Flyback power converter with programmable output and control circuit and control method thereof

A control method of a flyback power converter for supplying a programmable output voltage which is switchable between at least a first voltage and a second voltage according to a setting signal, wherein the first voltage is higher than the second voltage, the control method comprising:

• operating a power switch according to an operation signal, so as to convert the input voltage to the output voltage;
• generating a voltage sense signal according to the output voltage;
• generating a current sense signal according to a switch current flowing through the power switch;
• generating a feedback signal according to an output power and the setting signal;
• generating the operation signal according to the voltage sense signal, the current sense signal, and the feedback signal;
• reducing an operation frequency of the operation signal when the feedback signal is lower than a frequency reduction point;
• and
• adaptively adjusting the operation signal by at least one of the following methods according to the voltage sense signal, such that the flyback power converter maintains a same or relatively higher operation frequency of the operation signal and provides a same output current when the output voltage is switched to the second voltage as compared with when the output voltage is switched to the first voltage, to maintain a phase margin:
• (1) adaptively adjusting the frequency reduction point of the feedback signal according to the voltage sense signal;
• (2) adaptively adjusting a current gain according to the voltage sense signal, and amplifying the current sense signal with the current gain to generate a current sense gain signal, such that the current sense gain signal when the output voltage is switched to the second voltage, is higher than the current sense gain signal when the output voltage is switched to the first voltage;
• (3) adaptively adjusting a feedback attenuation according to the voltage sense signal, and attenuating the feedback signal with the feedback attenuation to generate a feedback attenuation signal, such that the feedback attenuation signal when the output voltage is switched to the second voltage, is lower than the feedback attenuation signal when the output voltage is switched to the first voltage;
• and
• (4) adaptively adjusting a slope compensation signal according to the voltage sense signal, and compensating a slope of the current sense signal with the slope compensation signal to generate a current sense compensation signal, such that the current sense compensation signal when the output voltage is switched to the second voltage, is higher than the current sense compensation signal when the output voltage is switched to the first voltage.

A control circuit of a flyback power converter for supplying a programmable output voltage which is switchable between at least a first voltage and a second voltage according to a setting signal, wherein the first voltage is higher than the second voltage;

• wherein the flyback power converter includes:
• a transformer circuit, which includes:
• a primary winding, for receiving an input voltage;
• a secondary winding, for generating the output voltage at an output node;
• and a tertiary winding, for generating a voltage sense signal according to the output voltage;
• a power switch circuit, which is coupled to the primary winding, for operating a power switch therein according to an operation signal, so as to convert the input voltage to the output voltage;
• a current sense circuit, which is coupled to the power switch circuit, for generating a current sense signal according to a switch current flowing through the power switch;
• an opto-coupler circuit, which is coupled to the secondary winding, for generating a feedback signal according to an output power and the setting signal;
• and the control circuit;
• wherein the control circuit reduces an operation frequency of the operation signal when the feedback signal is lower than a frequency reduction point;
• wherein the control circuit further adaptively adjusts the operation signal according to the voltage sense signal, such that the flyback power converter maintains a same or relatively higher operation frequency of the operation signal and provides a same output current when the output voltage is switched to the second voltage as compared with when the output voltage is switched to the first voltage, to maintain a phase margin;
• the control circuit comprising:
• a frequency control circuit, which is coupled to the tertiary winding and the opto-coupler circuit, for generating a clock signal according to the voltage sense signal and the feedback signal;
• a comparison circuit, which is coupled to the opto-coupler circuit and the current sense circuit, for generating a comparison signal according to the feedback signal and the current sense signal;
• and
• a flip-flop circuit, which is coupled to the frequency control circuit and the comparison circuit, for generating the operation signal according to the clock signal and the comparison signal;
• wherein the frequency control circuit adaptively adjusts the frequency reduction point of the feedback signal by adjusting the clock signal according to the voltage sense signal.

A control circuit of a flyback power converter for supplying a programmable output voltage which is switchable between at least a first voltage and a second voltage according to a setting signal, wherein the first voltage is higher than the second voltage;

• wherein the flyback power converter includes:
• a transformer circuit, which includes:
• a primary winding, for receiving an input voltage;
• a secondary winding, for generating the output voltage at an output node;
• and a tertiary winding, for generating a voltage sense signal according to the output voltage;
• a power switch circuit, which is coupled to the primary winding, for operating a power switch therein according to an operation signal, so as to convert the input voltage to the output voltage;
• a current sense circuit, which is coupled to the power switch circuit, for generating a current sense signal according to a switch current flowing through the power switch;
• an opto-coupler circuit, which is coupled to the secondary winding, for generating a feedback signal according to an output power and the setting signal;
• and the control circuit;
• wherein the control circuit reduces an operation frequency of the operation signal when the feedback signal is lower than a frequency reduction point;
• wherein the control circuit further adaptively adjusts the operation signal according to the voltage sense signal, such that the flyback power converter maintains a same or relatively higher operation frequency of the operation signal and provides a same output current when the output voltage is switched to the second voltage as compared with when the output voltage is switched to the first voltage, to maintain a phase margin;
• the control circuit comprising:
• a frequency control circuit, which is coupled to the opto-coupler circuit, for generating a clock signal according to the feedback signal;
• a gain control circuit, which is coupled to the tertiary winding and the current sense circuit, for generating the current sense gain signal according to the voltage sense signal and the current sense signal;
• a comparison circuit, which is coupled to the opto-coupler circuit and the gain control circuit, for generating a comparison signal according to the feedback signal and the current sense gain signal;
• and
• a flip-flop circuit, which is coupled to the frequency control circuit and the comparison circuit, for generating the operation signal according to the clock signal and the comparison signal;
• wherein the gain control circuit adaptively adjusts the current gain according to the voltage sense signal, and amplifying the current sense signal with the current gain to generate the current sense gain signal, such that the current sense gain signal when the output voltage is switched to the second voltage, is higher than the current sense gain signal when the output voltage is switched to the first voltage.

A control circuit of a flyback power converter for supplying a programmable output voltage which is switchable between at least a first voltage and a second voltage according to a setting signal, wherein the first voltage is higher than the second voltage;

• wherein the flyback power converter includes:
• a transformer circuit, which includes:
• a primary winding, for receiving an input voltage;
• a secondary winding, for generating the output voltage at an output node;
• and a tertiary winding, for generating a voltage sense signal according to the output voltage;
• a power switch circuit, which is coupled to the primary winding, for operating a power switch therein according to an operation signal, so as to convert the input voltage to the output voltage;
• a current sense circuit, which is coupled to the power switch circuit, for generating a current sense signal according to a switch current flowing through the power switch;
• an opto-coupler circuit, which is coupled to the secondary winding, for generating a feedback signal according to an output power and the setting signal;
• and the control circuit;
• wherein the control circuit reduces an operation frequency of the operation signal when the feedback signal is lower than a frequency reduction point;
• wherein the control circuit further adaptively adjusts the operation signal according to the voltage sense signal, such that the flyback power converter maintains a same or relatively higher operation frequency of the operation signal and provides a same output current when the output voltage is switched to the second voltage as compared with when the output voltage is switched to the first voltage, to maintain a phase margin;
• the control circuit comprising:
• a frequency control circuit, which is coupled to the opto-coupler circuit, for generating a clock signal according to the feedback signal;
• an attenuator circuit, which is coupled to the tertiary winding and the opto-coupler circuit, for generating the feedback attenuation signal according to the voltage sense signal and the feedback signal;
• a comparison circuit, which is coupled to the attenuator circuit and the current sense circuit, for generating a comparison signal according to the feedback attenuation signal and the current sense signal;
• and
• a flip-flop circuit, which is coupled to the frequency control circuit and the comparison circuit, for generating the operation signal according to the clock signal and the comparison signal;
• wherein the attenuator circuit adaptively adjusts the feedback attenuation according to the voltage sense signal, and attenuating the feedback signal with the feedback attenuation to generate the feedback attenuation signal, such that the feedback attenuation signal when the output voltage is switched to the second voltage, is lower than the feedback attenuation signal when the output voltage is switched to the first voltage.

A control circuit of a flyback power converter for supplying a programmable output voltage which is switchable between at least a first voltage and a second voltage according to a setting signal, wherein the first voltage is higher than the second voltage;

• wherein the flyback power converter includes:
• a transformer circuit, which includes:
• a primary winding, for receiving an input voltage;
• a secondary winding, for generating the output voltage at an output node;
• and a tertiary winding, for generating a voltage sense signal according to the output voltage;
• a power switch circuit, which is coupled to the primary winding, for operating a power switch therein according to an operation signal, so as to convert the input voltage to the output voltage;
• a current sense circuit, which is coupled to the power switch circuit, for generating a current sense signal according to a switch current flowing through the power switch;
• an opto-coupler circuit, which is coupled to the secondary winding, for generating a feedback signal according to an output power and the setting signal;
• and the control circuit;
• wherein the control circuit reduces an operation frequency of the operation signal when the feedback signal is lower than a frequency reduction point;
• wherein the control circuit further adaptively adjusts the operation signal according to the voltage sense signal, such that the flyback power converter maintains a same or relatively higher operation frequency of the operation signal and provides a same output current when the output voltage is switched to the second voltage as compared with when the output voltage is switched to the first voltage, to maintain a phase margin;
• the control circuit comprising:
• a frequency control circuit, which is coupled to the opto-coupler circuit, for generating a clock signal according to the feedback signal;
• a slope compensation control circuit, which is coupled to the tertiary winding, for generating the slope compensation signal according to the voltage sense signal;
• an adder circuit, which is coupled to the slope compensation control circuit and the current sense circuit, for compensating the slope of the current sense signal with the slope compensation signal to generate a current sense compensation signal;
• a comparison circuit, which is coupled to the opto-coupler circuit and the adder circuit, for generating a comparison signal according to the feedback signal and the current sense compensation signal;
• and
• a flip-flop circuit, which is coupled to the frequency control circuit and the comparison circuit, for generating the operation signal according to the clock signal and the comparison signal;
• wherein the slope compensation control circuit adaptively adjusts the slope compensation signal according to the voltage sense signal, such that the current sense compensation signal when the output voltage is switched to the second voltage, is higher than the current sense compensation signal when the output voltage is switched to the first voltage.