JPS5934868B2 - Non-contact ignition device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ignition system for an internal combustion engine, and more particularly to an improvement in an ignition system equipped with a current limiting circuit that limits the primary winding current so that it does not exceed a value necessary for ignition.

Conventionally, in this type of ignition device, as shown in Japanese Patent Publication No. 44-8545, a primary current detection resistor is provided between the emitter of the power transistor that controls the primary current of the ignition coil and the ground, and the voltage drop that occurs there is When the voltage rises above a predetermined value, part of the base voltage of the power transistor is shunted to ground to prevent the primary current from flowing beyond the current required for ignition, allowing the use of power transistors with smaller ratings. Are known.

In order to prevent the current limit value from being affected by temperature, it is also known to use a diode in a circuit that shunts the base current of a power transistor to ground.

However, in this conventional example, a leakage current flows through the diode before the current is limited, and as a result, there is a problem in that an extra drive current for one power transistor must be supplied.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a temperature-compensated current limiting circuit without leakage current which reduces the drive current of a power transistor.

The purpose of this is to shunt the base current of the power transistor to ground by providing a PNP transistor that allows the shunt current to flow through its own emitter-collector circuit, and by applying a predetermined constant voltage to the base of the PNP transistor. achieved.

That is, the emitter-collector current of the PNP transistor changes so as to offset the temperature change in the base current of the power transistor, so that the current limit value is not affected by the temperature change.

On the other hand, since the base voltage of the PNP transistor is fixed at a constant voltage, the PNP transistor does not conduct until the emitter potential of the PNP transistor reaches a value higher than this voltage by a predetermined value, so that no leakage current occurs.

When the power transistor is Darlington-connected, a diode is connected in the forward direction in the current path from the connection point between the base of the power transistor and the emitter of the PNP transistor to the ground through the emitter base of the I)NP transistor.

This is because when the power transistor is connected to Darlington, the change in Hapower I-Randiske base current with respect to temperature doubles, and since a PNP transistor alone cannot cancel out this temperature change, a diode with the same temperature characteristics as a PNP transistor is used. is provided in the forward direction in the current path through which the base current flows, and the temperature characteristics of this diode are also added to offset the temperature change in the base current of the power transistor.

An embodiment of the present invention shown in the drawings will be explained in detail below.

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing waveforms of various parts thereof.

In the figure, a pickup coil 1 is connected to the base of a waveform shaping NPN transistor 5 via a resistor 13.

The emitter of the transistor 5 is grounded, and the collector is connected to the base of the next stage NPN transistor 4 and the collector resistor 1.
Connected to one end of 2.

The emitter of the transistor 4 is grounded, and the collector is connected to one end of the collector resistor 11 and the base of the power transistor 3.

The emitter of the power transistor 3 is connected to the primary current detection resistor 14, and the collector is connected to the primary side of the ignition coil 15.

The battery voltage V is connected to the common end of the ignition coil 15 and the resistor 1
0 to the other end of the collector resistor 11, 12.

The voltage at the other end of this collector resistor is regulated by a Zener diode 7.

The most distinctive feature of this embodiment is that it includes a PNP transistor whose emitter is connected to the base of the power transistor and whose collector is grounded, and a resistor 8 and diode 6.
A series circuit consisting of a resistor 9 and a resistor 9 is connected in parallel to the Zener diode 7, and a resistor 8 and a diode 6 of the series circuit are connected in parallel to the Zener diode 7.
This is because the base of the transistor 2 is connected to the connection point.

An ignition plug 16 is provided on the secondary side of the ignition coil 15.

The operation in such a configuration will first be described in general.

As shown in FIG. 2, a positive and negative alternating voltage 1a is generated in the pick amplifier coil 1.

This voltage 1a is applied to the base of the transistor 5 via the resistor 13.

Transistor 5 is turned off when voltage 1a is negative;
When it is positive, an output voltage is generated according to the amplitude.

As a result, transistor 4 having the opposite phase to transistor 5 generates a collector voltage 5a as shown in FIG.

This collector voltage 5a is applied to the base of the power transistor 3, and the power transistor 3 is turned on when the transistor 4 is off, and turned off when the transistor 4 is on.

A primary current Ic flows through the primary side of the ignition coil 15 during the period in which the transistor 4 is off.

This primary current Ic reaches its maximum value when the power transistor 3 switches from on to off, and instantaneously becomes zero.

At this time, high voltage is generated on the secondary side of the ignition coil 15, and a spark discharge occurs at the ignition plug 16, causing ignition.

Next, the relationship between transistor 2 and the series circuit described above will be described.

Letting the base tffE of transistor 2 be Va, becomes.

However, R8... Value of resistor 8 R9... Value of resistor 9 Vz... Zener voltage Vf of Zener diode 7... Forward voltage of diode 6 Also, the conduction voltage between the emitter and base of transistor 2 is set to VB
E, the base voltage vb of the power transistor 3
(emitter voltage of transistor 2) is Vb = VBF, 1+Va - (2
) until the transistor 2 becomes conductive.

On the other hand, when the primary current Ic flows, the primary current detection resistor 1
4, a voltage drop occurs in accordance with the primary current.

This voltage drop is fed back to the base of the power transistor 3, the base voltage increases as the primary current increases, and when the base tJfEVb of the para-transistor 3 satisfies equation (2), the transistor 2 becomes conductive. Decrease the base current of power transistor 3.

As a result, the base voltage vb brings the power transistor 3 into an unsaturated state as shown in FIG. 2, thereby limiting the current.

Let the limit value of the primary current at this time be Ic max, and first
Next, the current balance condition equation for the current limiting loop is found as follows.

However, 2VBE2 is the total base-emitter voltage of the power transistor 3 (because it is a Darlington connection of two transistors), and R14 is the value of the resistor 14.

Therefore, the limit value Ic max of the primary current Ic is: becomes.

Let us find the temperature dependence of this limit value Icmax.

When the Zener diode 7 is used with a Zener voltage of 6 (V)ff, the temperature gradient of the Zener voltage Vz becomes almost zero.

Therefore, if used at this Zener voltage, (4)
The formula is:

Generally, therefore, equation (5) is becomes.

By the way, to reduce the value of equation (7), R8>R9
That's good.

For example, if the temperature coefficient of the diode (usually -2 mV/°C) is selected as the temperature coefficient of the limiting current value, the limiting current value becomes less susceptible to temperature changes.

Next, we will discuss leakage current.

In this embodiment, the base voltage vb of the transistor 3 is (1
Since no leakage current occurs until the value of the equation ) is reached, the drive resistor R11 can be set to the minimum value necessary to drive the power transistor 3.

In this embodiment, since the para-transistor 3 is a Darlington connection of two transistors, the change in base current with respect to temperature is doubled, so the temperature-offsetting effect of transistor 2 alone is not sufficient. A diode 6 is provided to compensate for the deficiency.

If the power transistor consists of one transistor, this diode 6 may be omitted.

In the above embodiment, the series circuit is composed of the resistor 8, the diode 6, and the resistor 9, but the diode 6 may be omitted and the diode 6 may be provided instead between the emitter of the transistor 2 and the base of the power transistor 3. .

The effects are also roughly the same. According to the present invention, primary current can be effectively limited without being affected by temperature.
At the same time, since the leakage current on the base side of the power transistor 3 can be greatly reduced, an ignition device with good precision using a power transistor with a small rating can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an embodiment of the present invention, and FIG. 2 is a waveform diagram of each part. 1...Pickup coil, 2...P
NP type transistor, 3...Power transistor, 15...Ignition coil.

Claims (1)

[Claims] 1. A power transistor that controls the primary current of an ignition coil, and a primary current detection resistor connected between the emitter of the power transistor and the ground, in which a voltage drop across the current detection resistor When the base voltage of the power transistor, which increases as the voltage increases, exceeds a predetermined value,
A PNP that causes part of the current flowing into the base of the power transistor to flow to ground through its emitter-collector circuit.
An ignition device for an internal combustion engine, characterized in that a transistor is provided, and a divided terminal voltage of a Zener diode is applied to the base of the PNP transistor. 2. In a device comprising a Darlington-connected power transistor that controls the primary current of an ignition coil and a primary current detection resistor connected between the emitter of the power transistor and ground, the increase in electrical drop of the current detection resistor When the base voltage of the power transistor, which increases accordingly, exceeds a predetermined value, a PNP transistor is provided that causes a part of the current flowing into the base of the power transistor to flow to ground via its emitter-collector circuit. A divided terminal voltage of the Zener diode is applied to the base, and a current path is sequentially applied from the connection point between the emitter of the PNP transistor and the base of the power transistor to the ground through the emitter and base of the PNP' transistor. An ignition device for an internal combustion engine characterized by having a diode connected in the direction.