A modified DC-to-AC power converter accomplishes power transfer to a load with electrical isolation, zero-voltage and zero-current switching, using a transformer core resetting mechanism. The power converter contains two switching devices, a main device connected in parallel and a secondary device connected in series with a transformer primary winding. A secondary winding of the transformer is connected through a two-port resonant link circuit to a resistive load. Zero-voltage switching and proper transformer-core resetting are achieved from the resonance that exists between the parasitic capacitance of the secondary switching device and the magnetization inductance of the transformer. A transformer leakage inductance facilitates zero-current switching; thus, reducing the turn-on switching loss in the conventional main switching device. The switching converter contains a lossless clamping circuit, to limit the voltage stresses across both of the power switching devices to the reflected output voltage appearing across the primary.
CONTINUING DATA AS CLAIMED BY APPLICANT
This application is a continuation-in-part of U.S. patent application Ser. No. 08/179,348, filed Jan. 10, 1994, U.S. Pat. No. 5,434,767.
In a control circuit for controlling a current resonance type DC/DC converter, a negative voltage detection arrangement produces a pulse while a both-ends voltage of a resonance capacitor has a negative voltage. A voltage level error signal generating circuit includes a capacitor which is charged during production of the pulse and generates a voltage level error signal where a voltage level rises. A timer produces a timer signal having a sawtooth waveform where a voltage level gradually rises. An off timing generating circuit compares the timer signal with the voltage level error signal to generate an off timing signal defining a timing for making a short-circuit switch turn off. Responsive to the off timing signal, a driving control signal generating arrangement generates a second driving control signal indicative of turning-off of the short-circuit switch.
A single ended forward DC-to-DC converter includes a transformer having a primary winding electrically connected to a primary switch and a secondary winding electrically connected to a secondary switch and a clamping capacitor. The clamping capacitor stores the magnetization energy from the secondary winding when the primary switch is turned off, thus causing the transformer core to be reset during the period that the primary switch remains off. The converter can use mosfets as the primary and secondary switches, such that a change in the voltage at the secondary winding of the transformer, due to the turning off of the primary switch, results in an automatic turning on of the secondary switch. The combination of the clamping capacitor and the mosfet switches increases the simplicity of the DC-to-DC converter while eliminating undesirable characteristics such as dead time and voltage stresses on the switches. The DC-to-DC converter of the present invention can be used to carry out synchronous rectification and zero voltage switching.
A switchable power converter includes an input section that receives an AC input voltage and rectifies the AC input voltage and a switchable converter section operative to receive the rectified AC input voltage and convert the rectified AC input voltage to an intermediate DC output voltage. The switchable converter section includes at least one configuration switch operative to switch the switchable converter section between a boost converter topology, for low input line voltages, and a SEPIC converter circuit topology, for high input line voltages, and also includes a coupled inductor. The coupled inductor eliminates an open-ended terminal in a load inductor thereby reducing antenna effect. Additionally, the coupled inductor achieves a current ripple steering effect in the boost converter topology, similar to that of the SEPIC converter topology, resulting in a smaller input current ripple requiring a smaller EMI filter.
A generalized active reset switching network using a small choke, a pair of switches, and a capacitor is revealed. The application of the generalized active reset switching network to any of a wide variety of hard switching power converter topologies yields equivalent power converters with zero voltage switching properties, without the requirement that the magnetizing current in the main power choke be reversed during each switching cycle. In the subject invention the energy required to drive the critical zero voltage switching transition is provided by the small choke that forms part of the generalized active reset switching network. The application of the generalized active reset switching network to buck, boost, buck boost, Cuk, and SEPIC converters is shown. A variation of the generalized active reset switching network which adds a single diode to clamp ringing associated with the parasitic capacitance of off switches is also revealed.
