JPS6327546B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method of inducing a high voltage in the secondary winding by cutting off a transistor that conducts a short-circuit current in the primary winding of an ignition coil. , relates to an internal combustion engine ignition circuit that is ignited by a spark plug.

[Conventional technology]

As this type of circuit, the one shown in FIG. 4 is generally known. An alternating current voltage is induced in the primary winding 31 of the ignition coil 3 by a rotating permanent magnet attached to a flywheel of a crankshaft of an internal combustion engine (not shown). When terminal A is in a positive state with respect to terminal C, the base current is supplied through resistor R ₁ , so that main transistor 1
conducts first. The voltage between terminals A and C is the resistance
The voltage is divided by R ₂ and R ₃ and applied to the base of the sub-transistor 2, and when the potential at the terminal A rises to a predetermined value, the sub-transistor 2 becomes conductive.
Then, the potential at point B decreases and the main transistor 1
The ignition coil 3 is immediately disconnected, a large voltage is induced in the secondary winding 32 of the ignition coil 3, a spark flies to the ignition plug 4, and the internal combustion engine is ignited.

[Problem that the invention seeks to solve]

In the internal combustion engine ignition circuit configured in this way, the smaller the resistance R ₁ is, the larger the base current of the main transistor 1 can be obtained, and even if the amplification factor of the transistor 1 is small, a large collector current can be obtained.
Therefore, it is desirable to reduce the resistance _R1 .
However, when the sub-transistor 2 becomes conductive and the main transistor 1 is turned off, and the point A becomes a high potential,
Since a current corresponding to the induced voltage flows through the resistor _R1 to the sub-transistor 2, it is necessary to increase the current capacity of the transistor 2 to match the high induced voltage during high-speed rotation, which increases the price and reduces power loss. also becomes larger. Therefore, the resistance R ₁ cannot be made very small. As a result, when the internal combustion engine rotates at low speed and the induced voltage is low, the current flowing through the main transistor 1 is small, the induced voltage in the secondary winding 32 is low, and the spark energy is low. On the other hand, it is also possible to use the main transistor 1 with a large amplification factor, but when the amplification factor is increased, this type of transistor usually has an emitter,
Since the voltage between the collectors becomes low and it becomes necessary to suppress the electromotive voltage of the primary winding 31 to a low level, it is not a good idea to use a main transistor 1 having an amplification factor higher than a certain level.

In addition, the back electromotive force generated in the coil may become larger than the withstand voltage between the emitter and collector of the main transistor 1, which may cause secondary breakdown of the main transistor 1. Therefore, a resistor R ₁ is installed between the base and collector of the main transistor 1. In addition, an avalanche diode 6 had to be connected.

Furthermore, since the waveform of the induced voltage differs depending on the type of coil, the resistor _R1 must be adjusted individually in order to match the magnitude of the current flowing through the main transistor 1 and the timing of the current cutoff to each coil.
It was not possible to standardize the ignition circuit.

An object of the present invention is to provide a constant current to a main transistor and a sub-transistor and to provide a function of protecting the main transistor from overvoltage with a simple configuration, regardless of the magnitude or waveform of the induced voltage in the ignition coil.

[Means for solving problems]

In order to solve the above problems, according to the present invention, a junction field effect transistor is provided between the collector and the base of the main transistor that conducts the short-circuit current of the primary winding of the ignition coil, and a switching field effect transistor is provided between the base and the emitter. The elements are connected in parallel, and the junction field effect transistor short-circuits its source and gate so that a constant current flows when the voltage applied between the source and drain changes, and The main transistor is set to undergo avalanche breakdown at a voltage lower than the breakdown voltage between the emitter and collector of the main transistor, and the main transistor is made conductive by the base current through the junction field effect transistor, and the switching element It is assumed that the wire will be disconnected as the conduction occurs.

[Effect]

Even if the voltage between terminals A and C changes from low voltage at low speed rotation to high voltage at high speed rotation, the current flowing to the base of main transistor 1 through the FET remains constant, and the current flowing to the base of main transistor 1 through FET remains constant. The current flowing through the sub-transistor 2 when the transistor 1 is turned off is also kept constant by the FET.

Furthermore, when the voltage between terminals A and C increases and exceeds the avalanche breakdown voltage between terminals S and D of the FET, breakdown current flows into the sub-transistor 2 via terminal D.
Secondary destruction of the main transistor 1 in the reverse direction does not occur.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, parts common to those in FIG. 4 are given the same reference numerals. Reference numeral 5 indicates a junction field effect transistor (hereinafter referred to as FET) used in accordance with the present invention, the structure of which is shown in FIG. That is, there are gate regions 52 and 53 sandwiching the p layer 51 forming a channel,
The p layer 51 includes p ⁺ layers 54, 5 for ohmic contact.
A source electrode 56 and a drain electrode 57 are provided via the source and drain terminals S and D.
are connected to each. The source electrode 56 is
p ⁺ layer 54 as well as gate regions 52 and 5
It is also connected to 3. When a voltage with the S side being positive is applied between terminals S and D, an empty layer extends from both gate regions 52 and 53 in p layer 51, and the effective cross-sectional area of the channel is adjusted. In this case, in the FET used in the present invention, the geometric structure of each layer and the impurity concentration of the p layer 51 are adjusted so that the current flowing between the terminals SD is constant regardless of the magnitude of the applied voltage. Furthermore, if this voltage increases, the n-layer 5
2 and the p ⁺ layer 55, and the impurity concentration of the p layer 51 is set so that avalanche breakdown occurs at a pn junction between the n layer 52 on the drain electrode 57 side at a certain voltage value between SD. It has been selected.
Such a FET is manufactured by growing a p layer 51 on an n-type substrate 53 by epitaxial method, for example, and
It is produced by forming an n layer that will become the n region and gate region 52 connected to the substrate 53 by a diffusion method from the layer surface, and further forming p ⁺ layers 54 and 55 by diffusion of an acceptor. Thereafter, a source electrode 56 and a drain electrode 57 which are short-circuited to the gate region are provided by metal vapor deposition. This FET
The source terminal S of the transistor 5 is connected to the collector of the main transistor 1, and the drain terminal D of the transistor 5 is connected to the base of the main transistor 1 and the collector of the sub-transistor 2, respectively.

Next, the operation of this ignition circuit will be explained. A terminal A is connected to the primary winding 31 of the ignition coil 3.
When a positive voltage is induced, a current flows to the base of the main transistor 1 through terminals S and D of the FET 5, and the main transistor 1 becomes conductive. A,
Even if the voltage across C increases, the current flowing through the FET 5 remains constant, so the short circuit current flowing through the main transistor 1 is held constant. When the voltage further increases and the voltage across the resistor R ₃ exceeds a certain value, the base and emitter of the sub-transistor 2 becomes forward biased, and the sub-transistor 2 becomes conductive. As a result, the collector potential of the sub-transistor 2 decreases, so that the current from the terminal D of the FET 5 flows through the sub-transistor 2, the main transistor 1 is immediately cut off, and the secondary winding of the ignition coil 3 is turned off. line 3
A large output voltage is generated at 2, a spark jumps to the ignition plug 4, and ignition is performed.

According to this circuit, even when the voltage between the terminals A and C is low, a sufficiently large current flows through the main transistor 1 because the resistance between the terminals S and D of the FET 5 is small. On the other hand, even if the voltage between terminals A and C rises, the current flowing to the base of main transistor 1 remains constant, and when sub-transistor 2 becomes conductive and main transistor 1 is briefly cut off, Because a constant current is always cut off regardless of the voltage between the
Output voltage can be stabilized. Also, main transistor 1
Even if the FET 5 is suddenly disconnected and a large reverse induced voltage is generated in the winding of the coil 3, the current through the FET 5 is kept constant, so no large current flows through the sub-transistor 2, and therefore the sub-transistor The current capacity of the transistor 2 can be reduced, and the cost can be reduced. Furthermore, even if the voltage between terminals A and C increases, if it exceeds the avalanche breakdown voltage between terminals S and D of FET 5, that is, the avalanche breakdown voltage between n-layer 52 and p-layer 51, the breakdown current will flow through terminal D. Flows into transistor 2. Therefore, the avalanche breakdown voltage between S and D is set lower than the breakdown voltage between the emitter and collector of main transistor 1 so that breakdown between the emitter and collector of main transistor 1 does not occur before avalanche breakdown between S and D occurs. If this is done, the main transistor 1 will not undergo reverse secondary destruction. i.e.
Since FET 5 has an overvoltage protection function and serves to prevent destruction of main transistor 1, it requires a protection element such as an avalanche diode 6 inserted between the base and collector of main transistor 1 as in the circuit shown in Figure 4. However, it is economically advantageous.

Figure 3 shows another embodiment, and the difference from Figure 1 is
The reason is that an n-channel junction field effect transistor is used as the FET5. In this case, FET5
The source terminal S of is connected to the base of the main transistor 1,
A drain terminal D is connected to the collector side of the main transistor 1. The point that the source electrode is short-circuited to the gate region is similar to the p-channel FET shown in FIG. 1, and the operation of the circuit is also exactly the same as in the case shown in FIG.

In FIGS. 1 and 3, the main transistor 1
Although the sub-transistor 2 is used as a switching element to absorb the current flowing to the base of the sub-transistor 2, a thyristor may be used instead. In this case as well, a device with a small current capacity is sufficient.

〔Effect of the invention〕

As described above, the ignition circuit according to the present invention uses a field effect transistor and has a constant current function and an overvoltage protection function, so that the ignition circuit can easily ignite regardless of the rotational speed of the internal combustion engine. The necessary spark energy can be obtained, and there is no need to increase the amplification factor of the shunt transistor.
Additionally, the necessary spark energy can be obtained regardless of the type of generator, making it possible to standardize the ignition circuit. Furthermore, the switching element for absorbing the base current of the main transistor can be one with a small current capacity, and there is no need to further connect an avalanche diode or the like to prevent secondary destruction of the main transistor, resulting in an economical and stable ignition circuit. be able to.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of the ignition circuit according to the present invention, Fig. 2 is a sectional view of a junction field effect transistor used therein, Fig. 3 is a circuit diagram of an embodiment different from Fig. 1, and Fig. 4. is a circuit diagram of an example of a conventional ignition circuit. 1: Main transistor, 2: Sub-transistor,
3: Ignition coil, 5: Junction field effect transistor.

Claims (1)

[Claims] 1 A junction field effect transistor is connected in parallel between the collector and the base of the main transistor that conducts the short circuit current of the primary winding of the ignition coil, and a switching element is connected in parallel between the base and the emitter, and the junction field effect transistor short-circuits its source and gate so that a constant current flows when the voltage applied between the source and drain changes, and the emitter of the main transistor with respect to the voltage applied between the gate and drain;
Each is set so that avalanche breakdown occurs at a voltage lower than the collector-collector breakdown voltage.
An internal combustion engine ignition circuit characterized in that said main transistor is made conductive by a base current flowing through said junction field effect transistor, and is then made conductive as said switching element becomes conductive.