JP5450255B2 - Switching power supply - Google Patents

Description

  The present invention relates to a multi-output switching power supply device having an active filter circuit.

  In a switching power supply device, there are many examples in which an active filter circuit is used as one of methods for improving the power factor and suppressing the harmonic current. Further, the active filter circuit can also support a commercial power supply of 100 [V] / 200 [V] input, and is one method suitable for realizing a so-called world wide input compatible switching power supply (Patent Document). 1).

  In a multi-output switching power supply device having an active filter circuit, the active filter circuit is configured so that the charging power required for charging the input side electrolytic capacitor and all the output power of the device can be covered simultaneously at the start-up and startup of the active filter circuit. Usually, the power capacity is set.

  With regard to the input voltage range input to the switching power supply device, for example, it corresponds to a wide range of input voltage fluctuation specifications where the minimum input voltage is about 1/4 of the maximum input voltage, and can be started under the conditions of the minimum input voltage and the maximum input current In the case of the active filter circuit, it is necessary to set the power capacity of the active filter circuit to a power capacity obtained by adding the total output power of the switching circuit to the charging power required for charging the input side electrolytic capacitor.

JP 2006-276341 A

  FIG. 4 shows a conventional switching power supply device. In the following, the output power rating of the switching power supply is 38 [W] (main output: 24 [V], 1.5 [A] / slave output: 5 [V], 0.4 [A]), Considering the efficiency of the switching circuit and the power factor of the active filter circuit, the input apparent power of the active filter circuit is about 50 [VA] (for example, input voltage: 20 [V], input current: 2.5 [A]) The case will be described. The apparent input power of the active filter circuit is a value when the switching power supply device is operated in a normal rated load state.

  In the active filter circuit, a voltage obtained by full-wave rectifying an AC input voltage from an AC input power supply (AC IN) by a diode bridge (DB1), an active filter control circuit (A1), a switching element FET (Q4), and an inductor ( The voltage is converted to a DC voltage (for example, 120 [V] between terminals of the electrolytic capacitor C2) via a step-up switching circuit composed of L1) and a diode (D1). According to the device adopting such an active filter system, compared with a switching power supply device that converts an AC input voltage into a DC voltage via only a diode bridge, the harmonic current affecting the AC power supply line is suppressed. In addition, the power factor can be improved (standard 0.99) to reduce the input apparent power, and the effective value of the AC input current can be reduced.

When the input voltage specification of the switching power supply shown in FIG. 4 is AC18 to 72 [V], in order to start the active filter circuit at any input voltage, the electrolytic capacitor C2 is charged and boosted to DC120 [V]. There must be. When the capacitance of the electrolytic capacitor C2 is 470 [μF], the energy when boosting from the minimum input voltage AC18 [V] (DC25 [V]) to DC120 [V] is based on Joule's law.
Charging energy = (1/2) CV ²
= 470 * 10 <-6> * (1202-252) / 2
= 3.237 [J]
If charging is performed in a time of 200 [ms], power of 3.237 [J] /0.2 [s] = 16.18 [W] is required. When the power factor of the active filter circuit at startup is 0.95, the input apparent power necessary for charging is 16.18 [W] /0.95≈17 [VA].

  FIG. 5 shows a time chart of each voltage of the switching power supply device shown in FIG. As described above, when the rating of the output power of the switching power supply is 38 [W], the input apparent power of the active filter circuit is about 50 [VA]. However, until the electrolytic capacitor C2 is charged when the active filter is activated (charging time: 200 [ms]), the input apparent power (17 [VA]) necessary for charging is added, and the input apparent power of the active filter circuit is added. The power becomes 67 [VA] in total (FIG. 5D).

  Also, when the input apparent power of the active filter circuit is 67 [VA], if the input voltage is 20 [V], the input current is 3.35 [A], compared to when operating at the rated output, The current capacity increases 1.34 times (3.35 [A] /2.5 [A]). As described above, in order to activate the active filter circuit, the set power capacity of the active filter circuit must be designed as 67 [VA] instead of 50 [VA], which is a main factor in increasing the cost of the apparatus. It was.

  Further, depending on the operating state of the system device on which the switching power supply device is mounted and other system devices, a resistance is interposed in the AC power supply line, which may cause the input voltage of the switching power supply device to further decrease from 20 [V]. There is. For example, when the input line resistance is 1 [Ω], a drop of 2.5 [V] (= 2.5 [A] × 1 [Ω]) occurs in the operation with a normal rated load, and the input voltage is 20 [Ω]. V] changes to 17.5V and falls below 18V, which is the lower limit of the input voltage specification. Further, when the input current increases from 2.5 [A] to 3.35 [A] at the time of start-up, the input voltage drops to 16.65 [V], which is largely out of the input voltage specification range. In this case, the input current is 67 [VA] /16.65 [V] ≈4 [A], and a voltage drop due to the line resistance occurs in a chain, resulting in a state in which startup is impossible. As described above, when operating a system device equipped with a conventional apparatus, there is a risk of starting failure such as failure to start normally.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a switching power supply device having a low cost and good start-up characteristics for an active filter circuit even when the input voltage range is wide.

  In the present invention, a DC input voltage obtained by rectifying and smoothing an AC input voltage is boosted to a predetermined primary DC voltage by an active filter circuit, and a primary side is connected by a first switching element connected to a primary winding of a transformer. Switching the DC voltage to induce an AC induced voltage in the secondary winding of the transformer, and generating the main output voltage from the secondary side DC voltage obtained by rectifying and smoothing the AC induced voltage by the rectifying and smoothing unit. A multi-output switching power supply comprising a main output switching regulator that outputs from a terminal, and a secondary output regulator that steps down a secondary DC voltage in a step-down regulator unit and outputs a slave output voltage from a slave output terminal; In order to achieve the above object, the main output switching regulator is interposed between the rectifying / smoothing unit and the main output terminal, and is turned on / off to rectify the main output switching regulator. The secondary switching regulator has a main output control circuit that controls the on / off state of the second switching element, and has a main output control. The circuit turns off the second switching element while the active filter circuit boosts the DC input voltage to the primary DC voltage after the slave output voltage is output from the slave output terminal, and the DC input voltage is set to the primary DC voltage. After the voltage is boosted, the second switching element is turned on, and the main output voltage is output from the main output terminal.

  According to this configuration, the second switching element is turned off while the active filter circuit boosts the DC input voltage to the primary DC voltage after the slave output voltage is output from the slave output terminal, and the master output switching regulator The output from the (main output terminal) is cut off. Then, after the DC input voltage is boosted to the primary DC voltage, the second switching element is turned on, and output from the main output switching regulator is performed. For this reason, the boost timing of the active filter circuit and the output timing from the main output switching regulator can be completely separated. Thus, when setting the power capacity of the active filter circuit, it is not necessary to add power required for boosting the active filter circuit to the total output power of the apparatus. In addition, an increase in input current with respect to the rated output operation can be avoided, and the occurrence of a starting failure can be prevented. Therefore, even when the input voltage range is wide, it is possible to realize a switching power supply device that has an active filter circuit at low cost and good start-up characteristics.

  Here, the main output control circuit includes a third switching element that switches the on / off state of the second switching element, and a threshold that is electrically connected to the slave output terminal and switches the third switching element from the off state to the on state. A delay capacitor capable of outputting a voltage. When the slave output voltage is output from the slave output terminal and the threshold voltage is output from the delay capacitor to the third switching element, the third switching element turns off the second switching element. The period from when the slave output voltage is output from the slave output terminal to when the threshold voltage is output from the delay capacitor is the active filter after the slave output voltage is output from the slave output terminal. The period is preferably equal to or longer than the period until the circuit boosts the DC input voltage to the primary DC voltage.

  According to this configuration, when the slave output voltage is output from the slave output terminal and the threshold voltage is output from the delay capacitor to the third switching element, the third switching element switches the second switching element from the OFF state to the ON state. Here, the period from when the slave output voltage is output from the slave output terminal to when the threshold voltage is output from the delay capacitor is the period from when the slave output voltage is output from the slave output terminal to when the active filter circuit performs primary input of the DC input voltage. Since the period until the voltage is boosted to the side DC voltage is equal to or longer than the period until the active filter circuit boosts the DC input voltage to the primary DC voltage, the second switching element is turned off and the main output terminal The main output voltage can be blocked from being output. For this reason, an increase in the set power capacity of the active filter circuit can be suppressed by appropriately setting the capacity of the delay capacitor so as to satisfy the above-described period conditions.

  The active filter circuit is connected to a boost inductor having a DC input voltage input to one end, a diode having an anode connected to the other end of the boost inductor, and a connection connecting the boost inductor and the diode. It has a fourth switching element controlled by a filter control circuit and a capacitor connected to the cathode of the diode, and is configured to generate a primary side DC voltage between the terminals of the capacitor by fully charging the capacitor. May be. According to this configuration, the output of the main output voltage is interrupted until the capacitor is fully charged, and an increase in the set power capacity of the active filter circuit can be suppressed.

  According to the present invention, even when the input voltage range is wide, it is possible to provide a switching power supply device that has an active filter circuit at low cost and good start-up characteristics.

It is a circuit diagram of the switching power supply concerning one embodiment of the present invention. It is a time chart of the switching power supply device shown in FIG. It is a circuit diagram of the switching power supply device concerning the modification of the present invention. It is a circuit diagram of the conventional switching power supply device. It is a time chart of the switching power supply device shown in FIG.

  FIG. 1 is a circuit diagram of a switching power supply device according to an embodiment of the present invention. The switching power supply device includes a main output switching regulator 1 and a sub output regulator 2. In the main output switching regulator 1, the input AC input voltage AC-IN (AC18 to 72 [V] in this embodiment) is full-wave rectified by the diode bridge DB1 and smoothed by the capacitor C1. The DC input voltage thus obtained is boosted to a predetermined primary side DC voltage (120 [V] in this embodiment) by the active filter circuit 11.

  The active filter circuit 11 includes a boosting inductor L1 to which a DC input voltage is input at one end, a diode D1 having an anode connected to the other end of the boosting inductor L1, and a connection connecting the boosting inductor L1 and the diode D1. It has a FET Q4 (corresponding to the “fourth switching element” of the present invention) connected and controlled by the active filter control circuit A1, and a capacitor C2 connected to the cathode of the diode D1. Then, when the capacitor C2 is fully charged, a primary side DC voltage is generated between the terminals of the capacitor C2.

  The primary DC voltage output from the active filter circuit 11 (capacitor C2) is guided to the primary winding (one end) of the transformer T1 and the starting resistor R3 that supplies the starting current to the switching control circuit A2. As a result, the voltage across the capacitor C4 connected to the auxiliary power supply terminal (Vcc) from the starting resistor R3 through the internal circuit of the switching control circuit A2 rises, and the pulse output (DRV) set to a predetermined switching condition is output from the transformer T1. The switching operation of the FET Q1 (corresponding to the “first switching element” of the present invention) connected to the primary winding (the other end) is started.

  The rectifying / smoothing unit 12 (the diode D4 and the capacitor C5 connected in series between the secondary windings of the transformer T1) connected to the secondary winding of the transformer T1 is an alternating current induced in the secondary winding of the transformer T1. A secondary side DC voltage is generated by rectifying and smoothing the induced voltage. At the same time, an AC voltage is also induced in the auxiliary winding of the transformer T1, and an auxiliary power supply voltage is generated between the terminals of the capacitor C3 through the rectifier diode D2. Further, the auxiliary power supply voltage is stably supplied to the auxiliary power supply terminal (Vcc) of the switching control circuit A2 through the diode D3.

  Thus, when the main output switching regulator 1 is activated, the auxiliary power supply voltage is supplied to the auxiliary power supply terminal (Vcc) of the switching control circuit A2, and at the same time, the auxiliary power supply terminal (Vcc) of the active filter control circuit A1 is also auxiliary. A power supply voltage is supplied. As the switching control circuit A2, for example, a switching power supply control IC “FA5541” manufactured by Fuji Electric Device Technology can be used. As the active filter control circuit A1, for example, an active filter control IC “manufactured by International Rectifier” IR1150 "can be used.

  The secondary side DC voltage is supplied to the main output (in this embodiment, the main output voltage: 24 [V], the main output current: 1.5 [A] via the FET Q2 (corresponding to the “second switching element” of the present invention). ]) From the main output terminal 13. As described above, the FET Q2 is interposed between the rectifying / smoothing unit 12 and the main output terminal 13, and is controlled to be turned on / off, whereby the rectifying / smoothing unit 12 and the main output terminal 13 are electrically connected (conducting / non-conducting). ) Can be switched.

  A feedback control circuit A3 is connected to the connection between the rectifying / smoothing unit 12 and the FET Q2, and the feedback control circuit A3 feeds back the amount of secondary DC voltage information to the switching control circuit A2 via the photocoupler PC1. Then, the switching operation of the FET Q1 is controlled so that the secondary side DC voltage is maintained at a predetermined voltage.

  The sub-output regulator 2 includes a step-down regulator circuit IC1 (corresponding to the “step-down regulator unit” of the present invention) and a main output control circuit 21. The secondary side DC voltage stabilized by the feedback control circuit A3 is input to the step-down regulator circuit IC1. The step-down regulator circuit IC1 outputs a voltage obtained by stepping down the secondary side DC voltage as a sub output (in this embodiment, a sub output voltage: 5 [V], a sub output current: 0.4 [A]) from the sub output terminal 23. Output. For the step-down regulator circuit IC1, a general-purpose three-terminal regulator “7805” or the like can be used.

  The main output control circuit 21 is connected to the output of the step-down regulator circuit IC1 and switches and controls the on / off state of the FET Q2. The main output control circuit 21 includes a resistor R8 having one end connected to the slave output terminal 23 (+5 [V]) and a capacitor C9 connected between the other end of the resistor R8 and GND (0 [V]) (the present invention). FET Q3 (corresponding to “delay capacitor” of FIG. 4), a gate connected to a connection point between the resistor 8 and the capacitor C9, a drain connected to the gate of the FET Q2 via the resistor R7, and a source grounded (“ Equivalent to “third switching element”). A resistor R9 is connected between the gate and source of the FET Q3, and a diode D5 is connected between the slave output terminal 23 and the gate of the FET Q3.

  When the slave output voltage is output from the slave output terminal 23, charging of the capacitor C9 is started via the resistor R8, and the charge voltage of the capacitor C9 is applied to the gate of the FET Q3. When the applied voltage exceeds the gate threshold voltage (threshold voltage for switching the FET Q3 from the off state to the on state), the FET Q3 is switched from the off state to the on state. As a result, the FET Q2 interposed between the rectifying / smoothing unit 12 and the main output terminal 13 is turned on and becomes conductive. As a result, the main output voltage is output from the main output terminal 13.

  Here, the period from the output of the slave output voltage from the slave output terminal 23 to the output of the gate threshold voltage of the FET Q3 from the capacitor C9 is from the output of the slave output voltage from the slave output terminal 23 to the active filter circuit 11. The capacitance of the capacitor C9 is set so as to be equal to or longer than the period until the DC input voltage is boosted to the primary side DC voltage (until the capacitor C9 is fully charged).

  Next, the operation of the switching power supply device configured as described above will be described. FIG. 2 is a time chart of the switching power supply device shown in FIG. When the AC input voltage AC-IN (AC18 to 72 [V]) is input, the auxiliary power supply voltage is supplied to the active filter control circuit A1 as described above, and the active filter control circuit A1 operates. As a result, the pulse output (DRV) set to a predetermined switching condition starts driving the FET Q4 through the resistor R1, and the voltage between the terminals of the capacitor C2 becomes the primary side DC voltage by the boosting operation by the boosting inductor L1 and the diode D1. The pressure is increased to. In this embodiment, the active filter control circuit A1 operates so as to stabilize the primary side DC voltage to 120 [V].

  Assuming that the time required for charging the capacitor C2 is 200 [ms], the input apparent power required for charging the capacitor C2 is 17 [VA] as described in [Problems to be Solved by the Invention]. .

  The main output switching regulator 1 switches the primary side DC voltage by the FET Q1, and generates the secondary side DC voltage by rectifying and smoothing the AC induced voltage induced in the secondary winding of the transformer T1 by the rectifying and smoothing unit 12. To do. The generated secondary DC voltage is stepped down by the step-down regulator circuit IC1 and output from the sub output terminal 23 as a sub output voltage (DC 5 [V]) (FIG. 2B). At the stage where the slave output starts to be output from the slave output terminal 23, the FET Q2 is in the OFF state, so that the master output is not output from the main output terminal 13. Therefore, the apparent input power required for the active filter circuit is about 20 [V] including the charge of the capacitor C2 and the sub output (FIG. 2D).

  When the slave output voltage (DC5 [V]) is output from the slave output terminal 23, charging of the capacitor C9 is started through the resistor R8. This charging voltage (voltage between terminals of the capacitor C9) is applied to the gate of the FET Q3, and when the applied voltage exceeds the gate threshold voltage, the FET Q3 is turned on. When the FET Q3 is turned on, the FET Q2 is turned on, the rectifying / smoothing unit 12 and the main output terminal 13 are in a conductive state, and the main output voltage (DC24 [V]) is output from the main output terminal 13. That is, unlike the prior art (FIG. 5C), the main output voltage is output from the main output terminal 13 after being delayed from the output from the slave output terminal 23 (FIG. 2C).

  In this embodiment, the period from when the slave output voltage is output from the slave output terminal 23 to when the gate threshold voltage is output from the capacitor C9 is the active filter circuit 11 after the slave output voltage is output from the slave output terminal 23. Is set to be equal to or longer than the period until the DC input voltage is boosted to the primary DC voltage. That is, the FET Q2 is turned off until the capacitor C2 is fully charged and a primary DC voltage is generated between the terminals of the capacitor C9. Thereby, the boosting timing (charging timing of the capacitor C2) of the active filter circuit and the output timing from the main output switching regulator 1 can be completely separated.

  As described above, according to this embodiment, the FET Q2 is turned off while the active filter circuit 11 boosts the DC input voltage to the primary DC voltage after the slave output voltage is output from the slave output terminal 23. . After the DC input voltage is boosted to the primary DC voltage, the FET Q2 is turned on, and the main output voltage is output from the main output terminal 13. For this reason, when setting the power capacity of the active filter circuit 11, it is not necessary to add the power required for boosting to the primary side DC voltage to the total output power of the apparatus. In addition, an increase in input current with respect to the rated output operation can be avoided, and the occurrence of a starting failure can be prevented. Therefore, even when the input voltage range is wide, it is possible to realize a switching power supply device that has an active filter circuit at low cost and good start-up characteristics.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, although the general-purpose three-terminal regulator “7805” or the like is used as the step-down regulator circuit IC1 in the above embodiment, a step-down regulator “SAI01” or the like manufactured by Sanken Electric may be used as shown in FIG. .

  FIG. 3 is a circuit diagram of a switching power supply device according to a modification of the present invention. When “SAI01” is used as the step-down regulator circuit IC1, an inductor L3 is inserted in series between the output terminal of the IC1 and the slave output terminal 23 as an external component, and the output terminal of the IC1 and GND (0 [0 [ V]) may be added with a diode D6. As shown in the figure, a bipolar transistor may be used in place of the FET as the “third switching element” (Q3) of the present invention.

DESCRIPTION OF SYMBOLS 1 Main output switching regulator 2 Sub output regulator 11 Active filter circuit 12 Rectification smoothing part 13 Main output terminal 21 Main output control circuit 23 Sub output terminal A1 Active filter control circuit C2 (Active filter circuit) Capacitor C9 Delay capacitor D1 (Active filter) Diode IC1 step-down regulator circuit (step-down regulator part)
L1 inductor (step-up inductor)
Q1 FET (first switching element)
Q2 FET (second switching element)
Q3 FET, bipolar transistor (third switching element)
Q4 FET (fourth switching element)
T1 transformer

Claims (3)

The DC input voltage obtained by rectifying and smoothing the AC input voltage is boosted to a predetermined primary DC voltage by an active filter circuit, and the primary DC voltage is reduced by a first switching element connected to the primary winding of the transformer. An AC induced voltage is induced in the secondary winding of the transformer by switching, and a main output voltage is generated from a secondary side DC voltage obtained by rectifying and smoothing the AC induced voltage by a rectifying and smoothing unit. A main output switching regulator that outputs,
In a switching power supply device comprising a secondary output regulator that steps down the secondary side DC voltage in a step-down regulator unit and outputs a secondary output voltage from a secondary output terminal.
The main output switching regulator is interposed between the rectifying / smoothing unit and the main output terminal, and is switched on / off to switch conduction / non-conduction between the rectifying / smoothing unit and the main output terminal. Having a second switching element;
The secondary output regulator has a main output control circuit that controls an on / off state of the second switching element,
The main output control circuit turns off the second switching element while the active filter circuit boosts the DC input voltage to the primary DC voltage after the slave output voltage is output from the slave output terminal. And switching the DC input voltage to the primary DC voltage and then turning on the second switching element to output the main output voltage from the main output terminal. The main output control circuit is electrically connected to the third switching element that switches the on / off state of the second switching element and the slave output terminal, and switches the third switching element from the off state to the on state. A delay capacitor capable of outputting a threshold voltage, and when the slave output voltage is output from the slave output terminal and the threshold voltage is output from the delay capacitor to the third switching element, the third switching element is The second switching element is configured to switch from an off state to an on state,
The period from the output of the slave output voltage from the slave output terminal to the output of the threshold voltage from the delay capacitor is from the output of the slave output voltage from the slave output terminal to the active filter circuit. 2. The switching power supply device according to claim 1, wherein the switching power supply device is equal to or longer than a period until the DC input voltage is boosted to the primary DC voltage. The active filter circuit is connected to a boosting inductor to which the DC input voltage is input at one end, a diode having an anode connected to the other end of the boosting inductor, and a connection connecting the boosting inductor and the diode. A fourth switching element controlled by the active filter control circuit, and a capacitor connected to the cathode of the diode,
3. The switching power supply device according to claim 1, wherein the primary side DC voltage is generated between terminals of the capacitor by fully charging the capacitor.

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