A method and an apparatus for implementing a semiconductor switch multi-stage drive circuit. The disclosed method and an apparatus reduce losses in a semiconductor switch when it is turned from an off state to an on state or from an on state to an off state. The reduction in losses is achieved without influencing the dv/dt across the semiconductor switch during a first time period while the semiconductor switch is switching. This reduction in losses is therefore achieved with very little increase in the noise generated due to rapid dv/dt during the first time period when the semiconductor switch is switching. The configuration of the circuitry to achieve this reduction in switching losses is such that benefits are less sensitive to manufacturing tolerances and temperature effects than alternative semiconductor switch drive schemes to achieve similar results.
To turn on a JFET, a two-stage turn-on current control is employed in a JFET driver circuit and a JFET driving method, by which a shortly pulsed high sourcing current is provided to turn on the JFET rapidly and efficiently, and a continuous low sourcing current is provided after the JFET turns on for reducing the power dissipation. After the JFET turns off, a negative charge pump is also employed to promise the JFET at a turn-off state. A special power sequence is further employed to ensure the JFET could be turned off during the power supply coupled to the JFET starts up.
An apparatus for regulating a power converter with multiple operating modes includes a switch coupled to an energy transfer element coupled between an input and an output of the power converter. A control circuit is also included, which is coupled to the switch to control the switch. The control circuit includes first and second duty cycle control modes to regulate power delivered to the output of the power converter. A transition between the first and second duty cycle control modes is responsive to a magnitude of a current flowing in the switch reaching a current threshold value.
An apparatus and method of switching a switch of a power supply in response to an input voltage signal are disclosed. According to aspects of the present invention, a power supply controller includes a switch duty cycle controller coupled to receive a feedback signal and a duty cycle adjust signal. The switch duty cycle controller is coupled to generate a drive signal coupled to control switching of a switch, which is coupled to an energy transfer element, to regulate energy delivered from an input of a power supply to an output of the power supply. The power supply controller also includes a gain selector circuit coupled to receive an input voltage signal, which is representative of an input voltage to the power supply, to generate the duty cycle adjust signal received by the switch duty cycle controller. The maximum duty cycle of the drive signal to be varied in response to a plurality of linear functions over a range of values of the input voltage signal.
A power supply controller measuring impedance includes a sense circuit coupled to a sense terminal. A regulation circuit is coupled to the sense circuit and is also coupled to regulate the sense terminal to a first voltage level when a current flowing through the sense terminal is less than a first threshold current level. The regulation circuit is further coupled to regulate the sense terminal to a second voltage level when the current flowing through the sense terminal reaches the first threshold current level. A response circuit is coupled to the sense circuit and is responsive to the current flowing through the sense terminal when the sense terminal is regulated at the second voltage level.
