The transformer's core in single ended forward converters is reset by a "magnetizing current mirror" consisting of a capacitor in series with an auxiliary switch which, during the OFF period of the primary switch, couples the capacitor to one of the transformer's windings to form a resonant circuit with the transformer's magnetizing inductance. The resonant circuit recycles the transformer's magnetizing energy by creating a mirror image of the magnetic flux between ON periods. This maximizes the flux swing available within a given core. The voltage stress on the primary switch is minimized as the voltage across the switch during the OFF period is approximately constant and automatically tailored to avoid dead time for arbitrary values of the switch duty cycle.

Optimal resetting of the transformer's core in single ended forward converters

A switching power supply is disclosed using a single transistor circuit which provides a constant output voltage for a range of input voltages extending from a nominal 115 volt power supply to a nominal 220/240 volt power supply without requiring a change in the circuit configuration throughout the range of input voltages. The circuit is disclosed in connection with a single transistor forward converter circuit, in which the transformer winding of the converter circuit is provided with a uni-directional clamp to prevent the transformer voltage of a given polarity from exceeding the clamping voltage magnitude. By clamping one polarity of the transformer voltage which is in series with the switching transistor, the maximum peak-to-peak voltage on the transistor is reduced from that which would be produced in the absence of clamping and enables the use of a power MOSFET transistor for the circuit. The clamping circuit is disclosed as a zener clamp and as a circuit including a parallel resistor and capacitor and series diode.

Switching power supply circuit having constant output for a wide range of input voltage

A switching converter, having a transformer having primary, secondary and auxiliary windings, an actively controlled switch, a capacitor and a first passive switch in series across the primary, the auxiliary winding of the transformer and a second passive switch being connected in series to the node between the capacitor and first passive switch, with the active switch being connected to a side of the primary winding opposite the first passive switch. The method energizes a transformer core with the primary winding and discharges a capacitor during an ON state; and clamps a voltage across the active switch with the capacitor, and transfers magnetizing energy to the secondary winding during an OFF state, to efficiently transfer energy corresponding to a switching transient to the load while limiting maximum active switch voltage.

Leakage energy recovering system and method for flyback converter

A voltage boost power converter circuit, having an input inductor, active switch, and a transformer having primary, secondary and auxiliary windings A clamping capacitor and a first passive switch are in series across the primary winding The auxiliary winding and a second passive switch are in series, connected to the node between the clamping capacitor and first passive switch The active switch is connected between ground the primary winding A bulk capacitor forms a series loop including the active switch and primary winding The method efficiently resets a the transformer, by transferring power to a load through the primary winding, and discharging a clamping capacitor through a separate inductively linked winding of the transformer during an ON state; and clamping the active switch voltage with the clamping capacitor, charging the clamping capacitor with a leakage inductance of the transformer, and charging the bulk capacitor during an OFF state

Voltage clamping system and method for a dc/dc power converter

Apparatus (and a method) useful in a switching power converter having a transformer and a primary switch for connecting a DC input source to a primary winding of the transformer during a portion of each of a succession of converter operating cycles, the apparatus includes a reset capacitor and a reset switch. Reset circuitry cooperates with the reset switch to connect and disconnect the reset capacitor in a manner which provides for resetting the transformer and which allows a current having a non-zero average value to flow in the reset switch. Another aspect is a method for limiting the slew rate in a switching power converter which includes a transformer and a reset circuit of the kind which non-dissipatively recycles the magnetizing energy stored in a transformer during each of a succession of converter operating cycles. The method includes sensing the magnetizing current which is flowing in said transformer, and allowing initiation of another converter operating cycle only if the magnetizing current meets a predefined criterion for safe converter operation. In embodiments of the invention the predefined criterion may be the magnetizing current passing through a predefined value, e.g., zero.

Control of stored magnetic energy in power converter transformers

The invention relates to a DC converter for transforming a DC voltage to an AC voltage of high frequency and including one or several switching means to effect this operation. The invention is specifically related to the use of premagnetization means for magnetizing the transformer core in order to increase the efficiency of the converter. This is effected by premagnetizing the core into saturation with a magnetic field which is opposite to the field generated by the current through the corresponding switching means. The transformer core will consequently operate in its saturated state from the point when the switching means is rendered conductive and the current through said switching means is increasing up to a certain value above which the core will operate in its nonsaturated state. This arrangement will provide a converter operating with substantially rectangular waveforms of the current supplied to the load, which means that the switching means can operate just below their maximum permissible current when energy is transferred from the current source to the load. The switching means will thus be utilized at a maximum thereby improving the efficiency of the converter.

Udden Per E C

Papers

An arrangement for premagnetizing a static dc converter