Patent ID: 6229389
Filing Date: 2001-05-08
Classification: H03F

Abstract:
In a class D amplifier with a bridge circuit, an over current limiting circuit comprising in combination:a self oscillating pulse width modulator including an integrator with feedback from the output of the amplifier and a comparator coupled to the output of the integrator;a bridge gate driver circuit coupled between the modulator and a MOSFET bridge circuit for controlling gates of the MOSFETs in the bridge circuit; the bridge circuit connected between high and low voltage power busses and comprising at least two MOSFETs connected in series with each other;a load impedance connected to the output of the bridge circuit;first and second over current sensing circuits each including a voltage conversion circuit for sensing the voltage drops across the MOSFETS to derive signals representative of the currents in the MOSFETS and each including a comparator circuit for comparing the current signal to reference signals and generating an over current output signal representative of an over current condition; andan over current limiting circuit, responsive to the over current output signal, and including a current source for injecting current into the integrator or extracting current from the integrator to reduce the effective input current to the integrator when the current in either MOSFET is greater than a current limit threshold.