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Is there anyone explain how this kind of circuit works? (suggestions of books/pdf/websites are very very welcome as well.)
I have fundamentals knowledge on those components but do not know how it works. eg. -Why choose the 2 resistors? by what criteria? -Why the coils wind in this way? and how the transistor is turned on. (It is the most difficult for me as I know very basic about transformer. It confuses me with the extra little coil)
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Just a very quick and dirty explanation:
Its just a very basic oscillator circuit. Without the 2T feedback winding, R1 and R2 would just bias the transistor as some level and nothing would really happen. The 2T feedback winding causes the level at the base of the transistor to "oscillate" due to positive feedback and the cycle repeats, at the resonant frequency of the transformer.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The transistor gets turned on through the 220ohm resistor. This induces voltage in the primary winding and in turn the feedback winding. The voltage developed on the feedback winding causes even more current to flow through the base.
Now, the current through primary is ramping up because of its inductance. At some point, the transistor can no longer sustain the current and gets de-saturated ( /or the core saturates and causes the voltage on the feedback winding to fall). The transistor turns off.
The energy stored in the core is released in the form of a flyback pulse, which has positive polarity on the collector and negative polarity on the base, holding the transistor off during the flyback pulse. When the voltages fall back, the cycle repeats.
It's worth noting that the running frequency has absolutely nothing to do with the transformer resonant frequency, as simply changing the voltage/resistors/core gap etc. can alter the frequency noticably.
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[Newbie]schematic exlanation needed
