JPH0228811A - Over-current detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an overcurrent detection device for load protection functions of air conditioners, electric refrigerators, etc., in which a one-chip microcomputer is used as a control device. When the control device is powered on, it is assumed that overcurrent has been detected for a predetermined period of time, and the power to the base drive circuit that outputs switching pulses to the load-driven power transistor circuit is turned off to prevent damage to the power transistor circuit. The present invention relates to an overcurrent detection device.

[Conventional Examples] In recent years, one-chip microcomputers have been used in air conditioners and electric refrigerators, and the inverter method has become mainstream for load control of these air conditioners and electric refrigerators.

In this inverter system, a microcomputer generates control pulses for a power transistor circuit that drives a load. Based on this control pulse, the power transistor circuit is switched and the load is controlled by the inverter. At this time, a pulse for switching the power transistor circuit is obtained by the base drive circuit based on the control pulse. In order to prevent the power transistor circuit from being destroyed by overcurrent, an overcurrent detection device is provided, and when overcurrent is detected, the control pulse is turned off in the microcomputer and the switching operation of the power transistor circuit is performed. This prevents overcurrent from flowing through the load and prevents damage to the power transistor circuit.

[Problems to be Solved by the Invention] By the way, in the above-mentioned overcurrent detection device, control pulses are generated after a predetermined time (initialization of the microcomputer) after the control device is powered on, and the overcurrent detection device is operated. However, immediately after the control device is powered on, the microcomputer boat that outputs the control pulses is in an unstable state, which may create a condition for short-term termination between the arms of the power transistor circuit. In other words, in such a case, the base drive circuit outputs a switching pulse that short-circuits the arms of the power transistor (for example, between the emitter and collector), causing the power transistor circuit to be destroyed. .

This invention has been made in view of the above problems, and its purpose is to provide an overcurrent detection device that can prevent damage to a power transistor circuit that drives a load immediately after power is turned on. .

[Means for Solving the Problems] In order to achieve the above object, the present invention drives a power transistor circuit in a microcomputer of a control device for an air conditioner, etc., and controls the load of the air conditioner, etc. using an inverter. In this case, the overcurrent detection device for detecting overcurrent in the power transistor circuit is provided with a pseudo signal generating means that outputs a signal deemed to be overcurrent detection for a predetermined period of time when the power of the control device is turned on, and the pseudo signal is Then, the power of the base drive circuit that outputs the switching pulse of the power transistor circuit is turned off.

Further, the overcurrent detection device of the present invention uses an integrator circuit with a C-R time constant as the pseudo signal generating means, and outputs a signal deemed to be the overcurrent for a period of the C-R time constant from when the power is turned on. This is how it was done.

[Function] With the above configuration, immediately after the control device is powered on, the integration circuit obtains a pseudo control signal that turns off the power to the base drive circuit for the time constant. In other words, even if the output port of the one-chip microcomputer of the control device is unstable and a control pulse that short-circuits the arms of the power transistor circuit is output from the output port, the control pulse that short-circuits the arms of the power transistor circuit is A switching pulse for switching the power transistor circuit cannot be obtained in the base drive circuit.

Therefore, immediately after the power is turned on, the power transistor circuit is not turned ON or OFF, and no short circuit occurs between the arms.

[Example] Embodiments of the present invention will be described below based on the drawings.

In FIG. 1, a commercial power source 1 is converted into a predetermined DC voltage by a rectifier 2 and is applied to a power transistor circuit 3. When the commercial power supply 1 is turned on, a control pulse is generated in the one-chip microcomputer 4, and a switching pulse is obtained in the base drive circuit 5 based on this control pulse. The power transistor circuit 3 is driven by this switching pulse, and the inverter control of the load 6 is performed. At the input stage of the power transistor circuit 3, a current detection resistor (shan 1-resistance) 7 is provided for detecting overcurrent. An overcurrent caused by a short circuit between arms of the power transistor circuit 3 is detected by the first current detection circuit 8 and the second current detection circuit 9 via the current detection resistor 7. In this case, the first current detection circuit 8 operates with a relatively low current, and the second current detection circuit 9 operates with a sudden large current due to a load short circuit or the like. Therefore,
The first current detection circuit 8 is provided with a resistance circuit 8a that detects the current change, and a coupler circuit 8b that isolates the detection signal, and the second current detection circuit 9 is provided with a resistance circuit 9a and a coupler circuit 8b that isolates the detection signal. , and a coupler circuit 9b are provided.

The detection signal from the first current detection circuit 8 is input to one input terminal of the 2-NAND circuit 11 via the integrating circuit 10, and the detection signal from the second current detection circuit 9 is input to the other input terminal. In the integrating circuit 10, immediately after turning on the commercial power supply 1 (powering on the control device), the C-R
A pseudo signal (L level signal) is obtained that indicates that an overcurrent has occurred during the time constant. Further, the output of the 2-NAND circuit 11 becomes H level when an overcurrent is detected in at least one of the first or second current detection circuits 8 and 9, and this output signal is inverted by the inverter circuit 12. is,
The signal is input to the RS flip-flop circuit 13.

The RS flip-flop circuit 13 is composed of two 2-NAND circuits 13a and 13b, and the inverted signal is 2
It is input to one input terminal of the NAND circuit 13b.

The output signal of the 2-NAND circuit 13a is input to the other input terminal of the 2-NAND circuit 13b, and the output signal is input to the input port A (overcurrent interrupt terminal) of the one-chip microcomputer (CPII) 4. . In addition,
When an L level signal is input to input port A, one-chip microcomputer 4 executes an overcurrent protection interrupt processing program. Further, the set signal from the output port B of the one-chip microcomputer 4 is input to one input terminal of the 2-NAND circuit 13a, and the output signal of the 2-NAND circuit 13b is input to the other input terminal. Further, the output signal of the 2-NAND circuit 13b turns on the power to the base drive circuit 5 via the PNP transistor 14.

This is an OFF control signal. Further, the above control pulse is output from the output port C of the one-chip microcomputer 4 to the base drive circuit 5.

Next, the operation of the above-mentioned structural acid load overcurrent detection circuit used in a control device such as an air conditioner will be explained based on the time chart shown in FIG.

First, when the control device is powered on, the output of the integrating circuit 10 becomes constant (H level) after the C.R time constant, as shown in FIG. 2(a). During the C/R time constant, it can be regarded as approximately L level, and as shown in FIG. 2(c), the output of the 2-NAND circuit 11 is maintained at H level. Then, since the output of the inverter circuit 12 is set to the L level, the output of the 2-NAND circuit 13b is set to the H level, as shown in FIG. 2(e), and the RS flip-flop circuit 13 is reset. This allows PNP
The type transistor 14 is turned off, and a power-off control signal is input to the base drive circuit 5. That is, while (
(While the output port is unstable when the power is turned on), the output of the 2-AND circuit 11 is reliably kept at the H level, so the base drive circuit 5 is not operated, there is no output of switching pulses, and the power transistor circuit The switching operation No. 5 is not performed.

In this way, no overcurrent flows through the power transistor circuit 3 during the time constant of the integrating circuit 10, that is, during the period when the output port of the one-chip microcomputer 4 is unstable. Note that the CR time constant may be slightly shorter than the reset period of the one-chip microcomputer.

Subsequently, after the above, as shown in FIG. 2(a), the output of the integrating circuit 10 is kept at H level, and before that, an L level set signal is output from output port B. The output of the 2 NAND circuit 13a is kept at H level (
The output of the 2-NAND circuit 13b is set to L level (as shown in FIG. 2(e)). Then, PNP
The type transistor 14 is turned on, and the base drive circuit 5 is turned on (power is supplied). Furthermore, as shown in FIG. 2(f), the initialization (resetting) of the one-chip microcomputer 4 is completed, and an H level signal is output from output port B, and a control pulse is output from output port C. is output.

Here, if the first and second current detection circuits 8 and 9 do not detect an overcurrent, the one-chip microcomputer 4 outputs a control pulse for inverter control of the load 6. As a result, a switching pulse is output from the base drive circuit 5, the power transistor circuit 3 is turned on and off, and the load is normally controlled by the inverter.

Furthermore, although not shown, when the first current detection circuit 8 detects an overcurrent, the output of the coupler circuit 8b is set to L level, and therefore the output of the 2-NAND circuit 11 is set to H level. Then, the output of the 2-NAND circuit 13b goes to H level, and the RS flip-flop circuit 13 is reset (the output of the 2-NAND circuit 13a goes to L level), so the one-chip microcomputer 4 is equipped with the conventional overcurrent detection function. An interrupt signal (L level signal) is input. That is, the one-chip microcomputer 4 executes interrupt processing for overcurrent protection, and for example, control pulses are no longer output from the output port. As a result, the power transistor circuit 3 is turned on.

OFF drive is not performed and inverter control of the load 6 is stopped.

When overcurrent detection is not performed, the output of the integrating circuit 10 protects the H level after the C-R time constant, as shown in FIG. 2(a). Then, after the above interrupt processing,
Since a set signal (L level signal) is output from output port B, the RS flip-flop circuit 13 is set (as shown in FIG. 2(g)). That is, the output signal of the 2 NAND circuit 13a is input to the input port A,
The one-chip microcomputer 4 executes a program that generates control pulses for controlling the load 6 as usual with the inverter.

In this way, when the load 6 is under inverter control, when an overcurrent is detected in the second current detection circuit 9 as shown in FIG. 2(b), the coupler circuit 9b outputs an L A level signal is output.

Then, as shown in FIG. 2(e), the output of the 2-NAND circuit 13b becomes H level, and the RS flip-flop circuit 13 is placed in a reset state. As a result, an L-level interrupt signal is input to the input port A, and the one-chip microcomputer 4 executes interrupt processing for overcurrent as in the conventional case.

In this way, when the power of the control device is turned on, while the output port of the one-chip microcomputer 4 is in an unstable state, the RS flip is performed in the integrating circuit 10 with a C-R time constant (longer than the unstable period). - The flip circuit 13 is reset and it is assumed that an overcurrent has been detected. Moreover, the output signal of the 2-NAND circuit 13b of the RS flip-flop circuit 13 is turned off when the base drive circuit 5 is turned off.
The control signal is F. Therefore, even if a control pulse with a condition that short-circuits the arms of the power transistor circuit 3 appears at the output port of the one-chip microcomputer 4 when the output port is in an unstable state when the power is turned on, the No switching pulse is input to the power transistor circuit 3. In other words, no overcurrent occurs due to the short circuit or the like, and the transistors of the power transistor circuit 3 can be prevented from being destroyed.

[Effects of the Invention] As explained above, according to the overcurrent detection device of the present invention, when the power is turned on in a control device such as an air conditioner that uses a one-chip microcomputer for load control,
An integrating circuit is provided that resets the RS flip-flop circuit that is reset by the overcurrent detection signal during the C-R time constant, and outputs a switching pulse to the load-driven power transistor circuit 3 during the reset state. Since a control signal for turning off the power of the base drive circuit 5 is obtained, while the output port of the one-chip microcomputer is in an unstable state, the power transistor circuit is not turned on or off, and the arm This prevents short-circuiting, etc., and prevents damage to the power transistor circuit.

[Brief explanation of the drawing]

FIG. 1 is a schematic circuit diagram of an overcurrent detection device showing an embodiment of the present invention, and FIG. 2 is a time chart diagram for explaining the operation of the overcurrent detection device. In the figure, 3 is a power transistor circuit, 4 is a one-chip microcomputer, 5 is a base drive circuit, 6 is a load,
7 is a current detection resistor, 8 is a first current detection circuit, 9 is a second current detection circuit, 1o is an integration circuit, 11.13a,
13b is a 2 NAND circuit, 12 is an inverter circuit, 13
1 is an RS flip-flop circuit, and 14 is a PNP type transistor. Patent applicant: Fujitsu General Co., Ltd. Patent attorney: Takuya Ohara

Claims (2)

[Claims] (1) In an overcurrent detection device that detects overcurrent in the power transistor circuit when a power transistor circuit is driven by a microcomputer in a control device of an air conditioner, etc., and the load of the air conditioner, etc. is controlled by an inverter. , a pseudo signal generating means is provided for outputting a signal regarded as overcurrent detection for a predetermined period of time when the control device is powered on, and the pseudo signal is used to turn off the power to the base drive circuit that outputs the switching pulse of the power transistor circuit.
An overcurrent detection device characterized in that it is set in an F state. (2) The pseudo signal generating means is an integrator circuit with C and R time constants, and outputs the signal deemed to be the overcurrent during the C and R time constants from when the power is turned on. Current detection device.