JP4143154B2 - Power supply device and electronic device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a step-down rectifying / smoothing circuit that is effective in reducing harmonic components, a power supply device configured by connecting a DC / DC converter at the subsequent stage of the step-down rectifying circuit, and a copier or printer equipped with the power supply device It is related with electronic equipment.
[0002]
[Prior art]
In recent years, problems such as malfunctions of various electronic devices due to distortion waveforms (power supply harmonic distortion) of commercial power supply lines have become serious. In order to suppress the occurrence of such harmonic distortion, laws that regulate harmonic components of input currents input to electronic devices are being developed.
[0003]
Generally, a capacitor input type rectifier circuit in which a capacitor 52 is provided on the output side of a diode bridge 51 as shown in FIG.
[0004]
Accordingly, only during the phase near the voltage peak of each commercial power supply, current flows from the commercial power supply Vin (AC) to the capacitor 52 through the diode bridge 51, and this causes the input current to flow from the commercial power supply Vin (AC) to the electronic device. Becomes a peak current waveform and includes many harmonic components.
[0005]
Conventionally, in order to sufficiently reduce such harmonic components, (1) one choke coil 53 between a commercial power source Vin (AC) and a diode bridge 51 of a capacitor input type rectifier circuit as shown in FIG. To increase the conduction angle of the input current. (2) As shown in FIG. 8, a boost type active filter circuit is used for the power input circuit to obtain an input current waveform similar to the input voltage waveform. Such a method has been proposed.
[0006]
In FIG. 8, 61 is a diode bridge, 67 is a flywheel diode (hereinafter simply referred to as a diode), 64 and 65 are choke coils, 62, 63 and 68 are capacitors, 66 is an FET, 60a, 60b, 69a, 69b is a resistor, 71 is a current detection circuit, 72 is a first voltage detection circuit, 73 is a second voltage detection circuit, 74 is a multiplier, 75 is an error amplification circuit, and 76 is a PWM (pulse width modulation) control circuit.
[0007]
However, according to the method (1) shown in FIG. 7, the inductance of the choke coil 53 needs to be about 10 mH. To achieve this, the choke coil 53 is enlarged, the circuit is made smaller and lighter. There was a problem that it was difficult to make it easier. This point will be specifically described.
[0008]
S1 to S3 in FIG. 9 indicate output voltage (rectified voltage) Vo (DC) with respect to the input voltage Vin (AC) obtained when the load power Po is 200 W in the power input circuit shown in FIGS. FIG. 10 shows the relationship between the output voltage Vo (DC) and the load power Po obtained when the input voltage Vin applied to the power supply input circuit is 230V.
[0009]
In both figures, S1 shows the characteristics when the capacitor input type rectifier circuit shown in FIG. 6 is used, and S2 shows the characteristics when one choke coil 53 is added to the capacitor input type rectifier circuit shown in FIG. S3 shows the characteristics when the step-up active circuit shown in FIG. 8 is used. S4 will be described later.
[0010]
As is apparent from FIGS. 9 and 10, in the circuit in which the choke coil 53 is added, when the load power Po increases or when the input current Iin increases due to a decrease in the input voltage Vin, the impedance of the choke coil 53 increases. The output voltage Vo is significantly reduced. For this reason, it is necessary to expand the operating range of the DC / DC converter connected to the subsequent stage to a low input voltage, or to increase the capacity of the capacitor 52 as a countermeasure against an instantaneous power failure. There has been a problem that the latter-stage DC / DC converter is increased in size.
[0011]
Further, according to the above method (2) shown in FIG. 8, the current ΔI flowing through the choke coil 65 when the transistor 66 is in the on state is the Ton during the on state of the transistor 66 and the inductance of the choke coil 65. Is represented by the following expression (1).
[0012]
ΔI = Vin / L65 * Ton (1)
As is clear from the equation (1), in order to reduce the burden on the transistor 66, it is necessary to increase the inductance of the choke coil 65 (generally, a choke coil of about several mH is used). Therefore, the size of the choke coil 65 or the current capacity of the transistor 66 must be increased. Further, since energy is stored in the choke coil 65 only when the transistor 66 is on, the peak value of the current flowing through the transistor 66 must be increased.
[0013]
Further, in order to realize a boost type active circuit, a complicated control circuit is required as shown in FIG. Therefore, even if the method (2) is used, there are problems that the efficiency is reduced due to the complexity of the power input circuit, the power input circuit is enlarged, the noise is increased, and the cost is greatly increased.
[0014]
In order to solve these problems, a step-down active filter circuit as shown in FIG. 11 has been proposed. In FIG. 11, the step-down active filter circuit has a diode bridge 110, which is connected to a commercial power source Vin. The output terminal of the diode bridge 110 includes a low-pass filter 111 including a choke coil 111a and capacitors 111b and 111c, a transistor 112a that is a switching element such as an FET, a flywheel diode (hereinafter simply referred to as a diode) 112b, and a smoothing capacitor 112c. And a step-down chopper circuit 112 composed of a choke coil 112d and connected to a circuit (not shown) such as a DC / DC converter in the subsequent stage.
[0015]
In this step-down active filter circuit, the inductance value of the choke coil 112d is set so that the choke coil 112d can operate in the current discontinuous mode even at the maximum load.
[0016]
The output terminal of the step-down chopper circuit 112 is connected to the input terminal of the differential amplifier circuit 114, and the output terminal of the differential amplifier circuit 114 is connected to one connection terminal of the error amplifier circuit 115. The other input terminal of the error amplifier circuit 115 is connected to the reference voltage Vref, and the output terminal is connected to a PWM (pulse width modulation) control circuit 116.
[0017]
The output voltage Vo of the step-down chopper circuit 112 is input to the error amplifier circuit 115 via the differential amplifier circuit 114 and compared with the reference voltage Vref. A signal corresponding to the difference between the output voltage Vo and the reference voltage Vref is input from the error amplifier circuit 115 to the PWM control circuit 116. The PWM control circuit 116 inputs a rectangular wave signal having an on / off ratio corresponding to the output signal of the error amplification circuit 115 to the transistor 112 a of the step-down chopper circuit 112. As a result, the output voltage Vo is feedback controlled so as to take a constant value according to the reference voltage Vref.
[0018]
In the above configuration, the voltage Vs after the commercial power supply Vin is rectified by the diode bridge 110 (hereinafter referred to as a rectified voltage) Vs is input to the low-pass filter 111, and the output of the low-pass filter 111 is input to the step-down chopper circuit 112. . The transistor 112a is controlled at a predetermined frequency sufficiently higher than the frequency of the input commercial power supply Vin and at a predetermined on-duty so that the output voltage Vo of the step-down chopper circuit 112 takes a predetermined value.
[0019]
By such an operation, the voltage Vs after rectification by the diode bridge 110 gradually increases as shown in FIG. 12A, and the period after the rectified voltage Vs is larger than the output voltage Vo, that is, from the time t1 to the time t2 in FIG. 12b and the current Is shown in FIG. 12B flows between time t3 and time t4. That is, since the conduction angle of the input current corresponds to a period in which Vs> Vo, by setting the output voltage Vo to an appropriate value (for example, Vo <250 V for the input 230V system), the harmonic current is reduced. It becomes possible to suppress.
[0020]
S4 in FIG. 9 shows the relationship of the output voltage (voltage after rectification) Vo (DC) to the input voltage Vin (AC) obtained when the load power Po is 200 W in the power supply input circuit shown in FIG. S4 in FIG. 10 shows the relationship of the output voltage Vo (DC) with respect to the load power Po obtained when the input voltage Vin is 230V.
[0021]
As is apparent from both figures, the output voltage Vo is controlled to take a constant value even when the load power Po changes, and also when the input voltage Vin is larger than a predetermined value (190 V in the illustrated example). It is controlled to take a constant value. Further, when the input voltage Vin is less than or equal to a predetermined value, the transistor 112a is always controlled to be on, and thus exhibits the same characteristics as those of a conventional capacitor input type rectifier circuit.
[0022]
The operation of the power supply input circuit shown in FIG. 11 will be described below with reference to FIG. FIG. 13 is a diagram showing changes in the output current Is of the diode bridge 110 and the current IL flowing through the choke coil 112d.
[0023]
At t1 in FIG. 13, when Vs> Vo, the current IL starts to flow through the choke coil 112d. For example, when the transistor 112a is turned on during the period Ton from t2 to t3, the current IL flowing through the choke coil 112d increases. When the transistor 112a is turned off at t3, the current IL flowing through the choke coil 112d gradually decreases and becomes zero at t4 after Toff 'has elapsed from t3. In addition, at time t5 (Toff> Toff ′) after the transistor 112a is turned off at t3, the transistor 112a is turned on again, and the same operations as those after t2 are repeated.
[0024]
The current IL flowing through the choke coil 112d changing in this way is obtained as follows.
[0025]
[Period of Vs ≦ Vo]
When the transistor 112a is on, the current IL flowing through the choke coil 112d and the transistor 112a is IL = 0. The current IL = 0 also when the transistor 112a is in the off state.
[0026]
[Period of Vs> Vo]
When the transistor 112a is on, the current IL flowing through the choke coil 112d and the transistor 112a is
IL = {(Vs−Vo) / Ld} * T
Where Ld: inductance of choke coil 112d
And increases with time T. Its peak value Ip is
Ip = {(Vs−Vo) / Ld} * Ton
It is.
[0027]
On the other hand, when the transistor 112a is off, the current IL flowing through the choke coil 112d and the diode 112b is
IL = Ip- {Vo / Ld * T}
And decreases with time T. Therefore, the time Toff ′ until the value of the current IL becomes 0 is
Toff ′ = {(Vs−Vo) / Vo} * Ton
It is represented by
[0028]
In the step-down active filter circuit, as shown in FIG. 13, Toff ′ <Toff (where Toff is a period during which the transistor 112a is turned off) even at the maximum load, that is, at the maximum load. However, the inductance value of the choke coil 112d is determined so that the choke coil 112d can operate in the current discontinuous mode. Thereby, all the energy stored in the choke coil 112d is released every period.
[0029]
Since the value of the input current Is is a value obtained by filtering the current flowing through the transistor 112a with the low-pass filter 111,
[0030]
[Expression 1]
Is = 1 / T * [(1/2) * Ton * Ip]
= Ton ^ 2 / (2 * T * Ld) * (Vs-Vo)
It is represented by
[0031]
The input current waveform is proportional to the difference (Vs−Vo) between the input voltage (voltage after rectification) Vs and the output voltage Vo. For example, when the rectified voltage Vs is a sine wave, by setting an appropriate value as the output voltage Vo (Is becomes a waveform obtained by cutting off a part of the sine wave), the conduction angle of the input current is Can be set to any value.
[0032]
It should be noted that the duty at which the transistor 112a is turned on is desirably set to be small enough to discharge all the energy stored in the choke coil 112d as described above, and the duty is the rectifier circuit. Is preferably set according to the load power applied to the power input circuit to which is applied, or according to the input current to the rectifier circuit.
[0033]
The step-down active filter circuit has the following excellent features.
[0034]
(1) By simply setting the reference voltage Vref to an appropriate value (by simply setting the rectified voltage Vo to an appropriate value), the conduction angle of the input current can be set. Harmonics can be suppressed with a simple configuration.
[0035]
(2) As shown in FIG. 9, when the input voltage is low, the characteristics similar to those of the capacitor input type rectifier circuit are exhibited. Therefore, as in the circuit shown in FIG. 7 in which the choke coil is simply added to the input, the load power It is possible to prevent a decrease (S2) in the output voltage Vo due to the increase in. For this reason, it is not necessary to expand the input voltage range of a DC / DC converter or the like connected to the subsequent stage to the low voltage side, and further, it is not necessary to increase the capacity of the smoothing capacitor as a measure against instantaneous power failure.
[0036]
(3) Since the output voltage Vo is controlled to be lower than the peak value of the input voltage, the upper limit value of the output voltage Vo can be set lower than that of the capacitor input type rectifier circuit and is connected to the subsequent stage. The input voltage range of a DC / DC converter or the like can be narrowed. Therefore, an element having a low withstand voltage can be used as an element such as a DC / DC converter connected in the subsequent stage, and the element can be reduced in size, reduced in noise, and reduced in cost.
[0037]
(4) When the step-up active filter circuit shown in FIG. 8 is used, the voltage applied to the choke coil 65 is Vs. However, according to the step-down active filter circuit, the voltage applied to the choke coil 112d is (Vs− Vo). Therefore, since the inductance value of the choke coil 112d can be reduced, the circuit can be reduced in size and cost.
[0038]
(5) The control circuit can be simplified as compared with the step-up active filter circuit.
[0039]
(6) Since the transistor 112a is a serial element of the rectifier circuit, the rectifier circuit can be used as an inrush current limiting circuit using the transistor 112a. Therefore, power devices such as a triac and a thyristor can be omitted as an inrush current limiting circuit required for a power supply input circuit using a conventional capacitor input type rectifier circuit or a boost type active filter circuit.
[0040]
(7) Since the configuration of the power supply circuit is simplified, noise can be reduced.
[0041]
[Problems to be solved by the invention]
However, the power supply device using the conventional step-down active filter circuit has the following problems.
[0042]
  In general,Alternating currentWhen the commercial power supply 230V is input, the output voltage of the step-down active filter circuit is controlled to be about 200V to 220V. However, in the step-down active filter circuit, for example, when the switching element is fixed to ON when the control circuit or the switching element fails, the peak value of the input commercial power supply (for example, 230 * 1 in the case of 230 V input)..4 = 322V). Therefore, an overvoltage protection measure is taken for the subsequent DC / DC converter.
[0043]
  This will be described more specifically. For example, considering the case where control is performed using the PWM control circuit 116 so that the output voltage of the step-down active filter circuit becomes 200 V, and the DC / DC converter 113 in the subsequent stage is designed in the forward type, the DC / DC Switching element of converterFor childSince a voltage of about 400 V is applied during normal operation, an element having a breakdown voltage of 450 V to 500 V is generally used as the switching element.
[0044]
However, when the step-down active filter circuit fails as described above, the input voltage is 322 V, a voltage of 644 V is applied to the switching element of the DC / DC converter, and an element with a withstand voltage of 500 V is damaged (generally a short mode failure).
[0045]
Therefore, there is a method using an element having a withstand voltage of 900 V as a switching element of the DC / DC converter. However, according to this method, the on-resistance of the switching element increases (in general, the on-resistance of the FET is the square of the withstand voltage). In addition to an increase in power loss and an increase in the size of the device, it is also disadvantageous in terms of cost.
[0046]
In addition, a switching device such as a triac can be added in series with the commercial power supply line to turn off the triac when overvoltage occurs. However, the input current flows to the on-voltage (about 1.5V) of this triac during normal operation. Therefore, considerable power loss occurs, and it is disadvantageous in terms of cost.
[0047]
Further, the conventional step-down active filter circuit has a problem that it is very difficult to design a choke coil. That is, when a choke coil is manufactured by winding a core material such as ferrite, the number of turns is reduced if an optimum inductance is to be obtained because the magnetic permeability of the core material is large. Then, when the switching element 112a is turned on,
(Input voltage-output voltage) * (ON time of switching element 112a)
Thus, only the magnetic flux is received by the choke coil having a small number of turns, the magnetic flux density of the core material is increased, the core loss in the core is considerably increased, and the temperature rise of the choke coil is increased.
[0048]
If there is a material with low loss and low magnetic permeability as the core material, it can be solved, but there is no suitable material. Even if it exists (the same applies to the air-core coil and the core having a large gap), the leakage of the magnetic field becomes large, causing current to flow in the magnetic field, leading to excessive copper loss and circuit (self- In many cases, it is inappropriate.
[0049]
It may be possible to connect N choke coils in parallel and use a relatively large number of turns to make the inductance of the choke coil 1 / N, but in that case, the current balance between the choke coils is secured. It is difficult to do and disadvantageous in terms of cost and size.
[0050]
  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a power supply device that enables an overvoltage protection configuration with low power loss and high cost in a combination of a step-down rectifier circuit and a subsequent DC / DC converter. To do. Moreover, it aims at providing the electronic device carrying this power supply device..
[0051]
[Means for Solving the Problems]
  In order to achieve the above object, in the first invention, the rectifying means for rectifying an AC commercial power supply, the voltage step-down means for stepping down the input voltage rectified by the rectifying means, and the output voltage of the voltage step-down means are In a power supply device configured by connecting a DC / DC converter to a subsequent stage of a step-down rectifier circuit having output voltage control means for controlling to a predetermined value lower than the peak value of the input voltage,The voltage step-down means has a choke coil and a switching element connected in series to the output side of the rectifying means, and steps down the input voltage rectified by the rectifying means based on the operation of the choke coil and the switching element. The output voltage control means is a switching element control means for controlling a period during which the switching element is in an ON state at a frequency higher than the frequency of the input commercial power supply and to the extent that current flows discontinuously through the choke coil. A current monitoring means for monitoring the current flowing through the switching element of the voltage step-down means, and when there is no longer a period during which the current flowing through the switching element is zero or less than a predetermined value; andThe operation of the DC / DC converter is stopped when the output voltage of the voltage step-down means, which is the output of the step-down rectifier circuit, becomes higher than a set value.
[0053]
  First2In the invention of the above,1'sIn the present invention, the operation of the DC / DC converter is stopped by fixing a switching element in the DC / DC converter off.
[0054]
  First3In the invention, the rectifying means for rectifying the AC commercial power supply, the voltage step-down means for stepping down the input voltage rectified by the rectifying means, and the output voltage of the voltage step-down means are controlled to a predetermined value lower than the peak value of the input voltage. In an electronic device that includes a power supply device configured by connecting a DC / DC converter at a subsequent stage of a step-down rectifier circuit having an output voltage control means that performs a predetermined operation using the power supply device as an operating voltage.The voltage step-down means of the power supply device has a choke coil and a switching element connected in series on the output side of the rectifying means, and an input rectified by the rectifying means based on the operation of the choke coil and the switching element The output voltage control means controls a period during which the switching element is in an ON state at a frequency higher than the frequency of the input commercial power supply and to the extent that current flows discontinuously through the choke coil. A configuration including a switching element control means, provided with a current monitoring means for monitoring a current flowing through the switching element of the voltage step-down means;The power supply deviceWhen there is no period during which the current flowing through the switching element is zero or less than a predetermined value; andThe operation of the DC / DC converter is stopped when the output voltage of the voltage step-down means, which is the output of the step-down rectifier circuit, becomes higher than a set value.
[0056]
  First4In the invention of the above,3In this invention, the operation of the DC / DC converter is stopped by fixing the switching element in the DC / DC converter to OFF.
[0061]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0062]
(First embodiment)
FIG. 1 is a block diagram showing a schematic configuration of the power supply device according to the first embodiment of the present invention. Elements common to those in FIG. 11 are denoted by the same reference numerals.
[0063]
  This power supply apparatus is configured by connecting a DC / DC converter 113 subsequent to the conventional step-down active filter circuit shown in FIG. 11, and further, an output of the step-down chopper circuit 112 that is an output of the step-down active filter circuit. An overvoltage detection circuit 117 that detects that the voltage Vo has become higher than a set value and outputs a stop signal CS is provided, and the DC / DC converter 113 receives the stop signal CS.In the DC / DC converter 113The switching element 113a is fixed off and the operation is stopped.
[0064]
Here, since the set value is generally controlled to about 200V to 220V at the time of 230V input in the step-down active filter circuit, it is set to 225V, for example.
[0065]
The DC / DC converter 113 includes a switching element 113a, a transformer 113b, diodes 113c and 113d, a choke coil 113e, and a smoothing capacitor 113f, and further includes a control circuit 113g that controls the switching operation of the switching element 113a. When the control circuit 113g receives the stop signal CS from the overvoltage detection circuit 117, the switching element 113a is fixed off.
[0066]
A case will be described in which the switching element 112a of the step-down active filter circuit is always turned on due to a failure or the like, and the step-down active filter circuit generates an output overvoltage.
[0067]
For example, when the gate signal of the switching element 112a is fixed to the “H” level and the switching element 112a is fixed to the on state due to a failure of the PWM control circuit 116, the step-down active filter circuit It becomes the same as the rectifier circuit, and rectifies and smoothes the peak value of the input commercial power supply Vin (AC). That is, in the case of 230 V (AC) input, the step-down active filter circuit outputs a voltage of 322 V (DC), and this voltage is supplied as the input voltage of the subsequent DC / DC converter 113.
[0068]
At this time, the overvoltage detection circuit 117 outputs the stop signal CS because the output voltage Vo has become higher than the set value. Upon receiving this stop signal CS, the control circuit 113g of the DC / DC converter 113 fixes the switching element 113a in the DC / DC converter 113 to be off and stops the switching operation.
[0069]
In a state where the switching element 113a of the DC / DC converter 113 is fixed off, the voltage applied to the switching element 113a is the input voltage 322V itself of the DC / DC converter 113. That is, with a commercial 230V (AC) input, even if the switching element 112a is fixed to the ON state due to a failure of the step-down active filter circuit, the voltage of 230 * 1.4 = 322V or more is The switching element 113a is not added.
[0070]
Therefore, a general 450V to 500V withstand voltage element can be used as the switching element 113a of the DC / DC converter 113. That is, for example, when the downstream DC / DC converter 113 is designed as a forward type by controlling the PWM control circuit 116 so that the output voltage Vo of the step-down active filter circuit becomes 200 V, Since a voltage of about 400 V (twice the input voltage Vin + α) is applied to the drain of the switching element 113a of the DC / DC converter 113 during normal operation (a state in which the switching element 113a is performing a switching operation). Generally, an element having a withstand voltage of 450V to 500V is used as the switching element 113a. The drain voltage waveform of the switching element 113a is shown in FIG.
[0071]
In addition, a voltage of 322 V (DC) is applied to the smoothing capacitor 112 c of the step-down active filter circuit, but a certain type of 250 V withstand voltage electrolytic capacitor does not fail even when a voltage of about 400 V is applied if the load is light. Things are also known. This electrolytic capacitor is used as the smoothing capacitor 112c of this embodiment.
[0072]
As described above, the power supply device according to the present embodiment stops the switching element of the subsequent DC / DC converter when the overvoltage of the output voltage of the step-down active filter circuit is detected. Therefore, the switching element of the DC / DC converter is stopped. And overvoltage breakdown of the secondary side rectifier diode and the like can be prevented.
[0073]
  The power supply device of this embodiment is used in an electronic device such as a copying machine.As operating voltageIn use, as described above, when the output overvoltage of the step-down active filter circuit is detected, if the DC / DC converter is stopped, the 5V power supply for controlling the device is lost, and the system goes down. At that time, by automatically turning off the main switch, the failure of the step-down active filter circuit does not spread to other blocks of the device.
[0074]
In such a power supply device of this embodiment, there is no power loss due to the overvoltage protection circuit unlike the conventional power supply device, and the cost is hardly increased.
[0075]
(Second Embodiment)
FIG. 3 is a block diagram showing a schematic configuration of a power supply device according to the second embodiment of the present invention. Elements common to those in FIG.
[0076]
In the configuration of FIG. 1, a zero current detection circuit 118 and an AND gate 119 are provided.
[0077]
  The zero current detection circuit 118 detects the current flowing through the switching element 112a of the step-down active filter circuit.MonitoringShi(Current monitoring means)Then, when there is no period when the current becomes zero or when the current becomes smaller than a predetermined value, the signal CG of “L” level is output. The AND gate 119 receives the “L” level signal CG from the zero current detection circuit 118 and the “H” level signal (when overvoltage is detected) from the overvoltage detection circuit 117, and then controls the control circuit 113g of the DC / DC converter 113. A stop signal CS is output. Thus, the switching element 113a of the DC / DC converter 113 is fixed off.
[0078]
  That is, the drain current of the switching element 112a of the step-down active filter circuit is monitored, and when the current becomes continuous (that is, when the switching element 112a is fixed on), the output voltage of the step-down active filter circuit When Vo becomes a predetermined value or more, it is determined (predicted) that an abnormal voltage has occurred in the output of the step-down active filter circuit (for example, the on-state of the transistor 112a is fixed), and the DC / DC converter in the subsequent stage 113 switching elements are fixed off(Switching element control means).
[0079]
As a result, it is possible to quickly and reliably detect an increase in the voltage of the smoothing capacitor 112c of the step-down active filter circuit, so that an overvoltage is applied to the switching element 113a of the subsequent DC / DC converter 113 even instantaneously. Anomalies can be detected and stopped without incident. Further, without worrying about malfunction of the detection circuit 117, the overvoltage detection point can be set in the vicinity of the step-down rectified voltage during normal operation (for example, about 205V).
[0080]
As described above, in the present embodiment, as a means for detecting the output overvoltage, a method for detecting that the period in which the current flowing through the switching element of the step-down active filter circuit is zero is eliminated, and the output voltage of the step-down active filter circuit is Since the direct detection method is combined, the response of the overvoltage protection means can be made quick and there is no malfunction.
[0081]
(Third embodiment)
FIG. 4 is a block diagram showing a schematic configuration of a power supply device according to the third embodiment of the present invention. Elements common to those in FIG. 11 are denoted by the same reference numerals.
[0082]
In the present embodiment, in the step-down active filter circuit shown in FIG. 11, as the choke coil of the step-down chopper circuit 112, a common mode choke coil 121 in which two windings are wound with the same number of turns on the same core is used. Two windings are connected in series so that magnetic fluxes generated from each other cancel each other.
[0083]
That is, the common mode choke coil 121 uses a common mode choke coil using a high permeability core material (for example, for countermeasures against power line noise). Inductance uses leakage inductance, and the amount of leakage magnetic field is also smaller than that of an air-core coil.
[0084]
Usually, the common mode choke coil is obtained by winding two windings (two in a single-phase system and three in a three-phase AC system) on the same core by the same number of turns. As a general application, as shown by 120 in FIG. 4, each winding is inserted in series with the L / N pole of the commercial power supply line, the inductance value is almost zero in the normal mode, and large in the common mode. It is used as a noise filter by connecting to a polarity where inductance can be seen.
[0085]
However, the two windings are not 100% coupled through the core, leaving a slight normal mode component inductance. This is called leakage inductance. In the case of the above filter, the leakage inductance is a slight impedance with respect to the commercial power supply frequency, but is sufficient for use in a step-down active rectifier circuit at about 100 KHz or higher.
[0086]
The leakage inductance is characterized by (1) several times larger than the air core inductance obtained by removing the core from the common mode choke coil. Zero. (3) Since the magnetic path is closed, the leakage magnetic field is smaller than that of an air core coil or a coil using a large gap core.
[0087]
In the present embodiment, the common mode choke coil having such characteristics is used as the choke coil in the step-down active filter circuit, so that it is equivalently low loss (low core iron loss), low permeability, and leakage. The choke coil has a small magnetic field and exhibits ideal characteristics. Furthermore, a common mode choke coil using a core material with a high permeability can obtain a sufficient leakage inductance, so that the number of turns of the winding is small and the copper loss in the winding is also reduced.
[0088]
(Fourth embodiment)
FIG. 5 is a block diagram showing a schematic configuration of a power supply device according to the fourth embodiment of the present invention, and the same reference numerals are given to elements common to FIG.
[0089]
In the present embodiment, in the step-down active filter circuit shown in FIG. 11, the common mode choke coil 130 in which two windings are wound around the same core with the same number of turns is used as the choke coil of the step-down chopper circuit 112. It is.
[0090]
The common mode choke coil 130 includes two windings, a first winding and a second winding, and a first winding, a smoothing capacitor 112c, and a second winding loop. The polarity is such that the magnetic flux generated by the windings cancel each other, and is connected to the high side and the low side of the step-down chopper circuit 112, respectively.
[0091]
By inserting the common mode choke coil 130 as described above, an effect as a common mode filter such as a subsequent DC / DC converter is produced, and the amount of noise filters to be inserted into the commercial power supply circuit can be reduced.
[0092]
【The invention's effect】
As described in detail above, according to the power supply device of the first invention, the overvoltage protection means for the failure of the switching element of the step-down rectifier circuit or the malfunction of the output voltage control means can be provided with low loss and low cost. Can be realized.
[0093]
  Also,First1And the second2According to the power supply device of the invention, overvoltage can be detected quickly and reliably. This makes it possible to detect and stop an abnormality without applying an overvoltage to the switching element of the subsequent DC / DC converter even instantaneously.
[0094]
  First3 andFirst4According to the electronic device of the invention, it is possible to prevent the failure of the step-down active filter circuit from spreading to other blocks of the device.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a power supply device according to a first embodiment of the present invention.
FIG. 2 is a drain voltage waveform diagram of a switching element in a DC / DC converter.
FIG. 3 is a block diagram showing a schematic configuration of a power supply device according to a second embodiment of the present invention.
FIG. 4 is a block diagram showing a schematic configuration of a power supply device according to a third embodiment of the present invention.
FIG. 5 is a block diagram showing a schematic configuration of a power supply device according to a fourth embodiment of the present invention.
FIG. 6 is a circuit diagram showing a conventional power input circuit (capacitor input type rectifier circuit).
FIG. 7 is a circuit diagram showing a conventional power input circuit.
FIG. 8 is a circuit diagram showing a conventional power input circuit (step-up active filter circuit).
FIG. 9 is a characteristic diagram of a conventional power input circuit.
FIG. 10 is a characteristic diagram of a conventional power input circuit.
FIG. 11 is a circuit diagram of a conventional step-down active filter circuit.
12 is a waveform diagram showing an operation of the circuit of FIG.
FIG. 13 is a diagram showing changes in the output current Is of the diode bridge and the current IL flowing through the choke coil.
[Explanation of symbols]
110 Diode bridge
111 Low-pass filter
112a switching element
112d choke coil
112 Step-down chopper circuit
113 DC / DC converter
113a Switching element
114 Differential amplifier circuit
115 Error amplification circuit
116 PWM (pulse width modulation) control circuit
117 Overvoltage detection circuit
118 Zero current detection circuit
121 Common mode choke coil

Claims (4)

Rectifying means for rectifying AC commercial power, voltage step-down means for stepping down the input voltage rectified by the rectifying means, and output voltage for controlling the output voltage of the voltage step-down means to a predetermined value lower than the peak value of the input voltage In a power supply device configured by connecting a DC / DC converter to a subsequent stage of a step-down rectifier circuit having a control means,
The voltage step-down means has a choke coil and a switching element connected in series to the output side of the rectifying means, and steps down the input voltage rectified by the rectifying means based on the operation of the choke coil and the switching element. With composition,
The output voltage control means includes a switching element control means for controlling a period during which the switching element is in an ON state at a frequency higher than the frequency of the input commercial power supply and to the extent that current flows discontinuously through the choke coil.
Providing a current monitoring means for monitoring a current flowing through the switching element of the voltage step-down means;
When the period when the current flowing through the switching element is zero or when there is no period smaller than a predetermined value, and when the output voltage of the voltage step-down means that is the output of the step-down rectifier circuit becomes higher than a set value, A power supply apparatus configured to stop the operation of the DC / DC converter. The stop of the DC / DC converter operation, the power supply device according to claim 1, characterized in that fixed to off the switching element in the DC / DC converter. Rectifying means for rectifying an AC commercial power supply, voltage step-down means for stepping down the input voltage rectified by the rectifying means, and output voltage control for controlling the output voltage of the voltage step-down means to a predetermined value lower than the peak value of the input voltage In an electronic device that includes a power supply device configured by connecting a DC / DC converter at a subsequent stage of a step-down rectifier circuit having a means, and that performs a predetermined operation using the power supply device as an operating voltage,
The voltage step-down means of the power supply device has a choke coil and a switching element connected in series on the output side of the rectifying means, and an input rectified by the rectifying means based on the operation of the choke coil and the switching element With a configuration that reduces the voltage,
The output voltage control means includes a switching element control means for controlling a period during which the switching element is in an ON state at a frequency higher than the frequency of the input commercial power supply and to the extent that current flows discontinuously through the choke coil.
Providing a current monitoring means for monitoring a current flowing through the switching element of the voltage step-down means;
The power supply device
When the period when the current flowing through the switching element is zero or when there is no period smaller than a predetermined value, and when the output voltage of the voltage step-down means that is the output of the step-down rectifier circuit becomes higher than a set value, An electronic apparatus characterized in that the operation of the DC / DC converter is stopped. 4. The electronic apparatus according to claim 3 , wherein the operation of the DC / DC converter is stopped by fixing a switching element in the DC / DC converter to be off.

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