JPS5941622Y2 - transistor amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a transistor amplifier that allows the idle current of the final stage transistor of a power transistor amplifier to be designed stably.

Conventionally, a 5EPP power amplifier having an idle current adjustment circuit for a final stage transistor has a circuit configuration as shown in FIG.

That is, the first stage consists of a differential amplifier of transistors Ql and Q2, and the emitters of transistors Ql - Q2 are connected to each other via a common emitter resistor island.
The base of is biased by a base bias resistor R1 and connected to the input end via an input coupling capacitor C1.

Then, a signal is obtained from the load resistor R3 connected to the collector of the transistor Q to be transmitted to the base of the next stage pre-drive transistor q, and the final output transistor Q4.
Q5 constitutes a 5EPP circuit, and emitter protection resistor R
An output is obtained from the common connection point of 5 and R6, is connected to a load such as a speaker, and is negatively fed back to the base of the transistor Q2 via a feedback resistor R7.

The gain of the power amplifier is generally determined by the ratio between the negative feedback resistor connected to the base of transistor Q2 and resistor R6.

Further, the series connection circuit of the resistive island, the diode D1p I)2, and the variable resistor VR serves as a load resistance for the transistor Q3, and also constitutes a bias circuit for the transistors Q4 and Qs.

The bias currents of both transistors Q4tQ5 can be changed by adjusting the variable resistor VR.

Generally, the base-emitter voltage VBE of a transistor has a temperature coefficient, so its operating point changes depending on the ambient temperature and the heat generated by the transistor itself, and the idle current also changes.

Therefore, in a circuit like that shown in Fig. 1, the diode Dl s D
By matching the characteristics of transistors Q4 and Qs with the VBE characteristics of transistors Q4 and Qs, and by thermally coupling the two, the idle current is made constant regardless of temperature, and its absolute value is adjusted by adjusting the variable resistor VR. Let's do it.

The method of adjusting the idle current using such a circuit configuration is to use the transistor Q4, the current amplification factor of %, and the diode DB.
e Since there are variations in the rise characteristics of D2, a variable resistor VR is almost always required, and this variable resistor VR must be adjusted for almost every unit.

Therefore, the present invention was developed to eliminate the above-mentioned drawbacks, and by detecting the idle current and forming a negative feedback loop that includes the idle current as well as the signal system, it eliminates the need for a variable resistor for adjusting the idle current. The purpose is to provide a transistor amplifier that does not

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 2, transistors QIO? which constitute two sets of differential amplifiers are shown. Qll and Q12. Q15 is composed of transistors of different conductivity types.Transistor QIOt
The differential amplifier configured by Qtt is connected to the negative power supply -B via the emitter common resistor R1□, and the transistor Q
The base of 1o is biased via the reference power source E1 and the bias resistor RIG, and a signal is applied from the input via the capacitor CtO.

The signal output obtained from the load resistor R13 of the transistor QIG is applied to the base of the next stage transistor Q14,
The signal output obtained from the load resistor R16 is applied to the base of the final transistor Q15, which
15 idle current I.

is detected by the voltage across the emitter resistor R17.

And negative feedback resistor R19j R21 and capacitor C12
The AC signal is negatively fed back.

Transistor Qlo like this? Qtt t Q1
4t Q16 and the above-mentioned resistor/capacitor connection circuit, there is a similar circuit connection that is symmetrical and complimentary connected around the ground.

That is, transistor QIO9Qll is transistor Q1
□, corresponding to Q13, capacitor Cl0C1
2 corresponds to C1l e C13, respectively, and the reference power source E
1 corresponds to the reference power supply E2, and the resistor RIOt R1□.

R13v R16t R17t Rlg t R21 are R1, respectively.

R23*RlstR4B, R20, and R22 correspond to each other, and the positive and negative input signals are transmitted and amplified via the symmetrical circuits described above.

To explain the operation in such a circuit configuration, this negative feedback circuit becomes full feedback for direct current due to capacitors C1□ and C13, and the base potential of transistor QIO, the emitter potential of transistor Q15, and the base potential of Q1□ The feedback operation works even if the emitter potentials of transistor Q18 become equal.

As a result, the emitter potential of transistor Q16 becomes equal to the reference power source E1, and the emitter potential of transistor Q17 becomes equal to the reference power source E2.

That is, E1+E2-I.

(R17+R18), now reference power supply E4 = R2
= E x and resistance R17=R48==Rx, then l
0=Ex/Rx.

At this time, the DC potential of the 5EPP output becomes zero.

On the other hand, since a general amplifier operates in the same way for AC signals, the gain for AC signals is G v: (R1
9+ R21) / R21p (R19= R20・R
21=R22) Therefore, the reference power source E1. E2 and resistance R1
By appropriately setting □ and R18, it is possible to obtain an idle current that is not affected by variations in the current amplification factor of the transistor, etc., so there is no need to provide a variable resistor for adjusting the idle current as in the prior art.

FIG. 3 shows another embodiment of the invention.

That is, in the embodiment shown in FIG. 2, the reference power source E1. R2
is inserted into the signal input side of the first-stage differential amplifier, but in Figure 3, the reference power supplies E1' and E2' are inserted into the negative feedback side of the first-stage differential amplifier, and a common bias resistor R30 is connected to the signal input side. shows.

This is the case where the capacitors C1□ and C13 used in FIG. 2 are removed, and a DC amplifier with gain up to DC is used.

In this case, the idle current of the final stage transistor Q16 t Q17 is ■.

= E x X G v / Rx. However, Gv
is the gain in the DC region.

In the case of this embodiment, the idle current can be adjusted by varying the gain Gv as a parameter.

As explained above, the present invention uses negative feedback of the transistor amplifier to set the idle current, so even if the circuit is configured with discrete elements, fluctuations in the idle current due to temperature can be suppressed. It has a particularly great effect when used in a power amplifier having a 5EPP circuit configuration, since it is not necessary to adjust the idle current due to variations in the elements.

[Brief explanation of drawings]

FIG. 1 shows a transistor amplifier with a conventional idle current adjustment circuit, FIG. 2 shows a transistor amplifier according to the present invention, and FIG. 3 shows another embodiment of the present invention. El e R2...Reference power supply.

Claims (1)

[Scope of utility model registration request] two differential amplifiers each having a common power input as a signal input and each comprising transistors of different conductivity types;
The output of the differential amplifier is connected between a final stage 5EPP circuit consisting of a pair of transistors of different conductivity types, and the transistors of the 5EPP circuit are inputted through separate amplification systems. A pair of resistors for detecting an idle current and a DC voltage source for setting a bias current of the differential amplifier are provided, and an output is obtained from a connection point of the pair of resistors, and the idle current detected by each of the pair of resistors is provided. A transistor amplifier characterized in that a detection signal is separately negatively fed back to the other input of the differential amplifier.