JPS59210705A - power drive circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power drive circuit for driving a low impedance load such as a speaker, and more particularly to a circuit for driving a load according to a rectangular wave input signal.

Speakers are often used in computer equipment to notify operators of errors, malfunctions, and other events. To drive such a speaker, it is also possible to use a power IC like a general audio device.

However, since PowerE-C is relatively expensive, and since this type of speaker may be driven with a rectangular wave signal, it is common to use a simpler power drive circuit that is cheaper.

FIG. 1 shows a power drive circuit that is widely used to drive alarm speakers such as those described above.

In the figure, the collector of transistor 5 is connected to power supply terminal 2 (positive voltage is supplied here) via resistor 4.
The emitter is connected to another power supply terminal (ground line here), and the base is connected to the signal input terminal 7.

A rectangular wave signal supplied to the signal input terminal 7 turns the transistor 5 on and off. That is, transistor 5
constitutes a switching circuit with a common emitter. The speaker 3 is connected to the collector of the transistor 5 via a variable resistor 1 for adjusting the volume and a capacitor for cutting the DC component.

Although this circuit is simple and relatively inexpensive, it has the disadvantage of poor power utilization because the resistors 1 and 4 are connected in series to the speaker drive current path. Another drawback is that the variable resistor 1 and the collector load resistor 4 need to have large power capacities.

In particular, the variable resistor 1 needs to be wound with a power of about 1 watt or more, which is disadvantageous in terms of cost and space.

The reason why the volume adjustment variable resistor 1 is placed on the load side is because the input impedance at the signal input terminal 7 is low and it is difficult to achieve the desired volume adjustment on the input side.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a resistor power drive circuit which has a better power utilization efficiency than the conventional one and which can reduce the power capacity of a variable resistor for controlling volume.

The power drive circuit of the present invention basically consists of an emitter W
It is composed of a Jfk type (7) switching circuit and an emitter follower circuit that drives a load according to the output of this circuit.

Next, an embodiment of the power drive circuit according to the present invention will be explained with reference to FIG.

In the figure, a transistor 13 forms a switching circuit with a grounded emitter. The base of this transistor is connected to the signal input terminal 11, and the collector is connected to the resistor 14.
The emitter is connected to a power supply terminal 12 (to which a positive voltage is supplied in this embodiment) via the emitter, and the emitter is connected to another power supply terminal (ground line in this embodiment).

Transistor 15 forms an emitter follower circuit. The collector of the transistor 15 is connected to the first power supply terminal 12 , the base is connected to the collector of the transistor 13 , and the emitter is grounded via a DC-cutting capacitor 16 and a speaker 19 . A diode 1 is connected between the base and emitter of the transistor 15.
7 are connected in parallel in the polarity direction shown. Further, a volume adjusting variable resistor 18 is connected in parallel between the collector of the transistor 13 and the ground line.

The transistor 13 is turned on by a rectangular wave signal (although not limited to a rectangular wave) applied to the signal input terminal 11.
Turn off.

During the off period of the transistor 13, the voltage supplied to the first power supply terminal 12 is connected to the erector load resistor 14 and the variable resistor 1.
The voltage divided by 8 is applied to the transistor 15, and current flows through the transistor 15 to the speaker 19. At this time, diode 17 is off. The magnitude of the speaker current, that is, the sound level of the speaker 19, can be adjusted by changing the resistance value of the variable resistor 18 and changing the base voltage of the transistor 15.

During the on period of the transistor 13, the base of the transistor 15 is substantially grounded, so that the transistor 15 is turned off. The charge in the capacitor 16 is then discharged through the diode 17 and the transistor 16.

As can be easily understood from the above explanation, the speaker 19
The drive current of capacitor 16 and transistor 1
It is supplied from the power supply via 5, and there is no resistance in between. Therefore, the power utilization rate is greatly improved. Further, since no speaker drive current flows through the collector load resistor 14 of the transistor 16 and the volume control variable resistor 18, the power capacity of each can be reduced to, for example, less than I. Therefore, as the variable resistor 18, it is possible to use a small, inexpensive resistor other than a wire-wound resistor.

As described above, the power drive circuit of the present invention has extremely high power utilization efficiency, and can sufficiently drive a general 8-ohm speaker with a TTL 5-volt power supply. Further, since a small variable resistor other than a wire-wound type variable resistor can be used as the volume adjusting variable resistor, it is advantageous in terms of cost and mounting space.

In the previous embodiment, the case of driving a speaker was described, but it goes without saying that the present invention can be applied to other low impedance loads.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional power drive circuit, and FIG. 2 is a circuit diagram showing an embodiment of the power drive circuit according to the present invention. 11... Signal input terminal, 12... Power supply terminal, 1-lower, 15... Transistor, 14... Resistor, 16... Capacitor 1 17... Diode, 1B... Variable resistor, 19 ...Speaker. Figure 1 Bacterium Z

Claims (1)

[Claims] 1. A first transistor whose collector is connected to a first power supply terminal, whose emitter is connected to a second power supply terminal, and whose base is connected to a signal input terminal through a resistor;
a second transistor whose emitter is connected to the second power supply terminal via a capacitor and a load, and whose base is connected to the collector of the first transistor; a diode connected in parallel in the opposite polarity direction to the base-emitter junction between the collector of the first transistor and the second transistor;
A power drive circuit consisting of a resistor connected between the power supply terminal and the power supply terminal. 2. The power drive circuit according to item 1, wherein a resistor connected between the collector of the first transistor and the second power supply terminal is made variable.