Astec International Limited

Xerox Corporation

David A Cross

Neal George Stewart

A forward converter circuit that includes elements capable of generating a zero volt switching (ZVS) signal across the power switch. The ZVS generating elements include a series combination of a switch and shunt inductance, which are connected in parallel across the primary winding of the power transformer. An offset capacitor is placed in series with the shunt inductance and is operated in conjunction with a control circuit to couple the magnetizing current from the primary winding of the power transformer and use it to charge the offset capacitor. This provides zero volt switching of the power switch at turn-on and turn-off, and reset of the core of the power transformer without the use of a tertiary winding. The circuit also achieves added protection of the power switch without the use of an active clamp.

Offset resonant ZVS forward converter

Effective harmonic correction without frequency, power or voltage limitations is achieved in a single-stage DC-to-DC converter by disconnecting the bulk capacitor of a typical single-stage converter during low voltage conditions, and by using various phase and cycle modulation techniques associated with a switchable auxiliary transformer winding which charges the bulk capacitor to control its voltage. A means is thus provided to control the level of harmonics generated depending upon the level of the AC output voltage. When the auxiliary winding is used as a clamp winding, full ZVS conditions are provided for both the auxiliary winding switch and the converter's primary winding switch. Energy can then also be directed, under independent control of the switched auxiliary winding, to independent power nodes, i.e., either the output capacitance and load, or the bulk capacitor. This ensures that the output voltage will not be affected during any period needed to recharge the bulk capacitor.

Line harmonic correcting flyback power converter

A continuous mode flyback converter circuit which includes elements capable of generating a zero volt switching (ZVS) signal across the power switch. The ZVS generating elements include a switched shunt inductance coupled in parallel with active clamp components and connected across the primary winding of the power transformer. The circuit reduces the reverse recovery current through the secondary stage rectifier and the current through the active clamp switch during operation of the converter. The ZVS generating elements may also be used for flyback converters which do not utilize an active clamp.

Offset resonance zero volt switching flyback converter

A boost converter circuit which includes elements capable of generating a zero volt switching (ZVS) signal across the power switch. The ZVS generating elements include a switched shunt inductance which is referenced to the positive rectified supply voltage instead of to the output voltage as with other ZVS techniques. This causes a reduction in the inductance value required for generating the ZVS signal, and a resulting reduction in the power loss associated with operation of the converter. The inventive circuit permits operation of the boost converter using high frequency FET devices or slower switching insulated gate bipolar junction transistors as the power switch.

Offset resonance zero volt switching boost converter

A thermally regulated power system, where the extent to which the temperature of a power module causes a change in the output power of the module depends on the output current of the module. Similarly, the extent to which the output current of the power module causes a change in the output power of the module depends on the temperature of the module. In one embodiment, a thermally regulated down slope power sharing system without a share line includes N+1 power modules coupled in parallel to the same output port, where N is an integer greater than one. The slope of the down slope curve of a power module is changed in response to the temperature of the power module such that a power module operating at a higher temperature outputs less current for a given bus voltage than a power module operating at a lower temperature. In another embodiment, the power system includes 2N power modules, where one group of N power modules is coupled to each other by a first share line and another group of N power modules is coupled to each other by a second share line. This allows the power output of the power modules to be controlled by thermally regulated down slope sharing and by temperature/current share lines.

Thermally aided power sharing of power supplies with or without an

An interleaved flyback electrical power converter system having a plurality of flyback power converters operated in continuous mode, each converter utilizing a power switch operated under zero voltage switching conditions. The interleaved flyback power converter system is highly efficient and compact, and is suitable for use in high power, high frequency applications.

Interleaved continuous flyback power converter system

A transient voltage protection circuit includes a normally closed switch connected between a rectifier circuit and a DC to DC converter. This switch is caused to switch to a current limit state when the voltage input to the DC to DC converter exceeds a first predetermined value, thereby protecting the DC to DC converter from voltages that exceed the converter's operational limits. The switch is returned to its normally closed state when the voltage input to the converter drops below a second predetermined lower value. A capacitor connected across the input terminals of the converter is charged up when the switch is closed and functions to supply power to the DC to DC converter when the switch is in its current limit state. The current limit state of the switch comprises the periodic switching of said switch between a normally closed state and an open state, said switch being caused to open when the voltage across said capacitor reaches said first predetermined value and to close when the voltage across the capacitor drops to said second predetermined lower value.

Transient over voltage protection circuit for electrical power converters

An electrical power converter system having a power factor correction circuit and a switching power converter. The power factor correction circuit converts the AC line voltage into an unregulated DC voltage referred to as the PFC voltage, which supplies an unregulated DC input voltage to the switching power converter. The switching power converter converts the unregulated DC input voltage into one or more regulated DC output voltages. The PFC voltage automatically adjusts to an appropriate value for achieving the desired power factor correction, converter efficiency, and converter temperature. In a preferred embodiment, the value of the PFC voltage is adjustable in response to a control signal produced by a PFC control circuit. The PFC control circuit measures the peak value of the input line current to determine whether the power factor is acceptable. If the power factor is acceptable, the PFC voltage will be maintained at a relatively low value. If the peak current is too high, indicating a poor power factor, the PFC control circuit will raise the value of the PFC voltage so that the power factor is improved. If excessively high temperatures occur, the PFC control circuit will lower the value of the PFC voltage so that the converter operates more efficiently and lower power losses occur. If highest efficiency operation is required under certain load conditions, the PFC control circuit will also lower the PFC voltage so that the converter operates more efficiently.

Power factor corrected electrical power converter

In a matrix array for the supply of an electrographic stylus writing apparatus, a plurality of styli are driven by short pulses through R/C networks. The styli are divided into subgroups and parallel capacitors connect the styli of each subgroup to a high voltage switch which is responsive to a capacitor pulse driver. Each stylus is also driven through a resistive line which completes the R/C circuit. The resistive lines are connected in parallel for similar styli of each group to a resistor enable pulsing circuit and all resistive lines are connected via isolation diodes to a resistor reset means. In operation, a short pulse from the capacitor driver circuit is applied to all the capacitors of a single group and an enabling pulse is applied to a predetermined single resistive line of each group so that the combined, enabled R/C circuit for a single stylus within one of groups is activated.

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Wrestlingworth, United Kingdom

David A Cross