JPS6282367A - Short-circuit detecting circuit - Google Patents

Abstract

PURPOSE:To decrease the number of components and to simplify circuit constitution by using a current detecting resistance and a comparing means in common to plural loads. CONSTITUTION:Loads RL1-RL3 are connected individually to switching transistors (TR) Q1-Q3 in series. The current detecting resistance 10 is connected to the emitters of the TRs Q1-Q3 through a line 9 in common. The voltage of the resistance 10 is divided by resistances R4 and R5 and the divided voltage is applied to the uninverted input terminal 13a of a comparing circuit 13 from a line 11 through a resistance 12. The circuit 13 leads out a low-level signal to a line l4 when the voltage at an input terminal 13b is higher than the voltage at the terminal 13a. Further, the output of the circuit 13 is inputted to a processing circuit 8 through a line l4. Thus, the number of components is decreased with the simple circuit constitution.

Description

TECHNICAL FIELD The present invention relates to a circuit for detecting a short circuit condition in a load and a switch connected in series with the load.

BACKGROUND ART In recent years, the electronics of engine control systems have been progressing, such as configurations in which fuel for internal combustion engines is supplied via a fuel injection nut. For this reason, f18! There is a growing possibility that an abnormality in the microcomputer that controls the system will have a major impact on the entire system. In particular, the output stage that drives the load of a computer may be permanently destroyed in a short period of time due to external factors.

In a typical prior art for solving this aym, as shown in FIG. 3, a control signal is given from a processing circuit 1 such as a microcomputer to a switching transistor 3 via an inverter 2, thereby The load t is controlled. A current detection resistor 5 is connected in series to the switching transistor 3, and its voltage is compared with a value set by a reference voltage setting circuit 7 in a comparison circuit 6.

When a low level signal is applied from the processing circuit 1 to the inverter 2, the switching transistor 3 becomes conductive and a load current flows through the load 4. Under normal conditions, when the load 4 is energized, the voltage of the current detection resistor 5 is lower than the voltage set in the voltage setting circuit 7, and therefore the output of the comparison circuit 6 is at the level.

When the load 4 is short-circuited, the voltage of the current detection resistor 5 exceeds the reference level, and the output of the comparison circuit 6 becomes high level. In this way short circuits can be detected.

In the prior art shown in FIG. 3, a current detection resistor 5, a comparison circuit 6, and a reference voltage setting circuit 7 are individually provided for each load 4. , Therefore, as the number of loads increases, the number of parts increases and the configuration becomes complex.

An object of the present invention is to provide a short circuit detection circuit that can detect short circuits for a plurality of loads by simplifying the configuration as much as possible.

Means for Solving the Problems The present invention provides a plurality of loads, a switch having one terminal connected in series to each load and receiving a control signal to change the switching mode, and a common f@ terminal of the switch. This short circuit detection circuit is characterized in that it includes a connected current detection resistor, and means for comparing the sum of control No. 43 and the voltage of the current detection resistor.

According to the present invention, the current detection resistor is provided in common to each load, and the comparison means compares the sum of the control signals and the voltage of the current detection resistor. The configuration is much simpler than the configuration in which a current detection resistor and comparison means are provided for each load as in the technology.

Embodiment FIG. 1 is an electrical circuit diagram of an embodiment of the present invention. A processing circuit 8 that controls an internal combustion engine installed in an automobile derives control signals from lines 71 to 3, and these signals are passed through inverters N1 to N3 having an oven flutter type converter. Further, the transistors are connected to the bases of switching transistors Q1 to Q3 via resistors R21 to R23. Loads RLI to RL3 are individually connected in series to switching transistors Q1 to Q3.

These loads RLI to RL3 may be, for example, fuel injection valves for each hole, or may also be electromagnetic blunters.The inverters N] to N3 are clamped via resistors R11 to R13. be done.

A current detection resistor 10 is commonly connected to the emitters of the switching transistors Q1 to Q3 via a line 9. 7Ilt The voltage of the current detection resistor 10 is the resistor R4, R
5, and the divided voltage is applied to line 1
1 is applied to a non-inverting input terminal 13a of a comparator circuit 13 via a resistor 12.

The control signals from the processing circuit 8 via the inverters N1 to N3 are sent to the guiodes D11 to D from the lines 14, 15.16.
13, and through resistors R31 to R33 to line 17. This line 17 is connected to the so-called 7-
The signal is applied to a current-voltage conversion circuit 18 called a Don amplifier. The current-voltage conversion circuit 18 derives a voltage proportional to the current flowing through the line 17 to the line 19. line 1
The two voltages are applied to the inverting input terminal 13) of the comparison circuit 30 via the resistor 20. A resistor 21 is connected in connection with the current-voltage conversion circuit 18 . The comparison circuit 13 derives a low level signal to line 4 when the voltage at the input terminal 13I is higher than the voltage at the input terminal 13a, and when the voltage at the input terminal 13I is lower than the voltage at the input terminal 13a, Deriving high level signals. The output of the comparison circuit 13 is input to the processing circuit 8 via the liner 4.

Let RL be the minimum value of the DC resistances of loads RLl to RL3, and let R10 be the resistance value of the current detection resistor]O, then R10<<RL...(1
) The resistor 21 connected in relation to the current-voltage conversion circuit 18 has a resistance value of, for example, 1 MΩ or more.

Under normal conditions when no short circuit occurs, the voltage at the input terminal 13a of the comparator circuit 13 is v(+), and the voltage at the input terminal 13I
), then V(-)>V(±)
...The resistance values of the voltage dividing resistors R4 and R5 are selected so as to satisfy the condition (2).

however R4 >> RI O... (3) R5>>RIO...(4) The operation will be explained with reference to Table 1 and FIG.

In operation mode M1, the processing circuit 8 is in line! 1~
A high-level signal is derived from the inverter 13, thereby rendering the oven collector type transistors included in the inverters N1 to N3 conductive. Therefore, the switching transistors Q1 to Q3 are cut off, and therefore the comparison circuit 1
The voltage applied to the input terminal 13a of No. 3 is zero as indicated by the broken line in FIG. The voltage ■1 applied to the input terminal 13b of the comparison circuit 13 is as shown by the solid line in FIG. 2, and is higher than the voltage applied to the input terminal 13a, so the comparison circuit 13 is connected to the line J! A low level signal is derived at 4, indicating that no short circuit has occurred.

Line in operation mode M2! 1~J! 1 out of 3
For example, assume that line 1 becomes low level. At this time, the oven collector transistor of the inverter N1 is cut off, so that a current flows through the line 14, and the input terminal 13b of the comparison circuit 13 is connected to the line !
By applying a low level control signal to 1,
A predetermined voltage ■2 is applied. At this time, the switching transistor Q1 becomes conductive, a load current flows through the load RLI, and a voltage is generated across the current detection resistor 10.

The voltage at the input terminal 13a is less than the voltage ■2. Comparison circuit 13 derives a low level signal on line 14, indicating normality.

In operation mode M3, the RISONO1. When the two wires No. 2 are at low level, current flows through line 14.15,
Correspondingly, the input terminal 13b of the comparator circuit 13 has line No. 1. J! A predetermined voltage (3) is applied by applying a low level signal to (2). Due to the conduction of the switching transistor Q i tQ2, the load RL
A negative vr current flows through I and RL2, and a voltage is generated in the current detection resistor 10 in response. At this time, the comparator circuit 13 also derives a low level signal to line No. 4,
Indicates that it is normal.

Switching transistors Q1 to Q3 and load RLI
When one of ~RL3 is short-circuited, the next operating modes M4 to M6 are entered.

First, assume that in operation mode M4, the collector and emitter of switching transistor Q1 are short-circuited. Line J! A high level signal is given to terminals 1 to 3, which causes the input terminal 13b of the comparator circuit 13 to
The voltage is Vl. At this time, the load RLI has
The load current flows through the short-circuited switching transistor Q1 and therefore the input terminal 13 of the comparator circuit 13
A voltage higher than voltage (1) is applied to a. Comparator circuit 13 therefore derives a high level signal to indicate that a short circuit has occurred.

In operation mode M5, the collector and emitter of the switching transistor Q1 are short-circuited, and the line! A low-level control signal is applied only to No. 2. At this time, the voltage v2 is applied to the input terminal 13b of the comparison circuit 13, and the load currents of the loads RLI and RL2 flow through the line 9. Therefore, the output of the comparison circuit 13 becomes high level.

Furthermore, in the operating mode M6, the load RLI is short-circuited, and the line 1f! 2, when a low level signal is applied to input terminal 13b of comparison circuit 13, voltage ■
3 is applied, but a large current flows in line 9 due to the short circuit of load RLI. Therefore, a high voltage is applied to the input terminal 13a of the comparison circuit 13. Therefore, the comparator circuit 13 outputs a high level signal to the line 14.

In this way, when the output of the comparator circuit 13 is at a high level, it is possible to detect that a short circuit has occurred.

The present invention is not only implemented for controlling internal combustion engines, but can also be widely implemented in other technical fields.

Effects As described above, according to the present invention, since the current detection resistor and the comparison means are used in common for a plurality of loads, the number of parts can be reduced and the circuit configuration can be simplified.

[Brief explanation of drawings]

Figure 1 is an electrical circuit diagram of one embodiment of the present invention, and Figure 2 is the electrical circuit diagram of one embodiment of the present invention.
FIG. 3 is a graph for explaining the operation of the embodiment shown in the figure, and FIG. 3 is an electrical circuit diagram of the prior art. 8... Processing circuit, 10... Current detection resistor, 13.
・Comparison circuit, 18 ・Current voltage conversion circuit, N 1
, N2. N3...Inverter, Ql, Q2. Q3...Switching transistor, RLI, RL2. RL3...Load, Di, D2. D3: Di 1. Di2. Di
3...Guiodo agent Patent attorney Number of strokes Keiichi Figure 1 +VB Figure 2 Figure 3

Claims (1)

[Claims] A plurality of loads, a switch having one terminal connected in series to each load and receiving a control signal to change its switching mode, and a current detection switch commonly connected to another terminal of the switch. A short circuit detection circuit comprising: a resistor; and means for comparing the sum of control signals and the voltage of a current detection resistor.