JPH0230931Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a pulse detection circuit that detects narrow, high-voltage pulse signals such as engine ignition pulses.

[Technical background of the invention and its problems]

Generally, the ignition pulse of an engine is output as a signal shown in Fig. 2 as an output waveform of a transistor igniter ignition system, for example, and the engine rotation speed is obtained by detecting and shaping the pulse signal or counting it. For example, Japanese Patent Laid-Open No. 51-122472 discloses a method for detecting such pulse signals.

That is, since such a pulse signal P is generated by a capacitor or coil that boosts the voltage to a high voltage for ignition, it is given as an oscillating waveform including a high voltage and narrow pulse P1 at the initial stage of ignition.

Since the pulse P1 normally reaches several hundred volts and has a pulse width of about 20 μsec, the pulse signal P is generally waveform-shaped by smoothing or the like, and detected based on the judgment level of a comparison circuit.

By the way, the comparison circuit's judgment level depends on the circuit's IC.
The voltage is normally set to about 2.5V by low voltage control using a low voltage control system, but even if the pulse signal P is waveform-shaped, it is not sufficiently shaped due to its vibration level, and the vibration component remains superimposed and is input to the comparator circuit. This may result in erroneous detection as several pulses input during pulse determination.

Therefore, if the pulse P1 that produces the highest peak value is detected in the pulse signal P, an accurate frequency can be obtained without detecting other low-level vibration waves, so the voltage is reduced to the judgment level region of the comparator circuit and detected. A method to do this is proposed.

That is, as shown in FIG. 3, a pulse signal P is input to the comparator circuit 1 from the pulse input terminal 3 through the resistor 2, and is compared with a judgment voltage level of, for example, 2.5V. Pulse input is being detected. The resistor 4 is grounded to form a voltage divider circuit with the resistor 2, and by setting the relationship of R2>R4 where the respective resistance values are R2 and R4, the voltage to the input terminal 3 that reaches several hundred volts can be reduced. The pulse signal P is lowered to the determination level region of the comparator circuit 1. As a result, the pulse signal P detected by the determination voltage level is the pulse P
Since only one portion is detected, low-level vibration waves are not detected, and the pulse signal P can be accurately determined as one pulse.

By the way, as a detection characteristic of the comparison circuit 1, it also has a detection time T of the pulse signal P, which is normally
The characteristics of IC implementation are such that the presence of a pulse signal is detected only when the voltage exceeds the judgment level for 30 to 40 μsec, so the pulse P
A signal with a width of 20 μsec like 1 will not be detected.

Therefore, by connecting the capacitor 5 and grounding it as shown in the figure, a time constant circuit is formed, and the fourth
As shown in the figure, the pulse width is extended by blunting the fall of the pulse P1, and the detection time T is ensured.

However, since the falling edge of pulse P1 is determined by the discharge time constant through resistor 4 of the capacitor, in order to lengthen this falling edge, the value of resistor 4 must be changed.
R4 must be increased, and the relationship of R2 >> R4, which was set to reduce the partial voltage of the pulse signal P entering the input terminal 3 to the judgment level region of the comparator circuit 1, cannot be maintained, and the value of the resistor 2 at the same ratio. If R2 is increased, there is a problem in that charging the capacitor 5 affects the rise of the pulse.

[Purpose of invention]

In order to solve the above problem, the present invention has stable and reliable pulse detection characteristics for narrow, high voltage pulses by changing the charging and discharging routes of the capacitor and giving appropriate waveforms to each. The purpose is to provide a detection circuit.

[Summary of the idea]

In the present invention, a first resistor and a diode are connected in series from a pulse input terminal to a judgment input of a comparison circuit, and a second resistor and a diode are connected in series to form a voltage dividing circuit with the first resistor.
A resistor is connected, a capacitor is connected from the cathode of the diode to ground, and a third resistor is connected in parallel with the diode, and the resistance value of the second resistor is set to the first and third resistors. It is characterized by being set sufficiently small compared to .

[Example of idea]

FIG. 1 shows an embodiment of the present invention, in which a first
A second resistor 4 forming a voltage divider circuit with the first resistor 2 is grounded, and a delay capacitor 5 is grounded to the judgment input line. Since this circuit is similar to the circuit shown in FIG. 3, the details will be omitted.

In this embodiment, a diode 6 is connected in series with the first resistor 2 and between the connection point of the capacitor 5 and the second resistor 4, and a third resistor 7 is connected in parallel with the diode 6. are connected.

In addition, the first to third resistors 2 in the above configuration,
When the resistance values of 4 and 7 are R2, R4, and R7, respectively,
Each resistance value is set in the relationship R2, R7》R4,
The ratio of R2 and R4 is set at a voltage division ratio that reduces the pulse P1, which reaches several hundred volts, to the judgment level region of the comparator circuit 1. It is set to a value that can sufficiently secure T.

According to the above configuration, when the pulse signal P input to the pulse input terminal 3 decreases to the judgment level region due to the voltage division ratio of the resistors 2 and 4 and quickly charges the capacitor 5 through the diode 5, the judgment input of the comparator circuit 1 occurs. is supplied to As a result, the input pulse rises relatively steeply, as shown in FIG. 4, and exceeds the determination voltage level of the comparator circuit 1. Next, the capacitor 5 is discharged through the resistors 7 and 4 due to the reverse connection of the diode, but the value of the resistor 7 is R7.
Since the voltage is set to be large, the discharge time becomes long, and as a result, as shown in FIG. 4, the state at or above the determination voltage level is maintained until the detection time T can be secured.

Therefore, the determination of the pulse signal P by the comparator circuit 1 becomes reliable by detecting the pulse P1.
Stable detection without false detection of low-level vibration waves can be achieved.

[Effect of idea]

As described above, the pulse detection circuit according to the present invention can reliably detect narrow, high-voltage pulse signals with a simple configuration, and can stably detect pulse signals superimposed with noise vibration waves, etc. It can be used as an effective detection circuit, especially when detecting the engine speed using the frequency of the ignition pulse.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram showing an embodiment of the pulse detection circuit according to the present invention, Fig. 2 is an explanatory diagram showing an engine ignition pulse signal as a narrow-width, high-voltage pulse signal, and Fig. 3 is a general pulse detection circuit diagram. FIG. 4 is a circuit configuration diagram showing an example of the detection circuit, and is an input waveform diagram for the determination level of the comparison circuit. DESCRIPTION OF SYMBOLS 1... Comparison circuit, 2... First resistor, 3... Pulse input terminal, 4... Second resistor, 5... Capacitor, 6... Diode, 7... Third resistor.

Claims (1)

[Scope of utility model registration request] In a pulse detection circuit including a comparison circuit that has a predetermined determination voltage level and determination time and detects the presence or absence of an input pulse by comparing the input pulse with the determination element, the pulse detection circuit has a narrow width. The detection target is a signal in which a high-voltage pulse signal and a low-voltage pulse signal that oscillates the judgment level of the comparison circuit are repeatedly output, and a first A resistor and a diode are connected in series, and a second resistor is connected to the anode connection point of the first resistor and the diode.
A resistor is connected to the cathode of the diode, a capacitor is connected to the cathode of the diode, the other ends of the second resistor and the capacitor are grounded, and a third resistor is connected in parallel with the diode. 1. A narrow-width, high-voltage pulse detection device characterized in that a resistance value is set to be sufficiently smaller than that of a first resistor and a third resistor.