18. When Rc does not equal Rch or RL in a PFN.

a. Charging waveform when Rc is less than Rch.

Figure 32 shows the

charge waveform of a PFN in which the characteristic resistance is less than

the source resistance. Notice how the voltage charges up in steps. Each

step after the second step is a little bit less than the preceding step. If

you draw a line through the tips of each step, you see that the line is

exponential.

That's why this charge is called an exponential charge.

If

the ratio of Rc to Rch changes, the steps will change somewhat but it will

still be exponential. You will see more steps on the scope if the mismatch

becomes worse.

Figure 34.

Rc less than Rch.

b. Discharging waveform when Rc is less than RL. Figure 35 shows the

exponential discharge across a load (magnetron) that has a greater

resistance than the characteristic resistance of its PFN. The oscilloscope

shows how the voltage across the resistor is highly negative at the start of

the discharge, and decreases in steps until it is completely discharged. As

before, the ratio of Rc to RL determines the amount of discharge in each

step. The greater the mismatch, the more steps there will be.

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