Temperature compensation in output feedback of a flyback power converter

• US 8,351,223 B2
• Filed: 07/19/2010
• Issued: 01/08/2013
• Est. Priority Date: 07/22/2009
• Status: Expired due to Fees

• Current Assignee: Richpower Microelectronics Corporation (KY) (MediaTek, Inc.)
• Original Assignee: Richpower Microelectronics Corporation (KY) (MediaTek, Inc.)
• Inventors: Huang, Pei-Lun, Chou, Ke-Chih
• Primary Examiner(s): Vu, Bao Q
• Application Number:
  US12/839,002
• Publication Number:
  US 20110018609A1
• Time in Patent Office: 904 Days
• Field of Search: 363/20, 363/21.01, 363/21.12, 363/21.15, 363/21.17, 363/21.18, 363/902, 363/907, 323/902, 323/907
• US Class Current: 363/21.12
• CPC Class Codes: H02M 1/0025 Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

A secondary circuit of a flyback power converter has a resistor network to monitor the output current of the flyback power converter, so as to generate a voltage to apply to a base of a bipolar junction transistor to thereby provide a collector signal for output feedback. The resistor network has a temperature-dependent resistance to compensate the temperature dependence of the base-emitter voltage imparted to the output current and thereby stable the output current.

Claims

1. A secondary circuit of a flyback power converter including a capacitor connected between an output end and a ground end to supply an output current, and a secondary coil of a transformer to provide a secondary current for charging the capacitor, the secondary circuit comprising:

a resistor network connected in a path of the output current to generate a voltage according to the output current, the resistor network comprising;

a current sense resistor connected between the ground end and the capacitor;

a resistor and a thermistor connected in series to each other and connected in parallel to the current sense resistor; and

a bipolar junction transistor having a base connected to the resistor network to receive the voltage and providing a collector signal for output feedback;

wherein the resistor network has a resistance varying with temperature to compensate for a temperature effect of a base-emitter voltage of the bipolar junction transistor on the output current.