Apple iPhone charger teardown: quality in a tiny expensive package. [9] Flextronics Patent 7,924,578: Two Terminals Quasi Resonant Tank Circuit describes the resonance circuit used in the iPhone charger, which is shown in the following diagram. Transistor Q2 drives the transformer. Transistor Q1 is the clamp transistor, which directs the voltage spike from the transformer into resonance capacitor C13. The innovative part of this circuit is that Q1 doesn't need special drive circuitry like ...

Apple iPhone charger teardown: quality in a tiny expensive package. [9] Flextronics Patent 7,924,578: Two Terminals Quasi Resonant Tank Circuit describes the resonance circuit used in the iPhone charger, which is shown in the following diagram. Transistor Q2 drives the transformer. Transistor Q1 is the clamp transistor, which directs the voltage spike from the transformer into resonance capacitor C13. The innovative part of this circuit is that Q1 doesn't need special drive circuitry like ...