Two-level switch driver for preventing avalanche breakdown for a synchronous rectification switch in a power converter operating in a low-power burst mode
First Claim
1. A switch driver for controlling a power switch in a switched-mode power converter, so as to prevent excessive voltage levels across a synchronous rectification (SR) switch of the power converter, the switch driver comprising:
- a pull-down driver switch for sinking current from a control terminal of the power switch;
a first pull-up driver switch for sourcing current to the control terminal, the first pull-up driver switch having a first on-state resistance;
a second pull-up driver switch for sourcing current to the control terminal, the second pull-up driver switch having a second on-state resistance substantially higher than the first on-state resistance;
a mode indication input;
a switch control input, which controls the pull-down driver switch, the first pull-up driver switch, and the second pull-up driver switch; and
a high-side control circuit configured to disable the first pull-up driver switch responsive to a burst-mode indication at the mode indication input,wherein the first and second pull-up driver switches are coupled to a same driver power supply having a same driver sourcing voltage, such that the same driver sourcing voltage is applied to the control terminal responsive to the first and/or the second pull-up driver switches being turned on.
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Accused Products
Abstract
Techniques are provided for avoiding an avalanche breakdown voltage across a synchronous rectification (SR) switch on the secondary side of an isolated switched-mode power converter operating in a low-power mode, e.g., a burst mode, during which a load of the power converter draws negligible current. This is accomplished via use of a two-level switch driver for controlling a power switch on the primary side of the power converter. The two-level switch driver is configured to source low current levels to a control terminal (e.g., gate) of the power switch during burst-mode operation. This low current reduces the slope of the rising edge of voltage pulses on the primary and secondary sides of the power converter which, in turn, limits the peak of the voltage ringing across the SR switch. By limiting the voltage in this manner, the SR switch avoids entering avalanche breakdown.
9 Citations
20 Claims
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1. A switch driver for controlling a power switch in a switched-mode power converter, so as to prevent excessive voltage levels across a synchronous rectification (SR) switch of the power converter, the switch driver comprising:
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a pull-down driver switch for sinking current from a control terminal of the power switch; a first pull-up driver switch for sourcing current to the control terminal, the first pull-up driver switch having a first on-state resistance; a second pull-up driver switch for sourcing current to the control terminal, the second pull-up driver switch having a second on-state resistance substantially higher than the first on-state resistance; a mode indication input; a switch control input, which controls the pull-down driver switch, the first pull-up driver switch, and the second pull-up driver switch; and a high-side control circuit configured to disable the first pull-up driver switch responsive to a burst-mode indication at the mode indication input, wherein the first and second pull-up driver switches are coupled to a same driver power supply having a same driver sourcing voltage, such that the same driver sourcing voltage is applied to the control terminal responsive to the first and/or the second pull-up driver switches being turned on. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for controlling a power switch in a switched-mode power converter so as to prevent excessive voltage levels across a synchronous rectification (SR) switch of the power converter, the power converter including a switch driver comprising first and second pull-up driver switches wherein the second pull-up driver switch has an on-state resistance substantially higher than an on-state resistance of the first pull-up driver switch, the method comprising;
- detecting that a load of the power converter is drawing a low power level;
responsive to the detecting, entering a burst mode of operation and disabling the first pull-up driver switch; andcoupling the first and second pull-up driver switches to a same driver power supply having a same driver sourcing voltage, such that the same driver sourcing voltage is applied to a control terminal of the power switch responsive to the first and/or the second pull-up driver switches being turned on. - View Dependent Claims (10, 11)
- detecting that a load of the power converter is drawing a low power level;
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12. An isolated power converter, comprising:
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an input for coupling to an input power source; an output for coupling to a load; a transformer comprising a primary winding and a secondary winding; a power stage configured to switch power from the input to the primary winding, the power stage comprising a power switch and a switch driver for controlling the power switch; a synchronous rectification (SR) switch configured to rectify power provided by the secondary winding, the SR switch having an SR voltage across first and second terminals of the SR switch and having an avalanche breakdown voltage level associated with the SR voltage; a controller configured to control a power transfer to the output by generating a switch control signal, and to generate a burst-mode indication upon detecting that the load is in a low-power state; wherein the switch driver comprises; a pull-down driver switch for sinking current from a control terminal of the power switch; first and second pull-up driver switches for sourcing current to the control terminal, wherein the second pull-up driver switch has an on-state resistance substantially higher than an on-state resistance of the first pull-up driver switch; a switch control input for coupling to the switch control signal; and a high-side control circuit configured to disable the first pull-up driver switch responsive to the burst-mode indication. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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20. A switch driver for controlling a power switch in a switched-mode power converter, so as to prevent excessive voltage levels across a synchronous rectification (SR) switch of the power converter, the switch driver comprising:
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a pull-down driver switch for sinking current from a control terminal of the power switch; a first pull-up driver switch for sourcing current to the control terminal, the first pull-up driver switch having a first on-state resistance; a second pull-up driver switch for sourcing current to the control terminal, the second pull-up driver switch having a second on-state resistance substantially higher than the first on-state resistance; a mode indication input; a switch control input, which controls the pull-down driver switch, the first pull-up driver switch, and the second pull-up driver switch; and a high-side control circuit configured to disable the first pull-up driver switch responsive to a burst-mode indication at the mode indication input, wherein the high-side control circuit comprises; a high-side pre-driver for controlling the first pull-up driver switch; and high-side logic circuitry having the mode indication and the switch control as inputs, and configured to disable the high-side pre-driver based upon the mode indication, wherein the second pull-up driver switch is not disabled based upon the mode indication.
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Specification