KR0184891B1 - Resistance measuring circuit using dc constant voltage - Google Patents

Abstract

The present invention relates to a resistance measuring circuit using a DC constant voltage, and more specifically, an in-circuit testing apparatus (IN-CIRCUIT) that enables the determination of the quality of a component by measuring resistance components in PCB assembly and inspection processes using a microprocessor. It corresponds to the element technology of TESTER).

In general, it can be divided into the constant voltage method and the constant current source in the measurement method of the resistance component, but according to the present invention is realized using the constant voltage method.

In other words, by supplying a stable constant voltage source through the D / A converter 20, it is possible to check whether the resistance of the correct capacitance is connected by measuring the resistance component is to minimize the defect rate of the process.

Description

Resistance measurement circuit using DC constant voltage

1 is a schematic overall circuit diagram of the present invention,

2 is a schematic circuit diagram according to the measuring principle of the present invention.

* Explanation of symbols for main parts of the drawings

10: microprocessor 20: D / A converter

30: current amplifier

40: DUT (Device Under Unit)

50: gain selector 60: A / D input gain selector

70: sample / holder 80: A / D converter

R ₁ -R ₁₁ : Resistor Q ₁ -Q ₂ : Transistor

OP ₁ -OP ₃ : OP Amp

The present invention relates to a resistance measuring circuit using a DC constant voltage,

More specifically, the present invention relates to a resistance measurement circuit using a DC constant voltage generated by generating a constant voltage through a D / A converter to measure resistance.

In general, in order to check whether a PCB is defective in the assembly and inspection process of a PCB using a micro-processor, the inserted resistance is measured in the PCB. Element technology of IN-CIRCUIT TESTER. The element technology for such an in-circuit inspection apparatus can be divided into the constant voltage source method and the constant current method in terms of the measurement method of the resistance component, and the present invention is realized by using a constant voltage.

In other words, by supplying a stable constant voltage source through the D / A converter and measuring the resistance component to check whether the resistance of the correct capacity is inserted into the PCB to provide a resistance measurement circuit using a DC constant voltage to reduce the process defects. Is there.

In order to achieve the object of the present invention with reference to the accompanying drawings, the present invention, as shown in Figure 1, the microcontroller for controlling the entire system and performing the operation by outputting the D / A value and the A / D value The processor 10 is connected with a D / A converter 20 for converting a digital analog value output from the microprocessor 10, and the current amplifier 30 is connected to the D / A converter 20. , D / A converter By amplifying the constant voltage output from D / A converter, it is possible to supply enough current to maintain constant voltage in the next stage.

In addition, the measurement target unit 40, which is composed of an H pin connected to an output terminal of the current amplifier 30 and an L pin connected to an input terminal of the gain selector 50 described below, is connected to the output side of the current amplifier unit 30. Both ends of the measurement target resistor R _X assembled to the PCB can be connected, and the OP amplifier OP ₂ is within the normal operating range according to the current value output from the measurement target unit 40. A gain selector 50 that selects an ideal gain to have a proper gain in the connection is provided to the measurement target unit 40, and is sufficient to drive the current output from the gain selector 50 sufficiently. A buffer circuit is adopted, and the A / D input gain selector 60 selects a gain so as to fall within the input range of the A / D converter described below according to the input current value.

In addition, the A / D input gain selector 60 is connected with a sample / holder 70 for sampling and holding an analog voltage value output from the A / D input gain selector 60. An A / D converter 80 for converting an analog value output from the sample / holder unit 70 into a digital value and outputting the digital signal to the microprocessor 10 is provided.

Reference numerals OP ₁ , OP ₂ , and OP ₄ are OP amplifiers, R ₁ to R ₁₁ are resistors, C ₁ is a capacitor, Q ₁ and Q ₂ are transistors, and S _{1 to} S ₈ are switches.

When explaining an embodiment of the present invention configured as described above are as follows.

According to the present invention having the measurement principle as shown in FIG. 2, when the constant voltage source V _S is applied and its current is i, the current i is gained through the resistance R _X assembled to the PCB. It flows through the resistor R _f to the op amp output stage.

Here, the current does not flow to the − input terminal of the OP amplifier because the OP amplifier input impedance is zero.

Also, since the op amp-input terminal and the + input terminal are virtual short-shots, the potential of V ₁ is 0 [V].

Eventually i

It can be represented as

Where Rx is the resistance to be measured,

Vs: Constant voltage source.

Since the flow direction of the current i, which is viewed from the output terminal Vo, is the reverse direction,

to be.

Where Rf is the gain resistance.

Since Vs and Rf are fixed values and Vo can be measured, the resistance Rx to be measured is

Becomes equal to

Substituting this equation into the present invention, as shown in FIG. 1, instead of Vs in the above equation, when the digital value for the constant voltage output is sent to the D / A converter 20 through the microprocessor 10, The / A converter 20 converts a digital value into an analog value and outputs the converted value, and the output value passes through the current amplifier 30 configured as the non-inverting amplifier OP ₁ . Correspondingly, the current flows through H pin → target resistance (Rx) → L pin.

As described above, the current through the L pin is applied to the output terminal of the OP amplifier OP ₂ of the gain selector 50.

In this process, the most suitable gain is selected in the gain selector 50 and current flows through the gain resistors Rf = R ₃ to R ₇ so that the voltage generated in the gain selector 50 is-value. An analog voltage value is input to the input terminal of the sample / holder 70 through an A / D input gain selector 60 composed of an inverting non-inverting circuit, that is, a non-inverting amplifier OP ₃ .

The analog value output from the sample / holder unit 70 is converted into a digital value through the A / D converter 80 and input to the microprocessor 10, and the value input to the microprocessor 10 is previously input. It is to calculate the resistance value of the measurement target resistance (Rx) through the calculation according to the program. More specifically, the data output from the microprocessor 10 via the data line (DL), D / A converter 20 ) Is changed to the analog value to become the constant voltage V ₁ .

This is due to the resistances R ₁ and R ₂ ,

Is output as

The D / A converter 20 outputs 6 bits to 0.156V to 10V, but outputs 0.05V to 3.20V through the attenuation source resistors R ₁ and R ₂ .

That is, Vin = (Vda * R ₂ ) / (R ₁ + R ₂ )

= (Vda * 4.7K) / (10K + 4.7K)

Where Vda = 0.156V and Vin = 0.05V

Vin = 3.15V when Vda = 10V.

If this voltage is selected, if there is a protection circuit, the general OP amplifier has only 10mA of output current. Therefore, sufficient current must be supplied. For this purpose, V ₂ is the OP amplifier (OP ₁ ) and transistors Q ₁ and Q. _Through a current amplifier 30 composed of _two .

The current amplifier 30 constitutes a circuit to supply a sufficient current to a voltage follower structure, and acts as a current buffer, so that V ₃ maintains the value of V ₂ .

On the other hand, the measurement target unit 40 is developed in the same structure as the measurement principle described in FIG. 2, and in order to measure the resistance Rx to be measured, an appropriate value is selected from the switches S ₁ to S ₅ . That is, if switch S ₁ is selected.

Becomes

As an example, if the measurement resistance is 40Ω, the gain resistance of the gain selector is 40, 400, 4K, 40K, 400K, and the gain = 1, 10, 100, 1000, 10000, but select the most ideal gain for measurement. .

A gain selector 50 via the current-value because, for input to the A / D converter 80 to a suitable value to highlight a +, a, a switch S ₆ ~S ₈ appropriate switches in order to control the gain Turn on.

If switch S ₆ is selected,

Becomes

The V ₅ value is then converted into a digital value in the A / D converter 80 via the sample / holder 70 and input to the microprocessor 10 via the data line DL.

Here, all resistances except the resistance Rx to be measured are fixed values, and since the values are known, the resistance Rx to be measured is

The value can be found by

The overall function of the circuit of the present invention is described again through the non-inverting amplifier OP ₂ of the gain selector 40 coming from the D / A converter 20 and again the non-inverting of the D / A input gain selector 50. When the output value becomes + while passing through the amplifier OP ₃ and passes through the sample / holder unit 70, and V ₅ is input to the microprocessor 10 by the A / D converter 80, the resistance values which are known in advance are substituted. Therefore, it is possible to measure the resistance Rx to be measured.

As described above, the present invention is to facilitate the resistance measurement using a constant voltage, it is an invention that can implement a circuit that can measure the resistance using a constant current.

Claims (1)

In the resistance measuring circuit device for measuring the resistance (Rx) measured on the PCB in the assembly and inspection of the PCB, the digital voltage output from the microprocessor 10 is changed to an analog value to output a constant voltage. A / a converter 20, a current amplifier 30 for amplifying and stably supplying a selected voltage output from the D / A converter 20, an H pin connected to an output terminal of the current amplifier 30, and The measurement target unit 40 to perform measurement by connecting the measurement target resistor Rx to the L pin connected to the input terminal of the gain selector 50 described below, and output from the measurement target unit 40. By the current value, the gain selector 50 for selecting the gain so that the OP amplifier OP ₂ has a proper gain within the normal operating range, and the current passing through the gain selector 50 are sufficiently driven. To fall within the input range of the A / D converter 80 described. An A / D input gain selector 60 for selecting gain, a sample / holder unit 70 for sampling and holding analog voltage values output from the A / D input gain selector 60, and a sample / A / D converter 80 for digitally changing the analog value sent out from the holder part 70, connected to the respective parts, and receives the output value of the A / D converter 80 to measure the resistance value through calculation Resistance measurement circuit using a DC constant voltage, characterized in that consisting of a microprocessor 10 to enable.