Capacitance Influence in Screen Grid Circuit of Electrosys/Itelco RF-Power Station
Explore the influence of capacitance in the screen grid circuit of an RF-power station, analyzing the impact on output pulse measurements, G2 voltage simulation, capacitor capacitance calculations, and connection effects. Discover insights on how capacitors can affect power supply performance and output power capabilities.
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Presentation Transcript
Influence of capacitance in the Screen Grid circuit of Electrosys/Itelco RF-power station. Rolf Wedberg Magnus Jobs, Antonio Frizzi 2025-03-18 1
The RF output Pulse at 400 kW. Measured without capacitors. Dip after 800 us. 2025-03-18 2
Simulated G2 voltage The picture shows the G2 voltage when switched to ground via a 2 200 Ohm resistor. The voltage drops from 900 V to 760 V and after the pulse overshoots to 1000 V. 2025-03-18 3
Calculation of capacitor capacitance. The G2 current is 240 mA during the pulse. The capacitance shall be as small as possible to not store much energy. Q = C * U = I * t t = 3.5 ms A good 70 uF capacitor is available. That will give: U = 0.24 * 3.5 E-3/70 E-6 = 12 V Much less than the measured 140 V voltage drop. 2025-03-18 4
Connection of capacitors. T1 T2 Technix Power Supply G2 DETECTORS C1 70uF U1 P T3 S G 0 0 K TH595 2025-03-18 5
Simulated G2 voltage with capacitor Added a 70 uF in parallell with the G2 power supply. The voltage drops from 900 V to 880 V and after the pulse overshoots to 910 V. 2025-03-18 6
Test with RF at 400 kW pulses with capacitors at both tetrode sections Without capacitors With capacitors 2025-03-18 7
Conclusions. The Screengrid power supplies are not able to keep constant output voltage at fast load changes. With capacitors in the G2 circuit the output power of the G2 power supplies can be reduced to 100 W instead of 3 kW. 2025-03-18 8
