JPS6223484B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching amplifier in which the output stage is composed of a grounded-emitter switching transistor. The purpose is to shorten the off time and prevent simultaneous conduction of switching transistors.

FIG. 1 shows a conventional example of a switching amplifier in which the output stage is composed of grounded emitter switching transistors.

In Fig. 1, 1 is a comparator, 2 to 5 are drive stage transistors and emitter resistors, and 6 to 9 are
10 and 11 are diodes, and 12 and 13 are coils and capacitors constituting a low-pass filter.

Next, the operation shown in FIG. 1 will be explained. First, an input signal and a triangular wave signal are applied to the input of comparator 1 in the case of a separately excited type, and an input signal and a feedback signal are added in the case of a self-excited type to generate a pulse width modulated square wave signal. make. The square wave signal drives drive stages 2-5 and output stages 6-9. The square wave signal at the output stage is then demodulated into a low frequency signal through low pass filters 12 and 13. Here, the diodes 10 and 11 are flywheel diodes for recovering the current energy of the coil 12.

In the output stage of FIG. 1, transistors 8 and 9 are alternately turned on and off to drive the coil 12.

By the way, a large amount of base current is normally injected during the ON period of the transistors 8 and 9. Thereby, a fairly large amount of charge is stored on the base electrode. This charge is transferred to resistors 6 and 7 during the off period.
The transistors 8 and 9 are turned off when the extraction is completed.

If this withdrawal time becomes longer, simultaneous conduction occurs because one transistor is turned on while the other transistor remains charged, resulting in a significant increase in power loss and transistors 8 and 9. There is a risk of destruction.

The amount of accumulated charge can be reduced by reducing the base current supplied from the drive stage, and the extraction time can also be shortened, but sufficient drive cannot be achieved at high output.

Also, if the values of resistors 6 and 7 are reduced, the extraction time will be shortened, but in that case, the current in the drive stage must be increased, which increases the loss in the drive stage and reduces the efficiency of the amplifier. There is a problem.

To solve this problem, by connecting a charge extraction transistor between the base and emitter of the switching transistor and driving it differentially with the switching transistor, the charge can be strongly extracted and the switching Switching amplifiers designed to prevent simultaneous conduction of transistors are quite effective.

FIG. 2 shows an example of a circuit configured as described above.

In FIG. 2, 1 to 13 correspond to the same numbers in FIG. 1, and 14 to 19 are transistors and common emitter resistors constituting a differential amplifier;
Reference numerals 20 to 23 are base resistors and transistors that constitute a charge extraction circuit.

First, when the output voltage of the comparator 1 is positive, the transistors 14 and 17 are conductive and the transistors 15 and 16 are non-conductive, so the switching transistor 8 and the extraction transistor 23 are turned on, and the coil 12 is turned on.
The input side of is driven positive.

Next, when the output voltage of the comparator 1 becomes negative, the switching transistor 9 and the extraction transistor 22 are turned on.

In this way, during the period when the switching transistor should be off, the extraction transistor included in the base circuit is turned on, so the charge accumulated in the base electrode of the switching transistor is strongly extracted, and at the same time Conduction is prevented.

By the way, in the circuit example of FIG. 2, the bases of transistors 14 and 16 and the bases of transistors 15 and 1
Since the bases of 7 are coupled, transistor 16 is turned on at the same time that transistor 14 is turned off, and transistor 14 is turned on at the same time that transistor 16 is turned off. Therefore, although the extraction transistors 22 and 23 shorten the charge extraction time of the transistors 8 and 9, it does not become zero, and therefore, simultaneous conduction of the transistors 8 and 9 occurs to some extent.

In order to prevent this, a configuration as shown in FIG. 3 can be used.

In FIG. 3, 1 to 23 correspond to the same numbers in FIG. 2, and 24 to 27 are bias resistors.

In FIG. 3, by applying a bias voltage between the base of transistor 15 and the base of transistor 17, when the output voltage of comparator 1 is within the range of this bias voltage, transistors 14 and 16
A so-called rest period occurs in which both transistors 8 and 9 are turned off, thereby preventing transistors 8 and 9 from becoming conductive at the same time.

Further, this bias voltage may be applied as shown in FIG.

In FIG. 4, 8 to 23 correspond to the same numbers in FIG. 2, 28 to 30 are transistors and current sources that constitute a differential amplifier, and 31 to 34 are
35 is a current source, 36 is a load resistor, and 28 to 36 constitute a comparator 1,
37 and 38 are bias resistors for creating a rest period.

By the way, switching transistors 8 and 9
The DC current amplification factor is generally 10 to 10 in the large current range.
20, which is quite low. Therefore, transistors 8 and 9 require a considerably large amount of base current at high output.

However, in the above circuit example, transistor 1
The drive current supplied from 4 and 16 is constant regardless of the output belt, so it must always supply a current that guarantees the required drive current at maximum output, so there is considerable power loss even at low output. There is a problem in that this increases the efficiency of the amplifier and reduces the efficiency of the amplifier.

The present invention is designed to prevent such a decrease in amplifier efficiency, and embodiments of the present invention will be described below.

FIG. 5 shows an embodiment of the present invention, in which the bases of the differential amplifiers 14 to 17 are connected to a low pass filter 1.
By connecting to the outputs of 2 and 13, the emitter current of the differential amplifiers 14 to 17 is changed according to the output level, supplying a small drive current when the output is small, and a large drive current when the output is large. It was designed to do so.

In FIG. 5, 8 to 38 correspond to the same numbers in FIG. 4, and 39 to 42 are differential amplifiers 1.
4 to 17 resistors and diodes for supplying emitter currents.

The embodiment of FIG.
Although the above effect can be obtained without the resistors 39 and 42, the effect is further enhanced by adding the resistors 39 and 40. Note that the diodes 40 and 41 are
Transistors 14 to 17 of the differential amplifier at high output
This is to prevent the common emitter from becoming reverse biased.

This embodiment uses a grounded emitter type switching transistor in the output stage, but as shown in Figure 6, a grounded collector type switching transistor is used in the output stage, and the above circuit is used in the drive stage. Even in the case where the above-described method is applied, simultaneous conduction of the drive stage transistors can be prevented.

In FIG. 6, numerals 1 to 23 correspond to the same numbers in FIG. 2, and 43 and 44 are output-stage common collector type switching transistors.

As described above, the present invention includes a common emitter type switching transistor in the output stage or drive stage, a charge extraction transistor in which the collector and emitter are connected between the base and emitter of the switching transistor, and one differential transistor. a differential amplifier whose output drives the base of the switching transistor and whose other differential output drives the base of the charge extraction transistor; a preamplifier that drives the differential amplifier; a low-pass filter connected to the output side of the switching transistor, and a switching transistor that drives the base of the switching transistor among one input electrode of the differential amplifier is connected to the output side of the low-pass filter; Since the other switching transistor is connected to the output side of the preamplifier, it is possible to prevent damage and decrease in efficiency due to simultaneous conduction of the switching transistors.
Furthermore, a drive current corresponding to the output level can be caused to flow through the switching transistor, and a decrease in efficiency of the amplifier can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional example, Figs. 2 to 4 are circuit diagrams devised in the process of completing the present invention, and Fig. 5 is a circuit diagram of a conventional example.
6 are circuit diagrams of a switching amplifier according to an embodiment of the present invention. 8, 9...Emitter grounded type output stage switching transistor, 14-19...Differential amplifier, 2
2, 23...Transistor for charge extraction, 24-
27... Circuit providing bias voltage, 12, 13
...Low-pass filter, 43, 44... Grounded collector type switching transistor.

Claims (1)

[Claims] 1. A switching transistor of a grounded emitter type in an output stage or a drive stage, a charge extraction transistor whose collector and emitter are connected between the base and emitter of the switching transistor, and one differential output. a differential amplifier whose differential output drives the base of the switching transistor and whose other differential output drives the base of the charge extraction transistor; a preamplifier that drives the differential amplifier; A low-pass filter is connected to the output side of the transistor, and among the input electrodes of the differential amplifier, the input electrode of the element that drives the base of the switching transistor is connected to the output side of the low-pass filter, and the other is connected to the output side of the low-pass filter. A switching amplifier connected to the output side of the above preamplifier. 2. In claim 1, the switching transistor, the extraction transistor, and the differential amplifier are each arranged symmetrically in positive and negative directions by complementary transistors, and an input electrode on the front-stage amplifier side of one of the differential amplifiers, By applying a bias voltage between it and the input electrode on the front stage amplifier side of the other complementary differential amplifier,
A switching amplifier characterized in that a rest period is provided in which both switching transistors in the complementary relationship are open. 3. The switching amplifier according to claim 1, further comprising one more stage of common collector type switching transistor connected to the collector side of the switching transistor.