JP2007330081A - Switching regulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a self-exciting converter of a switching regulator for high output at a low cost. <P>SOLUTION: An ET product monitor 230 acquires a voltage-time product of time and voltage value applied as a rectified DC voltage to a transformer 104. A switching control unit 250 compares the voltage-time product with a predetermined threshold value. It controls an FET106 depending on the comparison result, to invert switching state of the FET106 into a non-conductive state when a primary coil Np is conductive while into a conductive state when it is non-conductive. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a switching power supply apparatus and a switching power supply system, and more particularly to a switching power supply apparatus and a switching power supply system that are self-excited flyback power supply apparatuses.

A basic circuit diagram of a conventional self-excited flyback power supply is shown in FIG. 9, and the operation of the circuit will be described with reference to FIG.
A DC input voltage generated by the filter circuit 701, the rectifier circuit 702, and the smoothing capacitor 703 is applied to the primary winding Np of the transformer 704 from the commercial AC power supply 700. The collector of the switching transistor 706 is connected to the primary winding Np. A starting resistor 705 is connected between the positive terminal of the DC input and the base terminal of the switching element 706. When a base current of the transistor 706 flows from the DC input through the starting resistor 705, a collector current flows. As a result of flowing a current through the primary winding Np, the transformer 704 is excited. As a result, a voltage is induced in the secondary winding Ns. As a result, a positive feedback is performed such that the base current of the transistor 706 increases, the collector current further increases, and the current of the primary winding Np increases. The positive feedback is limited by a resistor 707 and a capacitor 717 connected between the auxiliary winding Nb and the base of the transistor 706, but the collector current of the transistor 706 continues to a value corresponding to the product of the base current and the DC amplification factor. If the collector current exceeds this value, the collector voltage shifts from the saturated region to the unsaturated region because of the insufficient base current of the transistor 706.

  As a result, the VCE of the transistor 706 increases and the voltage applied to the primary winding NP decreases, so the voltage of the auxiliary winding Nb also decreases and the base current of the transistor 706 decreases. In this way, as a result of positive feedback such as a further shortage of base current that further increases the collector voltage of the transistor 706, the transistor 706 is rapidly turned off. When the transistor 706 is turned off, back electromotive force is generated in each winding of the transformer 704, and a load current flows out from the secondary winding Ns through the rectifier diode 708 on the secondary side. This half-wave current is smoothed by the capacitor 709 to be a DC output. When the energy stored in the transformer 704 becomes zero, the output current also becomes zero. However, the slight residual energy remaining in the secondary winding Ns generates a voltage in the auxiliary winding Nb and makes the transistor 706 conductive again. Then, a current flows through the primary winding Np, the voltage of the auxiliary winding Nb rises, a base current of the transistor 706 flows, and then the same state as described above is repeated to maintain the switching state.

  When the output voltage increases in the above operation, the shunt regulator 711 is operated by the divided voltage by the resistors 713 and 714, and a current flows to the LED 710 a of the photocoupler 710 through the resistor 712. The LED 710a is turned on by this current, and the impedance of the phototransistor 710b in the photocoupler 710 is lowered. It is configured to output a constant voltage by such an operation that the switching element 706 is turned off when the impedance reduction turns on the transistor 715.

JP 62-152370 A Japanese Unexamined Patent Publication No. Sho 63-316668 JP-A-4-44075

  However, since the conventional method uses the winding output of the transformer as the power supply for the base current that drives the switching transistor, the gate waveform at startup and turn-on is not rectangular, and is sufficient to turn on. Can not get the correct voltage. For this reason, there is a problem that the loss of the switching transistor increases, and the efficiency of the switching transistor decreases as the temperature of the switching transistor increases. Further, when a steep load fluctuation or input voltage fluctuation occurs, it is difficult to keep the switching transistor off, and the transformer may be saturated. In addition, since the waveform rate of the current flowing through the transformer and the semiconductor is poor, there is a problem that it is not suitable for high power output, and so far it has been used only for small output and low cost power sources.

  The object of the present invention is to monitor the voltage and time product applied to the transformer and constantly monitor the state of the transformer to eliminate the unstable state of the power source, to perform stable operation and to output a large amount of power. A switching power supply device capable of solving the problems is provided.

  In order to achieve the above object, an aspect of the present invention includes a rectifier that rectifies a commercial power supply to generate a DC voltage, a transformer that is excited by applying the DC voltage to a primary winding, and an auxiliary to the transformer. A switching power supply comprising switching means for switching on and off the primary winding by switching with the induced voltage from the primary winding generated in the winding, and a voltage value at which the DC voltage is applied to the transformer Integration means for obtaining a voltage-time product that is a product of time and time, comparison means for comparing the voltage-time product with a predetermined threshold, and controlling the switching means in accordance with the comparison result so that the primary winding is conductive Control means for inverting the switching state of the switching means so as to be non-conductive when the winding is turned off and to be turned on when the winding is non-conductive. It is characterized in.

  Another aspect of the present invention includes a rectifier that rectifies a commercial power supply to generate a DC voltage, a transformer that is excited by applying the DC voltage to the primary winding, and the primary winding connected to the primary winding. A switching power supply comprising a switching means for conducting or non-conducting the winding, wherein the first constant current means for generating a first current corresponding to a forward voltage generated in the primary winding; A second constant current means for generating a second current corresponding to a flyback voltage generated on the line; an integration means for integrating the first and second currents; and comparing the integration result with a predetermined threshold value. Comparing means, and controlling the switching means according to the comparison result, so as to be non-conductive when the primary winding is conductive and to be conductive when the winding is non-conductive, The switching means Characterized by comprising a control means for inverting the etching condition.

  Here, the control means may have an auxiliary power supply function for generating power to be supplied to the comparison means and itself from the DC voltage, and shaping of a switching waveform that could not be achieved by a conventional self-excited converter. This contributes to the reduction of switching loss.

  Still another aspect of the present invention includes a rectifier that rectifies a commercial power source to generate a DC voltage, a transformer that is excited by applying the DC voltage to a primary winding, and an auxiliary winding of the transformer. A switching power supply comprising switching means for switching on and off the primary winding by switching based on an induced voltage from the primary winding, and detecting means for detecting a primary current flowing in the primary winding; Means for turning off the switching element in accordance with the primary current that has been detected, and detecting a voltage that appears in the auxiliary winding when the switching element is turned off, and in accordance with a voltage time product of the auxiliary winding voltage. A means for turning on the switching element is provided.

  According to the present invention, by monitoring the voltage-time product applied to the transformer and constantly monitoring the state of the transformer, the unstable state of the power source can be eliminated, stable operation can be performed, and high power can be output.

Example 1
FIG. 1 shows a circuit diagram that best represents the first embodiment of the switching power supply apparatus according to the present invention, and the operation of the circuit will be described with reference to the figure. In FIG. 1, reference numeral 107 indicates a gate resistance. The switching power supply according to this embodiment and the following embodiments can be used for an electrophotographic image forming apparatus.

  When an AC power is received from the commercial AC power supply 100 and applied to the rectifier diode 102 formed of a diode bridge via the filter circuit 101, a DC voltage is generated by the two-wave rectifier diode 102 and the primary rectifier capacitor 103. When the starting current is supplied to the control circuit 200 by the starting resistor 105 connected to the ET product monitoring unit 230 of the control circuit 200 that performs switching, the FET 106 that is a switching element is turned on, and the primary winding Np of the switching transformer 104 is turned on. Current begins to flow. This current generates a voltage in the forward direction in the auxiliary winding Nb, and the switching control power supply unit 210 in the control circuit 200 is supplied with power. On the other hand, since the secondary winding Ns is wound in the opposite direction to the primary winding Np, even if the voltage is excited, the secondary side rectifier diode 108 prevents current from flowing, and energy is supplied to the transformer 104. Will be stored.

  When the switching control unit 250 in the control circuit 200 turns off the FET 106, a voltage in the reverse direction to that when the FET 106 is on is generated in the primary winding Np by the energy stored in the transformer 104. A similar voltage is also generated in the auxiliary winding Nb and the secondary winding Ns. Since the voltage generated on the secondary winding Ns side is generated in the forward direction of the diode 108, the voltage from the diode 108 to the secondary rectifying capacitor 109 is increased. Charging is started and the voltage across the capacitor 109 rises. When the FET 106 is repeatedly turned on and off, the voltage across the capacitor 109 rises and the secondary output terminal voltage becomes equal to or higher than the desired voltage, and the shunt regulator 111 is operated by the voltage divided by the resistors 113 and 114. As a result, a current flows through the resistor 112 to the LED 110a of the photocoupler 110. By controlling the switching in this way, the secondary output voltage is controlled to be constant.

  A circuit diagram that best represents the switching control power supply unit 210 in the present embodiment is shown in FIG. 2, and the operation of the power supply unit will be described with reference to FIG.

  The capacitor 201 side is connected to the auxiliary winding Nb of the transformer 104. When the voltage is generated in the transformer 104 in the direction in which the diode 211 is conducted, the capacitor 201 starts to be charged. Further, the auxiliary winding Nb is also connected to the capacitor 201 and is charged by the auxiliary winding Nb. When the power is turned on, charging of the capacitor 201 is started by the starting resistor 105, and the voltage across the capacitor 201 increases. When the power supply voltage divided by the resistors 202 and 203 becomes higher than the sum of the Zener voltage of the Zener diode 204 and Vbe of the transistor 209, the transistor 209 is turned on, and the transistor 205 is turned on by the collector current of the transistor 209. . Once the transistor 205 is turned on, the voltage across the resistor 203 rises due to the resistor 208, so that the voltage across the capacitor 201 when the transistors 209 and 205 are turned on and the voltage across the capacitor 201 when turned off are changed. Such a circuit having hysteresis can prevent malfunction.

  A circuit diagram showing the ET product monitoring unit 230 in the present embodiment is shown in FIG. 3, and the operation of the monitoring unit will be described with reference to FIG.

  The anode side of the diode 231 and the cathode side of the diode 240 are connected to one end of the auxiliary winding Nb of the transformer 104. The common side of the resistors 242, 244, 233, 235 and the capacitor 239 is connected to the other end of the auxiliary winding Nb. When the FET 106 is turned on and a power supply voltage is applied to the primary winding Np, a voltage is also generated in the auxiliary winding Nb at the same time, and the diode 231 becomes conductive. A voltage proportional to the voltage across the auxiliary winding Nb is generated by the resistors 232 and 233, the same voltage as the voltage across the resistor 232 is applied to the resistor 236, and a constant current proportional to the voltage is passed through the transistor 237 and the diode 238. 239 to charge the capacitor 239. As a result, the voltage across the capacitor 239 increases. When the FET 106 is turned off, a reverse voltage is generated in the auxiliary winding Nb, so that the diode 231 becomes non-conductive and the diode 240 becomes conductive.

  As a result, a voltage proportional to the flyback voltage is applied to the resistor 241, and the same voltage as the voltage across the resistor 241 is applied to the resistor 245. Therefore, the discharge current from the capacitor 239 is discharged by a constant current source determined by the resistance value of the resistor 245 and the voltage across the resistor 245. As described above, the capacitor 239 is charged with a current proportional to the voltage of the auxiliary winding Nb and discharged with a current proportional to the flyback voltage. Therefore, the voltage across the capacitor 239 corresponds to the ET product (a magnetic flux) applied to the transformer 104. Therefore, the switching control unit 250 monitors the ET product (the voltage across the capacitor 239), and controls on / off of the FET 106 according to the monitoring result.

  FIG. 4 is a circuit diagram showing the switching control unit 250 in the present embodiment, and the operation of the control unit will be described with reference to FIG.

  In FIG. 4, two comparator circuits are configured. One has Darlington pair transistors 254 and 255 and Darlington pair transistors 256 and 257 at the input terminals, and the other has Darlington pair transistors 264 and 265 and Darlington pair transistors 266 and 267 at the input terminals. The transistor 265 is given an initial value by resistance division by resistors 261 and 262 and the transistor 255 by resistors 251 and 252.

  By supplying a voltage from the capacitor 239 to the transistor 267 through the resistor 269 and to the transistor 257 through the resistor 259, the transistor 270 is turned on when the voltage of the capacitor 239 is higher than the voltage of the resistor 262. Further, the transistor 260 is turned on when the voltage of the capacitor 239 is lower than the voltage of the resistor 252. The transistor 260 is connected to the FET 274, the transistor 270 is connected to the FET 273, and a flip-flop (F / F) is configured by both FETs.

  From the above, when the voltage of the capacitor 239 corresponding to the ET product is not less than the voltage of the resistor 252 and not more than the voltage of the resistor 262, the F / F output becomes high level. Further, when the voltage of the capacitor 239 is equal to or lower than the voltage across the resistor 262 and equal to or higher than the voltage across the resistor 252, the F / F output is at a low level.

  Here, the phototransistor 110 b of the photocoupler 110 is connected in series with the resistor 276, and the series circuit is connected in parallel with the reference voltage generating resistor 262. When the secondary output voltage rises, a current flows through the photocoupler 110 as described above, and the LED 110 of the photocoupler 110 emits light. For this reason, since the impedance of the phototransistor 110b decreases and the impedance of the series circuit decreases, the voltage across the resistor 262 decreases. As a result, the high period of the F / F output, that is, the ON time of the FET 106 is controlled so as to be shortened in accordance with the increase of the secondary output voltage, and the energy stored in the transformer 104 is reduced. It is controlled to operate stably.

  As described above, according to the present embodiment, it is possible to provide a highly reliable power supply device with improved operational stability by monitoring the state of the switching transformer of the switching power supply using the ET product.

(Example 2)
FIG. 5 shows a circuit diagram best representing the second embodiment of the switching power supply device according to the present invention, and the operation of the circuit will be described with reference to the figure. Here, description overlapping with the description of the first embodiment will be omitted, and the characteristic part of the present embodiment will be described.

  In this embodiment, the ET product (voltage time product) is not detected from the auxiliary winding, but the voltage applied to the primary winding Np of the transformer 504 in FIG. 5 is detected. When the FET 506 serving as a switching element is on, the resistor 548 generates a constant current and charges the capacitor 539 with a voltage proportional to the voltage applied to the primary winding Np. When the FET 506 is off, a constant current is generated by a voltage proportional to the flyback voltage of the transformer 504 to discharge the capacitor 539. Similar to the first embodiment, the comparator unit and the power supply unit 590 control the FET 506 by comparing the charging and discharging thresholds with predetermined values by the comparator.

  In FIG. 5, a block denoted by reference numeral 590 is a comparator unit and a power source unit of the switching control circuit. Details of the block are shown in FIG. 6, and the operation of the block will be described with reference to FIG.

  In FIG. 6, in response to a current flowing from the starting resistor 505, a parallel circuit of a Zener diode 577 and a capacitor 578 generates a power supply voltage. The comparator and the output F / F unit operate with this power supply voltage. In FIG. 6, two comparator circuits are configured. One has Darlington pair transistors 554 and 555 and Darlington pair transistors 556 and 557 at the input terminals, and the other has Darlington pair transistors 564 and 565 and Darlington pair transistors 566 and 567 at the input terminals. The transistor 565 is given an initial value by resistance division by resistors 561 and 562 and the transistor 555 by resistors 551 and 552.

  By supplying a voltage from the capacitor 539 to the transistor 567 through the resistor 569 and to the transistor 557 through the resistor 559, the transistor 570 is turned on when the voltage of the capacitor 539 is higher than the voltage of the resistor 562. Further, the transistor 560 is turned on when the voltage of the capacitor 539 is lower than the voltage of the resistor 552. The transistor 560 is connected to the FET 574, the transistor 570 is connected to the FET 573, and a flip-flop (F / F) is configured by both FETs.

  From the above, when the voltage of the capacitor 539 is not less than the voltage of the resistor 552 and not more than the voltage of the resistor 562, the F / F output becomes high level. Further, when the voltage of the capacitor 539 is equal to or lower than the voltage across the resistor 562 and equal to or higher than the voltage across the resistor 552, the F / F output is at a low level.

  As described above, in this embodiment, by directly monitoring the voltage of the primary winding Np, the FET as a switching element is controlled without using the auxiliary winding Nb. Therefore, the number of components is smaller than that in the first embodiment. With the configuration, it is possible to obtain the same effect as in the first embodiment. That is, in addition to the effects of the first embodiment, it is possible to increase the utilization efficiency of the switching element and the switching transformer, and to provide a small-sized and low-cost power supply apparatus with a low cost and a small number of parts.

(Example 3)
FIG. 7 shows a circuit diagram that best represents the third embodiment of the switching power supply according to the present invention, and the operation of the circuit will be described with reference to the figure. Here, description overlapping with the description of the first embodiment and the second embodiment will be omitted, and the characteristic part of the present embodiment will be described.

  In this embodiment, only the determination of the on-time when the switching element is turned on is performed by detecting the primary current flowing in the transformer 604, thereby further simplifying the circuit and promoting the miniaturization and cost reduction. Is. When the FET 606, which is a switching element, is turned off, the capacitor voltage is charged with a reverse voltage (flyback voltage), and the FET 606 is turned off when the value becomes a predetermined value by a comparator. When the FET 606 is turned on, a power supply voltage is applied to the primary winding Np of the transformer 606, and current starts to flow. When this current reaches a predetermined value, the transistor 680 is turned on, the FET 606 is turned off, and the output F / F shown in FIG. 8 is stopped.

  In FIG. 7, a block denoted by reference numeral 691 is a comparator unit and an output F / F unit. Details of the block are shown in FIG. 8, and the operation of the block will be described with reference to FIG. The switching control power supply unit 690 operates in the same manner as the switching control power supply unit 210 in FIG.

  In FIG. 8, a voltage dividing circuit using resistors 661 and 662 provides a reference voltage for a comparator including Darlington pair transistors 664 and 665 and Darlington pair transistors 666 and 667. The FETs 671 and 673 constitute an output flip-flop (F / F).

  When the voltage of the capacitor 639 in FIG. 7 becomes lower than the voltage across the resistor 662 in FIG. 8, the transistors 664 and 665 constituting the comparator are turned off and the transistors 666 and 667 are turned on. As a result, the transistor 670 is turned on and the output of the F / F is fixed to the high level. When the current exceeds a predetermined amount and the transistor 680 in FIG. 7 operates, the collector voltage of the transistor decreases, the output of the F / F connected to the collector of the transistor and the gate of the FET 674 become low level, and the transistor 606 is turned off.

  The ET product monitoring unit 730 charges the capacitor 639 to the output voltage of the auxiliary winding Nb via the diode 631 and the resistor 632 at the forward side output of the auxiliary winding Nb, and is proportional to the flyback voltage appearing in the auxiliary winding Nb. The off time is detected by discharging with a constant current source. The output voltage control is performed by connecting the resistor 683 and the phototransistor 610b side of the photocoupler 610 to both ends of the detection resistor 649 and the current detection resistor 648.

1 is a circuit diagram that best represents Example 1 of a switching power supply device according to the present invention; FIG. FIG. 3 is a circuit diagram illustrating a switching control power supply unit that is a main part of the first embodiment. FIG. 3 is a circuit diagram illustrating a voltage time product unit that is a main part of the first embodiment. FIG. 3 is a circuit diagram illustrating a switching control unit (comparator, output F / F) that is a main part of the first embodiment. It is a circuit diagram which best represents Example 2 of the switching power supply device according to the present invention. FIG. 6 is a circuit diagram of a main part of a second embodiment. It is a circuit diagram which best represents Example 3 of the switching power supply device according to the present invention. FIG. 6 is a circuit diagram of a main part of a third embodiment. It is a circuit diagram showing the prior art example of a switching power supply device.

Explanation of symbols

100, 500, 600 Commercial AC power supply 101, 501, 601 Filter circuit 102, 502, 602 Rectifier diode 103, 503, 603 Primary smoothing capacitor 104, 504, 604 Switching transformer 105, 505 Starting resistor 106, 506, 606 FET (switching element)
107 Gate resistors 108, 508, 608 Secondary rectifier diodes 109, 509, 609 Secondary smoothing capacitors 110, 510, 610 Photocoupler 200 Control circuit 210 Switching control power supply unit 230, 730 ET product monitoring unit 250 Switching control unit

Claims (4)

Rectifying means for rectifying a commercial power source to generate a DC voltage, a transformer that is excited by applying the DC voltage to the primary winding, and an induced voltage generated from the primary winding in the auxiliary winding of the transformer In a switching power supply device comprising switching means for switching to turn on or off the primary winding,
Integration means for obtaining a voltage time product which is a product of a voltage value and time at which the DC voltage is applied to the transformer;
Comparing means for comparing the voltage-time product with a predetermined threshold; and
The switching means is controlled according to the comparison result so that the switching means is turned off when the primary winding is turned on and turned on when the winding is turned off. A switching power supply comprising control means for inverting the state. Rectifying means for rectifying a commercial power supply to generate a DC voltage, a transformer that is energized by applying the DC voltage to the primary winding, and connected to the primary winding to make the primary winding conductive or non-conductive. In a switching power supply device comprising switching means,
First constant current means for generating a first current corresponding to a forward voltage generated in the primary winding;
Second constant current means for generating a second current corresponding to the flyback voltage generated in the primary winding;
Integrating means for integrating the first and second currents;
A comparison means for comparing the integration result with a predetermined threshold; and
The switching means is controlled according to the comparison result so that the switching means is turned off when the primary winding is turned on and turned on when the winding is turned off. A switching power supply comprising control means for inverting the state. The switching power supply device according to claim 2,
The switching power supply device characterized in that the control means has an auxiliary power supply function for generating power to be supplied to the comparison means and itself from the DC voltage. Rectifying means for rectifying a commercial power source to generate a DC voltage, a transformer that is excited by applying the DC voltage to the primary winding, and an induced voltage from the primary winding generated in the auxiliary winding of the transformer Switching power supply comprising switching means for switching based on the primary winding to conduct or non-conduct,
Detecting means for detecting a primary current flowing in the primary winding;
Means for turning off the switching element in response to the sensed primary current; and
A switching power supply apparatus comprising: means for detecting a voltage appearing in the auxiliary winding when the switching element is turned off, and turning on the switching element in accordance with a voltage time product of the auxiliary winding voltage.

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