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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I am hoping someone will clear this up for me referring to Kim Ladha's schematic
The circuit is run by a relaxation schmitt trigger oscillator. The current transformer, connected to the resistor, acts as a varying voltage source depending on the amount of current in tank. This serves as an input to a differentiator. The capacitor of the oscillator is serving two purposes.
Does the charging/discharging of the capacitor from the current transformer slow down the charging/discharging of the capacitor by the schmitt trigger? This slowing would then reduce the frequency, taking the tank away from resonance, when the current gets too high?
I presume one sets the frequency with the work in place at resonance and this circuit is a safe-guard from an excessive current condition?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
This is an example of entrainment. The oscillator gets "entrained" by the signal from the CT if it's strong enough, and locks to the resonant frequency of the work circuit. The principle of operation is similar to a PLL, but harder to analyze and the performance isn't as good.
Synchronization by entrainment was very popular in the 40s, 50s and 60s before cheap PLL ICs were available. Remember the Vertical and Horizontal Hold controls on old TV sets? They were adjusting a circuit not unlike Kim's.
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Current transformer feedback explaination please
