Manual

Preliminary

AIP900-0012-B0-001 Rev. A (01/2012)

1.2 Theory of operation

Please refer to the power circuit block diagram on the following page for a theory of operation of

theACSHPswitchedmodeAC-DCconversionsystem.The187-312VAC,50/60Hzinputisfed

throughacircuitbreakerintoafullwaverectier,whichinturnprovidesa120Hz(340Vpeak)

pulsetraintoaninputltercircuit.Theinputlterprovidesanominal290VDC"rawsupply",with

approximately30VP-P120Hzripple,tothetransistorswitchingcircuit.Thetransistorswitching

circuit“chops”therawsupplyintoa525VP-P,100kHz(nominal)rectangularwaveformwith

a nominal 66% duty cycle. This high frequency switching waveform is then fed into a ferrite

powertransformer,inwhichthewaveformis“steppeddown”andisolated.Arectiercircuitthen

converts the power transformer output to a DC pulse train with a nominal 160 V peak. Next, a

two-stageoutputlteraveragesandsmoothesthispulsetraindownward,providingthenominal

125VDCoutputwithlownoise.Avoltageerrorampliercircuitsensestheoutputvoltageand

compares it with the voltage reference to provide a voltage error signal. Similarly, a current error

amplier,usingashuntresistorandscalingamplier,sensestheoutputcurrentandcompares

it with the desired maximum output current, in order to provide a current error signal. These

signals are then fed into the pulse width modulator (PWM) via ORing circuitry so that either

voltageorcurrentregulationisachieved.ThePWMcontrolsthe"ON"timeoftheswitching

transistors,varyingtheoutputascommandedbytheerrorampliers.ThePWMalsosensesthe

switching transistor current on an instantaneous basis to provide cycle-by-cycle protection of the

switchingtransistors.Anauxiliarysupply,poweredviaasmall50/60Hztransformer,andaDC/

DC converter power the control circuit and front panel circuitry. The PWM receives the ON/OFF

command and clock signal from the front panel circuit and control circuitry.

1.0 Introduction