G, the drain current IQ11D of the switching element Q11, and the drain-source voltage VQ11DS of the switching element Q11 in this flyback converter circuit.
[0006]
In the case of this flyback converter circuit, the waveform of the drain-source voltage VQ11DS of the switching element Q11 is as shown in the bottom column of FIG. That is, the sum of the input voltage Vin from the power source E, the primary conversion voltage (np / ns) * Vo induced in the secondary winding N2 of the transformer T, and the spike voltage Vs (Vin + (np / ns ) * Vo + Vs) is the maximum value of the drain-source voltage VQ11DS of the switching element Q11.
[0007]
Accordingly, the switching element Q11 is required to have a breakdown voltage equal to or higher than the value of (Vin + (np / ns) * Vo + Vs) as a characteristic of the drain-source voltage VQ11DS.
[0008]
Next, another example of the flyback converter circuit is shown in FIG. 7, and an example of operation waveforms of the flyback converter circuit shown in FIG. 7 is shown in FIG.
[0009]
The flyback converter circuit shown in FIG. 7 is basically the same as the flyback converter circuit shown in FIG. 5 except that the switching element Q12 is connected in series with the primary winding np of the transformer T in addition to the switching element Q11. In addition, a clamp diode D11 is connected in series with the switching element Q11, a clamp diode D12 is connected in series with the switching element Q12, and an auxiliary control circuit 11 for controlling the gate of the switching element Q12 is added. is there.
[0010]
FIG. 8 shows waveforms of the gate signals Q11G and Q12G, the drain current IQ11D of the switching element Q11, and the drain-source voltages VQ11DS and VQ12DS of the switching elements Q11 and Q12 in this flyback converter circuit.
[0011]
In this flyback converter circuit, the drain-source voltages VQ11DS and VQ12DS of the switching elements Q11 and Q12 are clamped by the clamp diodes D11 and D12, respectively. Therefore, the withstand voltage of the switching elements Q11 and Q12 is the input voltage from the power supply E. A value about Vin is sufficient, and a flyback converter circuit can be configured using two switching elements having a lower withstand voltage than the circuit shown in FIG.
[0012]
However, in this case, it is necessary to set the winding ratio (np / ns) of the transformer T so that Vin> (np / ns) * Vo. If the primary conversion voltage (np / ns) * Vo is larger than the input voltage Vin, power is transferred from the secondary side of the transformer T to the primary side before the predetermined output voltage Vo is established, and flyback is performed. This is because the normal operation as a converter circuit is hindered.
[0013]
[Problems to be solved by the invention]
However, in the conventional flyback converter circuit described above, it is necessary to employ a switching element having a high breakdown voltage or a switching element having a low breakdown voltage can be used. / Ns), there is a problem that there are restrictions on the setting.
[0014]
Accordingly, an object of the present invention is to provide a power supply device that can use a switching element having a low withstand voltage and that is not particularly restricted with respect to a transformer.
[0020]
[Means for Solving the Problems]
According to the first aspect of the present invention, the DC input voltage applied to the primary winding of the transformer is switched by the on / off switching operation of two switching elements connected in series to the primary winding of the transformer, In a power supply device that obtains a predetermined DC output voltage by a rectifying and smoothing circuit connected to the secondary winding side, one of the element voltages applied to both switching elements when the two switching elements are turned off. A clamp circuit that connects and clamps a diode to the one switching element so that the applied element voltage becomes a DC input voltage, and the turn-off timing of one switching element that is clamped by the clamp circuit , turn-of the other switching element in which the diode is not connected Delaying the timing a predetermined time, is characterized in that it has a, and element voltage sharing control circuit for sharing the other switching element the device voltage of the remaining of the device voltage applied to the both switching elements.
[0021]
According to the present invention, when the DC input voltage is switched and supplied to the primary winding of the transformer by the on / off switching operation of the two switching elements, the element voltage sharing control circuit controls the side clamped by the clamp circuit. than the timing of turn-off of one switching element is intended to delay the timing of the turn-off of the other switching element for a predetermined time.
[0022]
Thus, as early as one of the switching elements that turn-off is applied element voltage corresponding to the DC input voltage is clamped by the clamp circuit, also remaining element voltage during turn-off is the other to turn-off delay of a predetermined time As a result, it is possible to use a switching element having a low withstand voltage as the two switching elements, and there is no particular restriction on the turns ratio of the transformer, so that a power supply of an arbitrary DC input voltage can be used. Can be used.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0024]
(Embodiment 1)
FIG. 1 shows a flyback converter circuit which is a power supply device according to the first embodiment of the present invention, and FIG. 2 shows signal waveforms of respective parts of the flyback converter circuit according to the first embodiment of the present invention. It is.
[0025]
The flyback converter circuit shown in FIG. 1 switches a DC input voltage Vin from a power source E by two switching elements Q1 and Q2 using MOSFETs at predetermined timings, respectively, so that a primary winding N1 (number of turns) np), the pulsed voltage induced in the secondary winding N2 (number of turns ns) of the transformer T is rectified by the rectifier diode Do, further smoothed by the smoothing capacitor CO, and output to the load R as the output voltage V0. It comes to supply.
[0026]
The output voltage V0 is fed back to the control circuit 1, and the control circuit 1 controls a gate signal (gate voltage) Q1G supplied to the gate of the switching element Q1 according to the level of the output voltage V0. The auxiliary control circuit 2 connected to the control circuit 1 controls the gate signal (gate voltage) Q2G supplied to the gate of the switching element Q2, thereby changing the switching timing of the switching elements Q1 and Q2 to change the output voltage. V0 is stabilized.
[0027]
The flyback converter circuit also includes an element voltage sharing control circuit comprising a clamp diode DC connected in series with the switching element Q1, a parallel capacitor Cl connected in parallel with the clamp diode DC, and a parallel capacitor Ch connected in parallel with the switching element Q2. is doing.
[0028]
The clamp diode DC has an anode connected to the drain of the switching element Q1 and a cathode connected to the anode side of the power source E.
[0029]
FIG. 2 shows waveforms of the gate signals Q1G of the switching elements Q1 and Q2, the drain current IQ11D of the Q2G switching element Q1, and the drain-source voltages VQ11DS and VQ12DS of the switching elements Q11 and Q2G in this flyback converter circuit.
[0030]
Next, the operation of the flyback converter circuit of the first embodiment will be described.
[0031]
When the operation of the flyback converter circuit is started, the switching elements Q1 and Q2 are turned on and off almost simultaneously as shown in FIG.
[0032]
When the switching elements Q1 and Q2 are turned on, an exciting current Ip flows through the primary winding N1 of the transformer T, and magnetic energy is accumulated. The secondary side of the transformer T is blocked by the diode D0 and does not flow.
[0033]
When the switching elements Q1 and Q2 are turned off, the excitation current Ip flows through the primary winding np while the induced voltage of the secondary winding ns is equal to or less than V0, and the parallel capacitors Cl and Ch connected to the switching elements Q1 and Q2. Keep charging.
[0034]
When the parallel capacitors Cl and Ch are sufficiently charged and the voltage of the primary winding np becomes Vin + (np / ns) * Vo, the magnetic energy of the transformer T is released to the output side via the rectifier diode D0.
[0035]
Here, the drain-source voltage VQ11DS of one switching element Q1 is clamped to the DC input voltage Vin by the clamp diode DC.
[0036]
Further, the remaining voltage (np / ns) * Vin + Vs generated in the primary winding np is applied between the drain and source of the other switching element Q2. Here, Vs is a spike voltage.
[0037]
However, the voltages applied to the switching elements Q1 and Q2 are not unconditionally Vin and (np / ns) * Vo + Vs. For example, the case where the parallel capacitance Cl is very large and the parallel capacitance Ch is small. Assuming that the drain-source voltage VQ11DS of the switching element Q1 does not increase even when the switching elements Q1 and Q2 are turned off, the voltage Vin + (np / ns) * Vo + Vs generated between the primary windings np is all switching elements. It will be applied to Q2.
[0038]
For example, even when the turn-off timing of the switching element Q1 is greatly delayed from the turn-off timing of the switching element Q2, the voltage generated in the primary winding np without increasing the voltage of the switching element Q1 as in the case described above. Vin + (np / ns) * V0 + Vs is all applied to the switching element Q2.
[0039]
Therefore, in the first embodiment, the capacitance value of the parallel capacitor Cl on the switching element Q1 side clamped so that the drain-source voltage VQ11DS becomes the DC input voltage Vin by the clamp diode Dc is set to the other switching element Q2 side. parallel sufficiently smaller than the capacitance of the capacitor Ch (capacitance value of the parallel capacitor capacitance values of Cl <parallel capacitance Ch), i.e., the rise of the voltage at the turn-off of the switching element Q1 during turn-off of the switching element Q2 and earlier than the rise of the voltage, and, as the switching elements Q1, Q2 are turned off at approximately the same time, peak drain-source voltage VQ12DS of the switching element Q2 after the drain-source voltage VQ11DS of the switching element Q1 is clamped to Vin It is intended to be
[0040]
As a result, it is possible to reduce the withstand voltage of the switching elements Q1 and Q2 with a configuration using one diode Dc, a parallel capacitor Cl, and a parallel capacitor Ch, and the conventional example with respect to the turn ratio of the transformer T. Thus, the power source E having an arbitrary DC input voltage VIN can be used.
[0041]
(Embodiment 2)
Next, Embodiment 2 will be described with reference to FIGS.
[0042]
FIG. 3 shows a flyback converter circuit which is a power supply device according to the second embodiment of the present invention, and FIG. 4 shows waveforms of respective parts of the flyback converter circuit according to the second embodiment of the present invention. is there. In the flyback converter circuit according to the second embodiment shown in FIG. 3, the same reference numerals are given to the components having the same functions as those of the flyback converter circuit according to the first embodiment shown in FIG. To do.
[0043]
The flyback converter circuit according to the second embodiment shown in FIG. 3 has substantially the same configuration as that of the flyback converter circuit according to the first embodiment described above, but a parallel capacitor having the same capacitance value in parallel with the switching elements Q1 and Q2. C is connected, and a delay circuit 3 that gives a predetermined delay time td to the driving signal Q1G of the switching element Q2 is added to the auxiliary control circuit 2, and the auxiliary control circuit 2 is configured as an element voltage sharing control circuit. Is a feature.
[0044]
As shown in FIG. 3, the delay circuit 3 is constituted by a series connection of a CR time constant circuit composed of a capacitor Cd and a resistor Rd and a buffer 4.
[0045]
FIG. 4 shows waveforms of the gate signals Q1G and Q2G of the switching elements Q1 and Q2 of the flyback converter circuit of the second embodiment, the drain current IQ11D of the switching element Q1, and the drain-source voltages VQ11DS and VQ12DS of the switching elements Q11 and Q2G. Show.
[0046]
In the flyback converter circuit of the second embodiment, the capacitance value of the parallel capacitor C on the switching element Q1 side clamped so that the drain-source voltage VQ11DS becomes the DC input voltage Vin using the clamp diode Dc, and the other Timing for equalizing the capacitance value of the parallel capacitor C on the switching element Q2 side and delaying the gate signal Q2G for the gate signals Q1G and Q2G of the switching elements Q1 and Q2 by a delay time Td from the gate signal Q1G by the delay circuit 3 Thus, the switching elements Q1 and Q2 are driven.
[0047]
That is, the rise of voltage during turn-off of the switching elements Q1 and earlier than the rise of the voltage at the turn-off of the switching element Q2, as shown in FIG. 4, the drain-source voltage VQ11DS of the switching element Q1 is Vin After clamping, the drain-source voltage VQ12DS of the switching element Q2 becomes a peak.
[0048]
This makes it possible to reduce the withstand voltage of the switching elements Q1 and Q2 with a configuration using one clamp diode Dc and adding the delay circuit 3, and also with regard to the turns ratio of the transformer T. The power supply E having an arbitrary DC input voltage VIN can be used without any particular restriction as in the example.
[0049]
【The invention's effect】
According to the first aspect of the present invention, a switching element having a low withstand voltage can be used as the two switching elements, and there is no particular limitation on the turns ratio of the transformer, and a power supply having an arbitrary DC input voltage is used. It is possible to provide a power supply device that can be used.
[0050]
According to the second aspect of the present invention, a switching element having a low withstand voltage can be used as the two switching elements in the configuration using two parallel capacitors, and there is no particular restriction on the turns ratio of the transformer. Therefore, it is possible to provide a power supply apparatus that can use a power supply of an arbitrary DC input voltage.
[0051]
According to the third aspect of the present invention, a configuration using an element voltage sharing control circuit for delaying the timing a predetermined time of turn-off of the other switching elements than the timing of turn-off of one switching element, two switching elements Thus, a switching device having a low withstand voltage can be used, and there is no particular restriction on the turns ratio of the transformer, and a power supply apparatus that can use a power supply of an arbitrary DC input voltage can be provided.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a flyback converter circuit which is a power supply device according to a first embodiment of the present invention.
2 is a signal waveform diagram showing signal waveforms at various parts of the flyback converter circuit shown in FIG. 1;
FIG. 3 is a circuit diagram showing a flyback converter circuit which is a power supply device according to a second embodiment of the present invention.
4 is a signal waveform diagram showing signal waveforms at various parts of the flyback converter circuit shown in FIG. 3;
FIG. 5 is a circuit diagram showing an example of a conventional flyback converter circuit.
6 is a signal waveform diagram showing a signal waveform of each part of the flyback converter circuit shown in FIG. 5;
FIG. 7 is a circuit diagram showing another example of a conventional flyback converter circuit.
8 is a signal waveform diagram showing signal waveforms at various parts of the flyback converter circuit shown in FIG. 7;
[Explanation of symbols]
1 Control circuit 2 Auxiliary control circuit 3 Delay circuit 4 Buffer C Parallel capacitor Ch Parallel capacitor Cl Parallel capacitor Dc Clamp diode Do Rectifier diode E Power source Q1 Switching element Q2 Switching element R Load T Transformer

Claims (1)

The DC input voltage applied to the primary winding of the transformer is switched by the on / off switching operation of two switching elements connected in series to the primary winding of the transformer, and connected to the secondary winding side of the transformer. In a power supply device that obtains a predetermined DC output voltage by a rectifying and smoothing circuit,
A diode is connected to the one switching element so that the element voltage applied to one of the two switching elements at the time of turn-off of the two switching elements becomes a DC input voltage. Clamping circuit to clamp,
The turn-off timing of the other switching element not connected to the diode is delayed by a predetermined time from the turn-off timing of one switching element on the side clamped by the clamp circuit, and the element voltage applied to both switching elements is An element voltage sharing control circuit for sharing the remaining element voltage to the other switching element;
A power supply device comprising:

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