JP3263194B2 - Power supply smoothing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply smoothing circuit for rectifying and smoothing an AC input voltage.

[0002]

2. Description of the Related Art FIG. 7 shows a capacitor input type smoothing circuit generally and widely used in the prior art, and FIG. 6 shows a conventional partial smoothing circuit. The capacitor input type smoothing circuit shown in FIG. 7 has an input current (charging current to the capacitor).
, The power factor is as low as 0.6 or less, and the harmonic distortion is large. In order to improve this, the partial smoothing circuit of Fig. 6 has been developed. The power factor has been improved to 0.9 to 0.95, and at the same time, the harmonic distortion has been greatly improved, and it is an effective method. Has been evaluated. However, one of the drawbacks of the partial smoothing circuit is that it connects to the output side (switching).
There is a problem that the power supply holding time (or instantaneous power failure characteristic) is shorter than that of the capacitor input type smoothing circuit.

This problem will be described below with reference to a capacitor input type smoothing circuit shown in FIG. FIG. 8 shows output voltage waveforms of the capacitor input type smoothing circuit and the partial smoothing circuit. A load such as a (switching) power supply is connected to the output side of the smoothing circuit. As can be seen from the output voltage waveform in FIG. 8, the partial smoothing circuit is connected to the output side as compared with the capacitor input type smoothing circuit. There is a disadvantage that the width of the operating voltage (the difference between the maximum voltage and the minimum voltage) of the (switching) power supply must be as large as about twice. In particular, since the minimum operating voltage of the partial smoothing circuit must be designed to be about 1/2 the value of the capacitor input type smoothing circuit, the minimum input voltage (for example, 85
V) There is no design margin for stable operation of the power supply for input voltages below. When a power failure or switch-off occurs, the relationship between the output voltage Vc1 (= Vc2) of the partial smoothing circuit and the output voltage Vc of the capacitor input type smoothing circuit becomes Vc1 ≒ 1/2 × Vc according to the illustration in FIG. Therefore, it can be seen that the output holding time of the (switching) source using the partial smoothing circuit is much shorter than that of the capacitor input type smoothing circuit. In order to solve this, the capacitance values of the capacitors C1 and C2 in FIG. 6 must be increased, so that the volume of the capacitors increases and the price also increases.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a partial smoothing circuit having a simple configuration and a long power supply holding time at the time of a power failure. By the way, the capacitor input type smoothing circuit has a long holding time at the time of power failure, but has poor power factor and harmonic distortion. On the other hand, the partial smoothing circuit has a short power holding time during a power failure, but has good power factor and harmonic distortion.
The embodiment of the present invention seeks to bring out the advantages of both the partial smoothing circuit and the capacitor input type smoothing circuit by loading the partial smoothing circuit with a simple circuit.

[0005]

According to the present invention, a switch element S is connected in parallel with a diode D1 of a partial smoothing circuit.
When there is no AC input voltage (at the time of power failure or input-side switch off), the switch element S is operated to turn on the switch element A
A C input voltage detection circuit is connected.

That is, the first diode D1 is connected between the negative electrode (-) of the first capacitor C1 and the positive electrode (+) of the second capacitor C2 in the direction in which the charging current flows, and A second diode D2 is connected between the negative electrode (-) of C1 and the negative electrode (-) of the second capacitor C2 in the direction in which the discharge current of the capacitor C1 flows. ) and the power supply smoothing circuit a third diode D3 is formed by connecting in a direction of flow of the discharge current of the capacitor C2 between the positive electrode (+) of the second capacitor C2, a first diode D1
And a switch element S connected in parallel, the power failure or input switch off is detected by the input voltage detection circuit DT on the AC input side.
Turns on the switch element S Te, a power supply smoothing circuit and outputs by adding the voltage charged in each of the capacitors connected in series with the capacitors C1 and C2.

[0007]

The present invention is configured as described above.
When the switch element S is turned on during a power failure or when the input switch is turned off, the capacitor C1 and the capacitor C2 are connected in series, so that the output voltage of the partial smoothing circuit instantaneously becomes twice the charged voltage of the capacitor C1 (or the capacitor C2). Becomes

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3, the same parts as those in FIGS. 5 to 7 are denoted by the same reference numerals, and redundant description will be omitted. Similarly to FIG. 6, when the AC input voltage is interrupted, the voltage (Vc1) of the embodiment shown in FIGS. 1 and 5 is changed from the voltage waveform of FIG. 8 to the voltage (Vc) of the capacitor input type smoothing circuit. It is about half the voltage. Vc1 = Vc2 ≒ 1 / 2Vc (Equation 1) where Vc1 = voltage of capacitor C1 Vc2 = voltage of capacitor C2 Vc = voltage of capacitor input type smoothing circuit Simultaneously with power failure (strictly speaking, a slight time delay) After), 5th
Power failure by detecting circuit DT of the AC input side of the AC input voltage as shown in FIG module is detected. The input voltage detection circuit DT
One end of the C input side has a diode D5, a resistor R1, and a resistor.
A parallel connection circuit of an anti-R2 and a capacitor C3 is connected,
Connect the emitter of NPN transistor Q to the parallel connection circuit
And connect the base and the connection point of the resistor R1 and the resistor R2 with a zener.
Connected by diode D6, collector connected to switch element S
And the resistor R1 and the other end of the AC input
Mode D4.
When the switch element S is detected and turned on, the capacitor C1 and the capacitor C2 are connected in series, so that the voltage in FIGS. 1 and 5 is instantaneously increased to the voltage Vc of the capacitor input type smoothing circuit, and the following equation is obtained. It is represented by Vc1 + Vc2 = 2Vc1 ≒ Vc (2 formulas)

FIG. 3 shows an equivalent circuit represented by equation (1), and FIG. 2 shows an equivalent circuit represented by equation (2). The time constant T in FIG.
_Since the time constant T 2 in FIGS. ₁ and ₂ is expressed by the following equations,
Each voltage-time characteristic shows a relationship as shown in FIG. _{T 1 = (c1 + c2)} Z = 2c1 Z ··· (3 type), where, c1 = the load impedance of the capacitance value Z = output capacitance value c2 = capacitor C2 capacitor C1

[0010]

(Equation 1)

As in FIG. 6, the voltage of the embodiment shown in FIGS. 1 and 5 has a larger voltage fluctuation range than that of the capacitor input type smoothing circuit as shown in FIG. Must be designed at a low value. Since the range of the operating voltage is large, generally, the minimum operating voltage Vop (min)
Usually has no margin for the minimum input voltage value on the power supply specification sheet.

This situation will be described with reference to the voltage-time characteristics shown in FIG. Assuming that the power outage occurred at the minimum input voltage, as in FIG. 6, the voltages in FIGS. 1 and 5 also have the minimum voltage Vc.
1 (min) = Vc2 (min), and the difference from the minimum operating voltage Vop (min) is small, and is substantially expressed by the following equation. Vop (min) = Vc1 (min)-. DELTA.V = Vc1 (min) (Equation 5) Here, .DELTA.V.apprxeq.0 V. Therefore, when a power failure occurs, the holding time in FIG. a t ₁ than a.

On the other hand, in the circuits shown in FIGS. 1 and 5, the switch element S is turned on at the same time as the power failure, and the circuit becomes an equivalent circuit shown in FIG. 2. Therefore, according to the voltage-time characteristics shown in FIG. The holding time at the time is t ₂ from the intersection B. t ₁ and t
The relationship of ₂ is represented by the following equation from the illustration of FIG. t ₁ < t ₂ ... (Equation 6)

[0014]

As described above, according to the present invention, it is possible to obtain a power supply using a partial smoothing circuit having a simple configuration and a long holding time at the time of a power failure.

[Brief description of the drawings]

FIG. 1 is a principle diagram of a power supply smoothing circuit of the present invention.

FIG. 2 is an equivalent circuit diagram of a main part of a power supply smoothing circuit according to the present invention.

FIG. 3 is an equivalent circuit diagram of a main part of a conventional power supply smoothing circuit at the time of a power failure.

FIG. 4 shows a power supply in the equivalent circuit of FIGS. 2 and 3.
It is a time characteristic diagram.

FIG. 5 is an embodiment of a power supply smoothing circuit of the present invention.

FIG. 6 is a conventional partial smoothing circuit diagram.

FIG. 7 is a diagram of a conventional capacitor input type smoothing circuit.

FIG. 8 is a diagram showing a relationship between an AC input voltage waveform, an output voltage waveform of each of a partial smoothing circuit and a capacitor input type smoothing circuit, and time.

[Explanation of symbols]

C1 first capacitor C2 second capacitor D1 first diode D2 second diode D3 third diode DT input voltage detection circuit DO commercial rectifier diode Z load S switch element (mechanical switch and semiconductor switch element) CO capacitor D4 Diode D5 Diode D6 Zener diode D7 Diode R1 Resistance R2 Resistance R3 Resistance R4 Resistance C3 Capacitor Q Transistor S1 Semiconductor switch element (thyristor)

Claims (1)

(57) [Claims] 1. A first diode D1 is connected between a negative electrode (-) of a first capacitor C1 and a positive electrode (+) of a second capacitor C2 in a direction in which a charging current flows.
Negative electrode (-) of the capacitor C1 and the second capacitor C2
The second diode D2 is connected between the negative electrode (−) of the first capacitor C1 in the direction in which the discharge current of the capacitor C1 flows, and further connected to the positive electrode (+) of the first capacitor C1 and the second capacitor C2.
A switching element S is connected in parallel with the first diode D1 in a power supply smoothing circuit in which a third diode D3 is connected between the positive electrode (+) of the second and the second diode D3 in the direction in which the discharge current of the capacitor C2 flows.
And, a power outage or an input switch off the AC input side input voltage
The switching element S is turned on upon detection by the pressure detection circuit DT, and the capacitors C1 and C2 are connected in series to connect each capacitor.
Power supply smoothing circuit, characterized in that adding and outputting voltages charged in the capacitor.