US 12,143,021 B2
System and methods for switching an active clamp flyback converter
Selvarajan Shanthosh, San Jose, CA (US); and Bryan Wayne McCoy, Phoenix, AZ (US)
Assigned to SEMICONDUCTOR COMPONENTS INDUSTRIES, LLC, Scottsdale, AZ (US)
Filed by SEMICONDUCTOR COMPONENTS INDUSTRIES, LLC, Phoenix, AZ (US)
Filed on May 27, 2022, as Appl. No. 17/804,404.
Claims priority of provisional application 63/202,304, filed on Jun. 4, 2021.
Prior Publication US 2022/0393597 A1, Dec. 8, 2022
Int. Cl. H02M 3/335 (2006.01); H02M 1/00 (2006.01); H02M 1/34 (2007.01)
CPC H02M 3/33507 (2013.01) [H02M 1/0058 (2021.05); H02M 1/342 (2021.05)] 19 Claims
OG exemplary drawing
 
1. A power converter system comprising:
an active clamp flyback (ACF) converter including:
a primary winding of a transformer coupled between a positive input and a switch node;
a main switch coupled between the switch node and a negative input of the ACF converter; and
an active clamp coupled between the positive input and the switch node, the active clamp including a clamp capacitor coupled in series with a clamp switch;
a pulse width modulation (PWM) controller configured to control ON/OFF states of the clamp switch and the main switch according to a PWM cycle operating at a PWM cycle frequency; and
a frequency controller configured to:
compare a fall period of a switch node voltage to a zero-volt-switching threshold to determine a negative current condition at the switch node;
detect a count of PWM cycles in a sequence of PWM cycles having a hard-switch condition characterized by the fall period reaching a timeout period; and
adjust the zero-volt-switching threshold based on the count.