Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M3/00—Conversion of DC power input into DC power output
  • H02M3/22—Conversion of DC power input into DC power output with intermediate conversion into AC
  • H02M3/24—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters
  • H02M3/28—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC
  • H02M3/325—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC using devices of a triode or a transistor type requiring continuous application of a control signal
  • H02M3/335—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
  • H02M3/33569—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
  • H02M3/33571—Half-bridge at primary side of an isolation transformer
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M3/00—Conversion of DC power input into DC power output
  • H02M3/01—Resonant DC/DC converters
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M1/00—Details of apparatus for conversion
  • H02M1/36—Means for starting or stopping converters
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
  • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

• This relates to DC-to-DC converters and, more particularly, LLC DC- to-DC converters.
• DC-to-DC converters may be found in many electronic devices.
• DC-to-DC converters are often found in PDAs (Personal Digital Assistant), cellular phones and laptop computers. These electronic devices often contain several sub-circuits with different voltage level requirements from that supplied by a battery or an external supply.
• a DC-to-DC converter converts a source of direct current from one voltage level to another voltage level in order to meet the voltage levels required by subcircuits.
• One method of providing DC-to-DC conversion is through the use of a linear regulator.
• a linear regulator may dissipate too much heat for devices such as laptop computers and cellular phones.
• DC-to-DC converters convert one DC voltage to another by storing the input energy temporarily and then releasing that energy to the output at a different voltage.
• the storage may be in either magnetic field storage components (e.g.
• This conversion method is more power efficient (often 75% to 98%) than a linear regulator, for example. This efficiency is beneficial to increasing the running time of battery operated devices.
• Inductor Inductor Capacitor Inductor Inductor Capacitor
• ZVS zero voltage switching
• An LLC converter operates in a resonant mode.
• signals having a fixed duty cycle (approximately 50%) and a variable period drive powers switches.
• Power MOSFETs Metal Oxide
• the start up time of an LLC converter is quite critical. At start up, the output capacitors of an LLC converter are usually discharged. When an LLC converter starts to charge a discharged output capacitor, the instantaneous current or surge current drawn through a power MOSFET can be too great and cause the power MOSFET to stop functioning. Gradually charging output capacitors during start up of an LLC converter can prevent a power MOSFET from being rendered inoperable.
• FIG. 1 is a schematic diagram of an embodiment of an LLC converter.
• FIG. 2 is a timing diagram of voltages applied to switches SW1 and
• FIG. 3 is a plot of gain of an embodiment of an LLC converter as function of the switching frequency Fs.
• FIG. 4 is a timing diagram of voltages applied to switches SW1 and
• FIG. 5 is a flow chart illustrating an embodiment of a method of reducing surge current in an LLC converter during start up.
• FIG. 6 is a schematic diagram of an embodiment of a full-wave non- center-tapped rectification circuit.
• the LLC converter includes a switching circuit, a resonant circuit, a rectification circuit, and a load.
• a surge current may be drawn through power switches in the switching circuit.
• the LLC converter starts in the PWM mode first.
• the signals driving the power switches are PWM (Pulse Width Modulated) signals having fixed periods and variable duty cycles. The use of PWM signals to drive the power switches gradually charge the output capacitors protecting the power switches against surge current.
• FIG. 1 is a schematic drawing showing an embodiment of an LLC converter 100.
• the LLC resonant circuit 104 in FIG. 1 includes a capacitor Cr, an inductor Lr, an inductor Lp, and a transformer Tr. The capacitor Cr, the inductor Lr and the inductor Lp are connected in series.
• the inductor Lr may be created by the leakage inductance of transformer Tr or a discrete inductor may be used as part of it.
• a combination of the magnetizing inductance Lm of transformer Tr and a discrete inductor placed in parallel with the primary winding Pr of the transformer Tr may be used to create inductor Lp.
• capacitor Cr is connected to a connection of inductor Lr at node N2.
• Another connection of inductor Lr is connected to a first end of primary winding Pr of the transformer Tr and a first connection of inductor Lp at node N3.
• a second end of primary winding Pr of transformer Tr and a second connection of inductor Lp are connected to ground.
• the rectification circuit 106 in this example is a full- wave center- tapped rectification circuit; however other types of rectification may be used such as full- wave non-center-tapped rectification (FIG. 6) or half-wave rectification.
• a first connection of the secondary winding Sr of the transformer Tr is connected to the anode of diode Dl at node N4.
• a second connection of the secondary winding Sr of the transformer Tr is connected to the anode of diode D2 at node N5.
• the cathode of Dl, the cathode of D2 and a first connection of capacitor CI are connected at Vout.
• Vout is the output voltage produced by the LLC converter 100.
• a second connection of the capacitor CI is connected to the center-tap on the secondary winding Sr of the transformer Tr at node N6.
• the resistor RL in the load 108 is connected at Vout and node N6.
• a capacitor CI is used as a low-pass filter.
• Other low-pass filters however may also be used, such as pi networks.
• FIG. 6 illustrates an embodiment of a full-wave non-center-tapped rectification circuit. Because the embodiment shown in FIG. 6 is not centered-tapped, four diodes, Dl, D2, D3, and D4, are necessary for full-wave rectification.
• the switching circuit 102 in this example includes two switches SW1 and SW2.
• the switches SW1 and SW2 are NFETs.
• the drain of SW1 is connected to DC voltage Vin.
• the source of SW1 and the drain of SW2 are connected at node Nl.
• Signals SI and S2 drive switches SW1 and SW2.
• the source of SW2 is connected to ground.
• Nl is connected to the output of switching circuit 102.
• the frequency Fs at which the switches SW1 and SW2 switch are controlled by signals SI and S2 (shown in FIG. 2).
• the amount of time, DT, that switch SW1 is on during a period T is determined by a duty cycle D (shown in FIG. 2).
• the duty cycle D in this example, has a value of approximately 0.5.
• the amount of time the switch SW2 is on is also D, but shifted by 180 degrees.
• Switches SW1 and SW2 may be implemented using transistors. In this embodiment of the invention, NFETs (N-type Field Effect Transistors) are used.
• FIG. 3 is a plot of gain of an embodiment of the LLC converter 100 as function of a resonant frequency Fo.
• the LLC converter 100 When the LLC converter 100 is operated near the resonant frequency Fo, as is usually the case, all the load (Q) curves converge.
• the equation for Q in this example is shown in equation (1):
• n in equation (1) for Q represents the turns ratio of the transformer Tr.
• the convergence of the load (Q) curves indicates that a wide range of loads may be driven without significant change in the switching frequency Fs.
• the output capacitor(s) CI are usually discharged because they have drained. Because the output capacitor(s) CI are usually discharged, the start up condition may be regarded as a temporary "short circuit.” Due to the inherent fixed duty cycle (approximately 50%) characteristic of resonant mode control, surge current drawn through the switches SW1 and SW2 of the LLC converter 100 may be too large. As a result, the switches SW1 and SW2 may be damaged.
• the LLC converter with the maximum frequency then gradually reduce the modulation frequency until the output voltage comes close to the setting point where a control loop closes and thereafter controls the voltage Vout.
• the maximum frequency allowable on the LLC converter is limited by the hardware; second, as shown in FIG. 3, the voltage modulation gain, instead of dropping to zero, will become flat when the frequency increases such that the voltage modulation gain is not low enough for a soft start.
• the output voltage will not ramp up from zero; rather, it will jump to some value and then start to ramp up from that value.
• the in-rush current as a consequence of this initial voltage jump, will cause higher stress on SW1 and SW2.
• SW1 and SW2 needs to be progressively increased.
• the LLC converter 100 is started in the PWM mode first.
• FIG. 4 illustrates an example of PWM signals for controlling surge current during start up.
• the PWM signals have a period T and a duty cycle D.
• the period T of signals S 1 and S2 is fixed while the duty cycle D is variable.
• the duty cycle D may vary from 0 to nearly 50 percent.
• PWM signals SI and S2 are used to slowly ramp up the voltage Vout on the load 108 from zero to a predetermined voltage near to the setting point of the voltage Vout. By varying the duty cycle, the amount of current drawn through switches SW1 and SW2 can be controlled so as to avoid destructive surge current.
• FIG. 2 illustrates an example of resonant mode signals S 1 and S2 for controlling the voltage Vout thereafter.
• the period T of the square- wave control signals S 1 and S2 is variable while the duty cycle D is fixed.
• the duty cycle D of the control signals SI and S2 is approximately 50 percent and signal S2 is approximately 180 degrees out of phase with control signal S I.
• the resonant mode control signals SI and S2 continue to increase the voltage on Vout until a predetermined voltage is reached. After the predetermined voltage is reached on Vout, the resonant mode signals S 1 and S2 regulate the voltage Vout by varying their frequency.
• FIG. 5 is a flow chart illustrating an embodiment of a method of reducing surge current in an LLC converter 100 during start up.
• the output voltage Vout is monitored. When the voltage Vout is less than a
• switches SW1 and SW2 are operated in the PWM mode.
• switches SW1 and SW2 change to resonant mode.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Dc-Dc Converters (AREA)

Priority Applications (2)

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Publications (2)

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• 2010
  • 2010-01-07 US US12/683,743 patent/US8018740B2/en active Active
  • 2010-12-13 JP JP2012548013A patent/JP2013516955A/ja active Pending
  • 2010-12-13 CN CN201080065116.3A patent/CN102783004B/zh active Active
  • 2010-12-13 WO PCT/US2010/060059 patent/WO2011084379A2/en not_active Ceased

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