Switched mode power supply controller and method
AssigneeMotorola, Inc.
InventorsJosef Halamik, Jefferson Hall
Life of this patent
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Abstract
A switched mode power supply has a transformer and a power switch to switch a primary current for operation in a critical conduction mode. The switched mode power supply has a controller which switches off a primary current when a peak current is reached. The primary current is switched on again when a zero current condition in the secondary is detected the first time after the primary current has been switched off and a minimum primary current off time has been reached.
Claims6
A switched mode power supply controller for a transformer and a power switch for switching a primary current of said transformer for operation in a critical conduction mode, said switched mode power supply controller comprising
- a control output for coupling to said power switch,
- a first circuit to detect a zero current condition on a secondary side of said transformer when said power switch is switched off;
- a timer circuit having a predetermined time delay, said time delay being started when said power switch is switched off;
- a second circuit comprising logic circuitry and a memory, said memory being set by said logic circuitry if the following conditions are fulfilled;
- said power switch is switched off and
- said zero current condition is detected the first time by said first circuit after said power switch has been switched off;
- said power supply controller switching said power switch on via said control output if said memory is set and said delay of said timer circuit has expired.
A switched mode power supply comprising a transformer having a power switch to switch a primary current of said transformer for operation in a critical conduction mode, said switched mode power supply having a power supply controller comprising
- a control output coupled to said power switch,
- a first circuit to detect a zero current condition on a secondary side of said transformer when said power switch is switched off;
- a timer circuit having a predetermined time delay, said time delay being started when said power switch is switched off;
- a second circuit comprising logic circuitry and a memory, said memory being set by said logic circuitry if the following conditions are fulfilled;
- said power switch is switched off and
- said zero current is detected the first time by said first circuit after
- said power switch has been switched off;
- said power supply controller switching said power switch on via said control output if said memory is set and said delay of said timer circuit has expired.
A method for controlling a switched mode power supply, said switched mode power supply comprising a transformer having a power switch to switch a primary current of said transformer for operation in a critical conduction mode, said method comprising the steps of
- a) switching said power switch off if a peak primary current is reached;
- b) switching said power switch on if both of the following conditions are met
- a predetermined time delay expired after said power switch is switched off in said step a);
- and
- a zero current condition is detected the first time after said power switch has been switched off.
Dependencies are inferred from the claim text.