Isolated dc/dc converters for wide output voltage range and control methods thereof

A power converter having first and second input terminals to receive an input signal from a voltage source to provide an output voltage or an output current to at least one load, comprising:

• (a) a transformer having primary and secondary windings;
• (b) a primary-side circuit, comprising:
• (i) first, second, third, and fourth series-connected switching devices connected across the first and second input terminals, the first and second switching devices being controlled by first and second switch control signals, respectively, and the third and the fourth switching devices being controlled by a third and a fourth complementary switch control signals, respectively;
• and
• (ii) a resonant tank circuit, the resonant circuit being coupled (1) between a first electrical node, being a common electrical node between the first and second switching devices, and a second electrical node, being a common electrical node between the third and fourth switching devices;
• and (2) to the primary winding of the transformer;
• (c) a secondary-side circuit coupled to the secondary winding of the transformer, the secondary-side circuit comprising a filter capacitor providing the output voltage or output current to the load;
• and control signals are periodic with a common switching period, (iii) within the common switching period, (1) each switch control signal has two rising edges and two falling edges;
• and either (2) the first rising edge of the first switch control signal lags the first rising edge of the fourth switch control signal by a first predetermined time, while the second rising edge of the first switch control signal leads the second rising edge for the fourth switch control signal by a second predetermined time, or (3) the first rising edge of the first switch control signal leads the first rising edge of the fourth switch control signal by a first predetermined time, while the second rising edge of the first switch control signal lags the second rising edge for the fourth switch control signal by a second predetermined time, and (iv) the control circuit varies the switching period, the first predetermined time, and the second predetermined time,
• wherein the control circuit operates the switching devices based on the output voltage or the output current, the controller being configured to operate in a first modulation mode and a second modulation mode, wherein under the first modulation mode, the switching devices are operated to generate the output voltage comprising three different voltage levels, and wherein under the second modulation mode, the switching devices are operated to generate the output voltage comprising two different voltage levels.

A power converter that receives an input signal from a voltage source to provide an output voltage or an output current to at least one load, characterized in that the power converter comprises:

• (a) a primary-side circuit comprising:
• (i) series-connected first and second pairs of series-connected switching devices, wherein the input signal is provided across the series-connected first and second pairs of switching devices;
• (ii) an LC resonant circuit connected between a first electrical node in the first pair of switching devices and a second electrical node in the second pair of switching devices;
• and
• (iii) an isolation transformer comprising first and second windings, wherein the first winding is connected between third and fourth electrical nodes in the LC resonant circuit;
• (b) a secondary-side circuit connected in parallel with the second winding of the isolation transformer, the secondary-side circuit comprising a filter capacitor adapted to provide at least one of the output voltage and output current to the at least one load;
• and
• (c) a control circuit, wherein the control circuit is adapted to operate the switching devices based on at least one of the output voltage and the output current, and the controller is configured to operate in a first modulation mode and a second modulation mode, wherein under the first modulation mode, the switching devices are operated to generate the output voltage comprising three different voltage levels, and wherein under the second modulation mode, the switching devices are operated to generate the output voltage comprising two different voltage levels.