JPS6111544B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC/DC converter that converts AC voltage into DC voltage by rectifying and smoothing it.

What is shown in FIG. 1 is an electrical circuit diagram showing an example of a conventional AC/DC converter of this type. In the figure, a rectifier circuit 1 rectifies an input alternating current voltage by half-wave or full-wave and sends out a negative polarity pulsating current voltage. The smoothing circuit 2 is composed of an amplifier A having a parallel circuit of a resistor Ro and a capacitor C in the feedback path and an input resistor _R1 , and smooths and amplifies the pulsating voltage of the rectifier circuit 1. Outputs a DC voltage corresponding to the voltage magnitude. According to this converter, the larger the time constant Ro·C, the smaller the ripple in the output DC voltage, but the response becomes slower as shown by the dotted line a in FIG. In other words, since the ripple and response time in this case are in an inverse relationship to each other, if the time constant is selected to speed up the response, there is a drawback that the ripple becomes larger.

In view of these points, it is an object of the present invention to provide an AC/DC converter with small ripple and quick response.

The present invention will be described in detail below with reference to the drawings.
FIG. 2 is an electrical circuit diagram showing an embodiment of the AC/DC converter according to the present invention. In FIG. 2, parts equivalent to those in FIG. 1 are given the same reference numerals, and their explanations will be omitted. The voltage dividing circuit 21 divides the input AC voltage into predetermined magnitudes, and can use, for example, a potentiometer. Note that the input terminal of the voltage dividing circuit 21 is connected to the input terminal of the rectifier circuit 1. The rising edge determination circuit 22 is, for example, an analog
It is composed of a comparator CMP1, and one input terminal is given the divided voltage v ₁ of the voltage dividing circuit 21, and the other input terminal is given the output voltage Eo of the smoothing circuit 2. When ₁ > Eo, a predetermined negative voltage -E ₁ is generated, and when v ₁ ≦Eo, zero or a specific positive voltage is generated. In this case, the comparator CMP1 will be described as having no hysteresis for convenience. The peak hold circuit 23 holds the peak value of the input AC signal,
A DC voltage v ₂ related to this peak value is output.
The drop judgment circuit 24 is composed of, for example, an analog comparator CMP2, and one input terminal is given the DC voltage v ₂ of the peak hold circuit 23, and the other input terminal is given the output voltage Eo of the smoothing circuit 2. The two are compared in magnitude, and when v ₂ <Eo, a predetermined positive voltage E ₂ is generated, and when v ₂ ≧Eo, zero or a specific negative voltage is generated. Note that, like the comparator CMP1, this comparator CMP2 will also be described as having no hysteresis for convenience.

The output end of the rise detection circuit 22 is connected through the first diode _D1 connected in the reverse direction, and the output end of the fall determination circuit 24 is connected through the second diode _D2 connected in the forward direction. Connected to one end of resistor R ₂ . The other end of the resistor R ₂ is connected to the input end of the amplifier A of the smoothing circuit 2. Note that the first and second diodes D ₁ and D ₂ may be connected to the input terminal of the amplifier A through separate resistors without being commonly connected to the resistor R ₂ .

The operation of the AC/DC converter of the present invention having such a configuration will be described next. First, in steady state,
It is assumed that the following equation holds between the peak value v _1p of the divided voltage v ₁ of the voltage dividing circuit 21 and the output voltage Eo of the smoothing circuit 2.

Eo=v _1p +ε ₁ However, ε ₁ can be selected to any value by changing the circuit constants.

The operation when the input AC signal rises is as follows. The divided voltage v ₁ of the voltage dividing circuit 21 changes in response to the rise change of the AC input signal, and the divided voltage v ₁ as shown by the dotted line in FIG. 3 is applied to the comparator.
Given to CMP1. Output voltage Eo of smoothing circuit 2
When is smaller than the divided voltage v ₁ (T ₁ region), the output of the comparator CMP1 shows a negative voltage −E ₁ . This negative voltage -E ₁ causes the first diode D ₁ to conduct, and a current of -E ₁ /R ₂ is added to the input terminal of the amplifier A via the resistor R ₂ . Therefore, the capacitor C is charged by the sum of the current −i _p flowing through the resistor R ₁ and the current −E ₁ /R ₂ flowing through the resistor R ₂ , but if R ₁ ≫ R ₂ is selected, that is, |− i _p ｜≪｜−E ₁ /R ₂ ｜
Therefore, the charging speed is extremely fast, and the output voltage Eo of amplifier A rises following the input AC signal as shown by line b in FIG. In the next T ₂ region, v ₁ < Eo
Therefore, the output of the comparator CMP1 becomes zero or a predetermined positive voltage, and the diode _D1 is turned off. Therefore, the capacitor C is charged only by the current i _p and the output voltage Eo is equal to the line C in FIG.
The steady state value is gradually reached as shown in . Note that if ε ₁ is made small, the period of the T ₁ region increases and the period of line C is shortened, so that the overall response time can be further shortened.

Next, the operation when the AC input signal falls will be explained. In steady state, it is assumed that the following equation holds between the output voltage v ₂ of the peak hold circuit 23 and the output voltage Eo of the smoothing circuit 2.

Eo=v ₂ −ε ₂ However, ε ₂ can be selected to any value by changing the circuit constants.

Now, when the AC input signal drops, the output v ₂ of the peak hold circuit 23 also drops accordingly, as shown in region T 3 in FIG. ₃ . This DC output v ₂ is ε
₂ or more and becomes smaller than the output Eo of the smoothing circuit 2, the output of the comparator CMP2 becomes a positive voltage E ₂
becomes. This positive voltage E ₂ causes the second diode D ₂ to conduct, and a current of E ₂ /R ₂ is added to the input terminal of the amplifier A via the resistor R ₂ . Since R _{1 ≫} R _{2 is} selected _{, |} −i _{p |} is peak hold circuit 2
3, the output V ₂ rapidly drops as shown by line d in FIG. 3. In this case, if ε ₂ is made smaller, the overall descent time can be further shortened.

However, the time constants Ro and C of the filter circuit in the feedback path of amplifier A can be made sufficiently large to reduce ripples in the output voltage Eo, and the time constants at rise and fall can be made sufficiently small to speed up the response. be able to.

Note that the same objective can be achieved by using a peak hold circuit in the voltage dividing circuit 21.

As explained above, according to the AC/DC converter of the present invention, the time constant of the filter circuit is made sufficiently large to reduce ripples in the output voltage, and the time constants at rise and fall are made sufficiently small. The response can be made faster, and the effect is great in practical use.

[Brief explanation of the drawing]

Figure 1 is a circuit example of a conventional AC/DC converter, Figure 2 is an electric circuit diagram showing an embodiment of the AC/DC converter according to the present invention, and Figure 3 is the operation of each part of the circuit shown in Figure 2. FIG. 1... Rectifier circuit, 2... Smoothing circuit, A... Amplifier, Ro, _R1 , _R2 ... Resistor, C... Capacitor,
21...Voltage dividing circuit, 22...Rise determination circuit, 2
3... Peak hold circuit, 24... Drop judgment circuit, CMP1, CMP2... Analog comparator, _D1 , _D2 ... First and second diodes.

Claims (1)

[Claims] 1. It has a rectifier circuit that rectifies an AC input signal, and an amplifier in which a parallel circuit of a resistor and a capacitor is connected to a feedback path, and converts the AC input signal into a DC signal by a smoothing circuit that smoothes the output signal of the rectifier circuit. The AC/DC converter includes a voltage dividing circuit that divides an AC input signal, a rise determination circuit that outputs a predetermined voltage when the output voltage of the smoothing circuit is smaller than the divided voltage of the voltage dividing circuit, and the AC input signal. a peak hold circuit that generates a DC voltage related to the peak value of the input signal; a drop determination circuit that outputs a predetermined voltage when the DC voltage is smaller than the output voltage of the smoothing circuit; and a predetermined voltage of the rise determination circuit. a first diode that is made conductive by a voltage and provides this predetermined voltage to the amplifier via a resistor; and a second diode that is made conductive by a predetermined voltage of the drop determination circuit and provides this predetermined voltage to the amplifier via a resistor. AC/DC converter equipped with a diode.