Control circuit, control method and flyback converter of primary-side feedback control thereof
AssigneeSilergy Semiconductor Technology (Hangzhou) LTD
InventorsHuiqiang Chen, Jianxin Wang
Life of this patent
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Abstract
The disclosure relates to a control circuit, a control method and a flyback converter of primary-side feedback control including the control circuit. On the basis of the current sampling signal feedback, the flyback converter of primary-side feedback control is controlled to operate in a constant on time mode when the input voltage is large, and is controlled to operate in a peak current mode when the input voltage is close to a valley. Thus, the peak value of the primary-side current may not become too small because of a decreased input voltage, further avoiding occurrence of an error sampling after a blanking time due to excessive variations in demagnetization time.
Claims12
A control circuit for controlling a power stage circuit in a flyback converter of primary-side feedback control, comprising:
- a current sampling circuit configured to sample a primary-side current and to obtain a current sampling signal;
- a voltage sampling circuit configured to sample a voltage across an auxiliary winding after a blanking time and to obtain a voltage sampling signal;
- and
- a control signal generating circuit configured to generate a switching control signal in accordance with said voltage sampling signal and said current sampling signal, in which said switching control signal is generated in a constant on time mode when said current sampling signal is larger than a current threshold at a constant on time point, and is generated in a peak current mode when said current sampling signal is smaller than said current threshold at said constant on time point,
- wherein said switching control signal controls a power switch in said power stage circuit, and said constant on time point is a time point at which said switching control signal maintains to be valid for a predetermined constant on time period.
A control circuit for controlling a power stage circuit in a flyback converter of primary-side feedback control, comprising:
- a current sampling circuit configured to sample a primary-side current and to obtain a current sampling signal;
- a voltage sampling circuit configured to sample a voltage across an auxiliary winding after a blanking time and to obtain a voltage sampling signal, in which said blanking time varies with a peak value of said current sampling signal;
- and
- a control signal generating circuit configured to generate a switching control signal having a constant on time period in accordance with said voltage sampling signal;
- wherein said switching control signal controls a power switch in said power stage circuit, and
- said voltage sampling circuit comprises:
- a blanking circuit configured to provide a blanking signal representing a first time when said peak value of said current sampling signal is smaller than a first value, and provide a blanking signal representing a second time when said peak value of said current sampling signal is larger than a second value, and provide a blanking signal representing a third time when said peak value of said current sampling signal is smaller than said second value and larger than said first value, wherein said third time is a function of said peak value;
- and
- a sampling circuit configured to sample a voltage in accordance with said blanking signal.
A control method for controlling a flyback converter of primary-side feedback control, comprising:
- sampling a primary-side current to obtain a current sampling signal, and sampling a voltage across an auxiliary winding after a blanking time to obtain a voltage sampling signal;
- controlling a power switch in said flyback converter of primary-side feedback control in accordance with said voltage sampling signal and said current sampling signal, wherein said power switch is controlled in a constant on time mode when said current sampling signal is larger than a current threshold at a constant on time point, and is controlled in a peak current mode when said current sampling signal is smaller than said current threshold at said constant on time point;
- and
- said constant on time point is a time point at which said switching control signal maintains to be valid for a predetermined constant on time period.
Dependencies are inferred from the claim text.