CN1074610C - Power-like amplifier output stage by adopting parallel voltage-stabilizing, quick thermal tracking biased compensation circuit - Google Patents

Power-like amplifier output stage by adopting parallel voltage-stabilizing, quick thermal tracking biased compensation circuit Download PDF

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CN1074610C
CN1074610C CN98111263A CN98111263A CN1074610C CN 1074610 C CN1074610 C CN 1074610C CN 98111263 A CN98111263 A CN 98111263A CN 98111263 A CN98111263 A CN 98111263A CN 1074610 C CN1074610 C CN 1074610C
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transistor
push
output stage
output
resistance
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CN1206957A (en
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王斌
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Abstract

The present invention relates to an output stage of a power amplifier of an A-AB type. The output stage adopts a biasing compensating circuit with parallel-connection voltage regulation and quick thermal tracking. The output stage is formed by combining a pre-push stage and a complementary feedback pair with low distortion, wherein the pre-push stage is connected into an emitter follower of an A type; the complementary feedback is formed by connecting PNP/NPN transistors. The pre-push stage adopts two parallel voltage stabilizing circuits with two efficiency output ends to provide a positive emitter power supply and a negative emitter power supply, and a pre-push transistor is tightly and thermally coupled with a push transistor of an output transistor pair. The good biasing stability can be arranged in a short time or a long time, and thus, the distortion is decreased; the saturation voltage drop is reduced; the efficiency is enhanced.

Description

Adopt parallel voltage-stabilizing heat to follow the tracks of the push-pull current amplifier of biasing circuit
What the present invention relates to is a kind of push-pull current amplifier that adopts parallel voltage-stabilizing heat to follow the tracks of biasing circuit, is mainly used in the following linear power amplifier of 500K HZ, as audio frequency amplifier.
Usually the power output stage design is adopted category-B or AB class push-pull circuit and is connected into voltage-tracing device mode, because efficient is higher so comparatively speaking.Sort circuit can select for use ambipolar pipe, field effect transistor and IGBT pipe to make efferent duct.How just can provide bias voltage to set up the intermodulation distortion of best quiescent current, reduction output stage? how just to make at supply voltage and ambient temperature changes or under the situation that semiconductor junction changes, it is stable that this bias voltage also must keep.
Though this problem has a lot of solutions, also there are following some shortcomings in what:
1), the circuit complexity, cost is higher;
2), regulative mode is very sensitive, unfavorable batch process;
3), because hot delay of feedback causes short time overcompensation (overcompensation causes quiescent current temporarily to descend, and follows intermodulation distortion to rise);
4), saturation voltage drop is bigger, efficient reduces;
5), the delay of local feedback loop causes the coefficient of stability to descend.
The objective of the invention is at above-mentioned deficiency, propose that a kind of to obtain current gain higher, the power output stage that distortion is very low, and the saturation voltage drop of this output stage is little, be applicable to the wide power voltage range, the power amplifier of big electric current, broadband operation, for example audio frequency amplifier, and can drive the load of complicated impedance operator, as loud speaker.
Technical solution of the present invention:
Existing the feedback push-pull circuit is constituted, wherein transistor Q by pre-complementation that is connected into by the PNP/NPN transistor that promotes a level and a low distortion that is connected into the category-A emitter follower 1Be that the pre-level that promotes is class-a amplifier, transistor Q 2Be to promote level, transistor Q 3Be output stage, transistor Q 2, Q 3Be class ab ammplifier, adopt two shunt regulating circuits that emitter-base bandgap grading positive supply B is provided by the bootstrapping of power amplifier output with promoting level in advance 2, negative supply B 1, and the pre-pipe that promotes is done thermal coupling closely with the promotion pipe of output transistor centering.
Promote pipe and promote pipe to make the 3rd shunt regulating circuit of thermal coupling and provide additional control by same and pre-to output stage biased.
Signal enters the middle power tube Q that is connected into emitter follower 1, Q 1Emitter-base bandgap grading be resistance R by a less resistance 1Series connection is than the resistance R of big resistance again 2And resistance R 3Receive positive supply B 2, transistor Q 1With transistor Q 2Base stage pass through resistance R 1, resistance R 5Serial connection.They are fastened on the same radiator, and closely and fast heat tracking is arranged between the two.
Be connected on power amplifier output and resistance R after voltage stabilizing circuit REG1 and capacitor C 1 are in parallel 2/ R 3Tie point between.
Advantage of the present invention:
Common circuit adopts two to three grades of complementary emitter follower designs, and obtains the heat feedback from the big radiator of power tube, causes temporary transient overcompensation owing to the heat feedback has time-delay, thereby causes intermodulation distortion.The present invention can guarantee that quiescent current will never drop to the level that causes intermodulation distortion, and transient distortion and of short duration intermodulation distortion also are avoided.Concrete advantage of the present invention can also be described below:
Even if 1 low load impedance (less than 4 ohm), highest audio scope (20KHZ) is no matter guarantee extremely low distortion and the signal level height too.Usually, intermodulation distortion is a subject matter during low level, and transistor current gain and other nonlinearities in parameters become subject matter during the big electric current of high level.This advantage will increase 10dB at least in conventional design total negative feedback could obtain.
2, this design is easy to realize, the circuit board actual measurement index and the simulation result that adopt the common transistor in market to constitute are very approaching.
3, this design is easy to expanded application, is applicable to bigger power amplifier.
Accompanying drawing 1 is the positive half cycle electrical schematic diagram of complementary push-pull output stage of the present invention.
Accompanying drawing 2 is embodiments of the invention figure
Accompanying drawing 3-1,3-2 are that of the present invention another implemented illustration, and it is to adopt mounted on surface module (SMD) to make " core promotion circuit " to apply to bigger power amplifier.
Accompanying drawing 4 is the enforcement illustrations that are added with the 3rd shunt regulator 3SR
Accompanying drawing 5 is the enforcement illustrations (IQ=52.67mA) that are added with the 3rd shunt regulator 3SR display power supply efficient under ± 50V situation.
Accompanying drawing 6 is the enforcement illustrations (IQ=37.4mA) that are added with the 3rd shunt regulator 3SR display power supply efficient under ± 25V situation.
Accompanying drawing 7 is electrical schematic diagrams of integrated package TL431
Accompanying drawing 8 is basic SMD schematic diagrams that are used for the power amplifier output stage.
Resistance value unit in the accompanying drawing is ohm.B 1Be power supply.
Further describe technical solution of the present invention below in conjunction with accompanying drawing:
A PNP transistor is connected into the emitter follower mode, and its load is by the accurate shunt regulating circuit bootstrapping of a Low ESR; And signal mixing NPN transistor thereafter driven the power output pipe in the common emitter mode, it is right to form a feedback.
A complete complementary push-pull A-AB class power output stage is constituted in brand-new mode by 3 pairs of complementary PNP/NPN transistors.Fig. 1 is its first half (the positive half cycle and the negative half period circuit of complementary push-pull output stage are the mirror image symmetry, therefore only analyze its positive half cycle circuit here):
Signal enters the middle power tube Q that is connected into emitter follower 1(PNP promotes level in advance), middle power tube Q 1Emitter-base bandgap grading by a less resistance R 1Series connection is than the R of big resistance value again 2And R 3Receive positive supply B 2, do not adopt common single emitter resistance or constant-current source here.The shunt regulating circuit PEG1 of low internal resistance makes the resistance R of flowing through 2Electric current keep the constant electrical power pipe Q that makes simultaneously 1Emitter current and transistor Q 2Base current keep constant.Transistor Q 2The emitter voltage signal in fact with electrical power pipe Q 1Input voltage signal identical (penetrate with work).Transistor Q 1And Q 2Be fastened on the same radiator in distinctive mode (leaning against privately), closely and fast heat tracking is arranged between the two.
Output high power valve Q 3The main transistor Q of quiescent current 2Emitter voltage decision.1 degree centigrade of the every rising of temperature of transistor, its Vbe value decline 2-2.5mV.If transistor Q 2The input biasing of base stage keeps wall fixed, and high power valve Q then flows through 3Electric current will rise always, up to resistance R 7On pressure drop and till the variation of Vbe value offsets.
But, because transistor Q 1And Q 2Thermo-contact is closely arranged, transistor Q 2Heating will be very soon cause transistor Q 1The be junction temperature rise thereupon, thereby reduce resistance R 5 and transistor Q 2The current potential of base stage.So, the resistance R of flowing through 7Electric current just can keep stable.
RV 1Be used for thereby quiescent current is finely tuned the variation that adapts to Vbe.
Amplifier moves under different working methods and loading condition, transistor Q 2Temperature will be along with transistor Q 2Dissipation power (VbeXIc) rise and rise.Even power supply B 2With transistor Q 2Temperature change within a large range, above-mentioned design still can keep bias stabilization.
Complementary feedback is to transistor Q 2/ Q 3Itself be a kind of connection of collector electrode output, compare that this connection has lower distortion and saturation voltage drop with common Darlington connection mode.
Voltage stabilizing circuit REGI and capacitor C 1Be connected on power take-off and resistance R after the parallel connection 2, R 3Tie point between, the bootstrapping effect of Chan Shenging can guarantee transistor Q like this 2Base stage obtain enough forwards be pushed to saturated, even input signal is subjected to the restriction that positive supply Vc aligns voltage swing (general Vc aligns the restriction of voltage swing), (generally being that VC deducts 1-2V).
Fig. 2 is a typical application circuit.250mw-50W in whole tone frequency scope, under positive and negative 23V supply voltage, 4 ohm of situations of load, the output stage total harmonic distortion is no more than 0.03%, at output 25W, 8 ohm of loads, under the frequency 20KHz, THD=0.01%.
Fig. 8 is the schematic diagram of SMD
Transistor Q 11, Q 12, Q 15And Q 16Be the small-sized SMD paster power tube of SOT-223 packing forms, these several power tubes will be welded direct on the dish of PCB by close installation together, and pad also plays heat radiation, and this connection will make transistor Q 12And Q 16The collector electrode thin slice tightly welded together, follow the tracks of transistor Q thereby have fabulous Rapid Thermal 15And Q 11The current collection collection utmost point also be so, shunt regulator (also being SMD surface mount elements packing forms) and resistance R 0, R 1, R 2, R 3, R 8, R 9And R 10And the biasing resistor (not shown) of shunt regulator all will be installed on this little SMD module, by being adjusted in transistor Q 11And Q 16Between a variable resistance (not shown) can adjust quiescent current.When this little SMD module is adjusted to the output stage of a certain resolution element composition of coupling (by transistor Q 13, Q 14, Q 17And Q 18Form) after, this little SMD can be complementary with other any one output stages and need not regulate in addition, and this is because its quiescent current is fully by transistor Q 11And Q 16Collector current control, and be not subjected to transistor Q 13, Q 14, Q 17And Q 18The influence that parameter (Vbe, hfe etc.) changes.
The operational process of SMD mode: (referring to Fig. 8)
Transistor Q 12Be a category-A emitter follower, and the resistance R of putting by low-resistance 1And R 2With signal mixing transistor Q 11, as the transistor Q of common emitter 11Promote transistor Q in the cobasis mode 13Emitter, transistor Q 11And Q 13This working method also can be called the cascode mode, transistor Q 13With signal mixing transistor Q 14Base stage, transistor Q 14Mode with cascode is worked, and will feed back 100% ground and pass to transistor Q 11Emitter.
The superiority of this mode is:
A) the transistor thermal coupling approach of surface encapsulation is shorter, and hot feedback delay is also shorter, thereby quiescent current variation is also just littler;
B) low-voltage makes the dissipation power of SMD reduce;
C) can fill preset to the static electricity of SMD with laser, be used for output stage arbitrarily.No matter the Vbe value of power output pipe how, can set up correct quiescent current equally.
D) push module of this compact can be widely used in dissimilar power amplifier output stages.
E) though low collector electrode one emitter voltage on these devices guaranteed in the high reliability and the fail safe that promote under the 250-400W output stage situation, can obtain very high current capacity (from a typical SOT-223 packaged device, as ZETEX FZT649/749 complementary pair, can obtain peak current) up to 8A.
F) in case after quiescent current was set, this module has become one in fact can extensively be used, and can the inner promotion level of changing, can directly be inserted in any one output design as shown and need not other adjustment.
About the 3rd shunt regulator 3SR
Prime power amplifier output stage must be worked under the situation that power supply alters a great deal sometimes, for example from+/-50V is to=1-25V, and the quiescent current of output stage stable as much as possible be crucial, the influence that must do not powered in other words and change, adopt the basic circuit of two shunt regulators, be close under the perfect situation at these two shunt regulators (be internal resistance less than 0.1 ohm, and under the very big situation of temperature change, have stable voltage) can work finely.In most examples, it is very important requiring quiescent current to keep highly stable under optimum value, so just being necessary to increase the 3rd shunt regulator as shown in Figure 4 (is made up of two transistor 2SD669 and 2SA970 with the stability that strengthens quiescent current, in this case, when 2SD669 and two are pre-when promoting pipe and promoting the equal thermal coupling of pipe (being installed on the same module radiator), can obtain best heat and follow the tracks of: the two couples of 2SB649 and 2SD669 are all like this.
Transistor Q1, Q2, Q3 in transistor 2SB649,2SD669 among Fig. 4 in the non-frame of broken lines, the 2SA1302 difference corresponding diagram 1.

Claims (4)

1, adopt parallel voltage-stabilizing heat to follow the tracks of the push-pull current amplifier of biasing circuit, it is fed back constituting by a pre-complementation that is connected into by the PNP/NPN transistor that promotes a level and a low distortion that is connected into the category-A emitter follower, wherein transistor Q 1Be that the pre-level that promotes is class-a amplifier, transistor Q 2Be to promote level, transistor Q 3Be output stage, transistor Q 2, Q 3Be class ab ammplifier, it is characterized in that the pre-level that promotes adopts two shunt regulating circuits by the power amplifier output that emitter-base bandgap grading positive supply B is provided 2, negative supply B 1, and the pre-pipe that promotes is done thermal coupling closely with the promotion pipe of output transistor centering.
2, employing parallel voltage-stabilizing according to claim 1 heat is followed the tracks of the push-pull current amplifier of biasing circuit, it is characterized in that it is resistance R by a less resistance that signal enters the emitter-base bandgap grading that is connected into the middle power tube of penetrating follower 1Series connection is than the R of big resistance again 2And R 3Receive positive supply B 2, transistor Q 1With transistor Q 2Base stage pass through resistance R 1, R 5Serial connection, they are fastened on the same radiator, and closely and fast hot the tracking arranged between the two, and providing the 3rd shunt regulating circuit that adds control to output stage biased is that pre-promotion pipe and promotion pipe are done thermal coupling.
3, employing parallel voltage-stabilizing according to claim 1 heat is followed the tracks of the push-pull current amplifier of biasing circuit, it is characterized in that voltage stabilizing circuit REG1 and capacitor C 1 are connected on power amplifier output and resistance R after in parallel 2/ R 3Tie point between.
4, employing parallel voltage-stabilizing according to claim 1 heat is followed the tracks of the push-pull current amplifier of biasing circuit, it is characterized in that promoting pipe and to promote pipe to make the 3rd shunt regulating circuit of thermal coupling and provide additional control to output stage biased by same and pre-.
CN98111263A 1998-04-27 1998-04-27 Power-like amplifier output stage by adopting parallel voltage-stabilizing, quick thermal tracking biased compensation circuit Expired - Fee Related CN1074610C (en)

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CN98111263A CN1074610C (en) 1998-04-27 1998-04-27 Power-like amplifier output stage by adopting parallel voltage-stabilizing, quick thermal tracking biased compensation circuit

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CN98111263A CN1074610C (en) 1998-04-27 1998-04-27 Power-like amplifier output stage by adopting parallel voltage-stabilizing, quick thermal tracking biased compensation circuit

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CN1074610C true CN1074610C (en) 2001-11-07

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102594271A (en) * 2012-02-22 2012-07-18 刘轶 Biasing circuit of power amplifier

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6727758B2 (en) * 2002-05-28 2004-04-27 Koninklijke Philips Electronics N.V. Fast cascaded class AB bipolar output stage
CN101882915B (en) * 2010-04-30 2012-10-03 苏州英诺迅科技有限公司 Push-pull type radio-frequency power amplifier with improved linearity

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0508711A1 (en) * 1991-04-11 1992-10-14 Nec Corporation Transistor direct-coupled amplifier
US5491448A (en) * 1994-07-29 1996-02-13 National Semiconductor Corporation Class AB output stage with improved frequency stability
US5606287A (en) * 1994-06-17 1997-02-25 Fujitsu Limited Operational amplifier having stable operations for a wide range of source voltage, and current detector circuit employing a small number of elements

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0508711A1 (en) * 1991-04-11 1992-10-14 Nec Corporation Transistor direct-coupled amplifier
US5606287A (en) * 1994-06-17 1997-02-25 Fujitsu Limited Operational amplifier having stable operations for a wide range of source voltage, and current detector circuit employing a small number of elements
US5491448A (en) * 1994-07-29 1996-02-13 National Semiconductor Corporation Class AB output stage with improved frequency stability

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102594271A (en) * 2012-02-22 2012-07-18 刘轶 Biasing circuit of power amplifier
CN102594271B (en) * 2012-02-22 2015-07-29 上海睿射电子科技有限公司 The biasing circuit of power amplifier

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