JP2001111422A - Comparing type a/d conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that A/D conversion operation is influenced by the superposition of serge voltage generated when comparing reference voltage to be applied to an analog input is obtained from a switching power supply in a comparing type A/D conversion. SOLUTION: A serge judgment circuit 13 judges whether serge voltage generated from a switching power supply 12 is not less than fixed level or not, and in a period that the serge voltage is held at the fixed level or more, stops the A/D conversion operation of an A/D conversion circuit 11. It is also available to obtain a signal synchronized with serge voltage and stop the A/D conversion operation by the signal in a serge voltage period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a comparison type A / D conversion circuit for converting an analog input signal into a digital signal, and more particularly to a comparison type A / D conversion circuit using a switching type control power supply.

[0002]

2. Description of the Related Art Recent power conversion equipment such as inverters and monitoring and control devices such as power systems and plants have a computer as a control center, and obtain control output and monitoring output through arithmetic processing using digital signals. I have.

In this type of device, measured values (speed, voltage,
It is necessary to convert an analog signal (e.g., current) into a digital value and take it into the computer. For this purpose, an A / D conversion circuit that converts an analog input signal into a digital signal is often used.

The A / D conversion circuit includes a comparison type in which each reference voltage determined by a voltage dividing ratio of a resistor is compared with a magnitude of an analog input voltage to convert the analog voltage into a digital value, and a D / A conversion circuit built-in. There are a successive approximation type for comparison and subtraction, and an integration type for integrating and counting analog inputs. Of these, the comparison type A / D converter circuit is used when the analog input is collectively compared with each reference voltage, so that a high-speed conversion operation can be obtained as compared with other methods and a high-speed control such as an inverter control device is desired. Is done.

FIG. 3 shows an example of a comparison type A / D conversion circuit. The resistor voltage dividing circuit 1 includes a plurality of resistors connected in series,
The output voltage of the stabilized DC power supply 2 by resistance-dividing obtain stepwise comparison reference voltage V ₀ ~V ₃ in. The comparing section 3 is provided with a plurality of comparators, and each comparator has a comparison reference voltage V _0.
Simultaneously comparing the magnitudes of ~V ₃ and the analog input voltage individually to obtain an output of logic "0" to each of the comparators.
The code conversion circuit 4 obtains encoded data corresponding to the analog input voltage from the logical output from the comparison unit 3.

[0006]

As a control power supply such as an inverter, a switching power supply is often used in order to make the power supply more compact and to improve the power supply efficiency. As shown in FIG. 4, the switching power supply obtains rectified and smoothed DC power from an AC power supply, and applies a pulse transformer PT to the semiconductor switching element SW as a DC power supply.
High-frequency switch (the number of switching elements SW tens kH _Z ~
Several hundred kH _Z) is taken out as a high-frequency pulse current obtained by stepping down or step-up in the secondary side of the pulse transformer PT by operation,
This is rectified and smoothed by a rectifier circuit REC to obtain a DC output.

[0007] Such a switching power supply is a comparative type A /
When used directly as the DC power supply 2 of the D conversion circuit or through a voltage dividing circuit, a surge voltage due to the high-frequency switch operation of the switching element SW is superimposed on the DC output of the switching power supply.

The existence of the surge voltage is determined by the resistance voltage dividing circuit 1
Appearing in the comparison reference voltages V _{0 to} V ₃ , the digital output is disturbed by the erroneous determination by the comparator 3, and the use of this digital value results in unstable control. Although the switching power supply is used as the power supply for the comparison unit 3 and the code conversion circuit 4, these parts are hardly affected by the surge voltage.

In order to solve the above-mentioned problem of surge voltage,
There are a method of controlling the switching of the switching element at a zero point of the voltage and current induced in the pulse transformer, a method of providing a surge suppression filter at the output of the switching power supply, and a method of using an analog dropper power supply instead of the switching power supply.

However, zero-voltage / current switching requires additional components such as semiconductor switches and reactors, which increases the size and cost. Also, the method of providing a filter requires a filter circuit, and A / A
The D conversion accuracy is deteriorated. In addition, the dropper power supply has a large power loss and is inefficient.

An object of the present invention is to provide a comparison type A / D conversion circuit which solves the above problems.

[0012]

According to the present invention, the A / D conversion is performed during a period in which the magnitude of the surge voltage level affects the A / D conversion result.
The A / D conversion operation is stopped, or the A / D conversion is performed during a period in which a signal synchronized with the surge voltage affects the A / D conversion result.
The effect of the surge voltage is removed by stopping the conversion operation, and is characterized by the following configuration.

(First invention) In a comparison type A / D conversion circuit for obtaining a comparison reference voltage for an analog input from a switching power supply, the A / D conversion is performed during a period when a surge voltage generated from the switching power supply is higher than a certain level. A surge determination circuit for stopping the operation is provided.

(Second invention) In a comparison type A / D conversion circuit for obtaining a comparison reference voltage for an analog input from a switching power supply, an A / D conversion operation is stopped by a signal synchronized with a surge voltage generated from the switching power supply. A synchronization signal generation circuit is provided.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which an A / D conversion operation is determined by determining a surge voltage level.

The A / D conversion circuit 11 is of a comparative type equivalent to that shown in FIG. 3, and the switching power supply 12 is configured as a circuit equivalent to that of FIG. give.

The surge judging circuit 13 extracts the DC output voltage of the switching power supply 12 by means of voltage dividing resistors R1 and R2, compares the divided voltage with a comparison reference voltage by a comparing circuit (inverting circuit) COM, and compares the magnitude with the reference voltage. 1
It is determined whether a surge voltage of a certain level or more has occurred in the DC output voltage of No. 2.

The comparison reference voltage of the surge determination circuit 13 is A
/ D is determined depending on, for example, the resolution conversion circuit 11, i.e. the detection voltage range (e.g., V due to a voltage V ₀ ~V ₃ in FIG. 3
_3- V ₂ ).

The judgment result by the surge judgment circuit 13 is A
/ D conversion circuit 11 is used as an enable input.
A signal for enabling / disabling the D conversion operation. Since the surge voltage appears periodically, the permission / non-permission signal is not permitted during the period when the surge voltage appears, and is permitted during the period when the surge voltage does not appear.

Therefore, by disallowing the A / D conversion operation during the period when the surge voltage is higher than a certain level,
The effect of the surge voltage on the conversion operation of the A / D conversion circuit 11 is eliminated. Also, during the period when the surge voltage is smaller than a certain level, the A / D conversion operation is permitted. In this case, A
Since the surge voltage is low for the conversion operation of the / D conversion circuit 11, the effect of the surge voltage does not appear on the conversion result.

The A / D conversion circuit 11 can cope with permission / non-permission of the A / D conversion operation by using an enable input of the code conversion circuit 4 in FIG.

(Second Embodiment) FIG. 2 shows another embodiment of the present invention. In the first embodiment, the permission / non-permission signal of the A / D conversion operation is obtained from the surge voltage level determination. On the other hand, in the present embodiment, the A / D conversion is performed by the synchronization signal generation circuit synchronized with the generation of the surge voltage. A conversion operation permission / non-permission signal is obtained.

The switching frequency of the switching power supply 12 is generally fixed, and the switching element SW shown in FIG. This allows
The surge voltage is generated at a constant cycle.

Therefore, the synchronizing signal generation circuit obtains a synchronizing signal delayed by a predetermined time from the on / off control signal of the switching element SW of the switching power supply 12, and converts this signal to an A / A signal.
By using the enable input of the D conversion circuit 11, the influence of the surge voltage on the A / D conversion operation is eliminated.

The generation of the synchronizing signal is realized by obtaining an on / off control signal through a delay circuit, using a monostable circuit, and the like.

In the first embodiment, the surge voltage level judging method limits the conversion permission depending on the resolution of the A / D conversion. On the other hand, in the present embodiment, there is no limitation, and the A / D conversion accuracy is high. The circuit can be applied to

[0027]

As described above, according to the present invention, the A / D conversion operation is stopped during the period in which the A / D conversion result is affected from the magnitude of the surge voltage level, or the signal synchronized with the surge voltage is used. Because the A / D conversion operation is stopped during the period that affects the A / D conversion result, the influence of the surge voltage is removed. Therefore, a circuit required for the surge voltage countermeasure compared with the conventional zero voltage / current switching is provided. It's easy.

Further, the accuracy of the power supply voltage can be increased and the A / D conversion accuracy can be increased as compared with the system in which a filter is provided in the switching power supply, and a switching power supply with higher power efficiency than the dropper power system can be used.

[Brief description of the drawings]

FIG. 1 is an A / D conversion circuit based on a surge voltage level determination according to an embodiment of the present invention.

FIG. 2 is an A / D conversion circuit synchronized with a switching signal according to the embodiment of the present invention.

FIG. 3 is an example of a comparative A / D conversion circuit.

FIG. 4 is a basic configuration of a switching power supply.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Resistor voltage dividing circuit 2 ... DC power supply 3 ... Comparison part 4 ... Code conversion circuit 11 ... A / D conversion circuit 12 ... Switching power supply 13 ... Surge judgment circuit

Claims (2)

[Claims] 1. A comparison type A / D conversion circuit for obtaining a comparison reference voltage for an analog input from a switching power supply, wherein the A / D conversion operation is stopped during a period when a surge voltage generated from the switching power supply is higher than a certain level. A comparison type A / D conversion circuit comprising a surge judgment circuit. 2. A comparison type A / D conversion circuit for obtaining a comparison reference voltage for an analog input from a switching power supply, wherein a synchronization signal generation circuit for stopping an A / D conversion operation with a signal synchronized with a surge voltage generated from the switching power supply. And a comparison type A / D conversion circuit.