Nautel XR12 Troubleshooting Manual

Also see for XR12: Installation manual Operation and maintenance manual Preinstallation manual

Contents

XR12 Troubleshooting Manual Detailed Circuit DescriptionsIssue 3.0 2009-07-28 Page 2-19RF drive power supply PWB (62 V) (NAPS10C)See electrical schematic Figure SD-31.The RF drive power supply PWB is a boost type switching power supply which provides a regulateddc supply voltage for the transmitter's RF drive amplifiers. A nominal +48V supply is applied to thedrain of switching FET Q1 through inductor L2. The gate of FET Q1 is driven with pulses frompulse width modulation (PWM) switching power supply control U1. This device is a fixed-frequencyPWM control circuit, incorporating the functions required for the control of a switching powersupply. Internal to the device is a sawtooth oscillator which is set to a nominal frequency of 100 kHzby external components R6 and C6. The output, PWM control pulses to the gate of FET Q1, isgenerated by the comparison of this sawtooth waveform with a feedback voltage sample from thejunction of U2-Cathode and the bias voltage created by VOLTAGE CONTROL potentiometer R3. Theresultant variable pulse width output (U1-8) is applied to the gate of FET Q1. Q1 turns on and off,ringing inductor L2 with the appropriate pulses to maintain the desired set dc output voltage. Diodepair U2 rectifies the signal and inductor L3 and capacitor C9 provide filtering for the RF Drive B+output voltage. A sample of the dc output voltage level is applied through zener diode CR1 to thebase of transistor Q2 which provides an alarm signal should the RF drive power supply fail. The RFDrive B+ Fail alarm output is normally at ground potential and switches to an open circuit conditionshould a failure occur in the RF drive power supply.