JPH043130B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching circuit that turns on and off an inductive load, and particularly to a switching circuit using bipolar transistor elements.

Some switching circuits for driving inductive loads on and off use bipolar transistor elements as switching elements, and FIG. 1 shows the basic circuit thereof. This is an example of a circuit in which an inductive load 1 such as a relay or a motor is turned on and off by a transistor _Q1 , and a driving pulse is applied to the base of the transistor _Q1 for a period from time _t1 to _t3 as shown in FIG. 2a. . During this time, transistor _Q1 is turned on and becomes saturated. time t ₃
Even if the drive pulse disappears at , the on-to-off transition of transistor Q ₁ is significantly delayed due to the base storage carrier in bipolar devices, as is well known. As a result, as shown in Figure 2b, V _CE (collector-emitter voltage) of transistor _Q1
and I _C (collector current) changes and the transistor
The collector loss P _C at _Q1 changes as shown in C in the same figure. In addition, the period from t ₁ to _{t 2} shows the delay due to the delay time and rise time of the transistor Q ₁ ,
The periods t ₃ to t ₄ and t ₄ to _{t 5} indicate storage time due to base accumulation effect and delay due to fall time, respectively.

As can be seen from Figure C, the collector loss P _C due to the storage time of the transistor increases significantly, and when the transistor is turned on and off frequently, the loss due to the transistor cannot be ignored. must also be considered.

Therefore, there is a method to make it easier to discharge the base storage carrier by providing a low resistance _R1 between the base and emitter of the transistor _Q1 , but this is not preferable because it requires increasing the base driving force of the transistor.

Fig. 3 is an example of a case where a chio-imp type rectifying and smoothing circuit is used as the load 1 to be switched, where _L1 and _C1 indicate a smoothing coil and a capacitor, and D indicates a flywheel diode. It is. This DC smoothed output V _D is used as a power source for a power amplifier (denoted as R _L ) in an audio device. For this purpose, a so-called chopper type transistor is used, which turns the switching transistor _Q1 on and off using a PWM signal 2 having a pulse width corresponding to the amplified output level of the power amplifier, and choppers the DC voltage +V _C.
This is the case with PWM power supply. By doing this,
A DC voltage V _D having a voltage level corresponding to the output signal level of the power amplifier is generated, and this is used as the voltage source of the power amplifier, thereby reducing the P _C of the power amplifying transistor and producing high-efficiency power. An amplifier is what is realized.

However, in _this circuit as well, P _C
cannot be ignored, and therefore, even if the resistance R ₁ is made small, the driving ability of the PWM drive source 2 must be increased accordingly.

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-loss switching circuit which has an extremely simple configuration and effectively improves the off-transition operation of a switching transistor.

The switching circuit according to the present invention connects a series circuit consisting of a capacitor and a resistor across an inductive load, derives a differential output signal at a voltage across the inductive load from a connection point between the capacitor and the resistor, and This differential output signal is used to turn on and off the base-emitter shorting transistor of the switching transistor.

The present invention will be explained below with reference to the drawings.

FIG. 4 is a circuit diagram of an embodiment of the present invention.
Parts equivalent to those in the figures are designated by the same reference numerals. In order to detect changes in the terminal voltage b of the load 1, a differentiating circuit including a capacitor C ₂ and a resistor R ₃ is provided between the terminal of the load 1 (collector output terminal of the transistor Q ₁ ) and a reference power source. Capacitor C ₂
The differential waveform c at the connection point between and resistor _R3 is the resistor
It becomes the base input d of the transistor Q ₂ via R ₄ and the capacitor C ₃ . this transistor
_Q2 is provided to short-circuit the base and emitter of the switching transistor _Q1 . still,
The resistor _R5 is for discharging the charge accumulated in the base of the short-circuiting transistor _Q2 , and has a low resistance.

FIG. 5 is an operating waveform diagram of the circuit in FIG. 4, and a
-d indicate the waveforms of signals a-2 of the circuit shown in FIG. 4, respectively. When the driving pulse a is applied to the base of the transistor Q ₁ during the period t ₁ to _{t 3} , the switching transistor Q ₁ is turned on, but at the time of transition from OFF to ON, the operation is similar to that of a conventional circuit. At this time, since the differential waveform c of the differential circuit is at a negative level, the shorting transistor _Q2 remains off.

When the drive pulse a disappears at time _t3 , the load terminal voltage b begins to rise from a low level to a high level. Therefore, the differential output c changes to a high level.
Since this is the base drive input of transistor Q ₂ , transistor Q ₂ is turned on at time t ₄ and its base waveform is clamped to V _BE2 (base-emitter voltage of transistor Q ₂ ) as shown in d. . At the same time, the charge accumulated in the base of transistor _Q1 is instantaneously discharged via this on-state transistor _Q2 , so that the so-called storage time is greatly improved compared to the conventional case. FIG. 5e shows the state of change in V _CE and I _C of the switching transistor Q ₁ , and f shows P _C . That is, the first
Compared to the conventional example shown in the figure, switching characteristics are improved, collector loss due to the transistor is also reduced, and the problem of heat generation is solved.

In addition, since the means for obtaining the differential output signal is realized by an impedance element connected between both ends of the inductive load, that is, a series circuit of C ₂ and R ₃ , the turn-off of the inductive load 1 is realized. It is possible to cancel the residual current that occurs when the load is applied, improve the braking characteristics of the load, and provide a circuit with even better switching characteristics.

FIG. 6 is a circuit diagram of another embodiment of the present invention,
Parts equivalent to those in FIGS. 3 and 4 are designated by the same reference numerals. That is, this example shows a case where the present invention is applied to a chopper type PWM power supply circuit. In this example, since the shorting transistor _Q2 is conductive when the transistor _Q1 is off, the transistor _Q1 is quickly turned off, and the P _C of the switching element _Q1 can be significantly reduced. Therefore, it is suitable for use in a power supply circuit of a high-efficiency power amplifier, but is not limited thereto.

As described above, according to the present invention, a series circuit including a capacitor and a resistor is connected in parallel to an inductive load,
A differential output signal is derived from the connection point between the capacitor and the resistor, and this differential output signal turns on and off the transistor for shorting between the base and emitter of the switching transistor, so that the base storage carrier of the switching transistor is It is possible to provide a low-loss switching circuit that can perform timely discharge, has an extremely simple configuration, and has excellent switching characteristics effectively, and can perform a switching operation with good braking characteristics against the inductive load.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an example of a conventional switching circuit, Figure 2 is a diagram showing the characteristics of the circuit in Figure 1,
FIG. 3 is a circuit diagram showing another example of the conventional switching circuit, FIG. 4 is a circuit diagram of an embodiment of the present invention, FIG. 5 is a waveform diagram of each part of the circuit in FIG. 4, and FIG. FIG. 3 is a circuit diagram of another embodiment of the present invention. Explanation of symbols of main parts, 1...Inductive load,
Q ₁ ... Switching transistor, Q ₂ ... Short circuit transistor, C ₂ ... Differential capacitor, R ₃
...Resistance for differentiation.

Claims (1)

[Claims] 1 A switching circuit for driving an inductive load on and off, in which a series circuit of a switching transistor, a capacitor, and a resistor for controlling on/off the current supplied to the inductive load is connected between both ends of the inductive load. means for deriving a differential output signal of the voltage across the inductive load from a connection point between the capacitor and the resistor; 1. A switching circuit comprising: a short-circuiting transistor that is driven to short-circuit between the base and emitter of the switching transistor.