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US 12,651,971 B2Granted
Active clamp flyback converter with accurate current sense and the method thereof
AssigneeChengdu Monolithic Power Systems Co., Ltd.
InventorsKun Yang, Naixing Kuang, Kai Wang
Life of this patent
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Abstract
An active clamp flyback converter with accurate sense of an output voltage is discussed. The active clamp flyback converter adopts a feedback voltage generator which generates a feedback voltage in response to an input voltage, a voltage at a switch node, an auxiliary control signal, and a current signal indicative of a current flowing through a primary winding.
Claims11
An active clamp flyback converter, comprising:
- a transformer, configured to receive an input voltage, the transformer including a primary winding, a secondary winding, and a leakage inductance;
- a main power switch, coupled between the primary winding and a primary reference ground, an electrical connection of the main power switch and the primary winding forming a switch node;
- an auxiliary switch, coupled between the switch node and the input voltage;
- a feedback voltage generator, configured to generate a feedback voltage in response to the input voltage, a voltage at the switch node, an auxiliary control signal, and a current signal indicative of a current flowing through the primary winding;
- and
- a controller, configured to generate a main control signal and the auxiliary control signal in response to the feedback voltage, to respectively control the main power switch and the auxiliary switch;
- wherein the feedback voltage generator comprises:
- a first sample & hold circuit, configured to sample and hold the current signal when the auxiliary switch is turned on for a first time length, to generate a first hold signal;
- a second sample & hold circuit, configured to sample and hold the current signal when the auxiliary switch is turned on for a second time length, to generate a second hold signal;
- and
- an operational circuit, configured to perform a multiplication operation on an inductance value of the leakage inductance, a difference between the first hold signal and the second hold signal, and a reciprocal of a time difference between the first time length and the second time length, wherein a multiplication result is added to the voltage at the switch node, and is subtracted by the input voltage, to generate the feedback voltage.
8 more elements
A feedback voltage generator used in an active clamp flyback converter, the active clamp flyback converter including:
- a main power switch coupled between a primary winding and a primary reference ground, and an auxiliary switch coupled between a switch node and an input voltage, the switch node being formed by an electrical connection of the main power switch and the primary winding, the feedback voltage generator comprising:
- a first sample & hold circuit, configured to sample and hold a current signal indicative of a current flowing through the primary winding when the auxiliary switch is turned on for a first time length, to generate a first hold signal;
- a second sample & hold circuit, configured to sample and hold the current signal when the auxiliary switch is turned on for a second time length, to generate a second hold signal;
- and
- an operational circuit, configured to perform a multiplication operation on an inductance value of a leakage inductance of the primary winding, a difference between the first hold signal and the second hold signal, and a reciprocal of a time difference between the first time length and the second time length, wherein a multiplication result is added to a voltage at the switch node, and is subtracted by the input voltage, to generate a feedback voltage.
2 more elements
A method used in an active clamp flyback converter, the active clamp flyback converter including:
- a transformer, a main power switch coupled between a primary winding and a primary reference ground, and an auxiliary switch coupled between a switch node and an input voltage, the transformer having the primary winding, a secondary winding and a leakage inductance, the switch node being formed by an electrical connection of the main power switch and the primary winding, the method comprising:
- delivering the input voltage received at the primary winding to the secondary winding by periodically turning on and turning off the main power switch, to generate an output voltage;
- turning on the auxiliary switch during an OFF period of the main power switch;
- sampling a current flowing through the primary winding, a voltage at the switch node, and the input voltage;
- generating a feedback voltage in response to the current flowing through the primary winding, the voltage at the switch node, the input voltage, and an auxiliary control signal;
- generating a main control signal and the auxiliary control signal in response to the feedback voltage, to respectively control the main power switch and the auxiliary switch;
- postponing the auxiliary control signal with a first time length, to generate a first delay signal;
- sampling and holding the current flowing through the primary winding in response to the first delay signal, to generate a first hold signal;
- postponing the auxiliary control signal with a second time length, to generate a second delay signal;
- sampling and holding the current flowing through the primary winding in response to the second delay signal, to generate a second hold signal;
- performing a multiplication operation on an inductance value of the leakage inductance, a difference between the first hold signal and the second hold signal, and a reciprocal of a time difference between the first time length and the second time length, to generate a multiplication signal;
- and
- generating the feedback voltage by adding the voltage at the switch node to the multiplication signal and subtracting the input voltage from the multiplication signal.
10 more elements
Dependencies are inferred from the claim text.