A direct current to direct current converter utilizes a MOSFET half-bridge configuration in which the inherent magnetizing and leakage inductances of the transformer are used as the only inductances in the frequency-determining circuit. Diodes are used to limit the voltages across the capacitor of the frequency determining circuit and hence limit the short circuit and open circuit characteristics of the converter. A self-starting circuit insures that the circuit will start up when initially energized.
A two-wire power supply switch connected in series with a load between two poles of an alternating current mains electrical power supply conventionally includes a main triac between two terminals of the switch which is turned on by the conduction of an optotriac with a time-delay relative to the zero crossing of the voltage between the switch terminals determined by the breakdown voltage of a series of Zener diodes. The switch includes a power supply unit with a rectifier bridge connected to one terminal directly and connected to the other terminal via a capacitor. An auxiliary triac shunting the capacitor is turned on by the optotriac on each zero crossing of the voltage between the switch terminals. This optimizes conditions when the switch is open and when the switch is closed separately.
Pursuant to the invention, the capacitance of the smoothing capacitor in the direct current intermediate circuit, which normally must be designed relatively large in a main supplied direct current regulator, is divided into two capacitances, of which one capacitance (K1), responsible for the smoothing, continues to bridge the direct current side of rectifier (G), while the other capacitance (K2), which absorbs the demagnetizing energy of an inductive load (L), bridges the half-bridge of the bridge circuit, which is remote from the rectifier, wherein the connecting point between the two half-bridges of the bridge circuit is decoupled from a feeding point of the intermediate circuit by an additional third diode (D3). Due to the invention, feedback effects on the electrical network are reduced and high switching-on currents can be reduced by a large smoothing capacitance, which was previously required for other reasons.
A circuit associated with a power converter, a method of operation thereof and a power converter employing the circuit or the method. The power converter has a primary switching circuit coupled to a tapped primary winding of an isolation transformer and a rectifier coupled to a secondary winding of the isolation transformer. The circuit is coupled across a tapped portion of the tapped primary winding. In one embodiment, the circuit includes: (1) an inductor, configured to reduce current spikes in the primary switching circuit caused by a reverse recovery phenomenon associated with the rectifier and to effect substantially zero voltage switching of a power switch of the primary switching circuit; and (2) a diode, coupled to the inductor via the tapped portion, configured to clamp a voltage across the rectifier. The tapped portion is configured to enable energy from the inductor to be recovered within the power converter.
The start-up circuit comprises a large valued resistor and a storage capacitor. A voltage sensing switch is connected to the junction of the resistor and storage capacitor on one hand and a voltage doubler on another. The voltage doubler is fed through a capacitor driven by a pair of switching elements arranged in a bridge configuration. The switching elements are driven by a control circuit which is supplied by the start-up and run circuitry. The output of the bridge feeds a resonant tank which is parallel loaded through the resonant capacitor by means of a transformer.
The voltage converter circuit has first and second input terminals, and first and second output nodes, and comprises: a first power switch connected between the first input terminal and the first output node; a second power switch connected between the first output node and the second input terminal; a first delay circuit having first and second terminals connected between the first input terminal and a control terminal of the first power switch; and a second delay circuit having first and second terminals connected between the first output terminal and a control terminal of the second power switch. Each delay circuit detects a variation in the voltage supplied on the respective first terminal and detects an operating condition of the respective power switch on the second terminal, and supplies to the control terminal of the respective power switch a switching on delay signal.
