Increasing Output Swing Power Operational Amplifiers typical circ

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Increasing Output Swing Power Operational Amplifiers typical circ

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APEX AN48 AN48
Increasing Output Swing Power Operational Amplifiers
typical circuit topologies used output stages power operational amplifiers, output voltage swing limited much less than applied power supply voltage. goal this application note illustrate several practical techniques drive amplifier output closer rail voltages, which enables power output increase significantly. some applications, output power increased much 50%. Certain power operational amplifiers allow user apply separate higher voltage supply input stage amplifier while output stage lower voltage. This arrangement achieves close-to-rail voltage swing since output devices, usually Enhancement Mode MOSFETs, driven close saturation higher voltage available drive gates. Another method improve output voltage swing modify amplifier's output stage adding some external output components. This application note explores these approaches through discussion typical examples with hope that users will create develop circuits meet their specific requirements based techniques shown here.
GENERAtING Boost VoltAGE
Many power operational amplifiers provide separate power supply pins input stage output stage. This allows user apply higher power supply voltage input circuitry than supply voltage applied output stage. voltage difference usually between 15V. This enables output devices driven close their saturation. this increased voltage swing needed, then input output power supply pins connected together providing equal supply voltage input output stages. example, Apex Precision PowerMP39 power operational amplifier1, depicted Figure separate pins input stage supply voltage, output stage supply voltage, that designer them together power them separately, outlined below.
Input Stages
Output Stages MP39 POWER OPERATIONAL AMPLIFIER
Figure separate Because power inputs input stage (±VB) separated from output stage (±VS) MP39, designer option applying higher potential each terminal, thereby allowing output voltage swing closer rail potentials (±VS). MOSFETs deliver maximum output current load. most applications, connected together. Since enhancement mode device, gate voltage must least higher than source voltage achieve lowest source drain voltage. case Q12, gate voltage must lower. This means maximum output voltage, full output current, will least lower than applying higher voltage gate voltage driven higher potential than forcing higher source voltage. indicated MP39 data sheet, absolute maximum boost voltage, specified higher than maximum boost supply current 22mA. AN48U
Copyright Cirrus Logic, Inc. 2009 (All Rights Reserved)
http://www.cirrus.com
MAY2009 APEX AN48UREV2
AN48
applications requiring output current less than 500mA, zener diode placed between adequate. this configuration power supply voltage would connected pin. This will automatically force input lower than this approach followed, output current would flow through zener diode which would have dissipate resulting power. This simple solution, very practical because MP39 deliver output currents 10A.
EmPloyING IsolAtEd dc-to-dc coNVERtERs
Isolated DC-to-DC converters used supply boost voltage. There many commercially available converters that suitable providing boost voltage. pair CALEX modules have been selected (available either surface mount through-hole configurations). input version offers input voltage range from isolated, regulated output 12V. modules required, -VB. testing performed with 40V. module powered from +40V supply (+VS) other module powered from -40V supply (-VS). Since outputs isolated, other input power supply arrangements could used, long supply voltages within module's operating input range. configuration depicted Figure voltage potential between terminals 52V.
POWER SUPPLY
DC-TO-DC CONVERTER
MP39
DC-TO-DC CONVERTER
POWER SUPPLY
Figure obtaining Boost pair DC-to-DC converters connected shown Figure powered power supplies that also provide voltages. output DC-to-DC converters connected between power operational amplifier terminals providing required boost voltage. maintain balanced load across power supplies, output converter connected series with supply common, second converter between -VS. outputs isolated convenient power sources applied long total voltage applied does exceed specified input range.
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dc-to-dc coNVERtERs FRom oFF-thE-shElF comPoNENts
cost DC-to-DC converter assembled using off-the-shelf components commonly available through common catalog distributors. schematic circuit diagram shown Figure This converter designed specific purpose providing VBOOST Apex power operational amplifier featuring separate power pins input power stages. Note that transformers Inductor Coiltronics part numbers available from Cooper Bussman. Because outputs totally independent, single converter will supply both plus minus VBOOST. input voltage range specified from 100V allowing additional flexibility. converter's switching frequency approximately 20kHz exhibits very radiated conducted noise components, assuming circuit layout ground scheme given careful attention. Transformer common mode filter that rejects common mode noise switching that occurs Timer preventing from feeding back source voltage. snubber circuit, consisting Capacitor Resistor R11, counteracts ringing that would other wise occur Transformers
4.7µF 113K 1N4148 1N4148 249K 0.01µF 330pF TLC555 TIMER 1N4739A IRF620PBF (HEATSINK REQUIRED) 1000pF MUR120
47µF
4.7µF 4.7µF
1N5350B
+VB1
-VB1
0.1µF
MUR120
47µF
+VB2 1N5350B -VB2
4.7µF 4.7µF
Figure low-cost dc-to-dc converter This converter employed supply boost voltages (+VB -VB) necessary increase output swing.
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table Parts list converter circuit shown Figure
REFERENcE dEsIGNAtIoN C11, C12,C6,C7 R1,R3,R8,R9,R10 dEscRIPtIoN CAPACITOR, CERAMIC, 4.7µF, 25V, CAPACITOR, CERAMIC, 330pF, 50V, MURATA CAPACITOR, TANTALUM, 47µF, 25V, AVX, TAP476K025CCS CAPACITOR, CERAMIC, 0.01µF, 100V, MURATA CAPACITOR, CERAMIC, 1.0µF, 50V, CAPACITOR, POLY FILM, 4.7µF, 250V, PANASONIC CAPACITOR, CERAMIC, 1000pF, 200V, KEMET CAPACITOR, CERAMIC, 0.1µF, 200V, KEMET 1N4148, DIODE, EQUIVALENT 1N5350, ZENER DIODE, SEMI 1N4739, 9.1V ZENER DIODE, SEMI MUR120, ULTRA FAST RECOVERY, RECTIFIER, SEMI 1N4739, 9.1V ZENER DIODE, SEMI CHOKE, COILTRONICS, DRQ-73-101-R IRF620PBF, MOSFET, 200V, 5.2A, VISHAY, RESISTOR, FILM, 1.0, RESISTOR, FILM, 249K, 0.25W RESISTOR, FILM, 301, 0.25W RESISTOR, FILM, 113K, 0.25W RESISTOR, FILM, 15K, CHOKE, COILTRONICS, DRQ-127-101-R TLC555 TIMER, I.C., 513-1314-1-ND 296-1857-5-ND 1N5350BRLGOSCT-ND 1N4739ADICT-ND MUR120RLGOSCT-ND 1N4739ADICT-ND 513-1251-1-ND IRF620PBF-ND PARt NUmBER (dIGI-KEy) 445-2886-ND 490-3724-ND 478-4181-ND 490-3813-ND 445-2884-ND EF2475-ND 399-4323-ND 399-4387-ND
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sAmPlE tEst cIRcUIt 200W PoWER oPERAtIoNAl AmPlIFIER dRIVING REsIstIVE loAd
this example MP39 power operational amplifier configured inverting amplifier with gain driving resistive load depicted Figure value compensation capacitor 220pf, complies with recommendation specified MP39 data sheet gain more, less than power supply voltage, ±40V. boost voltages, -VB, 12V. power delivered load 200W PEAK with boost voltage applied, 144W PEAK with boost voltage. This significant increase realized power important high-efficiency applications. MP39 datasheet limit output voltage swing ±8.8V. This means clipping could occur 31.2V without boost voltage.
12-14
-ILIM
+ILIM 220pF
MP39
18-20
15-17
0.05
COMMON
Figure test circuit This circuit with inverting gain 40V, used obtain plots Figures Figures waveforms shown below Figure depict output without boost circuits terminals tied terminals. Note that clipping output waveform occurs +34V -34V respectively, because output driven higher. However, with addition boost circuits with potentials 12V, output able swing supply rails, depicted Figure
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VOLTS
INPUT,
VOLTS
OUTPUT,
Figure Without Boost circuit With boost terminals tied terminals output voltages clipped ±34V. Consequently, output swing unable reach supply rails +40V 40V, respectively. this configuration amplifier only deliver 144W PEAK.
VOLTS
INPUT,
VOLTS
OUTPUT,
Figure With Boost circuit With addition boost circuits, output able swing rail potentials -VS, respectively. amplifier this configuration able deliver 200W PEAK approximately more power than when amplifier operates without boost circuits. AN48U
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modIFIcAtIoN oUtPUt stAGE ImPRoVE oUtPUt VoltAGE sWING
Shown Figure circuit based Apex PA96 power operational amplifier2 operating with power supply voltages ±40V. Resistors selected that maximum quiescent current creates voltage drop approximately 0.5V 0.6V across base-to-emitter junctions This keeps output transistors from turning conducting collector current when output voltage near zero. Resistors selected provide sufficient base current output voltage approaches rail allowing pull output closer supplies. note caution: although power operational amplifier current limit protected, output transistors have overcurrent protection will damaged their (Safe Operating Area) requirements exceeded.
3.5VP-P CCOMP100pF 22pF MJE15031 RLOAD 40VDC
MJE15031
PA96
40VDC
Figure composite Power Amplifier PA96 operational amplifier with additional output transistors, resistors This modification creates composite operational amplifier with extended output voltage swing.
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Figure below depicts circuit Figure reacts when resistors used showing circuit's output clipping. Figure illustrates same circuit behaves when three resistors have been added. Clipping longer occurs.
VOLTS
INPUT,
VOLTS
OUTPUT,
Figure composite Amplifier without modifications
VOLTS
INPUT,
VOLTS
OUTPUT,
Figure composite Amplifier with modifications AN48U
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mAINtAINING lINEAR PERFoRmANcE WIth oUtPUt VoltAGEs APPRoAchING NEGAtIVE RAIl
circuit shown Figure accepts input voltage levels, including zero, deliver output voltages from zero with single ended power supply. Apex PA75 dual power operational amplifier3 used because input voltage range includes negative supply voltage. However, PA75 output voltage does swing very near rails. PA75 consists operational amplifiers. pre-configured unity gain buffer, while other have gain programmed employed this circuit. This example enables output voltage drive grounded load zero volts. Diode must leakage zener diode circuit function. Since output voltage PA75 never reaches zero volts, leakage current flows through load resistor causing non-zero voltage load. feedback loop cannot correct this once output reaches it's minimum voltage. Notice plot Figure output response quite linear with respect input from zero 10V.
1N4148
PA75
MJE15031 RLOAD 4.99K
1N4622
Figure single Ended operation delivering output from Zero
OUTPUT VOLTAGE
INPUT VOLTAGE
Figure output Response circuit Figure
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coNclUsIoNs
Several methods extending output voltage swing power operational amplifiers have been described. circuits included this application note have been developed tested. schematics include components such by-pass capacitors, resistors diodes needed complete design. Circuit layout been addressed critical circuit configurations using Apex Precision Powerproducts. test results shown based typical performance specific device used each application. differences performance shown, with without modifications, will more dramatic when compared minimum voltage swing data sheet limits. additional information concerning power operational amplifiers with regard stability, thermal management, device protection, other topics, please refer relevant Application Note4.
References MP39 Power Operational Amplifier Data Sheet, Cirrus Logic, Apex Precision Power. PA96 Power Operational Amplifier Data Sheet, Cirrus Logic, Apex Precision Power. PA75 Dual Power Amplifiers Data Sheet, Cirrus Logic, Apex Precision Power. Techniques Stabilizing Power Operational Amplifiers, Application Note Cirrus Logic, Apex Precision Power
coNtActING cIRRUs loGIc sUPPoRt
Apex Precision Power product questions inquiries, call toll free 800-546-2739 North America. inquiries email, please contact tucson.support@cirrus.com. International customers also request support contacting their local Cirrus Logic Sales Representative. find nearest you, www.cirrus.com
IMPORTANT NOTICE Cirrus Logic, Inc. subsidiaries ("Cirrus") believe that information contained this document accurate reliable. However, information subject change without notice provided without warranty kind (express implied). Customers advised obtain latest version relevant information verify, before placing orders, that information being relied current complete. products sold subject terms conditions sale supplied time order acknowledgment, including those pertaining warranty, indemnification, limitation liability. responsibility assumed Cirrus this information, including this information basis manufacture sale items, infringement patents other rights third parties. This document property Cirrus furnishing this information, Cirrus grants license, express implied under patents, mask work rights, copyrights, trademarks, trade secrets other intellectual property rights. Cirrus owns copyrights associated with information contained herein gives consent copies made information only within your organization with respect Cirrus integrated circuits other products Cirrus. This consent does extend other copying such copying general distribution, advertising promotional purposes, creating work resale. CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS INVOLVE POTENTIAL RISKS DEATH, PERSONAL INJURY, SEVERE PROPERTY ENVIRONMENTAL DAMAGE ("CRITICAL APPLICATIONS"). CIRRUS PRODUCTS DESIGNED, AUTHORIZED WARRANTED SUITABLE PRODUCTS SURGICALLY IMPLANTED INTO BODY, AUTOMOTIVE SAFETY SECURITY DEVICES, LIFE SUPPORT PRODUCTS OTHER CRITICAL APPLICATIONS. INCLUSION CIRRUS PRODUCTS SUCH APPLICATIONS UNDERSTOOD FULLY CUSTOMER'S RISK CIRRUS DISCLAIMS MAKES WARRANTY, EXPRESS, STATUTORY IMPLIED, INCLUDING IMPLIED WARRANTIES MERCHANTABILITY FITNESS PARTICULAR PURPOSE, WITH REGARD CIRRUS PRODUCT THAT USED SUCH MANNER. CUSTOMER CUSTOMER'S CUSTOMER USES PERMITS CIRRUS PRODUCTS CRITICAL APPLICATIONS, CUSTOMER AGREES, SUCH USE, FULLY INDEMNIFY CIRRUS, OFFICERS, DIRECTORS, EMPLOYEES, DISTRIBUTORS OTHER AGENTS FROM LIABILITY, INCLUDING ATTORNEYS' FEES COSTS, THAT RESULT FROM ARISE CONNECTION WITH THESE USES. Cirrus Logic, Cirrus, Cirrus Logic logo designs, Apex Precision Power, Apex Apex Precision Power logo designs trademarks Cirrus Logic, Inc. other brand product names this document trademarks service marks their respective owners.
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Increasing Output Swing Power Operational Amplifiers typical circ

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