JPS6029227Y2 - low frequency amplifier circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a low frequency amplification circuit comprising an inverted Darlington circuit.

Conventionally, in audio circuits, a Darlington circuit has been used in the output stage of a low frequency amplifier circuit that obtains a large output voltage.

The low frequency amplification circuit using the inverted Darlington circuit illustrated in FIG. 1 will be explained below.

In FIG. 1, the power supply voltage Vcc and the negative power supply voltage -Vcc
A PNP transistor Tr□ and an NPN transistor Tr3 are connected in series between the PNP transistor Tr, an NPN transistor Tr2, and an NPN transistor T.
r3 and PNP transistor Tr each form an inverted Darlington circuit.

Furthermore, the NPN transistor Tr2 and the PNP transistor T
The emitter of r4 and the PNP transistor Tr1 to NPN
The collectors of the transistor Tr3 are commonly connected to serve as an output terminal 2, and the bases of the NPN transistor Tr2 and the PNP transistor Tr are commonly connected to serve as an input terminal 1.

A Darlington circuit as shown in FIG. 1 is generally used as a low frequency amplifier circuit that obtains a large output power.

A low frequency amplifier circuit consisting of a Darlington circuit, as shown in Figure 1, has the drawbacks of a very large current gain and the tendency to oscillate in the high frequency range, as well as poor thermal stability and the risk of thermal runaway. is always accompanied by

Therefore, it is necessary to supplement the Darlington circuit with various additional circuits.

The present invention was devised in view of the above-mentioned problems, and its purpose is to provide a highly reliable low frequency amplification circuit by supplementing an inverted rear-rington circuit with an additional circuit.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the present invention.

In Figure 2, the power PNP of the output stage of the low frequency amplifier circuit
) transistor Tr□ and power NPN transistor Tr
3 is connected in series between the power supply voltage CC and the ground, and the connection point A is the output terminal 2, and the power PNP transistor Tr, the NPN transistor Tr2, and the power NPN
) transistor Tr3 and PNP transistor Tr.

constitute an inverted Darlington circuit.

A common connection point B is the emitter of the NPN transistor Tr2 and the PNP transistor Tr in the input stage of the inverted Darlington circuit.

NPN transistor Tr2 and PNP transistor Tr4
is biased by two diodes and also constitutes a bias circuit for the output stage transistor.

Further, the bias of the output stage transistor is stabilized by the resistor R2.

A capacitor C1 is connected between connection points A and B, a capacitor C2 is connected between connection point B and ground, and a DC power source F1 is supplied.

In the case of a two-power supply system, the output stage transistor of the low frequency amplifier circuit is connected in series between the power supply voltage Vcc and the negative power supply voltage -Vce, and the connection point B is grounded.

Further, the base of the NPN transistor Tr5 is an input terminal 1, and 2 is an output terminal to which a load resistor is connected.

As shown in Figure 2, in a low frequency amplifier circuit consisting of two inverted Darlington circuits, a capacitor C1 is connected between connection points A and 8, and a capacitor C2 is connected between connection point B and the ground or negative power supply voltage. Inverted
Apply negative feedback to the Darlington circuit.

In particular, the capacitor C2 acts as a bypass capacitor in the high frequency range, and therefore can prevent the oscillation of the low frequency amplifier circuit consisting of the Darlington circuit in the high frequency range, and also provides feedback only at low frequencies to correct the phase. Stable operation can be obtained without

[Brief explanation of drawings]

FIG. 1 shows a general power low frequency amplifier circuit, and FIG. 2 shows a power low frequency amplifier circuit showing an embodiment of the present invention. Trl...PNP for power) transistor, Tr
2...NPN transistor, Tr3...
・Power NPN) transistor, Tr4...PN
P transistor, C1, C2... capacitor,
1...Input terminal, 2...Output terminal.

Claims (1)

[Scope of utility model registration request] In a low frequency amplifier circuit consisting of two inverted Darlington circuits, a PNP (PNP) in the output stage of the transistors forming the inverted Darlington circuits.
A first connection point A commonly connects the collectors of transistor Tr1 and NPN transistor Tr3, and a second connection point A commonly connects the emitters of input stage NPN transistor transistor Tr2 and PNP transistor Tr4 among the transistors forming the inverted Darlington circuit. 1. A low frequency amplification circuit comprising a capacitor between the second connection point B and a bypass capacitor at the second connection point B.