JPS59220071A - Switching control circuit - Google Patents

Abstract

PURPOSE:To improve the efficiency of a switching control circuit by circulating an energy accumulated in an inductance through a transistor for a circulating element to a load, thereby reducing the energy loss. CONSTITUTION:A switching output transistor Q5 is switched by a switching signal supplied to an input terminal IN through a driver circuit 11 which has transistors Q1,Q2,Q4, a diode Q3, resistors R1,R2 and a power source I. Energy which is accumulated in an inductance L during ON period of the transistor Q5 is supplied to a load 13 as a collector current of a transistor QB from the inductance L via the inductive kick of the inductance L. When the transistor Q5 becomes OFF, a circulating element drive circuit 14 is driven and the transistor QB which becomes a circulating element becomes instantaneously saturated state simultaneously upon occurring of the inductive kick.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching control circuit, and more particularly to an improvement in a freewheeling circuit section thereof.

[Technical background of the invention and its problems]

BACKGROUND ART Conventionally, as a switching control circuit widely used in general electronic equipment including audio equipment, there has been known a switching control circuit equipped with a freewheeling circuit and configured as shown in FIG. 1.

That is, for example, this is the case when a motor in a tape recorder is applied to a switching control circuit such as Baka, and the PWM (as shown in the figure) supplied to the input terminal IN is applied.
The switching output transistor Q5 is switched by a switching signal such as a /4 pulse width modulated wave) through a driver circuit 11 consisting of a transistor Q+ A smoothing circuit 12 consisting of an inductance L and a capacitor C converts the switching output into
and a load 13 via a diode D that serves as a freewheeling element.
The configuration is such that the voltage is applied to the

In this case, while the switching output transistor Q5 is on, current is supplied to the load 13 and energy is stored in the inductance L.

Then, when the switching output transistor Q5 enters the off period, a large back electromotive force, that is, an inductance drop occurs at that moment due to the action of trying to keep current flowing across the inductance L. Using this electromotive force, the energy stored in the diode D and the inductance L is circulated as a current to the load 13, thereby improving the driving efficiency.

However, in the conventional switching control circuit as described above, as shown in FIG. Since there is energy loss as shown in the shaded area in the figure, the effect cannot be ignored, especially in switching control circuits for low-voltage operation, and there is a problem in that the improvement of drive efficiency is hindered accordingly. Ta.

Note that FIG. 2 shows a voltage waveform when viewed from the 0 point in FIG. 1, where vcC is a power supply potential and GND is a reference potential point potential.

[Purpose of the invention]

Therefore, this invention was made in view of the above points, and it is possible to reduce energy loss and improve efficiency as much as possible, thereby making it suitable for low voltage operation. The purpose of the present invention is to provide a switching control circuit.

[Summary of the invention]

That is, the switching control circuit according to the present invention includes a switching output transistor that is switched by a switching signal, a load whose output is supplied via a smoothing circuit including an inductance and a capacitor when the switching output transistor is turned on, and the switching output transistor. When the inductance is turned off, the electromotive force due to the inductive kick of the inductance and the switching of the switching output transistor are driven by a drive signal that has an opposite phase relationship, and is a reflux element that circulates the energy accumulated in the inductance to the load. It is characterized by being equipped with a transistor for

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below with reference to the drawings.

That is, in FIG. 3, the same reference numerals are given to the parts configured in the same manner as in FIG.
Qtos diode Q7. Q9 and resistor R3r
This is a new configuration different from that shown in FIG. 1 in that a freewheeling element driver circuit 14 consisting of R4r and R5 is provided and a transistor is used as the freewheeling element.

Here, the transistor Q6 has its pace connected to the input terminal IN, its emitter connected to the reference potential point GND, and its collector connected to the diode Q7 with the illustrated polarity.
and is connected to the power supply Vcc via a resistor R3 in series.

Further, the transistor Q8 has its base connected to the collector of the transistor Q6 and its emitter connected to the power supply V.
CC, and its collector is connected to the reference potential point GND via a diode Q of the illustrated polarity and a resistor R4 in series.

The transistor QIO has its base connected to the collector of the transistor Q8, its emitter connected to the reference potential point, and its collector connected to one end of the drive current limiting resistor R5.

Furthermore, the transistor QB serving as a freewheeling element has its pace connected to the other end of the resistor R5, its collector connected to the power supply Vcc, and its emitter connected to the collector of the switching output transistor Q5.

In the above configuration, the driver circuit consisting of the transistors Qt + Q4, Qa, the diode Q3, the resistors R1 and R4, and the current source I is activated by the switching signal (for example, PWM wave) supplied to the input terminal IN. The switching of the switching output 2 transistor Q5 via 11 is the same as in the case of FIG.

However, in this case, the transistor QB which becomes a freewheeling element is a transistor Qa + Qs t Qlo % diode Q7. The above-mentioned switching output transistor Qs(') is driven in a reverse phase relationship with the switching via the freewheeling element driver circuit 14 consisting of Q9 and resistors R3+R4+R5.

The energy accumulated in the inductance during the ON period of the switching output transistor Q5 is supplied from the inductance L to the load 13 as the collector current ICQB of the transistor QB which becomes a freewheeling element due to the inductance kick of the inductance L as described above. However, according to the present invention, when the switching output transistor Q5 is turned off, at the same time as the above-mentioned inductive kick occurs, the freewheeling element driver circuit 14 is driven to bring the transistor QB, which serves as a freewheeling element, into a saturated state all at once. become.

Here, by using a transistor QB which becomes a freewheeling element with a sufficiently small on-resistance, the voltage waveform associated with [F] in Fig. 3 can be changed as shown in Fig. 4. Collector-emitter voltage vcll, QB(s
at) can be set to a value of 0.1 to 0.2 V or less, so energy loss is reduced compared to the forward voltage drop (approximately 0.7 V) when a diode is used as a freewheeling element as in the past. can be significantly reduced.

In this case, the forward direction drop voltage V due to the PN junction of the QB acid component from the pace current of the transistor QB, which is a freewheeling element, flows from the emitter and the rear. Since there is energy loss with BQB, ■cEQB(8at)
It is desirable to set the conditions of the freewheeling element driver circuit 14 so as to take into account both the power loss due to ×ICQIl and the power loss due to v8BQB×■BQB to obtain the most efficient value.

It goes without saying that the present invention is not limited to the embodiments described above and illustrated, and that various modifications and applications can be made without departing from the gist of the invention.

〔Effect of the invention〕

Therefore, as described in detail above, according to the present invention, an extremely good switching control circuit that can reduce energy loss and improve efficiency as much as possible, and is thus improved to be suitable for low voltage operation. It becomes possible to provide

[Brief explanation of drawings]

1 and 2 are block diagrams showing a conventional switching control circuit and waveform diagrams for explaining its operation, and FIGS. 3 and 4 show an embodiment of the switching control circuit according to the present invention. FIG. 2 is a diagram illustrating the configuration and its operation; FIG. IN...Input terminal, 1..Driver circuit, 12.
...Smoothing circuit, 13...Load, QB...Switching output transistor, L...Inductance, C...
・Capacitor, 14 reflux element driver circuit, ■cc
...power supply, GND...reference potential point, QB...(freewheeling element) transistor.

Claims (1)

[Claims] A switching output transistor that is switched by a switching signal, a load whose output is supplied via a smoothing circuit consisting of an inductance and a capacitor when the switching output transistor is on, and an inductive kick of the inductance when the switching output transistor is off. The electromotive force and the switching of the switching output transistor are driven by a drive signal having an opposite phase relationship, and the device includes a transistor for a freewheeling element that returns the energy stored in the inductance to the load. A switching control circuit characterized by: