JP2007336688A - Protective circuit for analyser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To protect an internal circuit in a constant current IC or a load itself without fail, even if such an abnormality of the load occurs that it cannot be protected by detection on a low side such as a short circuit to the earth of a cable of the load driven by a constant current. <P>SOLUTION: An overcurrent detecting circuit 1 is built in at the high side of the power source of the constant current IC2. A controller 4 functions as a stopping action circuit; and controls, with constant currents, the load 3 composed of a valve, a motor, etc. by usually inputting the control signal of a CPU5 into the constant current IC2 as it is. In the case that an overcurrent is detected, the breakdown of the load 3 is prevented by compulsively stopping the constant current IC2, thereby shutting down the internal circuit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an analyzer equipped with a load such as a valve or a motor, and relates to a protection circuit that prevents damage to the load and the drive circuit.

  An analyzer such as a gas chromatograph or a liquid chromatograph uses a valve or the like to control gas or liquid, and an analyzer such as an ICP emission spectrophotometer or spectrophotometer uses a motor or the like to select a wavelength. Various integrated circuits that drive these valves and motors are manufactured and used (see Patent Document 1).

  FIG. 2 is a diagram illustrating an example in which a load is bidirectionally driven with a constant current by the H-bridge method. In FIG. 2, reference numeral 20 denotes a constant current IC, which is an integrated circuit that drives the load 22 at a constant current by the H-bridge method. The load 22 is configured by a valve or a motor. When the current is detected by the detection resistor R connected to the low side (0V side) of the power supply and the transistors Q1 and Q4 are turned on while the current is fed back and the transistors Q2 and Q3 are turned off, the B terminal of the load 22 is changed to the A terminal. A constant current flows through. When the current direction is switched and a constant current flows from the A terminal to the B terminal, the transistors Q2 and Q3 are turned on and the transistors Q1 and Q4 are turned off. The control circuit 21 includes the feedback circuit and a circuit for controlling on / off of the transistors Q1 to Q4.

  FIG. 3 is a diagram showing an example in which a load is unidirectionally driven by a FET. The load 32 is configured by a valve or a motor. When the current is detected by the detection resistor R connected to the low side (0 V side) of the power supply and the FET (Q) is turned on while feeding back the current, a constant current flows from the B terminal of the load 32 to the A terminal. The control circuit 31 includes the feedback circuit and a circuit for controlling on / off of the FET (Q).

Conventionally, overcurrent detection and circuit protection of an integrated circuit driven by a constant current are performed by the following method. That is, in FIGS. 2 and 3, an overcurrent is detected by using the current detection function by the detection resistor R connected to the low side of the power supply, the internal circuit is shut down by this detection signal, and an error signal is output. send.
Japanese Patent Laid-Open No. 11-103524

In FIG. 2, when the B terminal of the load 22 is short-circuited to the ground due to a problem such as the wiring being sandwiched between the metal casings of the device, the transistor Q1 is turned on and the transistor Q1 short-circuits between 24V and 0V. Q1 burns out. Further, when the A terminal of the load 22 is short-circuited to the ground, when the transistor Q1 is turned on, the transistor Q1 is burned and a large current flows, so that the load 22 itself is damaged.
In addition, when the terminals A and B of the load 22 are short-circuited due to a problem such as damage to the wiring coating and contact between the core wires, the load 22 is short-circuited when the transistors Q1 and Q4 or the transistors Q2 and Q3 are turned on. Because of this state, an overcurrent greater than the design value flows in the transistors Q1 to Q4. According to an actual test, the transistors Q1 to Q4 do not burn out immediately, unlike the short circuit with the ground, but generate heat and eventually burn out.

  In FIG. 2, when an overcurrent protection element such as a fuse or a polyswitch (an overcurrent protection element composed of a thermistor having a positive temperature coefficient) is inserted on the high side (24V side) of the power source, the load as described above When an abnormality such as a short circuit of the cable to the ground occurs, the temperature rise of the overcurrent protection element takes time, and the transistor or the like is damaged before the protection function occurs.

  In FIG. 3, when the A terminal of the load 32 is short-circuited to the ground, the FET (Q) is not broken, but the load 32 is damaged.

  In order to solve the above problems, the present invention provides a circuit for performing constant current control on a drive driven by exchanging control data with a control circuit and a protection for an analyzer equipped with a function for protecting the load itself from damage. The circuit includes an overcurrent detection circuit incorporated on the power supply high side, and a stop operation circuit for stopping the overcurrent when the overcurrent is detected. The load is, for example, a valve for controlling the flow rate of the fluid, a motor for operating the optical system, or the like.

  By detecting overcurrent at high speed on the high side of the power supply, even if a load abnormality that cannot be protected by detection by the low side, such as a short circuit of the load cable to the ground, can be reliably protected. It becomes.

  The time obtained by combining the operation time of the overcurrent detection circuit and the operation time of the circuit operating in accordance with the overcurrent detection is sufficiently shorter than the time from when the abnormality occurs until the load or the drive circuit is damaged.

  An overcurrent detection signal detected by the overcurrent detection circuit is transmitted to the display unit of the analyzer, and it is displayed that an overcurrent has occurred in the drive circuit that performs constant current control. This display is not cleared until the analyst resets it.

  Examples of the present invention will be described below. FIG. 1 is a diagram showing the configuration of the protection circuit of the present invention. In FIG. 1, reference numeral 1 denotes an overcurrent detection circuit. When an overcurrent is detected, its output signal is set to a low level. The values of the resistors R1, R2, and R3 are determined so that the time for charging the capacitor C is extremely shorter than the time for discharging. Reference numeral 2 denotes a constant current IC, which is an integrated circuit that drives the load 3 at a constant current by the H-bridge method, and its internal configuration is shown by a constant current IC 20 in FIG.

  An overcurrent detection circuit 1 is incorporated on the high side of the power source of the constant current IC 2. The load 3 is composed of a valve or a motor. A control unit 4 functions as a stop operation circuit. The control unit 4 normally inputs the control signal of the CPU 5 to the constant current IC 2 as it is and performs constant current control of the load 3. However, when an overcurrent is detected, the constant current IC 2 is forcibly stopped and the internal circuit is shut down. Prevent damage to the transistor or load 3.

Since the present invention has the above configuration, the protection circuit of the present invention operates as follows.
(1) Under normal conditions, the current I is, for example, about 100 mA, the detection Tr (transistor) has a Vbe (base-emitter voltage) of about −0.13 V (= 1.3Ω × 100 mA), and the detection Tr is It remains off and the output signal of the overcurrent detection circuit 1 is at a high level. In this case, instead of the forced stop state, the control unit 4 inputs the control signal of the CPU 5 to the constant current IC 2 as it is, and the load 3 is subjected to constant current control.

  (2) When the B terminal of the load 3 (see the B terminal of the load 22 in FIG. 2) is short-circuited to the ground, for example, the current I becomes an overcurrent of 462 mA or more, the Vbe of the detection Tr is −0.6 V or less Then, the detection Tr is turned on, and the capacitor C is charged. At the same time, the output signal of the overcurrent detection circuit 1 becomes Low level. In this case, it is in a forced stop state, and the control unit 4 ignores the control signal of the CPU 5, forcibly stops the constant current IC2, shuts down the internal circuit, and prevents damage to the transistor and the load 3. In an actual test, the time required to shut down the internal circuit is about 30 μsec.

  (3) When the constant current IC2 is forcibly stopped and the internal circuit is shut down, the current I decreases, the Vbe of the detection Tr becomes about 0V, and the detection Tr is turned off, but the capacitor C is charged. Due to the remaining charge, the input voltage of the inverter HC04 maintains the high level. Until the input voltage falls below the High input threshold due to discharge, the output signal of the overcurrent detection circuit 1 maintains the Low level and continues the forced stop state.

  (4) When the input voltage falls below the High input threshold due to discharge, the output signal of the overcurrent detection circuit 1 becomes High level, the constant current IC2 is released from the forced stop state, and the load 3 is controlled by the control signal from the CPU5. Constant current control.

  (5) When constant current control is started, if the cause of the overcurrent, such as the B terminal of the load 3 being short-circuited to the ground, has not been repaired, the process returns to (2). While the cause is not repaired, repeat steps (2) to (5). However, since the operation time of (3) is extremely longer than that of (2) + (4) + (5), the transistor or the load 3 is not damaged.

  In the embodiment shown in FIG. 1, when an overcurrent is detected, the constant current IC2 is forcibly stopped and the internal circuit is shut down to prevent the transistor or the load 3 from being damaged. In addition, the present invention is applicable and the protection circuit is not limited to the illustrated example.

The overcurrent detection circuit 1 is constituted by a detection Tr or the like, but can be replaced by a commercially available high-side overcurrent detection integrated circuit.
In the embodiment, the forced stop state is intermittently released even if the cause of the overcurrent is not repaired, but a latch circuit is provided, and an overcurrent detection signal is input to the latch circuit to hold the forced stop state. . The held forced stop state is canceled when the power is turned on again or when the analyzer is reset.
In FIG. 1, the resistance inserted between the emitter and base of the detection Tr is 1.3Ω, but this is an example. For example, when detecting a current at 600 mA as an overcurrent, the resistance is 1.0Ω. is there.

  In the embodiment, the constant current IC2 is an integrated circuit (see FIG. 2) that is driven with a constant current by the H-bridge method. However, this is only an example, and a drive circuit that drives a load in a single direction with a FET (FIG. 3) Can be replaced with Thus, the protection circuit can have various configurations, and the present invention includes these modifications.

  The present invention relates to an analyzer equipped with a load such as a valve or a motor, and relates to a protection circuit that prevents damage to the load and the drive circuit.

It is a figure which shows the structure of the protection circuit of this invention. It is a figure which shows an example which carries out constant current drive of a load bidirectionally by H bridge system. It is a figure which shows an example which carries out constant current drive of the load by FET in one direction.

Explanation of symbols

1 Overcurrent detection circuit 2 Constant current IC
3 Load 4 Control unit 5 CPU
20 constant current IC
21 Control circuit 22 Load 31 Control circuit 32 Load

Claims (1)

  Built in the power supply high side in the circuit for constant current control of the load driven by sending and receiving control data to and from the control circuit and the protection circuit for the analyzer with the function to protect the load from damage An analysis device protection circuit comprising: an overcurrent detection circuit; and a stop operation circuit for stopping the overcurrent in accordance with the overcurrent detection.

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