JP2001045756A - Power supply - Google Patents

Abstract

(57) Abstract: A power supply device for supplying an output voltage applied to a secondary side of a transformer to a load by intermittently supplying a current to a primary side of the transformer.
Provided is an electric device capable of reducing the capacity of a smoothing capacitor provided on the next side. SOLUTION: A bidirectional photocoupler Q4 and a resistor R3 are provided.
The presence / absence of a power failure of the commercial power supply is detected by the circuit comprising the power failure detection signal ACDWN
* The reference voltage Vx input to the generation comparator COMP1 is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device such as a switching regulator, and more particularly, to a power supply device having a power failure detection circuit for detecting a power failure and outputting a notice signal indicating the power failure.

[0002]

2. Description of the Related Art A conventional power supply device, particularly a switching regulator, detects a power failure by a method as shown in FIGS. 6 and 7, for example. Before describing the method of detecting a power failure, first, the operation of the switching regulator will be briefly described.

FIG. 6 is a diagram showing an example of a circuit configuration of a switching regulator.

In FIG. 1, an AC power input from a commercial power supply Vin (AC) is a diode bridge circuit DB.
1 and the capacitor C1, rectified and smoothed, and B
A DC voltage Vin (DC) is applied to the point. This applied voltage Vin (DC) is high-frequency switched by a switching element (FET) Q1 through a primary winding N11 of a transformer T1, and a rectangular pulse voltage is applied to a secondary winding N21 of the transformer T1. , Diodes D11 and D12, coil L11 and capacitor C1
1 is rectified and smoothed by a circuit consisting of
Is output.

The output voltage Vo is detected by a detection circuit including resistors R11 to R13 and a Zener diode Q3.
The signal is fed back to the primary side via the photocoupler Q2.

The switching of the primary winding N11 also induces a voltage in the primary winding N12, and this induced voltage is rectified by a circuit including a diode D1 and a capacitor C3, and the PRM. The power supply PVcc of the CTL circuit 1 is used. PRM. The CTL circuit 1
The on / off ratio of the switching element Q1 is adjusted according to the feedback signal transmitted from the secondary side by the photocoupler Q2, and the output voltage Vo is controlled to a desired voltage.

Next, detection of a power failure by the conventional switching regulator will be described.

[0008] The output voltage Vo follows the following equation (1).

Vo = Vin (DC) × (N21 / N11) × {Ton / (Ton + Toff)} (1) where Ton indicates the on time of the switching element Q1, and Toff indicates the off time of the switching element Q1. Indicates time.

FIGS. 7A to 7E show a voltage Vin (AC) at point A, a voltage Vin (DC) at point B, an on / off ratio Ton / (Ton + Toff), and an output voltage V, respectively.
o is a diagram showing a transition of a power failure detection signal ACDWN *,
When the commercial power supply is cut off due to a power failure or the like at time t1 in the figure, the voltage Vin (DC) gradually decreases as shown in (b). Accordingly, the switching element Q1
The on-time Ton of is increased as shown in (1),
Control is performed to keep the output voltage Vo at a desired value.

[0011] The voltage Vin (DC) decreases, and at time t3
Then, the on-time Ton of the switching element Q1 is the maximum value (in the forward-switching type switching regulator in the illustrated example, Ton (max) = ｛Ton in general).
+ Toff｝ / 2), the output voltage Vo
Decreases as shown in (d). The voltage V at this time
The value of in (DC) is “Vmr”, and the voltage Vin (D
The value before C) starts to decrease is defined as “Vs”.

The time Ts from when the voltage Vin (DC) drops to reach “Vmr” from “Vs” due to the power failure
h is the output voltage Po = (Vo × Io) and the capacitor C
The value is determined as in the following equation (2) based on the energy stored in 1.

Tsh = C1 / 2 × {Vs ² −Vmr ² } / (Po / η) (2) where η indicates the energy conversion efficiency of the power supply circuit.

Here, in order to detect a power failure, the voltage Vi
n (DC) is detected by a voltage Vin (DC) detection circuit including a secondary winding N22 of a transformer T1, a diode D21, a capacitor C21, and a resistor R21.
Before in (DC) reaches “Vmr”, a power failure detection signal ACDWN * is generated and output to a subsequent system device to notify that a power failure has occurred. System equipment
In response to the signal ACDWN *, appropriate measures such as saving the memory contents are performed.

[0015]

However, the conventional power supply has the following problems.

That is, the voltage Vin (D
Assuming that the level of the voltage Vin (DC) that causes the power failure detection signal ACDWN * to decrease to “Vx” is reduced to “Vx”, generally in a commercial power supply, an instantaneous power failure and an instantaneous voltage drop can occur. To C, the voltage level V
x needs to be determined.

Condition A: As an instantaneous blackout of commercial power, Ts
= 20 ms (one cycle of commercial use), the output voltage is maintained and the power failure detection signal ACDWN * is not generated even if a momentary power failure from the rated voltage occurs. 1 at 70% of
Assuming zero cycle (200 ms), in this case, the output voltage is maintained and the power failure detection signal ACDWN * is not generated. Condition C: Disconnection of the commercial power outlet or power failure ($ 20 m
s), the holding time Th after the power failure detection signal ACDWN * is generated until the output voltage starts to decrease.
= 10 ms (time required for the system to take appropriate measures such as saving the memory contents) For example, Vs = 140 V, Vmr = 80 V, Po = V
In order to satisfy the condition B with o × Io = 100 W, η = 0.85, Ts = 20 ms, it is desired not to generate the power failure detection signal ACDWN * at the time of instantaneous voltage fluctuation.

Therefore, Vin (DC) at the time of instantaneous voltage fluctuation = 0.7 × 140 = 98V = V (dw
n) If the following voltage is set, for example, Vx = 97 V, the condition B is satisfied because the power failure detection signal ACDWN * is not generated at the time of instantaneous voltage fluctuation.

Next, condition A is considered.

When Vx = 97 V is set, to prevent the power failure detection signal ACDWN * from being generated even when an instantaneous power failure occurs, C = 2 × Ts / {Vs ² −Vx ² } × {(Vo × Io) / η｝ (3) Therefore, C = 2 × 20 ms / {140 V ² −97 V ² } × {100 W / 0.85} {40/1000 / {10191} × {118}} 463 μF (4) Satisfies A.

Next, condition C is considered.

When a power outlet is disconnected or a power failure occurs,
The time Th from when the power failure detection signal ACDWN * is generated to when the output voltage actually decreases is Th = C1 / 2 × {Vx ² −Vmr ² } / (Po / η).

Therefore, C1 = 2 × (Po / η) × Th / (Vx ² −Vmr ² ) ≒ 2 × 118 × 10 ms / (97 ² −80 ² ) ≒ 784 μF (5) In this case, the condition C is satisfied.

From the above equations (4) and (5), the smoothing capacitor C1 needs a capacity of 784 μF or more.

As described above, in the above-described conventional switching regulator, such a large capacitance is required to stably generate the power failure detection signal ACDWN *.

The present invention has been made in view of this point. By intermittently supplying the commercial power supply current to the primary side of the transformer, the output voltage applied to the secondary side of the transformer is reduced. It is an object of the present invention to provide a power supply device that supplies a load and that can reduce the capacity of a smoothing capacitor provided on the primary side of the transformer.

[0027]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides an intermittent supply of a rectified and smoothed commercial power supply to a primary side of a transformer, thereby applying the output to the secondary side of the transformer. A power failure detection circuit for detecting that the power supply of the commercial power supply has stopped due to a power failure, and a power supply device for rectifying and smoothing the commercial power supply voltage. A rectifying and smoothing circuit including at least a smoothing capacitor, a voltage detecting circuit for detecting a voltage value of a commercial power supply rectified and smoothed by the rectifying and smoothing circuit, and a voltage detected by the voltage detecting circuit. When the value falls below the reference voltage value, a signal output circuit that outputs a power failure notice signal, and variably controls the reference voltage value in accordance with the presence or absence of power failure detection by the power failure detection circuit. And having a control circuit.

[0028] Preferably, the power failure detection circuit comprises:
It is provided on the primary side of the transformer.

Further, preferably, a control circuit is provided on a secondary side of the transformer for controlling the output voltage to a predetermined voltage value, and the power failure detection circuit includes an output from the control circuit. The power failure detection is performed based on

[0030]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an electric circuit diagram showing a circuit configuration of the power supply device according to the first embodiment of the present invention.

The power supply device of the present embodiment is different from the conventional power supply device of FIG. 6 in that a circuit including a resistor R3 and a bidirectional photocoupler Q4 is provided and a reference for generating a power failure detection signal ACDWN *. Since the only difference is that the voltage Vx is variable, in FIG. 1, the same elements as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, a power failure of a commercial power supply is detected by a bidirectional photocoupler Q4 and a resistor R3. Based on the result, the reference voltage Vx input to the comparator COMP1 for generating the power failure detection signal ACDWN * is changed.

FIG. 2 is a diagram showing an example of an electric circuit for changing the reference voltage Vx according to the output of the bidirectional photocoupler Q4.

In the figure, the commercial power supply voltage Vin (A
C) is supplied, the bidirectional photocoupler Q4
Is turned on, and the transistor Q31 is turned off. As a result, the transistor Q32 is turned on, so that the reference voltage Vx input to the comparator COMP1 for generating the power failure detection signal ACDWN * becomes the Zener diode ZD31.
The voltage Vx = ZD31 × R36 / (R35 + R36) obtained by dividing the Zener voltage by the resistors R35 and R36.

Due to a power failure or the like, the commercial power supply voltage Vin (A
When C) is not supplied, the bidirectional photocoupler Q
4 is turned off, and the transistor Q31 is turned on.
As a result, the transistor Q32 is turned off, so that the comparator COMP1 for generating the power failure detection signal ACDWN *
Is a value obtained by dividing the Zener voltage of the Zener diode ZD by the resistors R35, R36 and R37. Vx = ZD31 × (R36 + R37) / (R35 + R3
6 + R37).

As described above, the reference voltage Vx is immediately changed when a power failure of the commercial power supply is detected.

Next, how the capacitance of the smoothing capacitor C1 is reduced by improving the power supply device of the present embodiment with respect to the conventional power supply device as described above will be described. This will be described using an example.

In a power supply having an output power Po = Vo × Io = 100 W and an energy conversion efficiency η = 0.85 of the power supply circuit, a DC input voltage Vin (DC) = 140 V = Vs, and a power failure occurs for a power failure time Ts = 20 ms. Then, if the DC input voltage Vin (DC) = Vx after the time Ts, the following equation holds: C1 / 2 × {Vs ² −Vx ² } = (Po / η) × Ts (6) I do.

Further, the DC input voltage Vin (DC) becomes the reference voltage Vx, a power failure detection signal ACDWN * is generated, and after the time Th = 10 ms, the DC input voltage Vin (DC)
Assuming that C) = Vmr = 80 V and the output starts to decrease, the following equation holds: C1 / 2 × {Vx ² −Vmr ² } = (Po / η) × Th (7)

From the above equations (6) and (7), C1 = 2 × (Po / η) × (Ts + Th) / (Vs ² −Vmr ² ) (8) ≒ 536 μF Vx = √ ｛(Th × Vs ²⁾ + Ts × Vmr ² ) / (Ts + Th)｝ (9) ≒ 103.9 V That is, when a power failure of the commercial power supply is detected, Vx = 10
When 3.9 V is set and a power failure of the commercial power supply is not detected, if Vx = 97 V, the capacitance of the smoothing capacitor C1 may be “536 μF”.

Therefore, 536 μF / 784 μF = 6
The capacitance of the smoothing capacitor C1 can be reduced to 8.4%.

As described above, in the present embodiment, the capacitance of the smoothing capacitor C1 can be reduced, thereby reducing the manufacturing cost and the size of the power supply device.

Further, by reducing the capacity of the smoothing capacitor C1, the energy of the rush current from the commercial power supply to the smoothing capacitor C1 can be reduced, and a series component from the commercial power supply to the smoothing capacitor C1, for example, a switch (Not shown), a rush limiting circuit (not shown) and the like can also use lower rated components.

Next, a power supply device according to a second embodiment of the present invention will be described.

The power supply according to the first embodiment detects the power failure of the commercial power supply directly by using the DC input voltage Vin.
Although (AC) is observed, the power supply device according to the present embodiment is different in that only the secondary side detects a power failure of the commercial power supply. With this configuration,
The present invention is useful when the input voltage on the primary side cannot be directly observed, such as when the substrate configuration is divided at point B in FIG.

FIG. 3 is an electric circuit diagram showing a circuit configuration of the power supply device according to the present embodiment. In the figure, the same elements as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 3, the commercial power supply frequency detecting circuit 2
Detects a power failure based on the frequency component of the commercial power included in the output of the Zener diode Q3, and based on the result,
Comparator COM for generating power failure detection signal ACDWN *
The reference voltage Vx input to P1 is changed.

FIGS. 5A to 5D respectively show point A,
FIG. 4 is a diagram showing changes in voltages applied to points B, C, and D.

In the figure, an AC voltage Vin (AC) input from a commercial power supply is connected to a diode bridge circuit DB.
1 and the capacitor C1, rectified and smoothed, and B
The voltage Vin (DC) generated at the point becomes a pulsating flow having a frequency component twice as high as the commercial power supply frequency. If PRM. C
When the TL circuit 1 is turned on / off at a constant rate, the switching element Q
When switching 1, the output voltage Vo becomes
A pulsating flow similar to point B results. In order to avoid this, the pulsating current is detected by an output voltage detecting circuit including resistors R11 to R13 and a Zener diode Q3.
The primary-side PRM. This is fed back to the CTL circuit 1.

The output voltage detecting circuit 2 and the PRM. Generally, the control response speed of the CTL circuit 1 is set sufficiently faster (about 3 kHz) than one cycle of the commercial power supply frequency. Therefore, the pulsating component is canceled and the pulsating component is eliminated (or sufficiently small) in the output voltage Vo. As a result, a voltage having a ripple twice the commercial power frequency is applied to point D. The power failure can be detected by detecting this by the commercial power frequency detection circuit 2.

FIG. 4 is an electric circuit diagram showing an example of the configuration of the commercial power supply frequency detection circuit 2. The commercial power supply frequency detection circuit 2 in FIG. 4 amplifies a pulsating component at point D by an amplifier circuit. The transistor Q32 is turned on by the AC component.

With this configuration, the present embodiment can provide the same effects as those of the first embodiment.

[0054]

As described above, according to the present invention,
The power failure detection circuit detects the power failure of the commercial power supply independently of the detection of the rectified and smoothed commercial power supply voltage value by the voltage detection circuit to distinguish between a commercial power failure and a commercial power supply voltage fluctuation. Separately, since the reference voltage value of the signal output circuit that outputs the power failure notice signal is variably controlled to change the output timing of the power failure notice signal, the capacitance of the smoothing capacitor included in the rectifying and smoothing circuit is reduced. As a result, the manufacturing cost of the entire device can be reduced, and the size of the device can be reduced.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing a circuit configuration of a power supply device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of an electric circuit that changes a reference voltage input to a comparator in FIG. 1;

FIG. 3 is an electric circuit diagram showing a circuit configuration of a power supply device according to a second embodiment of the present invention.

FIG. 4 is an electric circuit diagram showing an example of a configuration of a commercial power frequency detection circuit of FIG. 3;

FIG. 5 is a diagram showing changes in voltages applied to points A to D in FIG. 3;

FIG. 6 is an electric circuit diagram showing a circuit configuration of a conventional power supply device.

7 is a diagram showing an example of changes in voltages applied to points A, B, and C in FIG. 6, on / off ratios of switching elements, and power failure detection signals.

[Explanation of symbols]

 1 PRM. CTL circuit 2 Commercial power frequency detection circuit 3 Amplifier circuit C1 Smoothing capacitor C31 Capacitor C41, C42 Capacitor COMP1 Comparator D41 Diode DB1 Diode bridge circuit N11 Primary winding N12 Primary winding Q31, Q32 Transistor Q4 Bidirectional photocoupler R3 Resistance R31 to R37 Resistance R41, R42 Resistance T1 Transformer ZD31 Zener diode

Claims (3)

[Claims] 1. A power supply apparatus for intermittently supplying an output obtained by rectifying and smoothing commercial power to a primary side of a transformer to supply an output voltage applied to a secondary side of the transformer to a load. A power failure detection circuit that detects that the power supply of the power supply has stopped due to a power failure; and a rectifying / smoothing circuit including at least a smoothing capacitor provided on a primary side of the transformer for rectifying and smoothing the commercial power supply voltage. A voltage detection circuit for detecting a voltage value of a commercial power supply rectified and smoothed by the rectification and smoothing circuit; and a power failure notice signal when the voltage value detected by the voltage detection circuit falls below a reference voltage value. A power supply circuit, comprising: a signal output circuit that outputs a signal; and a control circuit that variably controls the reference voltage value depending on whether or not a power failure is detected by the power failure detection circuit. 2. The power failure detection circuit according to claim 1, wherein
The power supply circuit according to claim 1, wherein the power supply circuit is provided on a next side. 3. A control circuit provided on a secondary side of the transformer for controlling the output voltage to a predetermined voltage value, wherein the power failure detection circuit is based on an output from the control circuit. The power supply circuit according to claim 1, wherein the power failure detection is performed.