Agilent Technologies E3614A Service Manual download pdf (Page 18)

A-2

series pass transistors. Whenever the output voltage is below

the sloping V1 line, the control circuit inhibits four SCRs and

the input capacitors charge to a voltage determined by N1.

Figure A-2 indicates the windings that are connected as a

result of the other voltage decisions.

Figure A-2. Output Power Plot

The series regulators (Q1 and Q4) are part of a feedback loop

which consists of the driver and the Constant Voltage/Con-

stant Current error amplifier. The series regulator feedback

loop provides "fine and fast" regulation of the output while the

preregulator feedback loop handles large, relatively slow, reg-

ulation demands.

The regulator is made to alter its conduction to maintain a

constant output voltage or current. The voltage developed

across the current sampling resistors (R58 and R59) is the

input to the constant current error amplifier. The constant volt-

age error amplifier obtains its input by sampling the output

voltage of the supply.

Any changes in output voltage or current are detected and

amplified by the constant voltage or constant current error cir-

cuit and applied to the series regulator in the correct phase

and amplitude to counteract the change in output voltage or

current.

Two error amplifiers are included in a CV/CC supply, one for

controlling output voltage, the other for controlling output cur-

rent. Since the constant voltage amplifier tends to achieve

zero output impedance and alters the output current when-

ever the load resistance changes, while the constant current

amplifier causes the output impedance to be infinite and

changes the output voltage in response to any load resis-

tance change, it is obvious that the two amplifiers can not

operate simultaneously. For any given value of load resis-

tance, the power supply must act either as a constant voltage

source or as a constant current source - it can not be both;

transfer between these two modes is accomplished at a value

of load resistance equal to the ratio of the output voltage con-

trol setting to the output current control setting.

Full protection against any overload condition is inherent in

the Constant Voltage/Constant Current design principle since

there is not any load condition that can cause an output which

lies outside the operating region. For either constant voltage

or constant current operation, the proper choice of front panel

voltage and current control settings insures optimum pro-

tection for the load device as well as full protection for the

power supply.

The reference and bias circuit provides stable reference volt-

ages which are used by the constant voltage/current error

amplifier circuits for comparison purpose. The display circuit

provides an indication of output voltage and current for con-

stant voltage or constant current operating modes.

An operator error or a component failure within the regulating

feedback loop can drive a power supply's output voltage to

many times its preset value. The overvoltage protection cir-

cuit is to protect the load against this possibility. The circuit

insures that the power supply voltage across the load will

never exceed a preset limit.

Diode CR19 is connected across the output terminals in

reverse polarity. It protects the output electrolytic capacitor

and the series regulator transistors from the effects of a

reverse voltage applied across the output terminals.

The display power circuit provides voltage which is used by A/

D converter and LED drive.

MAINTENANCE

INTRODUCTION

This section provides performance test and calibration proce-

dures and troubleshooting information. The following opera-

tion verification tests comprise a short procedure to verify that

the power supply is performing properly, without testing all

specified parameters.

If a fault is detected in the power supply while making the

performance check or during normal operation, proceed to

the troubleshooting procedures. After troubleshooting, per-

form any necessary adjustments and calibrations. Before

returning the power supply to normal operation, repeat the

performance check to ensure that the fault has been properly

corrected and that no other faults exist.

Test Equipment Required

The following Table A-1 lists the equipment required to perform

the tests and adjustments of this section. You can separately

identify the equipment for performance tests, calibration, and

troubleshooting in the USE column of the table.

Operation Verification Tests

The following tests assure that the power supply is per-

forming properly. They do not, however, check all the speci-

fied parameters tested in the complete performance test

described below. Proceed as follows:

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 176 177

Agilent Technologies E3614A Service Manual Page 18

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