JPH04162811A - Power amplifier and its control method - Google Patents

Abstract

PURPOSE:To raise the output stably without malfunction by floating the base of a transistor (TR) being a component of an inverting circuit, and grounding the emitter via a resistor. CONSTITUTION:A resistor R3 is inserted between the emitter of a TR Q1 and GND. In such a case, since a filter voltage 7 is lower than a Vref6 just after application of power, a current I1 flows and currents I2, I3 flow much more than a steady-state value and the base of a TR Q2 rises more than that in the steady-state. Since a current I4 flows to the base of the TR Q1 in such a case, the TR Q1 acts like decreasing the base voltage of a TR 9. In such a case, since the voltage drop of the resistor R3 is in existence, the base of the TR Q9 is decided freely depending on the resistance of the resistor R3 and when the filter voltage 7 rises and a comparator 1 is switched, a time t1 when the base voltage of the TR Q2 drops is earlier than the rise in the base voltage of the TR Q9. Thus, the output rises stably without malfunction.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a power amplifier and its control method, and particularly to stabilizing the rise of output voltage after power is turned on.

Follow】! ”Illusion 1 Conventionally, this type of power amplifier has the following characteristics, as shown in Figure 4.
It consists of a comparator (1) 9-inverting circuit ■, a differential amplifier ■, an output stage (4), and a bias circuit ■. is NPNTr. In such a circuit configuration, after the power is turned on, the output voltage v0
is from about 0.1V to vo. rises to the midpoint of and then
Maintain midpoint potential. The operation of this circuit will be explained below.

Immediately after the power is turned on, the filter voltage ■ is lower than the V□, ■ of the comparator (1), so the current 11 is flowing, and as a result, the current values of I2 and I3 are larger than in the steady state flowing through the differential amplifier 3. As a result, the base potential of the transistor Q2 is higher than the normal state as shown in FIG. 5(a). Furthermore, when a current of 11 is flowing through the comparator (1), the transistor Q1 of the inverting circuit (■) is saturated, so the base potential of the transistor Q9 of the bias circuit (■) is as shown in Figure 5 (b). It is approximately at GND potential. As a result, since no base current flows through the transistor Q4 of the output stage (4), the emitter potential (output voltage VO) of the transistor Q5 is approximately the GND potential as shown in FIG. 5(C). In this case, transistor Q6 is in a saturated state.

Next, when the filter voltage ■ rises and the comparator (1) switches, the saturation of the transistor Q1 of the inverting circuit ■ is released, so the transistor Q of the bias circuit ■
9 rises at time t2 as shown in FIG. 5(b). Next, since the current I decreases, the differential amplifier ■
Current 12,1. decreases, and the base potential of transistor Q2 drops at time t1 as shown in FIG. 5(a).

As a result, the base current flows through the transistor Q4 at time t1, the transistor Q5 operates, and the output voltage vo (8) rises at time t1 as shown in FIG. 5(C).

of the day.

By the way, in the conventional power amplifier control method described above,
When power transistor QB transitions from the saturated state to the active region, power transistor Q5 operates rapidly, so that a large current momentarily flows through power transistor Q5. Since it flows to Q6, it is easy to oscillate.

Therefore, if protection circuits for power supply faults or ground faults are built into the same chip, these protection circuits will malfunction due to the above oscillation, causing the output voltage to drop. The problem was that it did not stand up.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a power transistor and a method for controlling the same, in which both transistors Q5 and QG do not go into operation at the same time when power transistors Q5 and QB are switched.

A power amplifier according to the present invention includes a comparator for comparing the reference voltage and the filter voltage according to claim 1, an inverting circuit and a bias circuit that operate according to the output of the comparator, and an inverting circuit and a bias circuit that operate according to the output of the inverting circuit. In the power amplifier, the base of the transistor constituting the inverting circuit is made floating, and the emitter is made floating. It is configured by grounding through a resistor.

The power amplifier of the present invention also includes a comparator that compares the reference voltage and the filter voltage according to claim 2;
An inverting circuit and a bias circuit that operate according to the output of the comparator, a differential amplifier that operates according to the output of the inverting circuit, and an output stage that operates according to the output of the differential amplifier and the bias circuit. In the power amplifier, a power supply voltage dividing means is provided in the bias circuit, and the voltage dividing point thereof is connected to the base of a transistor connected in parallel with a transistor that operates according to a reference voltage and the collector of a transistor constituting an inverting circuit. In addition, the base of a transistor whose collector Φ base is short-circuited is connected to the base of a transistor constituting an inverting circuit.

In addition, in the power amplifier control method of the present invention, in a push-pull type power amplifier that outputs the upper and lower waves of the waveform using NPN transistors, the output voltage is raised with the upper and lower power transistors being current-limited, and then the upper and lower power transistors are is configured by removing the current limit.

According to the above configuration, in a push-pull power amplifier that outputs the upper and lower waves of the waveform using NPN transistors,
By limiting the current of the upper and lower power transistors when the output voltage rises, instantaneous oscillations can be prevented, so even if a power fault or ground fault protection circuit is built into the same chip, it will not malfunction. Output rises stably.

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

FIG. 1 is an equivalent circuit diagram of a power amplifier according to an embodiment of the present invention. The difference from the conventional example shown in Fig. 4 is that the resistor R1 between the base of the transistor Ql and GND is removed, and the resistor R3 is inserted between the emitter of the transistor Ql and GND, and the other circuits are the same as the conventional example. Therefore, the same parts are given the same reference numerals.

Next, a comparator (1) including the above transistor Ql
The operation will be explained.

Immediately after the power is turned on, the filter voltage ■ is lower than Vrer (6), so the current! , is flowing, and the current value of 12 and I3 is larger than the steady value, and as a result, the transistor Q2
The base potential of , as shown in FIG. 2(a), has increased from the steady state. At this time, since current I4 is flowing through the base of transistor Ql, it operates to lower the base voltage of transistor Q9. In this case, transistor Q
Since the resistor R3 is inserted between the emitter GND of 1, there is a potential drop due to the resistor R3. As a result, the base potential of the transistor Q3 can be freely determined by the value of the resistance value R3, and the base potential of the transistor Q9 can be set to 0.9
When set to about V, the result is as shown in FIG. 2(b).

In this case, the voltage of the transistor Ql is
Since there is no resistance between the
The time t□ at which the base voltage of the transistor Q2 drops is earlier than the rise in the base voltage of the transistor Q9. Therefore, when the base potential of transistor Q9 is lower than the steady state, that is, when the current value of transistor Q8 is lower than the steady state,
Since the base of transistor Q2 is at a steady value, the output voltage V remains constant while the currents of power transistors Q5 and QB are limited. I23) stably rises without oscillation at time t1 in FIG. 2(C).

Output voltage V. After (8) stably rises, the transistor Ql is completely turned off and the base of the transistor Q3 reaches a steady value at time t3, so that the load connected to the output can be sufficiently driven.

Disaster 2 FIG. 3 is an equivalent circuit diagram of a power amplifier illustrating a second embodiment of the present invention. In this embodiment, the first
The collector of the transistor Q13 of the inverting circuit (2) of the embodiment is connected to a current mirror composed of transistors Q15 and Q1, and the collector of the transistor Q13 of the bias circuit (2) is
The emitter of transistor Q14 is connected to the connection point between the emitter of QIO and the base of QIO, its collector is grounded, and the base and QIO are connected. A resistor R1s is connected between the resistor R4 + base and GND, and the base is connected to the transistor Q.
Since this embodiment is the same as the first embodiment except that it is connected to the first collector, the same reference numerals are given to the same parts and the explanation thereof will be omitted.

In this embodiment, the filter potential ■ immediately after the power is turned on is V-
When it is lower than r(e, current I4 flows, so when the base potential of transistor Q14 falls below the base potential of transistor Qll, transistor Q14 operates and the emitter potential of transistor Q14 falls.

In other words, the base potential of the transistor Q9 is falling, and in this state, the filter potential ■ rises and the comparator (
When 1) is switched, first, the base potential of transistor Q2 becomes a steady value, and the output voltage V. (8) stands up. Next, current I4 decreases, transistor Q14 is cut off, and the base potential of transistor Q3 becomes a steady value. In this case, the base potential of transistor QB immediately after power is turned on can be adjusted arbitrarily using resistors R4+R5, so
Power transistor Q5. It is possible to select a value that does not cause QB to oscillate.

Oscillation B91 As explained above, the present invention prevents instantaneous oscillation by limiting the current of the upper and lower power transistors when the output voltage rises, thereby reducing the Even if a ground fault protection circuit is built into the same chip, there is no malfunction and the output is stable.

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram of a power amplifier according to a first embodiment of the present invention, and FIGS. 2(a) to 2(c) are voltage waveform diagrams showing the operation timing of FIG. 1. FIG. 3 is an equivalent circuit diagram of a power amplifier according to a second embodiment of the invention. Figure 4 is an equivalent circuit diagram of a conventional power amplifier.
The figure is a voltage waveform diagram showing the operation timing of FIG. 4. 1... Comparator, 2... Inverting circuit, 3... Differential amplifier, 4... Output stage, 5... Bias circuit, 8...Vrafz 7...Filter voltage, 8...Output voltage y. . w4.1 Illustrated Kankan 2 tl ↓ 1st edition "1"I tl 1 hour ↓ 1 hour → Noi 113 Figure 114

Claims (1)

[Claims] 1. A comparator that compares a reference voltage and a filter voltage, an inverting circuit and a bias circuit that operate according to the output of the comparator, and a differential amplifier that operates according to the output of the inverting circuit. In this power amplifier, which includes a differential amplifier and an output stage that operates according to the output of the bias circuit, the base of the transistor constituting the inverting circuit is floating, and the emitter is grounded via a resistor. A power amplifier featuring 2. A comparator that compares a reference voltage and a filter voltage, an inverting circuit and a bias circuit that operate according to the output of this comparator, a differential amplifier that operates according to the output of the inverting circuit, and this differential amplifier and In a power amplifier comprising an output stage that operates according to the output of the bias circuit, the bias circuit is provided with a power supply voltage dividing means, and the voltage dividing point thereof is connected in parallel with a transistor that operates according to a reference voltage. A power amplifier characterized in that the base of a transistor whose collector and base are short-circuited is connected to the base of a transistor that constitutes an inverting circuit and the collector of a transistor that constitutes an inverting circuit. 3. In a push-pull power amplifier that outputs the upper and lower waveforms using NPN transistors, the feature is that the output voltage is raised with the upper and lower power transistors current limited, and then the current limit of the upper and lower power transistors is released. How to control a power amplifier.