Resonant inverter including feed back circuit with source of variable bias current
View Patent ↗A resonant inverter with a self-oscillating driver IC for powering AC loads, such as gas discharge lamps or regulated DC/DC converters, includes a timing circuit that generates control strobe pulses that are injected into the timing circuit. The timing circuit is coupled to an inverter resonant tank through a feed back circuit providing phase lock for the resonant inverter. The feed back circuit includes a source of variable bias current connected to an input terminal of a zero signal detector to shift an angle at which polarity changes to control a frequency for the resonant inverter.
1. A resonant inverter comprising:
a self-oscillating driver circuit;
a timing circuit connected to an input of said driver circuit;
a zero signal detector that changes an output signal when an input signal received at a first input terminal changes polarity, an output of said zero signal detector being connected to said timing circuit;
a resonant tank connected to an output of said driver circuit; and
a feed back circuit that connects an output of said resonant tank to said first input terminal of said zero signal detector, said feed back circuit comprising a source of a variable bias current that is connected to said first input terminal of said zero signal detector to shift an angle at which polarity changes to control a frequency for the resonant inverter.
2. The resonant inverter of claim 1 , wherein said feed back circuit further comprises a phase compensator that is connected to a controller that includes said source of bias current.
3. The resonant inverter of claim 2 , further comprising a pair of switching transistors operated by said driver circuit and generating a voltage across an input of said resonant tank, wherein said output of said resonant tank is connected to said phase compensator.
4. The resonant inverter of claim 2 , wherein said phase compensator comprises two capacitors connected in series between said output of said resonant tank and a common terminal and a further resistor in parallel with one of said two capacitors that is closest to said common terminal.
5. The resonant inverter of claim 4 , wherein said phase compensator further comprises, in parallel with said further resistor, a pair of Zener diodes connected back-to-back.
6. The resonant inverter of claim 2 , wherein said controller comprises a second node that is connected to said first input terminal of said zero signal detector, said phase compensator, and said source of bias current.