JP4178423B2 - Method to protect circuit by detecting overvoltage of DC power supply - Google Patents

Description

  The present invention relates to a method for protecting a circuit by detecting an overvoltage of a DC power supply.

  As a method for protecting a circuit by detecting an overvoltage of a DC power supply of this type which has been conventionally used, one having a configuration shown in FIGS. 3 and 4 has been generally employed. That is, as shown in FIG. 3, the overvoltage is detected by the overvoltage detection circuit 35 that measures the voltage across the DC power supply, and the load is cut off. At this time, the regenerative transistor 34 operates at a voltage lower than the overvoltage. Therefore, it was protected by shutting off the input power supply by detecting overvoltage. Further, as shown in FIG. 4, the comparator 46 compares the voltage of the main circuit power supply with a voltage at a certain overvoltage level, and detects an overvoltage when it is larger.

  However, in the prior art having the configuration shown in FIG. 3, since the regenerative transistor 34 operates at a voltage lower than the overvoltage, there is a problem that the regenerative transistor 34 is damaged before the overvoltage is reached. In addition, even if an overvoltage occurs, the regenerative transistor 34 operates until the input power is cut off, and the regenerative transistor 34 is damaged. On the other hand, in the prior art having the configuration shown in FIG. 4, the voltage rises unless the power transistor module of the main circuit is cut off even if an overvoltage occurs. Therefore, if the main circuit is cut off slowly, the voltage increases and the power transistor module is damaged. There was a problem.

  SUMMARY OF THE INVENTION In view of the above problems of the prior art, an object of the present invention is to provide a method for protecting a circuit by detecting an overvoltage of a DC power supply.

  A method of protecting a circuit by detecting an overvoltage of a DC power supply according to the present invention includes a diode bridge, a main capacitor that stores a DC power supply, a regenerative transistor that consumes energy with a regenerative resistor at a predetermined voltage, a comparator, and a photo A method for protecting a circuit by detecting an overvoltage of a DC power supply of a circuit constituted by an isolator, an OR gate, and a microcomputer, wherein the power is turned on, a main capacitor is charged, and an input voltage is high. If the level of the second comparator is higher, the first photoisolator is turned on, and the stage in which the regenerative transistor operates and whether or not the input voltage exceeds the operating voltage of the regenerative transistor are determined by the second comparator level. Check the input power supply overvoltage by checking when the photoisolator is turned on. If, during operation of the regenerative transistor, by the OR gate at a high level, the third photo-isolator is turned off, and a step for protecting the regenerative transistor as dead, has. By the above means, it is possible to detect the overvoltage of the input power supply and protect the regenerative circuit composed of the regenerative resistor and the regenerative transistor.

  In addition, the method for protecting a circuit by detecting an overvoltage of a DC power supply according to the present invention includes a main capacitor that stores a DC power supply, a regenerative transistor that consumes energy with a regenerative resistor at a predetermined voltage, a power transistor module, and a DC A method of protecting a circuit by detecting an overvoltage of a DC power source of a circuit constituted by a motor driven by a power source, an A / D converter, and a microcomputer, and a regenerative operation of a regenerative resistor and a regenerative transistor From the current obtained by subtracting the current consumed by the regenerative resistor from the current returning from the motor, the increase in the voltage of the DC power supply after a predetermined time is calculated, and the voltage of the DC power supply after the predetermined time is overvoltage When the level is predicted, the power transistor module is shut down as an overvoltage abnormality. By the above means, the voltage can be suppressed to a certain level or less in order to detect an overvoltage abnormality and shut off the power transistor module as the main circuit, so that the power transistor module can be protected.

  As described above, the present invention can detect the overvoltage of the input power supply and can stop the operation of the regenerative transistor to protect the regenerative circuit composed of the regenerative resistor and the regenerative transistor. There is an effect that can be prevented. In addition, according to the present invention, the voltage can be suppressed to a certain level or less because the rise is taken into account when detecting the overvoltage abnormality and shutting off the base of the main circuit, so that the power transistor module as the main circuit can be reduced. It can be carried out with a margin without being damaged.

  Hereinafter, a first embodiment of the present invention will be described with reference to FIG. In FIG. 1, 1 is a diode bridge, 2 is a main capacitor for storing a DC power supply, 4 is a regenerative transistor that consumes energy with a regenerative resistor 3 at a certain voltage, 5 is a first comparator, 10 is a second comparator, 6 Is a first photo isolator, 8 is a second photo isolator, 11 is a third photo isolator, 7 is an OR gate, and 9 is a microcomputer (CPU).

  The operation of the circuit configured as described above will be described. First, when the power is turned on, the main capacitor 2 is charged. At this time, if the input voltage is high and higher than the level of the first comparator 5, the first photoisolator 6 is turned on and the regenerative transistor operates. Whether or not the input voltage exceeds the operating voltage of the regenerative transistor can be confirmed by turning on the second photoisolator 8 based on the level of the second comparator 10. As a result, the overvoltage of the input power supply is confirmed, and the OR gate 7 is set to the high level during the operation of the regenerative transistor, the third photoisolator 11 is turned off, and the regenerative transistor is protected from being inactivated.

  Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, 21 is a power transistor module, 22 is a main capacitor for storing a DC power source, 24 is a regenerative transistor that consumes energy with a regenerative resistor 23 at a certain voltage, 25 is a motor, 26 is an A / D converter, and 29 is It is a microcomputer (CPU).

The operation of the circuit configured as described above will be described. First, by a regenerative operation of the regenerative resistor 23 and the regenerative transistor 24, a predetermined amount is obtained from a current obtained by subtracting the current consumed by the regenerative resistor 23 from the current returned from the motor 25 (corresponding to the charge stored in the main capacitor). The amount of increase in the voltage of the DC power supply after the time is calculated, and when it is predicted that the voltage of the DC power supply after the predetermined time will be at the overvoltage level, the main circuit constituted by the power transistor module 21 is shut off as an overvoltage abnormality. The relationship between current and voltage is as follows.
ΔV = (1 / C) iΔt (1)
V: Voltage ΔV: Increase in voltage of the DC power supply after a predetermined time C: Capacitor capacity i: Current obtained by subtracting current consumed by the regenerative resistor from current returning from the motor t: Time Δt: Sample time Here, if Δt is taken as the sampling time, the voltage ΔV until the next sampling can be calculated. The current obtained by subtracting the current consumed by the regenerative resistor 23 from the current returning from the motor 25 (corresponding to the charge stored in the main capacitor) is obtained from the voltage and time thus far. V _S ≦ V _O + ΔV (2)
V _S : Overvoltage level V _O : A certain voltage ΔV: The following voltage difference (2) When an overvoltage level is reached as shown in the following equation (2), an overvoltage abnormality is determined.

  Further, in this embodiment, ΔV is obtained from the voltage difference so far. However, this is obtained by subtracting the regenerative circuit consumed from the load torque as a current, and the voltage is obtained from the equation (1). Accordingly, a comparison signal having a voltage level in place of the A / D converter 26 may be input.

It is a block diagram which shows the 1st Embodiment of this invention. It is a block diagram which shows the 2nd Embodiment of this invention. It is a block diagram of the conventional Example. It is a block diagram of the conventional Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 31 Diode bridge 2, 22, 32, 42 Main capacitor 3, 23, 33, 43 Regenerative resistor 4, 24, 34, 44 Regenerative transistor 5 1st comparator 6 1st photo isolator 7 OR gate 8 2nd photo Isolator 9, 29 Microcomputer (CPU)
DESCRIPTION OF SYMBOLS 10 2nd comparator 11 3rd photo isolator 21, 41 Power transistor module 25, 45 Motor 26 A / D converter 35 Overvoltage detection circuit 46 Comparator

Claims (1)

A main capacitor (22) for storing a DC power supply;
A regenerative circuit comprising a regenerative resistor (23) and a regenerative transistor (24) connected in parallel with the main capacitor (22);
A circuit comprising a power transistor module (21) in which the main capacitor (22) and a power input section are connected in parallel and a power output section is connected to the motor (25), and detecting an overvoltage of a DC power supply. A method of protecting
During the regenerative operation, the current obtained by subtracting the current flowing through the regenerative resistor (23) from the current returned from the motor (25) to the DC power source by driving the power transistor module (21), that is, the main capacitor ( 22) Based on the current charged in 22), the microcomputer (29) calculates the voltage increase of the DC power supply after a predetermined time,
When it is predicted that the voltage of the DC power supply after the predetermined time will be a preset overvoltage level, the power transistor module (21) is cut off as an overvoltage abnormality, and the main capacitor (25) is disconnected from the motor (25). 22) By stopping the regenerative current to 22), the rise of the voltage of the DC power supply is prevented, and the power transistor module (21) is protected from the overvoltage, thereby detecting the overvoltage of the DC power supply and protecting the circuit how to.

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