JPH04579Y2 - - Google Patents

Description

[Detailed description of the invention] "Purpose of the invention" (Field of industrial application) The present invention relates to a power amplifier used in audio amplifiers of audio equipment, etc., and is particularly suitable for improving the ability to suppress ripple components of the power supply. Regarding power amplifiers.

(Prior art) Conventionally, the circuit configuration of power amplifiers used in audio amplifiers, etc. of audio equipment is as follows.
Various things have been proposed.

Representative examples of this type of conventional power amplifier will be explained based on FIGS. 7 to 11.

First, the conventional power amplifier shown in FIG. 7 is an SEPP (single-ended push-pull) circuit with a two-stage Darlington connection.

Since this circuit operates in the same way on both the plus side and minus side, the plus side circuit shown in FIG. 8 will be described for convenience.

The base of transistor Q ₂ is the base of transistor Q ₁
The collectors of each are connected to the power supply VB through the power supply terminal _B. At the emitter of transistor _Q1 there is a resistor B _E1 ,
A resistor R _E2 is connected to the emitter of the transistor Q ₂ , and the other ends of each of the resistors R _E1 and R _E2 are connected to the output terminal O.

By the way, the power supply for a normal audio amplifier is
It is not a complete DC power supply, but consists of a pulsating current including ripple components, and therefore the transistor Q ₁ ,
A pulsating voltage containing a ripple component is also applied to the collector of _Q2 . In general, the collector junction resistance of a transistor has a large value but is finite, so a ripple component applied to the collector leaks to the emitter through the collector junction resistance, albeit slightly. This phenomenon occurs in transistors Q ₁ , Q ₂
Similarly, ripple components of the power supply flow to the emitter as I _R1 and I _R2 through the respective collector junction resistances. A part of the ripple component current I _R1 of the transistor Q ₁ becomes the base current I _Rb of the transistor Q ₂ and is amplified by the transistor Q ₂ . If the current amplification factor of transistor Q ₂ is β ₂ , then the emitter of transistor Q ₂ has
+β ₂ )I _Rb } ripple current will further flow.

Therefore, the amount of ripple current flowing through the load R _L is
[I _R1 +I _R2 +β ₂ I _Rb }, which increases by the amount generated by the Darlington connection, β ₂ I _Rb in the third term. Figure 9 focuses on the ripple current,
This is an equivalent circuit when the positive side circuit in Figure 8 is viewed from the power supply.If we consider the circuit between terminals O and B as one transistor, and find the equivalent internal resistance γ _c in that case, it is roughly as shown in equation (1). become.

γ _c ≒1/1/γ _c1 +1/γ _c2 +(R _E1 /γ _c1
−γ _e2 +R _E2 /γ _c2 )β ₂ /γ _b2 +R _E1 +(1+β ₂ )(γ
_e2 + R _E2 )...(1) However, γ _c1 : Collector junction resistance of transistor Q ₁ γ _c2 : Collector junction resistance of transistor Q ₂ γ _e1 : Emitter diffusion resistance of transistor Q ₁ γ _e2 : Emitter diffusion of transistor Q ₂ Resistance γ _b2 ; Base spread resistance of transistor Q ₂ β ₂ ; Current amplification factor of transistor Q ₂ The third term in the denominator of equation (1) above means that the equivalent internal resistance is reduced by the Darlington connection,
Therefore, more power supply ripple current is applied to the load.
It will flow to R _L.

By substituting typical values when there is no signal input in a normal audio amplifier into equation (1), we will compare the cases with and without the third term.

R _E1 = 150Ω, R _E2 = 0.22Ω γ _c1 = 100kΩ, γ _c2 = 10kΩ, β ₂ = 200, γ _e2 = 0.5Ω, γ _b2 << If there is a third term in R _E1 ... γ _c = 955Ω If there is no third term... γ _c = 9.1KΩ.

As mentioned above, the Darlington connection reduces the equivalent internal resistance to about 1/10, which means that more power supply ripple components flow into the load R _L.

As described above, the conventional power amplifier shown in FIG. 7 has a problem in suppressing power supply ripple components.

Next, the conventional power amplifier shown in FIG. 10 will be explained.

The purpose of this power amplifier is to lower the voltage between the collector and emitter of each transistor by cascode-connecting the transistors in the final stage, and to connect the base of the common-base transistor _Q5 to the base of the final stage transistor _Q6 . By applying a bootstrap to the base, the voltage between the collector and emitter of the final stage transistor is made constant regardless of the output. In other words, even if the load is a reactive load where the phase of current and voltage changes, the voltage between the collector and limiter of the final stage transistor is low and constant, so the safe operating area is wide. This results in a power amplifier that is hard to break.

Therefore, no consideration is given to increasing the suppression of power supply ripple components by cascode-connecting up to the final stage transistor.

In other words, the ripple current leaking through the constant current means between the collectors and bases of the common base transistors Q ₅ and Q ₈ is absorbed by the constant voltage means.
The current flows into the bases of the final stage transistors Q ₆ and Q ₇ through E ₁ and E ₂ , is amplified there, and flows to the load, so the ripple suppression ability, which should originally be very high, is lost. Also, at maximum output,
The saturation voltage of the final stage transistors Q ₆ and Q ₇ and the common-base transistors Q ₅ and Q ₈ occurs in series between the power supply and the load, which reduces the power supply utilization rate and results in an amplifier with poor thermal efficiency. There were flaws.

Furthermore, the conventional power amplifier shown in FIG. 11 will be explained.

The purpose of the cascode connection (transistors Q ₉ , Q ₁₀ ) of the driver stage in this power amplifier is that the driver stage transistors are MOS
-Since it is a FET, it has a large gate-drain capacitance, and in a normal source follower, this capacitance changes depending on the signal level, causing large distortion. Also, the drive capacity of the previous stage (voltage amplification stage) The aim is to take measures to prevent the capacitance from decreasing due to this capacitance change.

In other words, MOS-FETs (FET1, FET2) are connected in cascode with transistors Q ₉ and Q ₁₀ , and the bases of transistors Q ₉ and Q ₁₀ are connected to the MOS-FETs.
(FET1, FET2) are bootstrapped to the sources of each MOS-FET (FET1, FET2) to keep the drain-source voltage of the MOS-FET (FET1, FET2) low and constant. This eliminates the above-mentioned capacitance change and eliminates this drawback. In addition, for high power amplifier, MOS-FET (FET1,
When using FET2), it can be said that cascode connection is used so that it can be used at a low withstand voltage because there is no one with an appropriate withstand voltage. Therefore, it is not intended to improve the degree of suppression of the power supply ripple component by connecting the driver stages in cascode. Because the common base transistors Q ₉ , Q ₁₀
Since a resistor is connected between the base and collector of the transistors Q ₉ and Q ₁₀ , the power supply ripple component
A lot of it flows into the base. In addition, the remaining power supply ripple component current is generated by the MOS-FETs (FET1, FET2)
The current also flows into the sources of Qo, that is, the bases of the final stage transistors _Qo , where the current is amplified and flows to the load.

In this power amplifier, the driver stage and the final stage have separate power supply configurations, and if a stabilized power supply is used as the power supply for the driver stage, the ripple suppression ability can be significantly improved. But in that case, the cascode connection is
It is not involved in improving ripple suppression ability.

(Problems to be Solved by the Invention) As described above, all conventional power amplifiers have the problem that good results cannot be obtained in terms of suppressing power supply ripple components.

The present invention has been made in view of the above points, and its purpose is to provide a power amplifier that can easily improve the power supply ripple suppression ability of the Darlington connection stage.

"Structure of the invention" (Means for solving the problems) A power amplifier according to the invention includes first and second NPN transistors connected in a Darlington connection and first and second PNP transistors connected in a Darlington connection. Configured Complementary
In the power amplifier of the SEPP circuit, the second
The emitters of the NPN transistor and the second PNP transistor are connected to the output point via a resistor, and a third NPN transistor and a third PNP transistor are provided, and the third NPN transistor and the third PNP transistor are connected to the collectors of the first NPN transistor and the first PNP transistor, respectively, and a constant current is connected between the collector and base of the third NPN transistor and the third PNP transistor, respectively. means for connecting the bases of the third NPN transistor and the third PNP transistor to the second NPN transistor, respectively;
The third PNP transistor is connected to the emitter of the second PNP transistor through a constant voltage means.
The collectors of the NPN transistor and the third PNP transistor are connected to the collectors of the final stage transistors of the SEPP circuit configured by Darlington connections of the same polarity, and the power supplies of the respective polarities.

(Function) The power supply ripple suppression ability of the Darlington connection stage can be enhanced.

(Embodiment) An embodiment of the power amplifier according to the present invention will be described based on FIGS. 1 to 6.

First, a first embodiment of the power amplifier according to the present invention shown in FIG. 1 will be described.

The emitter of transistor _Q11 is the transistor
It is connected to the base of _Q12 and to the output terminal O through a resistor R _E1 . transistor
The emitter of _Q12 is connected to the output terminal O through the resistor R _E2 .
and transistors Q ₁₁ and Q ₁₂ are Darlington connected.

The collector of transistor Q ₁₁ is a transistor
The emitter of transistor _Q15 is connected to the emitter of transistor _Q15 , and the collector of transistor Q15 and the collector of transistor _Q12 are connected to power supply terminal B, respectively. transistor
Constant current means _CC1 is connected between the base and collector of _Q15 . Furthermore, a constant voltage means CV ₁ is connected between the base of the transistor Q ₁₅ and the emitter of the transistor Q ₁₂ , and the transistors Q ₁₅ and Q ₁₁ constitute a cascode connection circuit.

The above configuration was described for the positive polarity, but
The negative side, which is made up of transistors Q ₁₃ and Q ₁₄ and transistor Q ₁₆ , has a similar structure. Also, between the emitters of transistors _Q15 and _Q16 ,
Capacitor _C1 is connected.

The operation of the power amplifier of the first embodiment of the present invention constructed as described above will be explained based on FIG. 2, which shows only the positive polarity.

The base of the transistor _Q15 has a very high impedance from the power supply due to the constant current means _CC1 . On the other hand, since the internal impedance of the constant voltage means CV ₁ is very low compared to that of the constant current means CC ₁ , the base DC potential of the transistor Q ₁₅ is higher than the emitter potential of the transistor Q ₁₂ than the voltage of the constant voltage means CV ₁ . Only V _a is high, and it is short-circuited in terms of AC. On the other hand, the AC impedance of the emitter of transistor _Q12 is very low because transistor _Q12 is a Darlington connected emitter follower.

Therefore, the AC impedance of the base of transistor _Q15 is extremely low. Therefore,
Even if a ripple component exists at power supply terminal B, it hardly occurs at the base of transistor _Q15 . The emitter of transistor _Q15 , that is, the collector DC potential of transistor _Q11 is
From the base DC potential of Q ₁₅ , that transistor
Although the base-emitter potential of Q ₁₅ is lower by V _BE (approximately 0.6 V), the base-emitter of transistor Q ₁₅ is forward biased, so transistor Q ₁₅
Like the base of Q11, the collector of transistor _Q11 also has a very low AC impedance.

By the way, the base of transistor _Q15 has low AC impedance, so this transistor
Q ₁₅ constitutes a common base amplifier.

The internal resistance of a common base amplifier is higher than that of a transistor follower (grounded collector) circuit.
If the current amplification factor of Q ₁₅ is β ₅ , it is [1+β ₅ ] times higher. Therefore, when the same transistor as transistor Q ₁₁ is used as transistor Q ₁₅ , the internal resistance of transistor Q ₁₅ is usually 100 times or more that of transistor Q ₁₁ . Therefore,
The amount of ripple component leaking to the collector of transistor _Q11 through the internal resistance of transistor _Q15 becomes extremely small.

As described above, according to the power amplifier according to the present invention shown in _FIG .
2 of the collector resistance of CC ₁ and transistor Q ₁₅
Both of them have very high impedance, and the collector AC impedance of transistor _Q11 is very low, so that almost no ripple appears at the collector of transistor _Q11 .

Therefore, almost no ripple occurs at the emitter of the transistor _Q11 , and the current is not amplified by the transistor _Q12 .

Therefore, the equivalent internal resistance seen from the power supply terminal B of the Darlington connection stage formed by the transistors Q ₁₁ and Q ₁₂ is only the internal resistance of the transistor Q ₁₂ .

By the way, when this power amplifier outputs a large output, the collector current of transistor Q ₁₂ increases and the internal resistance decreases significantly, so many power supply ripple components are transferred to the load R _L through the internal resistance of transistor Q ₁₂ . It will flow. However, since it is small compared to the signal output current, there is little deterioration in playback quality due to the masking effect of the human ear.In fact, it is more important for the auditory sense when ripple components are mixed in with small signals. 1st related to
The power amplifier shown in the figure makes sense because it suppresses ripple components to a high degree in a small output region where the internal resistance of transistor _Q12 decreases little. Further, the transistor Q ₁₅ may be a transistor with the same current capacity as the transistor Q ₁₁ , and the heat generation is the same as that of the transistor _{Q 1} of the conventional power amplifier shown in FIG. Since the voltage across the transistor is constant, the voltage only needs to be a few volts, which is necessary for operation.
_Q11 heat generation can be greatly reduced. Therefore, with regard to heat dissipation, it is sufficient to take measures similar to those of the conventional power amplifier described above, and an inexpensive low-voltage transistor can be used as the transistor _Q11 . Also,
Since the transistor _Q11 generates less heat, there are many advantages such as improved bias stability. Furthermore, an embodiment of the power amplifier according to the present invention shown in FIG. 1 will be described.

The transistor Q ₁₆ , the constant current means CC ₂ , the constant voltage means CV _2, etc. are the same as the previous explanation, so they will be omitted, and here, the capacitor C ₁ connected between the emitters of the transistors Q ₁₅ and Q ₁₆ will be explained in particular.

In a normal B class amplifier, transistor _Q12
and Q ₁₄ cut off alternately. On the other hand, transistors _Q11 and _Q12 also operate to be cut off alternately when the output exceeds a certain level. In this case, transistors _Q15 and _Q16 are also cut off alternately, but at high frequencies of several KHz or more, the carrier accumulation effect of the transistors becomes noticeable. Furthermore, although negative feedback is normally provided in audio amplifiers, the amount of negative feedback is reduced, resulting in worse distortion than in a power amplifier having an output stage using a normal Darlington connection without transistors Q ₁₅ and Q ₁₆ . As a countermeasure to this problem, it has been proposed to insert a resistor between the emitters of transistors Q ₁₁ and Q ₁₃ to prevent transistors Q ₁₅ and Q ₁₆ from being cut off. This proposal is highly effective;
It is easy to implement. However, since the idle current of transistors Q ₁₅ and Q ₁₆ increases,
Heat loss in transistors Q ₁₅ and Q ₁₆ increases, and in some cases, a heat sink may be required for transistors Q ₁₅ and Q ₁₆ . Therefore, the transistor
without increasing the idle current of Q ₁₅ and Q ₁₆ .
In order _to create a _power amplifier that eliminates distortion factor deterioration, as shown in _{FIG .}
Insert capacitor _C1 between both emitters of.

The aforementioned distortion rate deterioration occurs at a relatively high frequency of several K.
Since this becomes noticeable at frequencies above Hz, by inserting a capacitor C ₁ between the emitters of transistors Q ₁₅ and Q ₁₆ , even if one of transistors Q ₁₅ or Q ₁₆ tries to cut off at frequencies above several KHz, The impedance of capacitor _C1 decreases,
Since current flows through the capacitor _C1 , it is no longer cut off, and distortion factor deterioration can be prevented. Furthermore, since the impedance of capacitor C ₁ is infinite when there is no signal, the idle current of transistors Q ₁₅ and Q ₁₆ does not increase rapidly even when capacitor C ₁ is inserted, and unnecessary heat generation can be suppressed. It has a big effect.

Next, a second embodiment of the power amplifier according to the present invention shown in FIG. 3 will be described.

The power amplifier of this second embodiment uses constant current diodes D ₂₁ and D ₂₂ as constant current means, and a Zener diode as constant voltage means.
D ₂₃ and D ₂₄ are used. As a constant voltage means,
Resistors may be used in place of the Zener diodes _D23 and _D24 , or both Zener diodes and resistors may be used.

FIG. 4 shows a third embodiment of the power amplifier according to this invention, in which a transistor is used as a constant current means.
Q ₃₇ and Q ₃₈ are used.

Resistors R ₃₁ and R ₃₂ are connected to the emitters of transistors Q ₃₇ and Q ₃₈ , and transistors Q ₃₇ and Q ₃₈
Diodes D ₃₁ and D ₃₂ are connected to the base of
Furthermore, resistors R ₃₃ and R ₃₄ are connected to the power supply. Therefore, transistor Q ₃₇ , diode D ₃₁ , resistor
R ₃₁ , R ₃₃ and transistor Q ₃₈ , diode
Since D ₃₂ and resistors R ₃₂ and R ₃₄ constitute a current mirror circuit, transistors Q ₃₇ and
The collector current of Q ₃₈ is the resistor R ₃₁ and R ₃₃ and the resistor
The amount flows according to the ratio of R ₃₂ and R ₃₄ . On the other hand, since a constant current always flows through the base currents of the transistors Q ₃₇ and Q ₃₈ due to the constant current diode D ₃₅ , their collector currents are also made constant, and the power of the second embodiment described in FIG. amplifier diode
The same effect as D ₂₁ and D ₂₂ can be obtained.

FIG. 5 shows a fourth embodiment of the power amplifier according to the present invention, and is an embodiment in the case of three-stage Darlington connection.

This power amplifier consists of transistors in the front two stages of Darlington connection, namely transistors Q ₄₁ ,
The collectors of Q ₄₂ and transistors Q ₄₄ and Q ₄₅ are connected to the emitters of transistors Q ₄₇ and Q ₄₈ , respectively.

Transistor Q ₄₁ , Q ₄₄ only Transistor Q ₄₇ ,
Although it is effective to connect the emitter of Q ₄₈ , an even higher effect can be obtained by connecting transistors Q ₄₂ and Q ₄₅ in the same way.

Figure 6 shows a fifth embodiment of the power amplifier according to the present invention, which has two sets of high and low power supplies and two sets of power amplification circuits corresponding to each set, and automatically controls them depending on the signal level. This example is implemented in a power amplifier having a signal switching means 1 which is operated by switching the signal. By implementing this on the high voltage side as shown in Fig. 6, if the low voltage side final stage transistors Q ₅₄ and Q ₅₈ are operating,
Since the ripple component of the high-voltage side power supply V _BH is small, the ripple suppression improvement effect can be further improved.

"Effect of the invention" According to the power amplifier according to the invention, the power amplifier according to the invention is constituted by first and second NPN transistors connected in a Darlington connection and first and second PNP transistors connected in a Darlington connection. In the power amplifier of the complementary SEPP circuit, the emitters of the second NPN transistor and the second PNP transistor are connected to the output point via a resistor, respectively, and the third NPN transistor is connected to the output point through a resistor.
a transistor and a third PNP transistor; the third NPN transistor and the third PNP transistor;
The emitters of the PNP transistors are connected to the collectors of the first NPN transistor and the first PNP transistor, respectively, and the third NPN transistor and the third PNP
A constant current means is provided between the collector and base of each of the transistors, and the bases of the third NPN transistor and the third PNP transistor are connected to the emitters of the second NPN transistor and the second PNP transistor, respectively. The collectors of the third NPN transistor and the third PNP transistor are connected through a constant voltage means, and the collectors of the final stage transistors of the SEPP circuit configured by Darlington connections of the same polarity and the power supplies of the respective polarities are connected to the collectors of the third NPN transistor and the third PNP transistor, respectively. By connecting and configuring them, it is possible to significantly reduce the flow of the ripple component of the power supply into the base of the final stage transistor, which has the effect of significantly reducing the flow of the ripple component of the power supply into the load at the time of small output. Furthermore,
The front stage transistors except the final stage transistor are
Since the voltage between the collector and emitter can be maintained at a constant voltage as low as necessary for operation, heat generation is suppressed and bias stability is improved. In addition, it has excellent features such as being easy to implement since no large heat loss occurs.

In addition, by inserting a capacitor between both emitters of the positive and negative side common base transistors, the base common transistor
Since cut-off can be prevented as described above, it is possible to prevent deterioration of distortion rate due to connection of a common base transistor, and this has excellent features such as not increasing heat loss of the common base transistor.

[Brief explanation of the drawing]

1 to 6 show embodiments of the power amplifier according to the present invention, FIG. 1 is a circuit diagram showing the first embodiment, and FIG. 2 is a circuit diagram of the power amplifier shown in FIG. 1. Explanatory diagrams of operations on the positive polarity side, Figures 3 to 6
The figures are circuit diagrams showing second, third, fourth, and fifth embodiments, respectively. 7 to 11 show conventional power amplifiers, FIG. 7 is a circuit diagram showing the first conventional example, and FIG. 8 is an explanation of the operation of the conventional example of FIG. 7 on the positive polarity side. 9 are equivalent circuit diagrams of the conventional example shown in FIG. 7 as viewed from the power supply side, and FIGS. 10 and 11 are circuit diagrams showing second and third conventional power amplifiers. Q ₁₁ , Q ₁₂ , Q ₁₃ , Q ₁₄ , Q ₁₅ ． Q ₁₆ ... Transistor, R _E1 , R _E2 ... Resistor, CC ₁ , CC ₂ ... Constant current means, CV ₁ , CV ₂ ... Constant voltage means, C ₁ ... Capacitor, R _L ... Load.

Claims (1)

[Claims for utility model registration] (1) Darlington connected first and second
In a power amplifier of a complementary SEPP circuit constituted by an NPN transistor and first and second PNP transistors connected in Darlington, the second NPN transistor and the second PNP transistor are connected to each other.
The emitters of the PNP transistors are each connected to the output point via a resistor, and a third NPN transistor and a third PNP transistor are provided, and the third NPN transistor and the third
The emitters of the PNP transistors are connected to the collectors of the first NPN transistor and the first PNP transistor, respectively, and the third NPN transistor and the third
A constant current means is provided between the collector and the base of each of the PNP transistors, and the third NPN transistor and the third
The bases of the PNP transistors are connected to the emitters of the second NPN transistor and the second PNP transistor, respectively, via constant voltage means, and the bases of the third NPN transistor and the third
The collectors of the PNP transistors are configured with Darlington connections of the same polarity.
A power amplifier characterized by connecting the collector of the final stage transistor of the SEPP circuit and the power supply of each polarity. (2) A request for registration of a utility model characterized in that both emitters of the third NPN transistor and the third PNP transistor connected to an SEPP circuit configured by a Darlington connection are connected via a capacitor. The power amplifier according to item 1.