Nautel Vector-LP VR125 Technical Instruction Manual

Contents

Vector-LP Radio Beacon Transmitter Technical Instruction Manual Page 6-5Section 6 Theory of Operation Issue 1.1The ac input is applied through 10 A circuitbreaker U5 and line filter U6. The ac voltagefor the RF power stage (RF power modulesA12 and A13) passes through thermistor RT1and choke L1. Thermistor RT1 limits theinrush current to the RF power modules.Choke L1 improves the power factor on theac lines applied to the RF power modules.The ac input is also applied to ac-dc universalpower supplies U2 and U3 (U3 optional, fordual side transmitters), which convert the acvoltage to low level dc voltages. The ac inputvoltage is also applied to the interface PWB(A11) for sampling by the control/monitorstage.Dc voltage is applied from an external 24 V or48 V battery connected to A16TB1. The dcvoltage is fused by F1 and applied to rectifierU8 and line filter U7 before being distributedto dc-dc universal power supply U10 andbattery boost PWB A16A1. The battery boostPWB boosts the dc voltage and applies it tothe RF power stage via rectifier U9.6.3.1 Interface PWBSee Figures SD-1 and SD-21. The interfacePWB (A11) provides an interface between theac-dc power stage and the rest of thetransmitter. It also contains voltage regulators(U1 and U2) that provide 9 V for the optionalmodem (via E5 and E6) and 24 V (limited to1A) for the ATU (via E3 and E4). It alsoprovides a dc sample of the ac input voltageto the control/display PWB as an aid indetermining if the ac input source is at anacceptable level.6.3.2 Ac/Dc Universal Input PowerSuppliesSee Figure SD-1. The ac/dc universal inputpower supplies [U2 (side A) and U3 (side B,if used)] are 110 W, universal ac input,multiple dc output power supplies. Thetransmitter’s ac input is applied to U2 andU3 and the regulated 24.5 V, 15.6 V, 5.6 Vand -15.5 V supplies are provided on theoutput. The outputs are applied through theinterface PWB to the remaining functionalblocks of the transmitter.6.3.3 Battery Boost PWB (optional)See Figures SD-1 and SD-25. The batteryboost PWB is a boost type switching powersupplies that provide a regulated B+ supplyvoltage to the transmitter when a 24 V or48 V battery is acting as the power source.A 24 V or 48 V supply is applied to the drainof switching FETs Q4 and Q5 throughinductors L1 and L4. The gate of FETs Q4and Q5 is driven with square wave pulsesfrom pulse width modulation switching powersupply controller U4 through push-pull bufferstage Q6/Q7. U4 is a fixed-frequency, pulsewidth modulation control circuit,incorporating the functions required for thecontrol of a switching power supply. Thedevice contains an internal sawtoothoscillator that is set to a nominal frequencyof 100 kHz by external components R22 andC14. The output pulse width modulatedcontrol pulses to the gate of FETs Q4 and Q5are generated by the comparison of thissawtooth waveform with a feed-back voltagesample from the output (CR6-cathode) andthe bias voltage created from the in-circuitresistors selected by the Battery Select 1(J1-18) and 2 (J1-19) inputs.The resultant variable pulse width, 100 kHzsquare wave at U4-8 (E) is applied to thegate of FETs Q4 and Q5 (through Q6/Q7)and turns it on and off with the appropriatepulses to maintain the desired set dc outputvoltage.The Battery Select 1 and 2 inputs, appliedfrom the control/monitor stage, change thelevel of Battery Boost (B+) voltage based onthe transmitter’s power level. See Table 6-1for the logic levels.Table 6-1: Battery Select LogicB+ VoltageVR250 VR125BatterySelect 1BatterySelect 279 V 55 V 0 0136 V 97 V 0 1236 V 167 V 1 1Invalid Invalid 1 0