JPS6038046B2 - transistor power amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transistor power amplifier particularly suitable for integrated circuit implementation.

Conventionally, a transistor power amplifier configured as shown in FIG. 1 is known.

In other words, this is a so-called SEPP (single-ended push-pull) power amplifier in which a complementary NPN transistor Tr2 and a PNP transistor Tr3 are connected to the collector circuit of the drive transistor Tr through bias diodes D, D2. It is something that
When an unexpected large current flows through the resistors R82 and RE3 inserted between the emitters of the complementary transistors Tr2 and Tr3, the voltage across the resistors is detected and the protective transistors Tr4 and Tr5 are driven. , a function of limiting the base current of complementary output transistors Tr2 and Tr3 to protect the transistors from destruction. By the way, when such a power amplifier is integrated into an integrated circuit,
Since the PNP transistors Tr3 and Tr5 each use a so-called wisteria-shaped PNP formed in the structure shown in FIG. 2, the power amplification factor 8 becomes extremely low compared to the NPN transistors Tr2 and Tr4.

Note that B, C, and E in FIG. 2 indicate a base electrode, a collector electrode, and an emitter electrode, respectively, and C and B are formed so as to surround E and C, respectively. Therefore, if the currents flowing through resistors RE2 and RE3 for overcurrent detection are the same (actually, the current flowing through resistor RE3 is slightly smaller)
, the base current of the output transistor Tr3, which has a low power amplification factor B, is much larger than the base current of the output transistor Tr2.

However, since the protection transistor Tr5, which should limit the base current of the output transistor Tr3, is also a horizontal PNP with a low power amplification factor of 8, the base current cannot be fully limited and the output transistor Tr3 is destroyed by a large current. There is. Therefore, the present invention has been made in view of the above points, and by making it possible to use an NPN protection transistor with a large power amplification factor even for a PNP output transistor among complementary output transistors. It is an object of the present invention to provide an extremely good transistor power amplifier which can simplify and reliably eliminate the above-mentioned conventional drawbacks even when integrated circuits are implemented.

An embodiment of the present invention will be described in detail below with reference to the drawings.

That is, as shown in FIG. 3, the input terminals IN, . The bases are connected to and the emitters are connected to resistors R8, . Negative power supply through −
Drive transistors Tr, . are bias diodes D, . ,D,2
and is connected to a positive power supply Vcc via a constant fin flow source ls.

The bias diode ○, . , D,2 are complementary NPN output transistors Tr,2.
and the bases of the PNP output transistors Tr, 3, and are also connected to the collectors of the protective NPN transistors T', 4 and the emitters of the NPN transistors Tr, 5, which will be described later. Resistors RE, 2, RE, 3 are connected in series between the emitters of the complementary output transistors Tr, 2, Tr, 3.
These resistors R8,2, R8,3 are for overcurrent detection, and their connection midpoints are the output terminals OUT, . connected to. The base of the tax protection transistor Tr,4 is connected to the emitter of the NPN output transistor Tr,2. Furthermore, the base of the protective transistor Tr,5 is connected to the connection midpoint of the resistors R8,2, RE,3 via the diode D,3 having the polarity shown, and the collector thereof is connected to the connection point of the protective transistor Tr,5. 4 and the connection midpoint of the resistors RE, 2, R8, and 3. Here, N becomes the protection transistor Tr,5.
A PN transistor is generally formed with a structure as shown in FIG. 4, and has a sufficiently higher power amplification factor B5 than the lateral PNP transistor shown in FIG.

The symbols in FIG. 4 have the same meanings as those in FIG. 2. In the above structure, the current flowing through the PNP output transistor Tr, 3 is lo, the base-emitter voltage of the transistor Tr, 3 is VB83, the T is . The base current of 3 is I
B3, and the emitter current of the protective NPN transistor Tr,5 is 185, and the base current is 1.

3 (equal to the operating current of diode ○3), and assuming that the base-emitter voltage is V885, VB853VBE
3, R8,310=VT1n(1.

3 no IS) A relationship is established.

However, here, V·,ls are the thermal voltage component and reverse saturation current of the transistor Tr,5. And RE, 3・L
is higher than the threshold fin pressure of diode D,3, as the lo component increases, its operating current lo3
has increased to 185 (185) 1.

3 IE5 represented by will also increase.

Therefore, drive transistors Tr, . Considering that the collector current of is fixed, 185 + 183 = Const. , and as 185 increases, IB3 decreases.

That is, the protection transistor Tr,5 operates to limit the base current IB3 of the PNP output transistor T',3 from exceeding a certain value, that is, it limits lo to keep it constant. On the other hand, RE,3・l
In the range where o is lower than the threshold voltage of diode D,3, lo3 is 0, so the protection NPN transistor Tr,5 does not operate, and is IE530.

In this way, since an NPN transistor with a sufficiently high power amplification factor a5 is used for the protection transistor Tr,5, a horizontal PNP with a low power amplification factor is used for the PNP output transistor Tr,3 to form an integrated circuit. Even when aiming at the current, it has the effect of sufficiently suppressing a large current of lo.

Note that in the above description, the diode D may be diode-connected using a transistor, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

Therefore, as described in detail above, according to the present invention, an NPN transistor with a large power amplification factor can be used as a protection for a PNP output transistor among complementary output transistors, so even if it is integrated into an integrated circuit, it will not be a problem. Yoni PN
It becomes possible to provide an extremely good transistor power amplifier that can easily and reliably protect the P output transistor without destroying it.

[Brief explanation of the drawing]

Figure 1 is a wiring diagram showing a conventional transistor power amplifier.
FIG. 2 is a block diagram of the lateral PNP transistor used in FIG. 1, FIG. 3 is a wiring diagram showing an embodiment of the transistor power amplifier according to the present invention, and FIG.
FIG. 2 is a configuration diagram of a transistor. Tr, 2, Tr, 3... Complementary output transistor,
Tr, 4, Tr, 5... Protection NPN transistor, D, 3... Diode, R8, 2, R8
, 3... Resistor (for excessive current detection). Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. An NPN output transistor whose emitter electrodes are each connected to an output terminal via a resistor, a PNP output transistor whose current amplification factor is lower than that of the NPN output transistor, and a base electrode of the PNP output transistor among these output transistors and the output terminal. A transistor power amplifier comprising a protective NPN transistor connected between the protective NPN transistor and a diode connected in a forward direction between the base electrode of the protective NPN transistor and the output terminal.