JP4858192B2 - DC power supply - Google Patents

Description

  The present invention relates to a DC power supply device including a plurality of flyback DC / DC converters whose input side is connected in series and whose output side is connected in parallel, and in particular, the voltage imbalance of a plurality of capacitors that divide the DC power supply voltage. It relates to the technology to prevent.

FIG. 7 shows the prior art of this type of DC power supply.
In the figure, 100 is a DC power source, 11, 12, 13 are capacitors connected in series between the positive and negative electrodes of the DC power source 100, 31, 32, and 33 are one ends of primary windings of the capacitors 11, 12, 13 respectively. Transformers 21, 22, 23 connected to one end are semiconductor switching elements 41, 42, 43, 61 connected between the other end of the primary winding and the other ends of the capacitors 11, 12, 13. 62, 63 are diodes, 51, 52, 53 are capacitors, 71, 72, 73 are gate circuits provided corresponding to the switching elements 21, 22, 23, 80 is a control circuit, and 141, 142, 143 is control. Photocouplers 131 and 132, which are driven by the circuit 80 and insulate the control signals to the gate circuits 71, 72 and 73 and send them out, are connected between the DC output terminals P and N. Detecting resistor, 90 photocoupler, 111 for forward current limiting resistor 121 is a switching regulator, 200 denotes a gate power supply for supplying power to the gate circuit 71, 72, 73.

  Here, the capacitor 11, the transformer 31, the switching element 21 and the like constitute a first-stage flyback DC / DC converter. Combined with the DC converter, a DC power supply device is configured which is composed of a three-stage flyback DC / DC converter in which the input side is connected in series and the output side is connected in parallel.

In this prior art, a voltage regulator is constituted by the voltage detection resistors 131 and 132, the forward current limiting resistor 111, the switching regulator 121, and the photocoupler 90. The voltage regulator is a reference voltage (inside the switching regulator 121). The output voltage target value) is compared with the output voltage detection value obtained by dividing the resistors 131 and 132, and the voltage is adjusted by the switching regulator 121 outputting a voltage corresponding to the deviation. The output (pulse width command value) of the voltage regulator is input to the control circuit 80 via the photocoupler 90. In the control circuit 80, the switching signals having the same width are insulated by the photocouplers 141, 142, and 143, and each gate circuit 71 is isolated. , 72, 73.
Then, by igniting the switching elements 21, 22, and 23 by the ignition signals from the gate circuits 71, 72, and 73, respectively, the electric power generated in the secondary windings of the transformers 31, 32, and 33 is added. Output is performed between the DC output terminals P and N, and control is performed so that the detected output voltage value matches the target value.

Here, the output side of the switching elements 21, 22, 23 of each stage is connected to the DC power supply voltage _{V in} the potential point divided by capacitors 11, 12 and 13, the capacitance of the capacitor 11, 12, 13 Since the reference potential of the upper gate circuit 71 is 2/3 V _in , the reference potential of the middle gate circuit 72 is 1/3 V _in , and the reference potential of the lower gate circuit 73 is 0 V, the control circuit In 80, the control signals and gate voltages sent to the gate circuits 71, 72, 73 are individually insulated using photocouplers and transformers.

In general, a flyback DC / DC converter has a feature that the number of parts is smaller than that of other DC / DC converters. However, if the DC power supply voltage is applied as it is to the series circuit of the transformer primary winding and the switching element with the DC / DC converter having a single stage configuration, if the DC power supply voltage is high, a high voltage switching element must be used. Don't be.
As for the transformer, when the input voltage is increased, the VT product is increased, and a core having a large cross-sectional area must be used in order to prevent magnetic saturation, and the transformer cannot be reduced in size.

In addition, the following numerical formula has shown the relationship of the voltage applied to the switching element in a flyback type DC / DC converter of 1 step | paragraph structure, a DC input / output voltage, etc.
_{V d = V in + n 1} / n 2 × V o × V l
V _d : voltage applied to the switching element,
V _in : DC input voltage (DC power supply voltage),
V _o : DC output voltage,
V _l : Bounce voltage due to transformer leakage inductance,
n ₁ : number of primary turns of the transformer,
n ₂ : Number of secondary turns of transformer

In order to solve the above problem, according to the DC power supply device comprising a plurality of stages of flyback DC / DC converters as shown in FIG. 7, a plurality of capacitors 11, 12, 13 connected in series with the DC power supply voltage. The divided voltages of the capacitors 11, 12, and 13 are applied to the switching elements 21, 22, and 23 through the primary windings of the transformers 31, 32, and 33, respectively.
For this reason, it is possible to reduce the withstand voltage of the switching element, and it is possible to reduce the size and cost of the entire device as well as downsizing due to a decrease in the transformer input voltage.
A DC power supply device having a main circuit similar to that shown in FIG. 7 is described in, for example, Patent Documents 1 and 2.

JP-A-62-210861 (page 4, lower right column, line 1 to page 5, lower right column, first line, FIG. 1, etc.) JP-A-62-81978 (page 3, lower right column, line 6 to page 4, upper right column, line 3, line 1, etc.)

In the DC power supply device shown in FIG. 7 and the like, since the voltages of a plurality of capacitors connected in series are inversely proportional to the conduction ratio of each switching element, each switching element has an inconvenience of being unbalanced unless it is switched with the same pulse width. is there. Further, in the method of individually controlling the DC / DC converters in each stage, if an imbalance occurs, pulse correction for eliminating the imbalance must be performed, which is the reverse of the voltage adjustment operation. . That is, if the voltage adjustment operation is simply performed, the pulse width is widened when the input voltage is lowered, and therefore, positive feedback is performed in a loop in which the input voltage is lowered. On the contrary, when the input voltage rises, the pulse width is narrowed down, so that the input voltage is positively fed back in a loop where the input voltage further rises. Furthermore, when the input voltage of the multi-stage DC / DC converter becomes unbalanced, the voltage duty of the switching element of the converter connected to the capacitor having a high voltage becomes severe, so that it is necessary to use a high withstand voltage element, It causes high cost.
In order to solve this, in the prior art according to Patent Document 1, a target voltage value to be shared by each stage capacitor is obtained from a DC power supply voltage, and the actual voltage value of each capacitor is detected to deviate from the target voltage value. A correction signal is created such that the zero becomes zero, and the correction signal is added to the automatic voltage adjustment signal obtained from the deviation between the output voltage setting value and the output voltage detection value to control the conduction rate of the switching element. Yes.
For this reason, a voltage detector for detecting the voltage of the capacitor at each stage is required, and the control circuit of the switching element may be complicated.

Furthermore, in the prior art according to Patent Document 2, in order to reduce current imbalance due to operation delay of each switching element, current flowing in a common input circuit of a plurality of stages of DC-DC converters is detected. The on-pulse width of the switching element is corrected according to the detected value.
Therefore, in this prior art, an input current detector is indispensable.

  Accordingly, the problem to be solved by the present invention is that it is possible to limit the voltage imbalance of a plurality of capacitors that divide the DC power supply voltage, and to simplify the circuit configuration and miniaturize the apparatus by minimizing the detector on the input side. An object of the present invention is to provide a direct current power supply device that is reduced in price.

In order to solve the above-mentioned problem, an invention according to claim 1 is directed to a transformer in which a primary winding is connected in series to a semiconductor switching element, a DC voltage is applied, and a series circuit of the primary winding and the semiconductor switching element. A plurality of stages of flyback DC / DC converters having capacitors connected in parallel;
The capacitors of the DC / DC converters at each stage are connected in series and both ends of the series circuit are connected to a DC power source, and the secondary winding of the transformer of the DC / DC converter at each stage is connected in parallel via a diode. In the DC power supply device connected to the DC output terminal,
A voltage regulator composed of a photocoupler, a switching regulator, and a resistor connected in series corresponding to the DC / DC converter of each stage is provided on the DC output terminal side, and based on the deviation between the output voltage target value and the output voltage detection value The obtained pulse width command value is individually fed back to each stage DC / DC converter via the photocoupler to control the semiconductor switching element of the DC / DC converter.

The invention according to claim 2 is the DC power supply device according to claim 1,
The voltage of the capacitor of the DC / DC converter in each stage is detected, and when the detected voltage value is lower than the set value, the semiconductor switching element of the DC / DC converter is turned off or the conduction ratio is lowered. And a voltage limiter for preventing the capacitor voltage from being lowered.

According to the first aspect of the present invention, the input voltage can be substantially balanced without providing a voltage detector or a current detector on the input side of each stage of the flyback DC / DC converter, and the circuit configuration is simplified. And cost reduction.
According to the second aspect of the present invention, the input voltage unbalance is promoted by monitoring the input voltage of each stage flyback DC / DC converter and controlling the switching element. Can be prevented.
In general, according to the present invention, it is possible to use a low-breakdown-voltage element as a switching element by limiting imbalance of the input voltage, and to reduce the voltage applied to the transformer. It is possible to realize a high DC power supply device.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, FIG. 1 is a main circuit configuration diagram of the first and second embodiments of the present invention, and the same components as those in FIG. In this main circuit, a transformer whose primary winding is connected in series to the semiconductor switching element and a voltage of 1 / N of the DC power supply voltage (N is an integer equal to or larger than 2, N = 3 in this example) are applied. A DC power supply device including three stages of flyback DC / DC converters including a capacitor.
FIG. 2 shows the flyback DC / DC converter for one stage in FIG. 1, and 100 ′ corresponds to a DC power source in which the voltage of the DC power source 100 in FIG.

  The main circuit shown in FIG. 1 is basically the same as the main circuit in the prior art shown in FIG. 7, and the DC power supply voltage is divided into three by the capacitors 11, 12 and 13, and the primary of the transformers 31, 32 and 33. A series circuit of windings and switching elements 21, 22, and 23 is connected in parallel to the capacitors 11, 12, and 13, and secondary sides of the transformers 31, 32, and 33 are connected to diodes 41, 42, 43, 61, 62, 63 and capacitors 51, 52, and 53 are connected in parallel to enable use of a low-breakdown-voltage switching element and a transformer with a low input voltage, thereby reducing the size of the circuit.

Here, the DC power supply device as shown in FIG. 1 has a problem that the voltages of the capacitors 11, 12, and 13 are unbalanced as described above, and as a result, the switching elements 21, 22, and 23 are transiently transferred. An excessive voltage may be applied.
In order to balance the input voltage, it is necessary to operate the switching element so that the output of the DC / DC converter including the capacitor whose voltage is increased increases and the output is reduced when the input voltage is decreased. For this purpose, the same ignition signal may be inputted to the switching elements of the DC / DC converters in the respective stages.

FIG. 3 is a waveform diagram showing an ignition signal for the switching element of each stage and the primary side current of the upper and lower transformers when the DC power supply device is constituted by a two-stage DC / DC converter.
In the figure, the dotted line indicates the primary side current when the voltage of the capacitor of each stage is the same, and since the average value is equal, the same power can be output. On the other hand, the solid line is the primary current when the voltage of the upper capacitor is higher than that of the lower capacitor, and the average current is also an unbalanced value.

In this case, when the input voltage of each stage to V _in, being equal upper and lower transformer inductance L, the input voltage is increased higher stage of di / dt by the following equation, that amount, the average current is also increased To do.
di / dt = V _in / L
Therefore, since the output of the stage with a high input voltage increases, the capacitor voltage will eventually be balanced.
However, in practice, the capacitor voltage operates with a steady deviation that is allowed by the difference in the pulse width of the ignition signal and the difference in the inductance of the transformer.

Therefore, the first embodiment of the present invention is configured as shown in FIG. In the following description, the circuit configuration will be described with a focus on differences from FIG.
In FIG. 4, control circuits 81, 82, 83 are individually provided corresponding to the gate circuits 71, 72, 73 of the flyback type DC / DC converter at each stage. Further, the transformers 31A, 32A, and 33A of the respective stages are provided with tertiary windings 241, 242, and 243, and connection points between the diodes 221, 222, and 223 connected to both ends of the transformers and the capacitors 231, 232, and 233 are provided. The resistors 211, 212, and 213 are connected to the respective ends of the capacitors 11, 12, and 13, and both ends of the capacitors 231, 232, and 233 are connected to the gate circuits 71, 72, 73 and the control circuits 81, 82, 83, respectively. Reference numerals 201, 202, and 203 denote gate power supplies.

Further, resistors 131 and 132 are connected in series between the DC output terminals P and N in the same manner as in FIG. 7, and feedback photocouplers 91 and 82 corresponding to the control circuits 81, 82, and 83 of each stage are connected. A voltage regulator is configured by connecting a series circuit of light emitting diodes (LEDs) 92, 93, a forward current limiting resistor 111, and a switching regulator 121 in series. This voltage regulator compares the reference voltage (output voltage target value) inside the switching regulator 121 with the output voltage detection value obtained by the voltage division of the resistors 131 and 132, and the switching regulator 121 according to the deviation. By adjusting the voltage, the deviation between the output voltage target value and the output voltage detection value is converted into the forward current (pulse width command value) of the photocouplers 91, 92, 93.
The output terminals of the photocouplers 91, 92, 93 are connected to the control circuits 81, 82, 83.

According to the first embodiment shown in FIG. 4, forward currents of the same magnitude flow through the light emitting diodes of the feedback photocouplers 91, 92, and 93, although there is an influence due to variations in the current transfer rate (CTR). Each of the control circuits 81, 82, 83 receives a pulse width command value, which is a deviation between the output voltage target value and the output voltage detection value of the same magnitude, via the photocouplers 91, 92, 93. Individual feedback to the DC converter. Therefore, substantially equal pulse width command values can be fed back to the control circuits 81, 82, 83, and the switching elements 21, 22, 23 are ignited via the gate circuits 71, 72, 73. The outputs of the stage transformers 31A, 32A, 33A can be made equal.
In this case, if the transformers 31A, 32A, and 33A have the same inductance, the transformer with the higher input voltage outputs a larger amount of power. Therefore, the control works in the direction of lowering the input voltage, and in a steady state, each stage. The voltages of the input-side capacitors 11, 12, 13 are equal.

Here, as described above, when the switching elements 21, 22, and 23 of each stage are individually ignited, the timing of starting igniting is not aligned, and the input voltage is changed in a transient state such as a start-up or a load fluctuation. May become unbalanced.
In particular, as long as the control power can be supplied from the gate power supplies 201, 202, and 203 using the tertiary windings 241, 242, and 243 as in the first embodiment, it is possible to operate up to a relatively low voltage. When the unbalance occurs, almost all of the DC power supply voltage is applied to the capacitor in one stage, and there is a possibility that the advantage of sharing the DC power supply voltage by a plurality of series capacitors may not be utilized.

The second embodiment of the present invention solves the above problems, and FIG. 5 shows the circuit configuration thereof.
In FIG. 5, 401, 402, and 403 are control units, each of which corresponds to a circuit combining the control circuits 81, 82, and 83 and the gate circuits 71, 72, and 73 in FIG.
The power supply of these control units 401, 402, 403 is not shown, but a power supply voltage is supplied from a gate power source configured by providing a tertiary winding in the transformers 31, 32, 33 as in FIG. Is done.
Accordingly, the second embodiment of each stage corresponds to a configuration obtained by adding voltage limiting units 301, 302, and 303 described below based on the first embodiment.

Since the voltage limiters 301, 302, and 303 at each stage have the same configuration, the configuration will be described using the voltage limiter 301 provided corresponding to the upper control unit 401 as an example.
Reference numeral 311 denotes a voltage detector for detecting the voltage of the capacitor 11, and the voltage detection value is given to one input terminal of the comparator 331. Reference numeral 321 denotes a setting device, in which a shared voltage of the capacitor 11 with respect to the DC power supply voltage is set in advance. This voltage setting value is given to the other input terminal of the comparator 331.
The output terminal of the comparator 331 is connected to the base of the NPN transistor 341, and the collector and emitter thereof are connected to the control unit 401 and are connected to the collector and emitter of the phototransistor constituting the photocoupler 91.

The operation of this embodiment will be described. When the voltage detection value by the voltage detector 311 becomes equal to or lower than the voltage setting value by the setting device 321, the output signal of the comparator 331 becomes “High” level, and the NPN transistor 341 is turned on. Here, FIG. 8 shows the relationship between the forward current of the photocoupler 91 and the pulse width, and the characteristic is that the pulse width becomes narrower as the forward current increases. Therefore, when the NPN transistor 341 is turned on, the control unit 401 performs the same operation as when the output voltage is increased, and reduces the conduction rate of the ignition signal of the switching element 21 to narrow the pulse width or Turn off completely.
For this reason, since the power supply from the transformer 31 decreases or becomes zero, the promotion of imbalance due to the further decrease of the input voltage is prevented, and the input voltage does not decrease below an arbitrary voltage set value. Can do. This produces an effect that the breakdown voltage can be lowered when the switching elements 21, 22, and 23 are selected.

Here, the DC power supply device comprising a DC / DC converter of a three-stage configuration as shown in FIG. 5, the voltage setting value by the individual setting unit (e.g., set 321) to 1/4 of the voltage _{V in} of the DC power supply 100 When set, the maximum input voltage value of each capacitor in consideration of the element withstand voltage is V _in / 2 according to the following formula.
V _in −V _in / 4−V _in / 4 = V _in / 2

The above example is a case of a three-stage configuration, but the number of series connection stages of the DC / DC converter (capacitor) when the voltage set value by the setting device = DC power supply voltage / (number of series connection stages of DC / DC converter + 1) The relationship between the number of divisions) and the maximum input voltage value of each stage capacitor is shown in FIG.
By increasing the number of divided capacitors and individually monitoring the input voltage at each stage by the voltage limiter described above to control the switching operation, the breakdown voltage of the switching element or the like can be lowered.

It is a main circuit block diagram of 1st, 2nd embodiment of this invention. It is a block diagram of the flyback type DC / DC converter for one stage in FIG. It is a wave form diagram which shows the primary side electric current of the ignition signal of the switching element in the DC power supply device of 2 steps | paragraphs, and an upper stage and a lower stage transformer. It is a specific block diagram of 1st Embodiment of this invention. It is a specific block diagram of 2nd Embodiment of this invention. In 2nd Embodiment of this invention, it is a figure which shows the relationship between the division | segmentation number of a capacitor | condenser, and the input voltage maximum value of the capacitor | condenser of each stage. It is a circuit diagram which shows a prior art. It is a figure which shows the relationship between the forward current of a photocoupler for pulse width feedback, and a pulse width.

Explanation of symbols

11, 12, 13, 51, 52, 53, 231, 232, 233: capacitors 21, 22, 23: semiconductor switching elements 31, 32, 33, 31A, 32A, 33A: transformers 41, 42, 43, 61, 62 , 63, 221, 222, 223: Diodes 71, 72, 73: Gate circuits 81, 82, 83: Control circuits 91, 92, 93: Photocouplers 100: DC power supplies 111, 131, 132, 211, 212, 213: Resistor 121: Switching regulator 201, 202, 203: Gate power supply 241, 242, 243: Tertiary winding 301, 302, 303: Voltage limiter 311: Voltage detector 321: Setter 331: Comparator 341: NPN transistor 401, 402, 403: Control unit P, N: DC output terminal

Claims (2)

A flyback DC / DC having a transformer in which a primary winding is connected in series to a semiconductor switching element, and a capacitor to which a DC voltage is applied and connected in parallel to a series circuit of the primary winding and the semiconductor switching element With multiple converters,
The capacitors of the DC / DC converters at each stage are connected in series and both ends of the series circuit are connected to a DC power source, and the secondary winding of the transformer of the DC / DC converter at each stage is connected in parallel via a diode. In the DC power supply device connected to the DC output terminal,
A voltage regulator composed of a photocoupler, a switching regulator, and a resistor connected in series corresponding to the DC / DC converter of each stage is provided on the DC output terminal side, and based on the deviation between the output voltage target value and the output voltage detection value A direct-current power supply device, wherein the obtained pulse width command value is individually fed back to each stage DC / DC converter via the photocoupler to control the semiconductor switching element of the DC / DC converter. The DC power supply device according to claim 1,
The voltage of the capacitor of the DC / DC converter in each stage is detected, and when the detected voltage value is lower than the set value, the semiconductor switching element of the DC / DC converter is turned off or the conduction ratio is lowered. A DC power supply device comprising a voltage limiting unit that prevents a decrease in the capacitor voltage.

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