Control circuit and control method of flyback converter

Patent metadata

Field	Value
Publication number	US-10972012-B2
Application number	US-201816118480-A
Country	US
Kind code	B2
Filing date	Aug 31, 2018
Priority date	Sep 20, 2017
Publication date	Apr 6, 2021
Grant date	Apr 6, 2021

Abstract

Embodiments of the present application provide a control circuit and a control method of a flyback converter, the control circuit comprises: a first sampling module, a second sampling module, and a control module; the first sampling module is coupled to the control module and the flyback converter, and outputs a first voltage signal to the control module; the second sampling module is coupled to the control module and the flyback converter, and outputs a second voltage signal to the control module; where the first voltage signal reflects an input voltage of the flyback converter, the second voltage signal reflects an output voltage of the flyback converter; the control module outputs a control signal according to the first voltage signal and the second voltage signal, and the control signal reflects a turn-on time of the switch in the flyback converter.

First claim

What is claimed is:

1. A control circuit of a flyback converter, comprising:
a first sampling module, a second sampling module, a dimming module and a control module;
the first sampling module being respectively coupled to the control module and the flyback converter, and outputting a first voltage signal to the control module;
the second sampling module being respectively coupled to the control module and the flyback converter, and outputting a second voltage signal to the control module;
the dimming module being coupled to the control module and configured to outputting a dimming signal, as an instruction signal, to the control module;
wherein the first voltage signal reflects an input voltage of the flyback converter, and the second voltage signal reflects an output voltage of the flyback converter; the control module outputs a control signal according to the dimming signal, the first voltage signal and the second voltage signal, and the control signal reflects a turn-on time of a switch in the flyback converter,
wherein the turn-on time of the switch of the flyback converter is calculated according to the instruction signal, an inductance of a primary side winding in the flyback converter, the first voltage signal and the second voltage signal,
wherein the instruction signal reflects an expected value of an output current of the flyback converter,
wherein the first sampling module comprises a first resistor and a second resistor; one end of the first resistor is coupled to an input end of the flyback converter, and the other end of the first resistor is coupled to the second resistor; and one end of the second resistor is coupled to the first resistor, the other end of the second resistor is grounded; a coupling point between the first resistor and the second resistor is coupled to the control module, and outputs the first voltage signal to the control module,
wherein the flyback converter is an isolated flyback converter; the control circuit further comprises a primary side auxiliary circuit, and an auxiliary winding of the primary side auxiliary circuit is wound around a primary side of a transformer of the flyback converter; wherein the second sampling module is coupled to the flyback converter through the primary side auxiliary circuit;
wherein the primary side auxiliary circuit further comprises a diode and a capacitor;
an anode of the diode is coupled to a first end of the auxiliary winding, a cathode of the diode is coupled to one end of the capacitor, and the other end of the capacitor is coupled to a second end of the auxiliary winding;
the second sampling module comprises a third resistor and a fourth resistor;
wherein one end of the third resistor is coupled to a cathode of the diode, the other end of the third resistor is coupled to the fourth resistor; and
one end of the fourth resistor is coupled to the third resistor, the other end of the fourth resistor is grounded; a coupling point between the third resistor and the fourth resistor is coupled to the control module, and outputs the second voltage signal to the control module,
wherein the number of turns of the auxiliary winding is the same as the number of turns of a secondary side winding of the flyback converter, and/or a turn-on voltage drop of the diode of the primary side auxiliary circuit is the same as a turn-on voltage drop of a secondary side diode of the flyback converter;
wherein the turn-on time is calculated as follows:

t
on

⁢
_Dim

=

2
⁢

t
s

⁡

(

R
⁢

⁢
3

+

R
⁢

⁢
4

R
⁢

⁢
4

⁢

V
O_Sense

+

V
F

)

⁢

N
S

N
A

⁢

L
P

⁢

D
Dim

⁢
k

R
⁢

⁢
1

+

R
⁢

⁢
2

R
⁢

⁢
2

⁢

Assignees

• Delta Electronics Shanghai Co

Inventors

• Fu Xiaoping
• Zhang Xinghua

Classifications

• H02M1/0009

  Devices or circuits for detecting current in a converter · CPC title

• H02M3/33515 Primary

  with digital control · CPC title

• H03M1/1245

  Details of sampling arrangements or methods · CPC title

• H02M1/08

  Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters · CPC title

• H02M3/33523 Primary

  with galvanic isolation between input and output of both the power stage and the feedback loop · CPC title