Agilent Technologies E3616A, E3614A, E3617A, E3615A service manual Load Considerations

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LOAD CONSIDERATIONS

This section provides information on operating your supply with various types of loads connected to its output.

PULSE LOADING

The power supply will automatically cross over from constant- voltage to constant current operation in response to an increase (over the preset limit) in the output current. Although the preset limit may be set higher than the average output current, high peak currents (as occur in pulse loading) may exceed the preset cur- rent limit and cause cross over to occur. If this cross over limiting is not desired, set the preset limit for the peak requirement and not the average.

REVERSE CURRENT LOADING

An active load connected to the power supply may actually deliver a reverse current to the power supply during a portion of its operating cycle. An external source can not be allowed to pump current into the supply without loss of regulation and possi- ble damage to the output capacitor of the power supply. To avoid these effects, it is necessary to preload the supply with a dummy load resistor so that the power supply delivers current through the entire operating cycle of the load devices.

Figure 16. Reverse Current Loading Solution

OUTPUT CAPACITANCE

An internal capacitor, connected across the output terminals of the power supply, helps to supply high-current pulses of short duration during constant voltage operation. Any capacitance added externally will improve the pulse current capability, but will decrease the safety provided by the current limiting circuit. A high-current pulse may damage load components before the average output current is large enough to cause the current limit- ing circuit to operate.

The effect of the output capacitor during constant current opera- tion are as follows:

a.The output impedance of the power supply decreases with increasing frequency.

b.The recovery time of the output voltage is longer for load resistance changes.

c.A large surge current causing a high power dissipation in the load occurs when the load resistance is reduced rapidly.

REVERSE VOLTAGE LOADING

A diode is connected across the output terminals with reverse polarity. This diode protects the output electrolytic capacitors and the series regulator transistors from the effects of a reverse volt- age applied across the output terminals. For example, in series operation of two supplies, if the AC is removed from one supply, the diode prevents damage to the unenergized supply which would otherwise result from a reverse polarity voltage.

Since series regulator transistors cannot withstand reverse volt- age, another diode is connected across the series transistor. This diode protects the series regulators in parallel or auto-parallel operation if one supply of the parallel combination is turned on before the other.

BATTERY CHARGING

The power supply's OVP circuit contains a crowbar SCR, which effectively shorts the output of the supply whenever the OVP trips. If an external voltage source such as a battery is connected across the output, and OVP inadvertently triggered, the SCR will continuously sink a large current from the source; possibly damaging the supply. To avoid this a diode must be connected in series with the output as shown in Figure 17.

Figure 17. Recommended Protection Circuit for

Battery Charging

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Contents Agilent E361xA 60W Bench Series DC Power Supplies AprilSafety Summary Operating Instructions General Information Temperature Coefficient Operating Temperature RangeMeter Programming Resolution Line FuseInput Power Requirements InstallationInstallation Data Initial InspectionOperating Instructions TURN-ON Checkout ProcedurePower Cord Operating Modes Local Operating ModeConnecting Loads Operation Beyond Rated OutputRemote Analog Voltage Programming Remote Operating ModesRemote Voltage Sensing AUTO-PARALLEL Operation MULTIPLE-SUPPLY OperationNormal Parallel Operation Normal Series Operation Gramming according to the remote-programming instructionsAUTO-SERIES Operation Total output voltage to ground must not exceed 240 VdcAUTO-TRACKING Operaton = slave output voltageLoad Considerations Service Information Operation Verification Tests MaintenanceTest Equipment Required Measurement Techniques Type Required Characteristics USE Recommended ModelPerformance Tests Line Regulation Source Effect Constant Voltage CV TestsLoad Regulation Load Effect Load Transient Response TimePARDPeak-to-Peak Measurement PARDRipple and NoisePardrms Measurement Constant Current CC Tests CV Drift StabilityAdjustment and Calibration Procedure CC Drift StabilityReference and Bias Circuit TroubleshootingOverall Troubleshooting Procedure Regulating Loop TroublesSymptom Checks and Probable Causes Overvoltage Protection Circuit TroublesStep Action Response Probable Cause Step Measure Response Probable Cause Replaceable Parts Table A-10. Replaceable Parts List Table A-10. Replaceable Parts List Contd R28,111 0698-3228 Resistor 49.9K +-1% .125W TF TC=0+-100 RESISTOR-VAR 10K +-10% ALL IC V RGLTR-FXD-POS 4.8/5.2V TO-220 PKG ALL DIODE-GEN PRP 180V 200MA DO-35 ALL Table A-11. Component Value Model Page Page Page Page Manual Supplement Constant Voltage Mode T EAlternative Voltage Programming Using Resistors Programming Voltage Common to the Minus OutputProgramming Voltage Common to the Minus Output Constant Current Mode Constant Current with Voltage ProgrammingCurrent Monitoring Remote Resistor Programming Connections Remote Resistor Programming, Constant VoltageRemote Resistor Programming, Constant Current Certification Declaration of Conformity
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