Agilent Technologies AGILENT MODELS 6023A and 6028A service manual Constant-Current CC Circuit

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Constant-Current (CC) Circuit

The Constant-Current Circuit compares the output current to the user-set CC PROGRAM Voltage to produce the CC CONTROL Voltage. As with the CV Circuit, two comparison amplifier loops accomplish the comparison. OCS is the voltage across Current-Monitoring resistor A1R3, and it senses the output current for the outer loop which is the unit's output current.

To compensate for the fraction of the output current which flows through the unit's output-voltage sensing resistors and not through the load, CC Monitor Amplifier A2U1 adds a fraction of V-MON to OCS. It amplifies that sum to produce the outerloop current-sense voltage, I-MON. I-MON also connects through protective circuitry to rear-panel terminal IM for remote monitoring of the output current. In volts it is equal to 1/6 of the output current in amperes, and is 5Vdc for 10Adc full output.

Differentiation of IVS develops a current-proportional voltage which senses the innerloop current flowing into the capacitive output filter. CC Error Amplifier A2U2B sums this differentiated innerloop voltage with I-MON and subtracts the sum from the CC PROGRAM Voltage to produce the CC CONTROL Voltage. In CC mode the CC CONTROL Voltage varies from about--0.5Vdc to +1.0Vdc at the cathode of diode A2CR19. CC Clamp A2U2A limits the CC PROGRAM Voltage to about 5.6 peak volts.

Settings of the rear-panel CC Programming Switches the B3, B2 and B1 MODE switch settings allow the CC PROGRAM Voltage to come from the front-panel CURRENT Control, from an external voltage applied between terminals IP and /P, or from an external resistor between IP and /P. When using either the CURRENT Control or external resistor, current from the CC Constant-Current Source flows through the applicable resistance to develop the CC PROGRAM Voltage.

Overvoltage Protection (OVP) Circuit

The Overvoltage Protection Circuit (OVP) shuts down the unit when a monitored 1/30 fraction of the output voltage exceeds the limit voltage set by the front-panel op ADJUST Control. If the output voltage exceeds the preset limit, the OVP inhibits the PWM, triggers the Down Programmer, lights the OV LED and latches itself on until the unit is turned off. The Bias Voltage Detector resets the OVP at turn-on of the unit. option 002 allows remote reset of OVP.

Power-Limit Comparator

Two comparisons with the Ip-RAMP VOLTAGE provide POWER LIMIT and CONTROL V LIMIT, two of the four inputs for the PWM. POWER LIMIT is the output of the Power Limit Comparator A2U14A. The comparator compares the IpRAMP VOLTAGE with the power-limit reference voltage of about 1.0Vdc. The reference is adjustable with the POWER LIMIT calibration trim pot A2R25. The POWER LIMIT sets the maximum primary current in power transformer A1T1 by going low and turning off the PWM when the Ip-RAMP VOLTAGE exceeds the reference.

Primary current is proportional to output power, and POWER LIMIT turns off the PWM when the CONTROL V LIMIT would otherwise allow the unit to deliver more than about 200 watts. This occurs during transient load increases, step increases in CV Program Voltage and when the combination of the CV PROGRAM Voltage and the CC PROGRAM Voltage calls for more than 200 watts. The Power-Limit Comparator produces the power-limited portion of the unit's output characteristic curve in Figure 4-1 and is the essence of the unit's Autoranging power.

Control-Voltage Comparator

The Control-Voltage Comparator A2U16 produces the CONTROL V LIMIT input to the PWM by comparing the IpRAMP VOLTAGE to the CP control-port voltage. In CV or CC operation CP is one diode-drop more than the lower of the CV and

CCCONTROL Voltages. CONTROL V LIMIT goes low and turns off the PWM when the Ip-RAMP VOLTAGE exceeds CP. The A2R113-A2R114 voltage divider steers control of CP by its connection at the anodes of series diodes A2CR19 and

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Contents Autoranging Certification Safety Summary Printing History Safety Symbol DefinitionsTable of Contents Replaceable Parts Circuit Diagrams TroubleshootingSafety Considerations ScopeItem Description Manual RevisionsIntroduction Calibration ProcedureTest Equipment Required Operation Verification TestsTest Equipment Required Type Required Characteristics USE Recommended Model1KVA Initial SetupMON Calibration ProcedureIout VoutMeasurement Techniques Performance TestsCR7 Constant Voltage CV Tests Current-Monitoring Resistor SetupBasic Test Setup RMS Measurement Test Setup, CV Pard Test Peak-To-Peak Measurement Test Setup, CV Pard Test KHz Noise, CV Peak-to-Peak Pard 6023A 6028ALoad Transient Recovery Waveform Constant Current CC Tests CC Pard Test Setup Initial Troubleshooting Procedures TroubleshootingPIN no Signal Name Control Board Test Connector, A2J7Vdc WAVEFORM/CONDITIONS SourceElectrostatic Protection Repair and ReplacementA2 Control Board Removal Overall Troubleshooting Procedure A4 Power Mesh Board RemovalA3 Front-Panel Board Removal A1 Main Board RemovalSetup Using the TablesNode MeasurementMain Troubleshooting Setup Main Troubleshooting SetupModified Mains Cord Set For Troubleshooting Front-Panel Troubleshooting Troubleshooting No-Output FailuresA2J7-26 A2J7-25 PWM-ON PWM-OFF Defective Check Functional CircuitsBoard Symptoms Defective Circuit Check Components Troubleshooting Bias SuppliesSymptoms Defective Check Functional Circuits Board Node + Measurement SourceMeasurement Source Node +Node + N0DE Troubleshooting AC-Turn-on Circuits Power Section BlocksSetup Measurement Source Setup MeasurementRelay Enable Troubleshooting PWM & ClockPower Limit + OUT Troubleshooting DC-To-DC ConverterPWM-ON PWM-OFFTroubleshooting CC Circuit Troubleshooting CV CircuitTroubleshooting OVP Circuit Troubleshooting Down ProgrammerA4U4OUT Waveforms SET Voltage Vdc Node + Page Block Diagram Overview Autoranging PowerBlock Diagram Simplified Schematic Simplified Schematic Down Programmer DC-to-DC ConverterConstant-Voltage CV Circuit Pfet Control Signals Timing DiagramConstant-Current CC Circuit Power-Limit ComparatorOvervoltage Protection OVP Circuit Control-Voltage ComparatorPulse-Width Modulator PWM Initial-Ramp CircuitBias Voltage Detector AC-Surge Dropout DetectorDisplay Circuits Second-Delay CircuitPage Reference Designators Replaceable PartsDescription Abbreviations Ordering InformationCR1 Electrical PartsCR2 CR3XA2P2 XA2P1Mechanical Parts Control Board Assembly CR3 Page Page Page VR4 VR3VR5 DS1 CR5DS5 VR1 IC A/D Cmos 3-1/2 DGTVR2 Pfet NPN SIChassis Electrical TS1A2 Board Mechanical Parts A1TB1A3 Board Mechanical Parts A4 Board Mechanical PartsOption 240 240V Operation Option 220 220V OperationComponent Location and Circuit Diagrams Schematic Diagram Notes Pin locations for other semi-conductors are shown below Top View, Top Covers Removed Main Board A1 Component Location Control Board A2 Component Location Front-Panel Board A3 Component Location Power Mesh Board A4 Component Location Page Page General Information SpecificationsOption 002 Hardware Input Compliance Voltage ± Current Programming Enable Table A-1. Specifications, Option Remote ProgrammingOutput Impedance 10.2 k ohm ± 5% Temperature Coefficient Status IndicatorsPower-on Preset Remote Trip and Remote Reset TimingMaximum Output Voltage logic high + On State logic lowBias Supplies DC Output Ratings 25C ± Table A-1. Specifications, Option Pulse TimingShort Circuit Output Current Pard TypicalConnector Assembly Procedure InstallationOperation Figure A-1. Mating Connector AssemblyLocal/Remote Programming Resistance Voltage or Current Figure A-4. Calculating Value of Series Dropping Resistor Remote Resistance ProgrammingFigure A-5. Remote Resistance Programming Remote Monitoring Remote Control Status IndicatorsOvervoltage Remote ResetFigure A-8. Remote Control Power-On PresetMultiple Supply System Shutdown AC Dropout Buffer CircuitBias Supplies MaintenanceTroubleshooting Current Programming Troubleshooting Resistance and Voltage ProgrammingFigure A-11. Troubleshooting Current Programming of CV Mode Figure A-13. Troubleshooting Status Indicators Page REF. Desig Model no Description Table A-3. Replacement Parts100 101 VR9OLD Symbol NEW Symbol Indicator and Qualifier SymbolsLogic Symbols and Definitions 102 DefinitionsSchematic Diagram Notes 103 Schematic NotesFigure A-15. Option 002 Board, Component Location 104 Schematic NotesFigure A-16. Option 002 Board, Schematic Diagram 105 Page Model 6028A Model 6023A107 108 From