JPS62178162A - Transistor-switching circuit - Google Patents

Abstract

PURPOSE:To suppress and control noise jamming effectively without incurring a collector loss of a switching transistor by decreasing a feedback capacity in OFF-state transition as compared with that in ON-state transition of said switching transistor. CONSTITUTION:If a switching control signal 104 is made ON, a base current 114 flows into a transistor 10 and an electric current 116 flows through a capacitor 22. Also, an electric current 118 flows through a series circuit of diode 24 and capacitor 26. Accordingly, the feedback capacity of the transistor 10 becomes the sum of capacities of capacitors 22, 26. If the switching control signal 104 is made OFF, the feedback capacity of the transistor 10 becomes only a capacity of the capacitor 22 because the diode 24 is actuated in the opposite direction to said switching control signal 104.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a transistor switching circuit capable of controlling the duty ratio of current supplied to an inductance load, and in particular to reducing radiation noise generated during duty ratio control. This invention relates to a transistor switching circuit capable of

(Background of the Invention) This type of circuit is known from Japanese Patent Laid-Open No. 51-83118, and an example of the conventional circuit is shown in FIG.

The switching of the transistor 10 shown in the figure is controlled by a switching control circuit 12 composed of a microcomputer or the like, and the duty ratio of the current supplied from the battery 14 to the inductance load 16 is controlled by the switching control.

During this duty ratio control, transistor 1
0 is turned on, the battery 14° and the inductance load 16. Current flows in the loop 100 of the transistor 10, and when the transistor 10 is turned off, the load 1
A loop 102 is formed in which the current flowing through the load 16 returns to the load 16 via the diode 18.

In order to perform this duty ratio control, a switching control signal 104 is supplied from the switching control circuit 12 to the base of the transistor 10 via a resistor 20.
A capacitor 22 is connected between the base and collector of the transistor 10.

FIG. 3 shows characteristics for explaining the operation of the conventional circuit shown in FIG. 2, in which characteristic 106 shows the collector voltage of transistor 10, and characteristic 108 shows its collector current.

In FIG. 3, at time t1, the switching control signal 104
turns from OFF to ON, the collector current of transistor 10 increases during period T1 as shown in characteristic 108, the current flow switches from loop 102 to loop 100, and from time t2 the collector voltage of transistor 10 changes to characteristic As shown at 106, the voltage decreases from the power supply voltage to the ground level over a period T2.

Thereafter, when the switching control signal 104 is turned from ON to OFF at time t3, the collector voltage of the transistor 10 rises from time t4 as shown by characteristic 106 after the accumulation time T3 has elapsed, and at time t5 when T4 has elapsed during ttr1.
The supply voltage is reached at

Then, from time t5, the collector current of the transistor 10 decreases over a period T5 as shown in characteristic 108, and the current flow switches from the loop 100 to the loop 102.

When the above switching is performed in the transistor 10, noise radio waves are radiated to the in-vehicle AM radio.
This becomes the noise of the car's AM radio.

The noise occurs over the period T, Juoh 2, during which the transistor 10 switches from OFF to ON, and the period T4 +Ts, during which the transistor 10 switches from ON to OFF, and the noise level increases as the time required for switching the transistor 10 becomes shorter. .

When the transistor 10 is used as a switching element of the inductance load 16, T4>T2 and Ts>T+ due to the accumulation effect of minority carriers, so the period T+ during which the transistor 10 changes from OFF to ON
+T2 is taken into consideration when noise countermeasures are taken for the in-vehicle AM radio.

The noise reduction level is generally required to be -15 dB or more, and for this reason, the conventional circuit shown in FIG. By forming an integrating circuit using the capacitor 22, the period T2 is set to 10 μsec or more.

However, if the capacitance of the capacitor 22 is determined from the characteristic 110 in FIG. 4 so that the period T2 is 10 μSec or more, the period T2 is determined from the characteristic 110 in FIG.
4 is 40 .mu.sec or more. Therefore, in the prior art, there was a problem in that a large collector loss occurred in the transistor 10 in order to reduce the noise caused by the switching of the transistor 10.

(Object of the invention) The present invention has been made in view of the above-mentioned conventional problems, and
The purpose is to provide an i~ transistor switching circuit that can effectively reduce switching noise without increasing collector loss.

(Structure and Effects of the Invention) In order to achieve the above object, the present invention provides a method for controlling the capacitor connected between the switching 1 and the collector base of the transistor only at the ON transition of the switching transistor between the ON transition and the OFF transition. It is characterized by a switching circuit that inserts other capacitors in parallel.

(Description of Embodiments) Hereinafter, preferred embodiments of the transistor switching circuit according to the present invention will be described based on the drawings.

FIG. 1 shows a preferred first embodiment of the circuit according to the present invention, and the same members as in FIG.

In the figure, a diode 24 is connected between the base and collector of the transistor 10. A series circuit of capacitor 26 is connected in parallel to capacitor 22, and diode 2
The anode 4 is located on the base side of the transistor 10.

A resistor 28 is connected in parallel to this diode 24, and a predetermined potential is applied to the capacitor 26 by this resistor 28.

The capacitance of the capacitor 22.26 is approximately 2200pF,
The switching frequency of the transistor 10 is 20KH2 which is higher than the audible frequency, the switching current is 20A, and the base current is 20 times the saturation level.

In FIG. 5, at time t1, the switching control signal 104
When the current changes from OFF to ON, a base current 114 flows into the transistor 10 and a current 116 flows into the capacitor 22.

Since the diode 24 is in the forward direction with respect to the switching control signal 104, a current 118 flows through the series circuit of the diode 24 and the capacitor 26.

Therefore, in that case, the feedback capacitance of the transistor 10 is the sum of the capacitances of the capacitors 22.26, that is, approximately 10,000 pF.
Therefore, as understood from the characteristic 110 in FIG. 4, the period T2 becomes 10 μSCC or more.

After that, when the switching control signal 104 changes from ON to OFF at time t3, the diode 24 becomes in the opposite direction with respect to the switching control signal 104, so the feedback capacitance of the transistor 10 is approximately 2200p of the capacitor 22 alone.
F, which is significantly smaller than the feedback capacitance (approximately 10,000 pF) when the transistor 10 is turned on.

Therefore, as understood from the characteristic 112 in FIG. 4, the period T4 is equal to or longer than 10 μsec like the period T2.

FIG. 6 explains the noise reduction effect of the embodiment in FIG. 1, and as understood from the characteristic 120 in the figure, the period T2.
If T4 is both 10 μsec, -15, +18
A sufficient noise reduction level as described above has been obtained.

As explained above, according to this embodiment, the transistor 1
Since the feedback capacitance is reduced by the switching of the diode 24 at the time of OFF transition of 0, the period T4 can be shortened to a level sufficient for noise reduction for the car RAM radio, and is not extended unnecessarily. It becomes possible to significantly reduce collector loss.

Next, a second preferred embodiment of the circuit according to the present invention will be described with reference to FIG.

In this figure, in this embodiment, an FET 30 is used in place of the diode 24 in FIG. 1, and the FET 30 is controlled by a Q signal 122 of a monostable multivibrator 32.

In the monostable multivibrator 32, as can be understood from FIG. 8, the period T starts from when the switching control signal 104 is turned on from OFF.

A Q signal 22 that is ON over +T 2 is obtained, so the feedback capacitance is the combined capacitance of the capacitors 22 and 26 when the transistor 10 is turned on, and the combined capacitance of the capacitors 22 and 26 when the transistor 10 is turned on. Only capacity.

Therefore, according to this embodiment, it is possible to obtain effects similar to those of the first embodiment.

Note that in some cases, it may be necessary to flow a base current with a considerable margin in consideration of the decrease in the parameter hfe due to transistor manufacturing variations in the temperature range -40"C to +85°C. In that case, conventionally, the transistor 10
When switching, there is a risk that only the accumulation time increases and the rise time and fall time become unbalanced, but in both of the above embodiments, even if the base current is set to a large value, the transition time at the rise and fall changes. Since they can be selected separately, there is no such risk and stable switching is possible.

Furthermore, in order to stabilize the switching operation of the transistor 10 in FIGS. 1 and 7, it is necessary to apply a predetermined potential to the capacitor 26 while the switching control signal 104 is OFF. Therefore, it is preferable to set the period to be shorter than the period determined by 2×capacity of capacitor 26×(value of resistor 20+value of resistor 28).

And the resistor 28 is a diode 24. It is not necessary to connect it in parallel to FET30, and
In the figure, a resistor 2 is connected to the base side of the transistor 10.
It is also possible to connect one end of 8 to ground.

(Effects of the Invention) As explained above, according to the present invention, the feedback capacitance during the OFF transition of the switching transistor is reduced compared to the ON transition of the switching transistor. This makes it possible to effectively suppress and prevent noise interference to.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first preferred embodiment of the present invention, and FIG.
3 is a waveform diagram for explaining the operation of the conventional device shown in FIG. 2. FIG. 4 is a feedback capacitor low period 721T4 characteristic diagram in the conventional device shown in FIG. 1 is a waveform diagram for explaining the operation of the embodiment, FIG. 6 is a period T2°T4-noise reduction level characteristic diagram in the embodiment of FIG. 1, and FIG. 7 is a circuit diagram showing a second preferred embodiment of the present invention. FIG. 8 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 10... Transistor 16... Inductance load 18... Diode 20... Resistor 22... Capacitor 24... Diode 26... Capacitor 28... Resistor 30... FET 32... Monostable multivibrator patent applicant Nissan Motor Co., Ltd. Figure 5 1.12131415 Figure 6 Figure 7 Figure 8 1T1 (T2

Claims (1)

[Claims] (1) In a transistor switching circuit in which a capacitor is connected between the connector base of a switching transistor, a switching method in which another capacitor is inserted in parallel with the capacitor only during ON transition of the switching transistor between ON transition and OFF transition. A transistor switching circuit comprising: a circuit.