JPH0653750A - Power ic - Google Patents

Abstract

PURPOSE:To prevent an output transistor(TR) from being destroyed by supplying a current to a power supply line via a diode being an emitter-open transistor(TR) when a voltage at an output midpoint reaches an abnormally high voltage. CONSTITUTION:The integrated circuit is provided with an output TR Q1 at a power supply side for current delivery and a ground side TR Q2 for current absorption, and also a diode QX being an open emitter TR connecting an output midpoint O to which both TRs Q1, Q2 are connected and a power supply line, and the TR QX is formed in the same region as that of the TR Q1 while the collector is used in common. Since the TR QX is the open emitter TR and acts like a diode, when a level at an output terminal OUT is higher than a power supply line +B due to any cause, a prescribed current flows to the power supply line via the TR QX. As a result, the output TR Q1 is bypassed and then no reverse current flows to the output TR Q1, thereby protecting the output TR Q1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to protection against erroneous connection of a power IC used for amplification in the final stage of audio equipment.

[0002]

2. Description of the Related Art Conventionally, a power IC has been used for amplification at the final stage of audio equipment, and a pair of output transistors Q1 and Q2 connected in series as shown in FIG. 3 is used at the output stage of this power IC. Is provided. The output midpoint O of the output transistors Q1 and Q2 is connected to the speaker SP via an external output capacitor Cout. Therefore, the AC audio signal is supplied to the speaker SP by driving the output transistors Q1 and Q2 complementarily.

Such a power IC is assembled in an audio device (set), but a speaker is often not built in such a set, so that the speaker is connected to the set and the power source is connected later. Be done from. In the final connection, if an incorrect connection occurs, power is turned on or off in a specific order, or a speaker is connected or disconnected, the output transistor on the power supply side There is a problem that a large reverse voltage is applied to Q1 and this is destroyed.

That is, a large reverse voltage is applied to the output transistor Q1 in the following cases.

(A) With the speaker SP connected, the main power supply is turned on and the power supply line L is set to Vcc.
As a result, the output midpoint O changes around 1/2 Vcc. On the other hand, since the opposite side of the output capacitor Cout becomes the ground level, the electric charge corresponding to this is stored in the output capacitor Cout. Next, in a state where the output capacitor Cout is charged, the speaker SP is disconnected, the power is turned off, and then the speaker SP is connected again. Rush current flows, and the BE junction of the output transistor Q1 is destroyed. That is, in the normal case, the BE junction of the output transistor Q1 has a reverse breakdown voltage of about 7.2 V, and the voltage drop at the BC junction is 0.
Although it is about 6V, in the above case, a voltage higher than this may be applied to the transistor Q1 in the reverse direction, a reverse current flows through the output transistor Q1, and the BE junction is destroyed.

(B) Under the condition that various devices are connected to the main power supply line L and the load here is extremely heavy, when the main switch is turned off, the power supply line L becomes extremely fast at the ground level (0 potential). Shift down to. In the worst case, turning off the main switch is the same as shorting the power supply line L to the ground. In such a case, the charge accumulated in the output capacitor Cout flows as a rush current from the output midpoint O toward the power supply line L, and thus the output transistor Q1 may be destroyed by this current.

(C) In an actual set, the speaker is often connected later, and if the power source V is erroneously connected to this speaker connection end, a large voltage is applied here. Therefore, a voltage corresponding to the power source V is applied to the series circuit of the output capacitor Cout, the emitter / collector path of the output transistor Q1 and the power source capacitor Cv, and the output transistor Q1 is destroyed.

[0008]

In order to solve the above problem (a), a resistor Rx having a resistance value of 10 times or more that of the speaker is arranged in parallel with the speaker to form a discharge path of the output capacitor Cout. Conceivable. As measures against the above (b) and (c), a current limiting resistor of about 1Ω is inserted in the path of the output terminal to the speaker, thereby limiting the rush current, and the power supply is connected in parallel with the output capacitor Q1. -A method of inserting a large current capacity diode Dx that bypasses between the output terminals can be considered. By such a method, it is possible to prevent the BE junction from being destroyed by applying a large reverse voltage to the output transistor Q1.

[0009] However, these methods use the power I
There is a problem in that a discharge resistor, a diode, and the like must be connected as an external element of C, which increases the number of steps and increases the cost. Further, there is a problem that a part of the signal flows to the ground by these means, which causes a loss.

The present invention has been made to solve the above problems, and relates to a power IC capable of effectively setting a high reverse breakdown voltage in an output transistor on a power supply side.

[0011]

According to the present invention, there is provided a power source for outputting an audio signal from an output midpoint to which both transistors are connected and which has a power source side output transistor for current discharge and a ground side transistor for current sink. IC
In, there is a diode connecting the output midpoint and the power supply line, and the diode is formed in the same region as the power supply side output transistor with a common collector.

[0012]

According to the present invention, as described above, the IC has the diode for connecting the output midpoint and the power supply line. The diode is formed in the same region as the output transistor with a common collector. Therefore, the size of the IC can be made very small. Further, the contact of the base can be made large similarly to the output transistor, and local heat generation can be prevented here. Also, since this diode is used in the C-B forward direction, its impedance is sufficiently higher than the reverse breakdown voltage of the output transistor, and this diode is not destroyed.

Further, in the EB forward diode, the reverse breakdown voltage may be exceeded at the time of steady signal amplitude, but in the CB emitter open transistor, the reverse breakdown voltage is sufficiently large. Don't worry.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a main configuration of a power IC according to the present invention, which is an NPN output transistor Q.
1, Q2 are connected in series between the power source + B and the ground. The connection point between the transistors Q1 and Q2 (the output midpoint O) is the output terminal OUT and the output capacitor Cout.
Is connected to the speaker SP via. A power supply capacitor Cv is connected to the power supply line + B.

On the other hand, the base of the output transistor Q1 is connected to the collector of a PNP type drive transistor Q3 whose emitter is connected to the power source. The drive transistor Q3 is responsive to a signal input to its base. A base current is supplied to the output transistor Q1. Therefore, a current obtained by amplifying the base current of the output transistor Q1 is supplied from the power supply to the speaker SP. on the other hand,
The base of the output transistor Q2 is connected to the collector of a PNP type drive transistor Q4 whose collector is connected to the ground, and a current corresponding to a signal input to the base of the drive transistor Q4 is applied to the base of the output transistor Q2. It becomes an electric current. Therefore, the current obtained by amplifying the base current of the output transistor Q1 is output terminal OUT.
Flows from the ground to the ground. Therefore, the transistor Q
A push-pull type amplifier is configured by 1 and Q2. The NPN transistor Q5 is for supplying an operating current to the driving transistor Q4, and the diodes D1 and D2 are for holding the base of the transistor Q5 at a predetermined potential.

In the present embodiment, the output midpoint O
An open-emitter transistor Qx for connecting the power supply line + B and the power supply line + B is provided. Since the emitter open transistor Qx operates as a diode, if the level of the output terminal OUT becomes higher than the power supply line + B for some reason, a predetermined current flows through the emitter open transistor Qx toward the power supply line, Bypass output transistor Q1. Therefore, a reverse current does not flow in the output transistor Q1 and can be protected.

Next, the structures of the emitter open transistor Qx and the output transistor Q1 in this embodiment will be described with reference to the explanatory view of FIG. In this example, the transistors Q1 and Qx are NPN transistors. The substrate 10 is a P-type substrate, on which an N-type epitaxial layer 12 is formed. The side of the N-type epitaxial layer 12 is separated from other islands by the element isolation portion 14. The N ⁺ region provided at the bottom of the N type epitaxial layer is the channel stop 16.

Then, the N-type epitaxial layer 12
Is output transistor Q1 and emitter open transistor Q
It is a collector of x. Further, the P region 20 provided in the N type epitaxial layer 12 is the transistor Q1.
And the N region provided in the P region 20 serves as the emitter of the output transistor Q1. Also, P
The region 24 becomes the base region of the emitter open transistor Qx.

As described above, the N type epitaxial layer 12 is formed.
However, since it is shared as the collectors of two transistors, the chip size can be reduced as compared with the case where the element isolation region and the channel stop are independently provided. Further, no wiring is required between the collectors of both transistors Q1 and Qx. Furthermore, this protective transistor Qx
It is sufficient for the area of 1 to be about 1/10 of the size of the output transistor Q1. Further, by making the collector contact and the base contact of these transistors sufficiently large, it is possible to prevent local heat generation when a current flows through the protection transistor Qx. The work of making such a large contact can be easily performed during the patterning process.

[0020]

As described above, according to the power IC of the present invention, the protection transistor can be formed in the chip, and the output transistor can be protected without increasing the chip area. You can Also,
Since the circuit is built in the chip, the user does not need to work externally and the power IC can be used efficiently.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a main configuration of a power IC according to the present invention.

FIG. 2 is an explanatory diagram showing configurations of an output transistor Q1 and a protection transistor Qx in the same embodiment.

FIG. 3 is a circuit diagram showing a configuration of an output stage of a conventional power IC.

[Explanation of symbols]

 Q1 Power supply side output transistor Q2 Ground side output transistor Qx Emitter open transistor (diode)

Claims (1)

[Claims] 1. A power IC which has a power supply side output transistor for discharging current and a ground side transistor for absorbing current, and outputs an audio signal from the output middle point where both transistors are connected, A power IC, comprising a diode connected to a power supply line, the diode being formed with a common collector in the same region as the power supply side output transistor.