US 11,942,871 B2
Startup of secondary controller for primary controller powered from AC line
Rashed Ahmed, Fremont, CA (US); Pavan Kumar Kuchipudi, San Jose, CA (US); Myeongseok Lee, Campbell, CA (US); and Murtuza Lilamwala, San Jose, CA (US)
Assigned to Cypress Semiconductor Corporation, San Jose, CA (US)
Filed by Cypress Semiconductor Corporation, San Jose, CA (US)
Filed on Dec. 18, 2020, as Appl. No. 17/127,523.
Prior Publication US 2022/0200476 A1, Jun. 23, 2022
Int. Cl. H02J 7/00 (2006.01); G06F 1/26 (2006.01); G06F 13/42 (2006.01); H02M 7/219 (2006.01)
CPC H02M 7/219 (2013.01) [G06F 1/266 (2013.01); G06F 13/4282 (2013.01); H02J 7/0042 (2013.01); G06F 2213/0042 (2013.01)] 20 Claims
OG exemplary drawing
 
1. A method, comprising:
receiving, at a primary side controller in an alternating current to direct current (AC-DC) converter, a rectified AC voltage through a pair of diodes, wherein the primary side controller is coupled to a discharge circuit and the discharge circuit is configured to discharge an external capacitor based on an undervoltage threshold;
determining, by the primary side controller, whether a control signal has been received from a secondary side controller, wherein the primary side controller is on a primary side of a transformer and the secondary side controller is on a secondary side of the transformer;
in response to determining that the control signal has not been received, increasing, by the primary side controller, a duty cycle of a primary field effect transistor (FET) that is coupled to the transformer;
determining, by the primary side controller, whether the rectified AC voltage of the AC-DC converter is below the undervoltage threshold;
in response to determining that the rectified AC voltage of the AC-DC converter is below the undervoltage threshold:
determining, by the primary side controller, a current duty cycle of the primary FET; and
turning off, by the primary side controller, the primary FET.