A power converter nearly losslessly delivers energy and recovers energy from capacitors associated with controlled rectifiers in a secondary winding circuit, each controlled rectifier having a parallel uncontrolled rectifier. First and second primary switches in series with first and second primary windings, respectively, are turned on for a fixed duty cycle, each for approximately one half of the switching cycle. Switched transition times are short relative to the on-state and off-state times of the controlled rectifiers. The control inputs to the controlled rectifiers are cross-coupled from opposite secondary transformer windings.

High efficiency power converter

In a forward DC to DC converter (Fig. 4), switching losses are virtually eliminated by exploiting a controlled amount of leakage inductance of a transformer (10) in combination with a capacitor (15) to allow a switch (12) to turn on and off essentially at zero current. The combination of the secondary leakage inductance of the transformer (10) and the capacitor (15) defines an effective LC circuit having a characteristic time scale for the rise and fall of the current drawn from a voltage source (11). Power is converted by cyclically transferring a quantum of energy from the voltage source (11) to a current sink (load) via the effective LC circuit. The sink current is cyclically carried by a rectifier (16) which prevents the LC circuit from becoming a resonant circuit and leads to a unidirectional flow of energy from source to load.

Forward converter switching at zero current.

A family of quasi-resonant converters is disclosed as comprising a voltage source, a transformer having primary and secondary windings, and a switch for periodically coupling the voltage source to the primary winding, whereby a charging current appears on the secondary winding. The transformer exhibits a characteristic leakage inductance. A capacitor exhibiting a characteristic capacitance is coupled to the secondary winding to form a resonant circuit including the leakage inductance and the capacitor. The secondary winding is coupled to apply the charging current to the capacitor. A rectifying circuit couples the capacitor to a load, whereby the voltage stored in the capacitor is delivered to the load. The capacitor is directly connected to the secondary winding and to the rectifying circuit to permit positive and negative going voltages to be stored therein, whereby magnetic flux within the core of the transformer is dissipated and the transformer magnetically reset.

Resonant converters with secondary-side resonance

An electronic ballast for a discharge lamp (8) for restricting and stabilizing the lamps current. The ballast comprises a high frequency oscillator for connection to a D.C. supply which consists of two transistors (1,2) connected in series, with a base drive transformer (3) coupled between them to bring the transistors (1,2) into alternating phase operation. A resonance circuit connected in series with the primary winding (4) of the transformer (3), comprises an inductor (7), resonance capacitors (10 and 11) and a capacitor (9) coupled in parallel with the lamp (8). The lamp (8) is, in turn, connected in series with the resonance circuit. In addition, a filter capacitor (c) having a high charging ability is coupled between the terminals of the D.C. supply. The resonance capacitors (10 and 11) are connected in series between the terminals of the D.C. supply, and diodes (23, 24) are connected parallel to them, and the last part of the resonance circuit is connected to a point common for the capacitors and the diodes, e.g. by means of the electrode (8a) of the lamp (8).

Electronic ballast for a discharge lamp

A power supply with automatic arcing control and overload protection includes an electronic switch in an oscillator circuit with a primary winding of a step-up transformer. A high voltage, secondary winding of the transformer is loosely magnetically coupled to the primary winding. The frequency of oscillation of the oscillator circuit decreases as a load impedance across the secondary winding of the transformer decreases. In the case of arcing or shorting of an output circuit of the power supply the frequency of oscillation decreases below a pass band of the output circuit, thereby reducing the output current of the power supply.

Power supply with arcing control and automatic overload protection

A pair of switching transistors, serially connected across a common DC source, have a junction returned to one of the source terminals through the primary of an output transformer in series with the primary of a control transformer and with a frequencyselective network which includes a blocking capacitor and discriminates against frequencies above a predetermined switching frequency established either by the network itself or by a tuned secondary circuit of the control transformer.

Hoffmann Gunther

Papers

Direct-current converter with overload protection