Switched mode power supply method and apparatus
View Patent ↗In one or more embodiments, a switched mode power supply circuit is configured to monitor and control its output voltage during discontinuous conduction mode (DCM) operation, to prevent output over-voltage conditions. For example, in one embodiment, a switched mode power supply circuit is configured to operate selectively in continuous conduction mode (CCM) and discontinuous conduction mode (DCM), and it includes a control circuit that is configured to detect an output over-voltage condition during DCM operation. The control circuit reduces the output voltage of the switched mode power supply circuit responsive to detecting the output over-voltage condition, such as by activating a pull-down device and/or temporarily reverting the switched mode power supply circuit to continuous conduction mode (CCM) operation.
1. A switched mode power supply circuit comprising:
a regulation circuit configured to operate selectively in a discontinuous conduction mode (DCM) wherein the regulation circuit stops cycling high-side and low-side switches in a switched output of the regulation circuit, such that the high-side and low-side switches are off and the switched output floats, and in a continuous conduction mode (CCM) wherein the regulation circuit cyclically switches the high-side and low-side switches on and off; and
a control circuit configured to monitor an output voltage of the switched mode supply circuit during DCM operation of the regulation circuit and temporarily revert the regulation circuit to CCM operation responsive to the output voltage reaching a defined over-voltage limit by being configured to:
temporarily reactivate the regulation circuit such that it performs one or more cycles of on/off switching of the high-side and low-side switches to relieve the over-voltage condition;
detect that that inductor current in a switching circuit inductor transitions from positive load current to zero or negative load current, said switching circuit inductor being associated with generating the output voltage via switching by the regulation circuit; and
responsive to said detecting, deactivate the regulation circuit such that it returns to DCM operation.
2. The switched mode power supply circuit of claim 1 , wherein the control circuit comprises a voltage monitoring circuit to monitor the output voltage, a current monitoring circuit to monitor the inductor current, and wherein the control circuit reverts the regulation circuit to CCM operation responsive to the voltage monitoring circuit and returns the regulation circuit to DCM operation responsive to the current monitoring circuit.
3. The switched mode supply circuit of claim 2 , wherein the current monitoring circuit comprises a zero crossing detection circuit that is configured to detect zero crossings of the inductor current.
4. The switched mode power supply circuit of claim 1 , wherein a first voltage threshold defines the defined over-voltage limit, and wherein the control circuit is further configured to generate a fault signal or initiate a shut-down of the switched mode power supply circuit responsive to detecting that the output voltage reaches a second voltage threshold that is higher than the first voltage threshold.
5. A method of controlling a switched mode power supply circuit that selectively operates in a continuous conduction mode (CCM) wherein a regulation circuit of the switched mode power supply circuit cyclically switches high-side and low-side switches of a switched output on and off to regulate an output voltage of the switched mode power supply circuit and a discontinuous conduction mode (DCM) wherein the regulation circuit stops cycling the high-side and low-side switches, such that the high-side and low-side switches are off and the switched output floats, the method comprising:
detecting an output over-voltage condition during DCM operation of the switched mode power supply circuit; and
temporarily reverting the switched mode power supply circuit to CCM operation responsive to detecting the output over-voltage condition by:
temporarily reactivating the regulation circuit such that it performs one or more cycles of on/off switching of the high-side and low-side switches to relieve the output over-voltage condition;
detecting that inductor current in a switching circuit inductor transitions from positive load current to zero or negative load current, said switching circuit inductor being associated with generating the output voltage via switching by the regulation circuit; and
responsive to said detecting, deactivating the regulation circuit such that it returns to DCM operation.
6. The method of claim 5 , wherein detecting an output over-voltage condition during DCM operation of the switched mode power supply circuit comprises using a monitoring circuit to monitor the output voltage relative to one or more voltage thresholds.
7. The method of claim 5 , wherein detecting an output over-voltage condition during DCM operation of the switched mode power supply circuit comprises detecting that the output voltage is at or above a first voltage threshold, the method further comprising generating a fault signal or initiating shut-down of the switched mode power supply responsive to detecting that the output voltage is at or above a second voltage threshold that is above the first voltage threshold.
8. The method of claim 7 , further comprising latching the fault signal.