JPH06331203A - Load driving circuit - Google Patents

Abstract

PURPOSE:To provide a load driving circuit equipped with a diagnostic function which can eliminate the port of a diagnostic control circuit. CONSTITUTION:At a control signal generating circuit 13, (a) output is set at 'L' corresponding with the turning on of an air conditioning switch 11, and a load 12 is operated by setting a terminal 131 at 'H' and turning on an MON transistor 16 of a diagnosis control circuit 15. When an overcurrent flows to the MOS transistor 16, an MOS transistor 19 for detection is turned on by an overcurrent detection circuit 18, and the terminal 131 is set at 'L', and at the same time, the MOS 16 for control is turned off. At this point, since the electric current is lowered, an output from the overcurrent detection circuit 18 becomes 'L', the MOS transistor 16 is turned on, and an overcurrent flows again, and an overload is detected, and an oscillating motion takes place. This oscillating motion appears on the terminal 131, and is monitored as a monitor output, and by the oscillation of the monitor output, the overcurrent of the MOS transistor 16 is judged, and the (a) output is fixed at 'H'.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load drive circuit having a function of monitoring abnormality such as output short circuit.

[0002]

2. Description of the Related Art In an air conditioner device, for example, a switching MOS that forms a load control circuit by generating a load control output in a control circuit such as a CPU to which the switch input is supplied when an air conditioner switch is operated.
The transistor is controlled to engage the air conditioner magnet clutch to activate the air conditioner. That is, the switching MOS transistor is conductively controlled so as to supply an exciting current to the magnet coil of the air conditioner magnet clutch, which is a load, corresponding to the load control output.

In this case, if the output of the switching MOS transistor is short-circuited to the power supply for some reason, an overcurrent may flow to the switching MOS transistor and destroy the MOS transistor. Therefore, when such a failure occurrence is detected, the MO
It is necessary to control the S transistor to be off to protect this MOS transistor. At the same time, it is necessary to output a diagnostic signal that notifies the occurrence of a failure in the MOS transistor.

To perform such an air conditioner control, for example, a circuit device having a diagnostic function as shown in FIG. 4 is used. This circuit device includes a control circuit 32 such as a CPU to which the output from the air conditioner switch 31 is supplied.
When the air conditioner switch 31 is turned on, a control output is obtained from the control output terminal 33 of the control circuit 32. This control output is supplied to the MOS transistor 34 that constitutes the switching circuit, and the MOS transistor 34 is turned on in accordance with the control output, and power is supplied to the load 35 composed of the magnet coil of the air conditioner magneteck latch.

Here, the amount of current flowing through the MOS transistor 34 or the state of heat generation is monitored by a detection circuit 36 for overcurrent or overheat, and when overcurrent or overheat of the MOS transistor 34 is detected. The diagnosis monitor input is supplied to the diagnosis input terminal 37 of the control circuit 32. The detection circuit 36 is supplied with a power supply Vcc for operating a comparator provided therein.

That is, a sense circuit 38 is constituted by the MOS transistor 34 and the detection circuit 36. Based on the diagnosis monitor input from the sense circuit 38,
In addition to detecting that an overcurrent has flown into the MOS transistor 34, the control circuit 32 turns off the control output from the output terminal 33 to turn off the MOS transistor 34.
Protects S-transistor 34 from destruction.

In such a circuit device, a sense circuit 38 is connected to a control circuit 32 for performing a load control command operation to form a circuit device having a diagnostic function. Between the circuit 32 and the signal line corresponding to the output terminal 33 for the load control command, the signal line for the diagnostic monitor is required and the configuration becomes complicated. It is necessary to provide this port and the port for diagnosis monitor, which causes a problem that the number of ports of the control circuit 32 increases.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and the diagnosis control when a failure occurs in the load drive circuit together with the control of the load is performed in a single terminal portion. In addition, the present invention intends to provide a load drive circuit that can be realized with a simplified configuration of the sense circuit section.

[0009]

A load drive circuit according to the present invention comprises a load to which power is supplied, and a control signal output means generates a control signal of a predetermined level for operating the load in response to a control command. Let A first switching element that is connected in series to the load and controls the on / off state of the load based on the control signal is provided, and an overcurrent or overheat of the first switching element is provided in the overcurrent / overheat detection means. For detecting the overcurrent or overheat by the overcurrent / overheat detecting means, the predetermined level of the control signal is changed to turn off the first switching element, and the first switching element is turned off. A second switching element is provided which sets the control signal to the predetermined level and turns on the first switching element again when overcurrent or overheat is no longer detected due to the turning off. And the control signal output means,
The repetitive fluctuation of the control signal is detected to determine the overcurrent state or the overheat state of the first switching element.

[0010]

In the load drive circuit thus constructed,
The first switching element is on / off controlled based on the control signal from the control signal output means, and the power supply supplied to the load is controlled. In such load control,
The overcurrent / overheat detection means detects overcurrent or overheat of the first switching element for load control, and the level of the control signal is variably switched according to the detection of overcurrent or overheat. The first switching element is turned off in the detected state of current or overheat. When the first switching element is turned off, the power supply to the load is cut off and the overcurrent or overheat in the first switching element is avoided, and the overcurrent / overheat detection means circuit detects overcurrent / overheat. Instead, the first switching element is turned on again. Therefore, in the state where the overcurrent or overheat is detected when the first switching element is turned on, the level of the control signal is repeatedly changed unless the cause of the overcurrent or overheat is avoided. However, in such a situation, the control circuit determines the overcurrent state or overheat state of the first switching element, and the appropriate protection operation is performed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration thereof, and this embodiment shows an example in which a load 12 which is a control coil of an air conditioner magnet clutch (ACMG) is controlled based on a command from an air conditioner switch 11.

A command signal associated with the operation of the air conditioner switch 11 is input to the control signal output circuit 13 composed of a CPU. In the control signal output circuit 13, for example, when the switch 11 is turned on and a command to operate the air conditioner is input from the switch 11, the control signal output circuit 13
Reads this and sets the a output to the low level "L". This output a is the MO which constitutes this circuit 13.
It is input to the gate of the S transistor 14, and the transistor 14 is turned off.

The terminal 131 of the control signal output circuit 13 has a resistor R
This terminal is connected to the power supply Vcc via 1
131 is grounded through transistor 14. Further, this terminal 131 is connected to the terminal 151 of the diagnosis control circuit 15 which is a sense circuit via the resistor R2, and this terminal 151 is connected to the gate of the control MOS transistor 16. The MOS transistor 16 constitutes a switching circuit for controlling the load 12.

As described above, when the air conditioner switch 11 is turned on, the output a of the control signal output circuit 13 is set to the "L" level, the transistor 14 is turned off, and the transistor 14 is turned off. Depending on the control MOS
The potential at the point b, which is the gate of the transistor 16, is set to the high level "H", and the transistor 16 is turned on. This MOS transistor 16 controls the circuit between the load 12 whose one end is connected to the power source + B and the ground. When the transistor 16 is turned on, the power source is connected to the load 12 and the air conditioner magnet clutch operates. When the air conditioner is turned on, the air conditioner is activated. A current detecting resistor 17 is connected between the load 12 and the ground point.

Here, the terminal 131 of the control signal output circuit 13 is
The load control output connected to the gate of the control MOS transistor 16 is taken out and is also used as a monitor input terminal for diagnostics. A diode 132 is connected to the terminal 131, and the signal at the terminal 131 is connected to the DIAG. The monitor output c is incorporated in the control circuit 13.

The resistor 17 includes a control MOS transistor 16
The current that flows to the load 12 via the
A voltage corresponding to the current flowing through the MOS transistor 16 is generated between both ends of 17. A voltage having a value corresponding to the current obtained by the resistor 17 is supplied to the overcurrent detection circuit 18, and when the current flowing through the control MOS transistor 16 becomes larger than a predetermined value. Comparator 181
The output of the comparator 181 causes the detection MOS transistor 19 to be turned on.

The comparator 181 supplies power from a point between the load 12 and the control MOS transistor 16. That is, the power supply of the comparator 181 is output terminal 15
Since it is connected to 2, the overcurrent detection circuit 15 is configured to operate when there is an abnormality in which the output terminal 152 and the power supply are short-circuited.

Note that the control MOS transistor is normally operated.
Power is supplied to the comparator 181 even when 16 is in the OFF state, but at this time, no current flows in the control MOS transistor 16 and the detection resistor 17, so that even if the comparator 181 operates, this control system Will not be adversely affected.

That is, in this embodiment, power is supplied from one point between the load 12 and the control MOS transistor 16, focusing on the fact that the current detection circuit 15 should be operated only when an abnormality occurs. Therefore, the comparator 181
It is not necessary to bother to bring the power source for activating the power source from the voltage source, and therefore the wiring can be simplified. Further, as will be described later, in this embodiment, since the diag control circuit 15 is composed of one chip, the number of terminals of the one-chip IC can be further reduced in this case.

This detection transistor 19 is a control MOS
It is connected between the gate of the transistor 16 and the ground point, and when the overcurrent is detected by the detection circuit 18, the gate of the transistor 16 is grounded and the potential at the point b is used as the ground potential.
The S transistor 16 is turned off. That is, it is possible to prevent the control MOS transistor 16 from being destroyed by interrupting the current flowing through the control MOS transistor 16 when the overcurrent is detected.

In this embodiment, the control signal output circuit 13 is composed of one IC chip, and the diagnosis control circuit 15 is composed of another IC chip. Therefore, the diagnosis control circuit 15 includes a terminal 151 to which a control input is supplied and a terminal 152 to which the load 12 is connected.
And a terminal 153 for grounding is further provided to form a three-terminal configuration, and the terminal 151 is connected to the control signal output circuit 13.

FIG. 2 shows the states of the signal waveforms of the respective parts corresponding to the control of the device constructed as described above. In this device, the air conditioner (A / C) switch is turned on / off as shown in the figure.
It shall be controlled off. In the control signal output circuit 13, when the input from the air conditioner switch 11 is the off input, the output a is set to the high level “H”, and the switch
Low level “L” when the input from 11 is ON input
When the switch 11 is turned off so that the air conditioner is stopped, the output a is "H" and the MOS transistor 14 is turned on. Therefore, in this state, the power supply Vcc is grounded via the resistor R1 and the transistor 14, the potential at the point b becomes "L", the control MOS transistor 16 is turned off, and the load 12 is turned on.
Is not supplied with current. Further, since the terminal 131 becomes "L", the DIAG monitor output c becomes "L".

When the air conditioner switch 11 is turned on, the output a becomes "L", the transistor 14 is turned off, the potential at the point b becomes high level, the control MOS transistor 16 is turned on, and the clutch coil of the load 12 is turned on. An exciting current is supplied to the air conditioner to activate the air conditioner. In this case, DIA
The G monitor output c is set to "H".

In the state where the operating current is supplied to the load 12, there is no obstacle such as the output of the control MOS transistor 16 being short-circuited to the power supply, and when the load current is in the normal state, it is detected. The overcurrent does not flow through the resistor for use 17, the output from the comparator 181 in the overcurrent detection circuit 18 is "L", and the detection MOS transistor 19 is held in the off state. Therefore, the potential at point b is "H"
The load 12 is maintained at the level and the operating state of the load 12 is maintained.

In such an operating state, that is, when the air conditioner switch 11 is on and the point b potential is "H", if the output of the control MOS transistor 16 is short-circuited to the power supply When the current flowing through the MOS transistor 16 increases and the current flowing through the detection resistor 17 also increases and becomes an overcurrent state, the output from the comparator 181 becomes "H" and the detection MOS transistor 19
Is turned on. Therefore, control MOS transistor
The potential at point b, which is the base of 16, becomes "L", the transistor 16 is turned off, the load current is cut off, and the control M
The OS transistor 16 is protected.

Here, the potential of the terminal 131 of the control circuit 13 becomes a voltage obtained by dividing the power supply voltage Vcc by the resistors R1 and R2. The voltage divided by the resistors R1 and R2 is determined to be "L" when viewed from the control circuit 13,
By setting the values of the resistors R1 and R2, the level of the terminal 131 becomes "L" and the DIAG monitor output c becomes "L" when the detection MOS transistor 19 is turned on.

When the current flowing through the control MOS transistor 16 is cut off, the overcurrent state disappears at this point, so the output of the overcurrent detection circuit 18 becomes "L" and the detection transistor 19 is turned off. Then, the control MOS transistor 16 is turned on, and the control MOS transistor 16 is turned on.
The electric current will flow again.

At this time, if there is still a short circuit between the output of the control MOS transistor 16 and the power supply, the output from the overcurrent detection circuit 18 becomes "H" and the detection transistor 19 is turned on. The control MOS transistor 16 is turned off again. Then, the control MOS transistor 16 is repeatedly turned on and off, and the oscillation operation is performed. By such an operation, a current may flow or be cut off in the control MOS transistor 16.
Overcurrent that would damage the MOS transistor 16 does not flow.

Here, when the control MOS transistor 16 is turned off due to an overcurrent, that is, when the potential at the point b becomes "L", the output of the control signal generation circuit 13 is reduced even though the output a is "L". The terminal 131 becomes "L". Therefore, the monitor output c starts oscillating in response to the oscillating operation of the control MOS transistor 16, and the continuation of this oscillating operation is detected by the control circuit 13, and the control M
The overcurrent state of the OS transistor 16 is determined.

When this overload state is determined, the control signal generation circuit 13 performs a process of constantly keeping the output a at "H", and the control MOS transistor 16 is always set to OFF. Specifically, when the monitor output c is monitored by the control signal generating circuit 13 and the monitor output c oscillates a specified number of times within a specified time range, it is determined that an overcurrent flows through the control MOS transistor 16. Judgment is made and the a output is constantly set to "H".

FIG. 3 shows a control signal generating circuit 13 of this circuit device.
Shows the flow of operations in step 101.
The condition of the air conditioner switch 11 is determined by
When 11 is not turned on, the routine proceeds to step 102, where the output a is set to "H" level. In this state, the MOS transistor 14 is turned on and the control MOS transistor 16
Is turned off, and the operating current is not supplied to the load 12.

When the air conditioner switch 11 is turned on, the routine proceeds from step 101 to step 103, the a output is made "L", the transistor 14 is turned off, and the potential at the point b of the gate of the control MOS transistor 16 is "H". Then, the transistor 16 is turned on, the operating current is supplied to the load 12, the air conditioner magnet clutch is turned on, and the air conditioner is put into the operating state.

In step 104, such a DIA
The change in the G monitor output c is monitored to determine whether or not it should be determined that the load 12 is short-circuited. As described above, when such a short-circuit occurs, the control MOS transistor is used.
Since 16 is repeatedly turned on and off, this repetition occurs, for example, more than the specified number in the specified time range, and the short circuit of the load 12 is determined in the state determined to be the oscillation state.

If it is determined in step 104 that the load 12 is short-circuited, the process proceeds to step 105, in which a
The output is fixed to "H" and the DIAG monitor output c is fixed to "L" level in step 106.

In this embodiment, the control MOS is used.
An example of detecting an overcurrent of the transistor 16 and making an abnormality determination has been described, but by changing the detection resistor 17 to a thermistor, the overheated state of the MOS transistor 16 can be detected, and an abnormality determination is made by this overheat detection. You may do it.

[0036]

As described above, according to the circuit device of the present invention, the diagnosis control circuit and the control signal output circuit which form the sense circuit are connected by one signal line,
The occurrence of a fault such as a short circuit of the load is detected based on the high or low level signal of one terminal of the control signal generation circuit, and the protection operation from the overload of the load is appropriately performed.
Therefore, this diagnostic control circuit can be configured to have the minimum number of terminals, and the number of input / output ports of the control signal generation circuit can be effectively reduced.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram illustrating a circuit device having a diagnosis function according to an embodiment of the present invention.

FIG. 2 is a signal waveform diagram illustrating the operation of the above embodiment.

FIG. 3 is a flowchart for explaining the operation flow of the embodiment.

FIG. 4 is a configuration diagram showing an example of a conventional device.

[Explanation of symbols]

11 ... Air conditioner switch, 12 ... Load, 13 ... Control signal output circuit, 131 ... Terminal, 15 ... Diag control circuit, 16 ... Control M
OS transistor, 17 ... Detection resistor, 18 ... Overcurrent detection circuit, 19 ... Detection MOS transistor.

Claims (1)

[Claims] 1. A power source, a load to which the power source is supplied, a control signal output means for generating a control signal of a predetermined level for operating the load in response to a control command, and a series connection to the load, A first switching element for controlling the on / off state of the load based on the control signal; an overcurrent / overheat detection means for detecting overcurrent or overheating of the first switching element; and an overcurrent / overheat detection When the overcurrent or overheat is detected by the means, the predetermined level of the control signal is changed to turn off the first switching element, and the overcurrent or overheat is not detected by turning off the first switching element. And a second switching element that sets the control signal to the predetermined level when turning on the first switching element again. The control signal output means detects a repeated fluctuation of the control signal to determine an overcurrent state or an overheated state of the first switching element.