JPS61261665A - Current limiting type non-contact ignition device - Google Patents

Abstract

PURPOSE:To prevent oscillation of constant electric current by working current- limiting transistors for controlling the base current for a power transistor in the active area within the current limiting section of the current limiting type non-contact ignition equipment. CONSTITUTION:When alternating current signal Vp from an electromagnetic pick-up coil 4 turns from positive to negative, output from a control circuit part 5 becomes large, turning off a transistor 19 and turning on a power transistor 22. Then, voltage decline at the primary current detecting resistor 15 steps up, and when declining voltage at a resister 12 in the standard voltage circuit (8, 11, 12, 17, 18) and the resister 15 becomes almost equal, the transistor 20 is turned off and a transistor 21 is turned on. Due to this, the transistor 21 draws the base current of the power transistor 22, thereby putting current limiting function into full play, but if the drawing of base current goes too far, power decline portion at the resister 15 diminishes, thereby turning on the transistor 20. At this time, however, the current flowing through the resister 16 also flows through the base for transistor 21, resulting in avoidance of switching actions on the part of the transistor 21.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a current limiting circuit, and relates to a current limiting circuit. The present invention relates to a non-contact ignition device with current limiting suitable for improving # performance.

[Background of the invention]

As shown in Figure 4 of Japanese Patent Publication No. 55-4948, the conventional current limiting circuit detects the primary coil current (hereinafter referred to as primary current) with an emitter resistor, and turns on the transistor 39 when the primary current reaches a predetermined value. The current is limited by drawing the base current of the power transistor 43.

However, the oscillation phenomenon of the primary voltage (collector voltage of the power transistor) in the current limiting section is not taken into account. There is a VC to provide the equipment.

[Summary of the invention]

When a conventional current limiting circuit is combined with an ignition coil having a small primary constant, the primary voltage oscillates in the current limiting section, which could cause the electronically controlled fuel injection device or tachometer to mistrigger and malfunction. In this case, the current amplification factor of the power transistor is large and it operates near the cutoff region during current limiting, and the primary constant of the ignition coil is small, so the change in the primary current in the current limiting section is large. The operation of the current limiting transistor is a switching operation. The present invention has been made in view of the above points, and it is possible to ensure that the current limiting transistor always operates in a stable active region, rather than in a switching operation, even when the primary constant of the ignition coil is small. This prevents the oscillation phenomenon of the primary voltage.

[Embodiments of the invention]

An example of a circuit for implementing the present invention will be explained below with reference to FIG.

In the figure, 1 is a battery, 2 is a key switch, 3 is an ignition coil, 30 spark plugs, and 4 is an electromagnetic pickup coil that generates positive and negative alternating current signals synchronized with the rotation of the engine.

Reference numeral 5 denotes a control circuit section that controls the ON time of the power transistor 22 based on the output signal of the pickup coil 4. 6 to 16 are resistors, 17 is a diode, 18 is a Zener diode, and 19 to 21ti transistors.

Resistance 8 to 16, Zener diode 18, diode 1
7. A current limiting circuit is constituted by transistors 2Q and 21Vc. Omitting the resistor 16 results in a conventional current limiting circuit. Hereinafter, the circuit operation when the resistor 16 is omitted will be explained using the waveform diagram in FIG.

In the electromagnetic pickup coil 4, a positive and negative alternating current signal Vp shown in FIG. 2(a) synchronized with the rotation of the engine is generated. The signal Vp is input to the control circuit section 5, and the output waveform of the control circuit section 5 becomes as shown in FIG. is LO
WK force, transistor 19 turns off, so resistor 7
, 10, the power transistor 22 is turned on. The primary current waveform Ic flowing through the power transistor 22 is as shown in FIG. 2(C). When the primary current Ic flows, the voltage drop across the primary current detection resistor 15 increases. Resistors 8, 11, 12, Zener diode.

18, the diode 17 constitutes a reference voltage circuit of the current limiting circuit, and when the voltage drops of the resistor 12 and the resistor 15 are almost equal, the transistor 20 is turned off, and the resistor 9.13
A base current flows to the transistor 21 through the transistor 21FiON. The beta current of the power transistor 22 in the transistor 21 decreases, and the voltage drop across the resistor 15 also decreases.

Therefore, the transistor 20 is turned on, and the transistor 21
This decrease in the base current of the power transistor 220 causes the base current of the power transistor 220 to increase, and the primary current Ic increases again. The current is limited by repeating this process.

Forward voltage drop of diode 17 and transistor 2
Since the temperature characteristics of the 00 base-emitter voltage are almost the same, there is almost no change in the current limit value with temperature. Resistance 13.
14 divides the voltage between the collector and emitter of the transistor 20 so that the voltage of the transistor 21 does not exceed VcONL before the current limit period. However, this conventional current limiting circuit has the problem that when combined with an ignition coil having a small primary constant (primary resistance and primary inductance), the primary voltage (collector voltage of the power transistor 22) waveform V oscillates in the current limiting section. (Figure 2(d)). If the simulator-controlled fuel injection device or tachometer is mistriggered due to oscillation of the primary voltage V+, a medium-high secondary voltage will also be generated on the secondary side of the engine stall or the tachometer needle oscillation.

This is because the power transistor has a large current amplification factor, operates near the [fi disconnection region] during current limit, and the primary constant of the ignition coil is small, so the change in primary current in the current limit section is large. This is due to the fact that the operation of the current limiting transistor is a switching operation that goes back and forth between the cutoff region and the vicinity of the saturation region. Even with conventional current limiting circuits, the above problem is likely to occur when the primary constant of the ignition coil is large.

The present invention was made to prevent oscillation in the current limit section of the primary voltage V that occurs when the ignition coil is combined with an ignition coil having a small primary constant. That is, in the current limiting section, the oscillation of the primary voltage v1 is prevented by ensuring that the current limiting transistor (21 in FIG. 1) operates in a stable active region. This will be explained with reference to FIG. For explanation of the current limit section, the transistor 19 is assumed to be OFF.

Each constant is set so that the current flowing through the resistor 16 flows into the transistor 20 via the resistor 14 or the resistor 13 and the transistor 21 is not ON until the current limit is applied. The operation of the current limiting circuit is as described above.
If the base current of 2 is drawn in too much, the primary current Ic decreases, and the voltage drop across the resistor 15 decreases. Therefore, the transistor 20 turns on, but the current flowing through the resistor 16 not only flows through the transistor 20iC via the resistor 13 but also flows to the base of the transistor 21, so the operation of the transistor 21 becomes a switching operation. operating in a stable active region.

(e) and (OK in FIG. 2) respectively show the primary current waveform 1cs and the primary voltage waveform V when the resistor 16 is connected.

Furthermore, in the circuit configuration shown in FIG. 1, depending on the setting value of the resistor 16, the current limit value may increase as the battery voltage increases. If the resistor 16 is set to such a value and the current limit value is set to a high value, there is a possibility that the operation of the power transistor 22 will exceed the safe operating range due to a load dump surge, etc., and it may be destroyed. There is. A load dump surge occurs when the terminal of battery 1 is disconnected during normal operation, and the peak value of the surge voltage is approximately 60
V and is applied to the power line of the ignition device. Although not shown in the ignition system of FIG. 1, there is an abnormal voltage ignition stop in the control circuit section 5 that forcibly turns the transistor 19 to VCON when the battery voltage exceeds about 30V to prevent the power transistor 22 from being destroyed. Built-in circuit. However, until the ignition stop circuit operates, the power transistor 22 is operating normally, and as described above, there is a possibility that the power transistor 22 may exceed the safe operating range and be destroyed.

In such a case, the resistor 10 in FIG. 1 may be replaced by the resistor 16 on the base line of the power transistor and the transistor 21.
By connecting to the 0 point between the collector and the collector, a fail-safe function can be provided. In other words, the higher the battery voltage, the more the power transistor 2
Since the base current of resistor 2 increases and the voltage drop across resistor 10 increases, the current flowing through resistor 16 increases, causing transistor 21 to lower the ONL and current limit value before reaching the predetermined current limit value. . For example, if the current limit value is set to 8A, it can be set to 7A at 28V or higher.

FIG. 3 shows another embodiment of the invention. Elements with the same numbers as in FIG. 1 have the same function. 51 in the control circuit section 5
The t'i resistor 52 is a transistor. Also resistance 51
The Vcc line to which one end is connected is clamped to a constant voltage. The ON state of the transistor 52 and the ON state of the power transistor 22 are synchronized. Resistor 1 in Figure 3
The function of resistor 6 is the same as that of resistor 16 in FIG. 1, and the transistor 21 can be reliably operated in a stable active region instead of a switching operation within the current limit section. Further, in FIG. 3, when a resistor 16' shown by a dotted line is used in place of the resistor 16, the same function can be achieved, and oscillation of the primary voltage within the current limiting section can be prevented. Further, in FIG. 3, even if the resistors 16 and 16' are not used and a small resistor (not shown) is connected between the emitter of the transistor 21 and the ground, the transistor 21 can be operated in a stable active region.

Instead, it can be operated reliably in a stable active region, which has the effect of preventing oscillation of the primary voltage.

According to the embodiment shown in FIG. 1, when the battery voltage rises abnormally, such as when a load dump surge is applied, the base current of the power transistor increases, so that the current limiting transistor sets the predetermined current limit. This has the effect of providing a fail-safe function in which the current is limited early before reaching the rcONL value.

Furthermore, since it is sufficient to add only one resistor to the conventional current limiting circuit, it is possible to suppress an increase in size and cost.

Furthermore, there is an effect that it can be combined with an ignition coil having a small linear constant.

〔Effect of the invention〕

Since the current limiting transistor can be reliably operated in a stable active region within the current limiting section, it is possible to prevent oscillation of the primary voltage.

[Brief explanation of the drawing]

FIGS. 1 and 3 are waveform diagrams of each part of FIG. 2 and FIG. 1, which are an example of a circuit for implementing the present invention.

Claims (1)

[Scope of Claims] 1. A power transistor that intermittents the primary coil current of the ignition coil, a control circuit section that controls the energization time of the power transistor, and a current limiting circuit that controls the maximum value of the primary coil current to a predetermined value. In the equipped non-contact ignition device,
A current-limiting non-contact ignition device characterized in that a current-limiting transistor for controlling the base current of the power transistor is operated in an active region within a current-limiting section. 2. A current-limiting non-contact ignition device according to the invention set forth in claim 1, wherein the base current of the power transistor is shunted to the base of the current-limiting transistor. 3. In the invention as set forth in claim 1, a current is supplied to the base of the current limiting transistor from a source other than the base line of the power transistor in the ON period of the power transistor. Limited type non-contact ignition device. 4. A current limiting non-contact ignition device according to the invention as set forth in claim 1, characterized in that current is supplied from a constant voltage source to the base of the current limiting transistor. 5. In the invention as set forth in claim 2, a connection point between a resistor for shunting the base current of the power transistor to the base of the current limiting transistor and the base line of the power transistor, and the power transistor A current-limiting non-contact ignition device characterized in that a base resistor is inserted between the base electrodes of the ignition device.