Input voltage detection device in electronic load

Abstract

The invention discloses an input voltage detection device in an electronic load, which is composed of a reference signal, an operational amplifier, a transistor, a resistor and a comparison unit, the reference signal, the transistor and the resistor form a constant current source circuit, the reference signal is used for inputting a predetermined reference voltage to the operational amplifier, and the comparison unit is used for comparing the reference voltage to the operational amplifier. The operational amplifier detects the voltage on the resistor, compares the voltage with a reference voltage, controls to output a driving signal to the transistor and further controls the current flowing through the transistor, to-be-detected signals Load + and Load-are added to the two ends of the transistor and the resistor, the input of the comparison unit is the driving signal of the transistor, and by detecting the amplitude of the driving signal, the current of the transistor is detected. And whether the constant current source circuit works normally is judged, so that the magnitude of the voltage between the to-be-detected signals Load + and Load-is detected. The voltage of the input end of the load is detected in a phase-changing manner through the constant-current source circuit, and the detection precision and the anti-interference capability are higher.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic loads, and in particular to an input voltage detection device in an electronic load. Background Art

[0002] In electronic load applications, it is sometimes necessary to detect a small voltage between the load inputs load+ and Load- to determine whether the object under test is connected to the load end. The voltage threshold for judgment is usually between tens of mV and hundreds of mV. There are two common methods: 1. Using an operational amplifier combined with a comparator. Figure 1 As shown in the figure, the operational amplifier processes the signals Load+ and Load- to be detected, scales the voltage difference between the two to a suitable amplitude, and then sends it to the input end of the subsequent comparator. The other end of the comparator inputs the preset comparison threshold voltage. The output of the comparator is the output state of the voltage detection. 2. It is the way of combining the operational amplifier with the ADC. Figure 2 As shown, the same signal to be tested Load+ and Load- are input into the op amp amplifier, scaled to a suitable amplitude and then sent to the analog-to-digital converter. The voltage is converted into a digital quantity by the analog-to-digital converter and input into the microcontroller. The input voltage value is judged in the microcontroller. However, both of these require the use of an op amp amplifier to scale the input signal to a suitable amplitude. The voltage between the signals to be detected Load+ and Load- is usually several hundred to more than one thousand volts. When the rated input voltage of Load+ and Load- is relatively high, the usual practice is to attenuate the voltage to a suitable amplitude, generally within 10V, through a voltage divider resistor coupled to an op amp amplifier. First, the relatively high voltage of the signals to be detected Load+ and Load- means that the resistance value of the voltage divider resistor is selected to be relatively large. The large resistance value coupled to the circuit form inherent capacitance or parasitic stray capacitance in the circuit will greatly limit the bandwidth of the sampling circuit, resulting in a slow response speed. Secondly, the proportional attenuation of the voltage divider resistor will also be relatively large. At this time, the voltage of tens to hundreds of mV that needs to be detected will also be attenuated very small, perhaps only tens of uV. At this time, the signal amplitude is extremely small, and the subsequent comparison voltage path is difficult to accurately analyze the tiny voltage. In addition, the inherent noise of the circuit and a little bit of noise coupled from the outside world will greatly affect the detection of the tiny voltage. Therefore, due to the noise and bandwidth of the system, it will be very difficult to distinguish the voltage of tens to hundreds of mV in time and accurately. Summary of the invention

[0003] The purpose of the present invention is to address the deficiencies of the prior art and provide an input voltage detection device in an electronic load, which detects the load port voltage and converts it into another physical quantity in the form of a circuit for detection, with higher detection accuracy and anti-interference ability.

[0004] The present invention discloses an input voltage detection device in an electronic load, which is composed of a reference signal, an operational amplifier, a transistor, a resistor Rs and a comparison unit. The reference signal, the transistor and the resistor Rs constitute a constant current source circuit. The reference signal is used to input a predetermined reference voltage Vref to the operational amplifier. The operational amplifier detects the voltage on the resistor and compares it with the reference voltage to control the output drive signal to the transistor, thereby controlling the current flowing through the transistor. When stable, the current I of the constant current source circuit is Vref / Rs. The signals to be detected Load+ and Load- are applied to both ends of the transistor and the resistor. The input of the comparison unit is the drive signal of the transistor. By detecting the amplitude of the drive signal, it is judged whether the constant current source circuit works normally, thereby detecting the voltage between the signals to be detected Load+ and Load-.

[0005] Furthermore, the signal to be detected Load+ is added to the drain of the transistor, the signal to be detected Load- is added to one end of the resistor, the other end of the resistor is respectively connected to the inverting input of the operational amplifier and the source of the transistor, and the reference signal is used to input a predetermined reference voltage to the non-inverting input of the operational amplifier.

[0006] Furthermore, the rated voltage of the transistor exceeds the voltage between the signals to be detected Load+ and Load-, and the transistor has a minimum on-resistance Rd limit. When the voltage between the signals to be detected Load+ and Load- is higher than I* (Rd + Rs), the constant current source circuit works normally. When the voltage between the signals to be detected Load+ and Load- is lower than I* (Rd + Rs), the current of the constant current source circuit is always less than Vref / Rs, and the constant current source circuit cannot establish negative feedback. By detecting the amplitude of the driving signal output by the operational amplifier to the transistor through the comparison unit, it can be determined that the constant current source circuit cannot work normally, thereby detecting that the voltage between the signals to be detected Load+ and Load- is low.

[0007] Furthermore, the comparison unit is a comparator circuit or a clamping diode.

[0008] Furthermore, the detection device is disabled by setting the reference voltage Vref to a negative value.

[0009] The technical solution of the present invention has the following beneficial effects: the present invention discloses an input voltage detection device in an electronic load, which detects the load port voltage and converts it into another physical quantity in the form of a circuit for detection, and detects the load input terminal voltage in a disguised manner through a constant current source circuit, so that the detection accuracy and anti-interference ability are stronger. By detecting the transistor drive voltage amplitude, the load input terminal voltage is judged, which allows a small voltage to be detected in a very large voltage input range, and the response bandwidth is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The schematic diagram of the circuit for detecting the load input voltage by combining an operational amplifier with a comparator.

[0011] Figure 2 The schematic diagram of the circuit for detecting the load input voltage by combining an operational amplifier with an ADC.

[0012] Figure 3 The present invention is a circuit diagram of the device disclosed in the present invention. DETAILED DESCRIPTION

[0013] The technical solution of the present invention is described in detail below, but the protection scope of the present invention is not limited to the embodiments.

[0014] like Figure 3 As shown, the present invention discloses an input voltage detection device in an electronic load, which is composed of a reference signal, an operational amplifier U1, a transistor Q1, a resistor Rs and a comparison unit. The signal to be detected Load+ is added to the drain of the transistor Q1, and the signal to be detected Load- is added to one end of the resistor Rs. The other end of the resistor Rs is connected to the inverting input end of the operational amplifier U1 and the source of the transistor Q1 respectively. The reference signal is used to input a predetermined reference voltage Vref to the in-phase input end of the operational amplifier U1. The operational amplifier U1 detects the voltage on the resistor Rs and compares it with the reference voltage Vref, controls the operational amplifier U1 to output a driving signal to the transistor Q1, that is, controls the gate voltage of the output transistor Q1, and then controls the current flowing through the transistor Q1. When stable, the current I flowing through the transistor Q1 is Vref / Rs. The reference signal, the transistor Q1 and the resistor Rs constitute a constant current source circuit. The input of the comparison unit is the driving signal of the transistor Q1. By detecting the amplitude of the driving signal, it is determined whether the constant current source circuit works normally, thereby characterizing the voltage between the signals to be detected Load+ and Load-.

[0015] The transistor Q1 is selected to have a rated voltage exceeding the voltages of the signals Load+ and Load- to be detected. At the same time, the transistor Q1 has a minimum on-resistance Rd limit. When the voltage V between the signals Load+ and Load- to be detected is relatively high, that is, when V > I*(Rd + Rs), the constant current source circuit can operate normally, and the drive voltage of the transistor Q1 is approximately 3 to 5V. When the voltage V between the signals Load+ and Load- to be detected is relatively low, that is, when V < I*(Rd + Rs), at this time, limited by the minimum on-resistance Rd of the transistor Q1, the current I of the constant current source circuit is always less than Vref / Rs, and the operational amplifier U1 can never establish a negative feedback stable state. The drive voltage of the transistor Q1 is always in the saturation state. Without other amplitude limiting circuits, this drive voltage will saturate near the positive power supply of the operational amplifier U1. If the power supply of the operational amplifier U1 is ±12V, then the drive voltage of the transistor Q1 is about 10V at this time. When the drive voltage output by the operational amplifier U1 changes significantly, it can reflect the magnitudes of the voltages of the signals Load+ and Load-. When the voltage between the signals Load+ and Load- to be detected becomes small and approaches the minimum on-resistance Rd of the transistor Q1, the drive voltage can be detected and judged by the comparison unit. By detecting the amplitude of the drive voltage of the transistor Q1, the present invention can judge the voltage at the load input terminal, allowing for the detection of tiny voltages within a very large voltage input range and having a high response bandwidth. The reference signal gives the reference voltage Vref according to the voltage amplitude to be detected and the minimum on-resistance Rd of the selected transistor Q1.

[0016] The input of the comparison unit of the present invention is the drive signal of the transistor Q1. By detecting the amplitude of this drive signal, it is judged whether the constant current source circuit is operating normally, thereby characterizing the magnitude of the voltage between Load+ and Load-. This comparison unit can be implemented by a comparator circuit or a clamping diode. It is also possible to disable this detection circuit by setting the reference signal Vref to a negative value. The device disclosed in the present invention converts the detection of the load port voltage into the detection of a physical quantity in another circuit form, and变相 detects the voltage at the load input terminal through the constant current source circuit, with stronger detection accuracy and anti-interference ability.

[0017] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as a limitation of the present invention itself. Various changes can be made in its form and details without departing from the spirit and scope of the present invention defined by the appended claims.

Claims

1. An input voltage detection device in an electronic load, characterized in that: The invention is composed of a reference signal, an operational amplifier, a transistor, a resistor Rs and a comparison unit. The reference signal, the transistor and the resistor Rs constitute a constant current source circuit. The reference signal is used to input a predetermined reference voltage Vref to the operational amplifier. The operational amplifier detects the voltage on the resistor and compares it with the reference voltage to control the output drive signal to the transistor, thereby controlling the current flowing through the transistor. When stable, the current I of the constant current source circuit is Vref / Rs. The signals to be detected Load+ and Load- are applied to both ends of the transistor and the resistor. The input of the comparison unit is the drive signal of the transistor. By detecting the amplitude of the drive signal, the voltage between the signals to be detected Load+ and Load- is detected.

2. The input voltage detection device in an electronic load according to claim 1, characterized in that: The detection signal Load+ is added to the drain of the transistor, the detection signal Load- is added to one end of the resistor, the other end of the resistor is respectively connected to the inverting input end of the operational amplifier and the source of the transistor, and the reference signal is used to input a predetermined reference voltage Vref to the non-inverting input end of the operational amplifier.

3. The input voltage detection device in an electronic load according to claim 1, characterized in that: The rated voltage of the transistor exceeds the voltage between the signals to be detected Load+ and Load-, and the transistor has a minimum on-resistance Rd limit. When the voltage between the signals to be detected Load+ and Load- is higher than I* (Rd+Rs), the constant current source circuit works normally. When the voltage between the signals to be detected Load+ and Load- is lower than I* (Rd+Rs), the current of the constant current source circuit is always less than Vref / Rs, and the constant current source circuit cannot establish negative feedback. By detecting the amplitude of the driving signal output by the operational amplifier to the transistor through the comparison unit, it can be determined that the constant current source circuit cannot work normally, thereby detecting that the voltage between the signals to be detected Load+ and Load- is low.

4. The input voltage detection device in an electronic load according to claim 1, characterized in that: The comparison unit is a comparator circuit or a clamping diode.

5. The input voltage detection device in an electronic load according to claim 1, characterized in that: By setting the reference voltage Vref to a negative value, the detection device is disabled.

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