JPS60152108A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To protect a power supply side output transistor (TR) and a resistor between a current and a bootstrap capacitor by detecting fluctuation of power supply so as to interrupt the current path of said resistor. CONSTITUTION:An input signal Vin is applied to a circuit I conducting class A voltage amplification and class B current amplification via an operational amplifier 1, where the signal is power-amplified and outputted, and when a power supply is normal, an overvoltage detecting TRQ1 is turned off and control TRs Q21-Q23 are turned off and power supply side output TRs Q8, Q9 and common side output TRs Q10, Q11 are driven. If a surge is mixed to the power supply, the overvoltage detection TRQ1 is turned on and the TRs Q2, Q21-Q23 are turned on, the TRs Q3, Q4 are turned off and since no current flows to a bootstrap resistor R6, no heat dissipation is caused. Moreover, the TRs Q5-Q9 are all turned off and the destruction of the output TRs is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an amplifier circuit having an overpressure retention function.

[Background technology]

In various audio devices, an overvoltage testing circuit is provided to check the amplifier circuit from a power source or the like.

Prior to the invention of the present application, the present inventor studied a power amplifier circuit as shown in FIG.

The human power (No. A vin') is supplied to the operational amplifier 10 input terminal via the DC blocking capacitor CI.

Transistor Q+ performs class A voltage amplification, diodes D, , D, li are for level shifting, and resistor Rx ld
This constitutes the collector load of transistor Q. Further, the power supply side transistor Q and the ground side transistor Q operate as output transistors. Negative feedback resistor "A'RB" sets the closed loop voltage gain of the operational amplifier, and negative feedback capacitor C2 busses the AC component to ground to supply DC voltage to negative feedback terminal H.

When the input signal Vin is supplied, the output transistor Q,
, Q are driven, and the voltage at point X is changed and compared to the voltage at point X, and the speaker SP is driven via the output capacitor C8.

On the other hand, circuit pro-vriA is an overvoltage detection circuit, and the base voltage of the overvoltage detection transistor Q is.

The resistor R1, the zener diode DIlK, has a constant zener voltage V. is maintained. Resistance R,,
, R,, are voltage dividing resistors, and 1. The emitter voltage of Ia voltage detection transistor Q4 is specified.

In the amplifier circuit, when a surge voltage of 10 VccIM is applied to the source, the base voltage VC remains almost constant and the emitter fl
As the voltage increases, the overvoltage detection transistor Q is turned on. The base current is also supplied to the control transistor QllK, which turns it on. As a result, the base of the power supply side output transistor Q is almost grounded, and it is turned off.

By the way, the emitter data of the output transistor Q on the power supply side is
Negative feedback capacitor? Charging C1 or output capacitor C3 [! The voltage holds t at a voltage level of -2-Vcc for 2QQm8ec...l. On the other hand, l! Since the base of the source side output transistor Q is grounded, the base-emitter is reverse biased, and the inventor's studies have revealed that the protection of the transistor Q is maximized within the range of transistor characteristics. I felt pressured.

Furthermore, the present inventors have studied not only the power amplification circuit described above but also a power amplification circuit provided with a bootstrapper and a boot capacitor. In a power amplifier circuit having a bootstrap capacitor, a bootstrap resistor is provided between the +vcc power supply and the power supply vcc' whose voltage is increased by the bootstrap capacitor. And X
Due to the voltage holding action of the bootstrap capacitor whose potential at the point is vcc, the power supply VC, 'tLv'
=v +↓V ・・・・・・・・・・・・・・・・・・
・・・・・・・・・(11CCCC2CC rises to the highest voltage level given by this [11
Since the highest voltage level given by the equation drives the base of the power supply side output transistor, this transistor is in saturation. In addition, when the surge voltage is applied to the VcowL source, the voltage difference between both ends of the bootstrap resistor set between the +vcc power supply and the vcc' power supply is maximum, from the Vcc' power supply shown in equation (1) above. become. Since the bootstrap resistor has a relatively low resistance value of 50Ω to 100Ω, the surge voltage is V. A large current flows when applied to a ct source.

Therefore, the bootstrap resistor inside the IC generates high heat inside the IC, but in order to prevent this, it is necessary to
The inventor's studies have revealed that the area of the bootstrap resistor within the circuit must be increased. I
In C&C, it is not preferable to use a large area for one resistor because it impairs the improvement of the degree of integration. However, the resistance value of the bootstrap resistor is the bootstrap resistor.

Since the capacitor also has a function of compensating for one frequency characteristic by a time constant with the capacitor, its resistance value cannot be determined simply by considering heat generation when a surge voltage is supplied.

[Purpose of the invention]

An object of the present invention is to provide an I increase circuit that can protect the output transistor on the power supply side when a surge voltage or the like is supplied to the power supply, and also protect the bootstrap resistor when using a bootstrap capacitor. It is in.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief summary of the invention disclosed in this specification is as follows.

That is, the switch 9 connected in series with the bootstrap resistor 86 is detected by comparing the voltage fluctuation of +vcc with the reference voltage obtained from the Zener diode and turns on the overvoltage detection transistor Q1.
Turns off the transistor Q4, cuts off the current path between the +vcc power supply and the +vcc power supply, and
Control transistor Q□.

By turning on Q□ and Q□, the constant current load transistor Q7 and the power supply side output transistors Qa and Q*, which constitute the power amplifier circuit, are rendered inactive.

Power supply side output transistor Qa when power supply voltage fluctuates
= This achieves the purpose of the present invention, which is to protect Q*.

〔Example〕

An embodiment of a power amplifier circuit to which the present invention is applied will be described below with reference to FIG. Note that the power amplifier circuit shown in this embodiment is a semiconductor integrated circuit (hereinafter referred to as IC) V.
It is assumed that the system is configured as C.

The input signal vJ,1 is supplied to the input terminal t+-JVc of the operational amplifier l via the DC blocking capacitor co%1 terminal. Deduction: Output signal V of amplifier 1. is supplied to the base of the A-class band width transistor Q□. The negative feedback resistors RA and RB set the closed loop 't'1 pressure gain of the operational amplifier l, and the capacitor C1 supplies 11 current direct voltage to the negative feedback terminal H. The circuit pro question surrounded by the dotted line is A RrK pressure amplification and B class? 1 from the flow amplification button
A constant current load transistor Q, which would have a force increase of 1 and 5 in a row,
and level shift diode 1), L), D,
constitutes the collector load circuit of the class A amplification transistor Qlt. Note that the Darlington-connected transistors Q,,Q.

are power supply side output transistors for current amplification, and transistors QIo and QIlt/''ilk are ground side output transistors for current amplification;

Q, h Qllll + Q++ form the Bi-pu, V-chable output stage.

Circuit pro Vri■ and control transistors Q□, Q□.

Qt8 operates to protect the source side transistor when surge 1 is applied. Also.

circuit pro 0. When a surge voltage is applied to the river.

This is to protect the bootstrap resistor R6.

First, we will describe the operation of the circuit when the +vcc power supply is supplied with a normal voltage level.

The base of the transparent pressure detection transistor R3 is connected to the pressure ti, and the resistance R
The voltage dividing resistor R3 and the Zener diode DI maintain the voltage at a constant voltage level.The voltage dividing resistor R3 and R1 define the voltage across the emitter of the overvoltage detection transistor Q1.

has been turned off. Therefore, transistor Q
, is also turned off, and the transistor Q is connected via the resistor R6.
, is supplied with a base voltage.

Then, the transistor Qs operates in the on state, and the voltage drop across the resistor R causes the switch of the circuit
A bias voltage is supplied to transistor Q4, which turns on. Therefore, the switch transistor Q
The voltage between the collector and emitter of , is substantially in a shut state, and a bootstrap voltage +Vcc is generated in the line AI by the bootstrap capacitor C8, and the time constant of this bootstrap voltage +Vcc is the bootstrap voltage +Vcc.
The product of the pull-up resistor R6 and the bootstrap capacitor C3 is set.

Further, the transistors Qw and Qa form a current mirror circuit, and the input side current of the transistor QIIK flows through the bias resistors R, , R8. At this time, 1. , pull-removal capacitor C, [thus, the pull-removal capacitor C, [thus, 9
The pull portion is removed. +Vc,: The output side current of transistors Q and K flows from the power supply through diode D,
A bias H4 voltage is supplied to the constant current load transistor Q7 by the forward voltage VFK of the diode D3.

When the +vcct source is at the Nishinomiya voltage level, the overvoltage detection transistor Q is off as described above, so the control transistors Q□, Q□, Q! 3 is not supplied with base current. Therefore, the control transistors Q□, Q□, Q,
3 are all turned off, and circuit block I performs normal circuit operation. That is, by supplying the input (it number vin), the power supply fullll output transistor Q
8, Q,, and a grounded output transistor Q,. ,Q
□ is driven and the output signal V is output to the 4th terminal. ut is obtained. Output signal V. ut is.

The speaker SP [supplied through the output capacitor C,
You can get audio output.

Next, we will describe the circuit operation when a surge voltage is supplied to the 10 VCC power supply.

Even if the +-vcc voltage source suddenly rises due to surge voltage.

The base voltage of the overvoltage detection transistor Q is held substantially constant by the Zener diode D1.

However, since the emitter voltage rises rapidly in response to the surge magnetic pressure, the overvoltage detection transistor QIK is supplied with the voltage VBIQ□ between the pace emitter and the voltage VBIQ□, which operates in the on state.

Therefore, the base current is supplied to the transistor Q, and at the same time it turns on, the control transistor Q
Since the base current is also supplied to □, Q□eQ13, these operate in the on state at the same time.

The above operation of transistor Q reduces its collector pressure and turns transistor Q off. Then, resistor R5 [[current does not flow, switch O transistor Q
The base of 4 is at a negative level with respect to the +VcctlL source, which causes off-state aK operation. Therefore, no additional current flows through the bootstrap clean resistor R, and no heat is generated as determined by I''R.

7j, fljllltj transistor Q2. ~Q□ By supplying the busy base current tl, the circuit operates as described below.

', that is, the control transistor Q2. Since each base of the transistor JeQ1 is grounded by operating in the on state, the output side current does not reach υIL. Therefore, the forward voltage of the diode D3 cannot be obtained, and a bias voltage is not supplied to the constant fl flow load transistor 07, so that the transistor is turned off.

By turning on the master control transistor Qtt, the collector of the constant current load transistor Q and the base of the output transistor Q8 are grounded. Therefore, both transistors Q7, Q, and R are turned off.

Further, the control transistor Q23 is in the on state P, II Ii
By operating CWJh, the emitter of the output transistor Q8 and the base of the output transistor Q are grounded. Therefore, the output transistor Q is also forcibly turned off.

As described above, each transistor Qt of one circuit block E =
Qa - Qe are all turned off to prevent their destruction.

〔effect〕

+11 +V,. When a surge voltage or the like is supplied to the power supply, by detecting this and cutting off the current path of the bootstrap resistor R6, it is possible to prevent excessive current from flowing through the bootstrap resistor R6. .

121 According to (1) above, the bootstrap resistance and the knob resistance R
Even if 8 is formed on the same semiconductor substrate as the amplifier circuit, there is no need to expand the area to prevent heat generation, and the degree of integration of semiconductor multipliers is improved. This effect can be obtained.

(By switching the power supply side output transistor of the 31 amplifier circuit to a non-operating state, the effect of preventing damage when a surge voltage is supplied is obtained.

[Not available!] ]

In the above description, the present invention has mainly been described in terms of the use of an amplifier circuit, which is the field of application in which the invention was made by the present inventor, but is not limited thereto.

For example, it can be used in automobile audio equipment, etc., which have severe fluctuations in pressure.

Furthermore, the switch transistor Q, is 11 directions ri
If there is a large difference between the collector-emitter bottom current when the transistor operates in the opposite direction and the collector-emitter bottom current when the transistor operates in the opposite direction, the collector-emitter bottom current of this transistor. The above difference may be canceled out by connecting diodes in parallel between the terminals.

[Brief explanation of drawings]

FIG. 1 shows a circuit diagram of an amplifier circuit studied by the inventor prior to the present invention, and FIG. 2 shows a circuit diagram showing an embodiment of an amplifier circuit to which the present invention is applied. 1 ・=intv width unit, Q+, Qa, Qs, C4
. QHa Qs a Qt e Qs + Qa # Q
+osQ1zQ 11 a Q **・Qffi3°°
°Tra'dister・i)1・U,・D,,D,,I),
, D, ... diode, C0. C1a CR* C11e C4...Capacitor, i
, n. m...Circuit block, +Vcc, +vcc...Power supply, v5. ...Input signal, ■. ut...output signal. Figure l Figure A Figure 2 E!

Claims (1)

[Claims] 1.16 Source 11 Detect the fluctuation of the work pressure and connect between the 1α source voltage and the potential point obtained from the bootstrap capacitor + jvc. Features a fence expansion circuit.