Secondary controller for a flyback converter including a sense resistor fault detection

Patent metadata

Field	Value
Publication number	US-10033285-B1
Application number	US-201715627253-A
Country	US
Kind code	B1
Filing date	Jun 19, 2017
Priority date	Jun 19, 2017
Publication date	Jul 24, 2018
Grant date	Jul 24, 2018

Abstract

A power system and related methods provide sense resistor fault detection and safe operation of switching power converters and connected devices such as portable electronic devices powered by the switching power converter. The power system detects an open circuit or short circuit condition of the sense resistor and controls output current of the switching power converter to ensure safe operating conditions of the power system and connected equipment. The power system can also detect initial inrush current of the connected equipment and detect a duty cycle of the switching power converter to positively detect a short circuit condition of the sense resistor.

First claim

We claim:

1. A secondary controller for a flyback converter, comprising; a measurement circuit configured to measure a sense resistor voltage across a sense resistor connected in series with a secondary winding in the flyback converter, wherein the measurement circuit comprises an operational amplifier having a first input connected through a first resistor to a first terminal of the sense resistor and having a second input connected through a second resistor to a second terminal of the sense resistor; an analog-to-digital converter; and a matched pair of current-source transistors such that an output of the operational amplifier is coupled to a gate of each current-source transistor and such that a source of a first one of the current-source transistors is coupled to the first input of the operational amplifier and a source of a second one of the current-source transistors is coupled to provide an input to the analog-to-digital converter; and a logic circuit coupled to the measurement circuit and configured to switch off an output power switch for the flyback converter responsive to the sense resistor voltage exceeding a first threshold.

2. The secondary controller of claim 1 , wherein the first threshold is an open-circuit threshold and wherein the logic circuit is configured to detect an open-circuit fault at the sense resistor responsive to the sense resistor voltage exceeding the open-circuit threshold.

3. The secondary controller of claim 1 , wherein the first threshold is an inrush-current threshold value and wherein the logic circuit is configured to detect a short-circuit fault at the sense resistor responsive to the sense resistor voltage exceeding the inrush-current threshold value.

4. The secondary controller of claim 1 , wherein the logic circuit is further configured to compare a duty cycle for a terminal voltage of the secondary winding to a duty-cycle threshold and to turn off the output power switch based on detecting a short circuit condition when the duty cycle is above the duty-cycle threshold and the sense resistor voltage is below the first threshold.

5. The secondary controller of claim 1 , further comprising:
a data cable interface for connecting to a mobile device, wherein the secondary controller is configured to alert a primary controller when the secondary controller detects the mobile device through a data channel in the data cable interface.

6. The secondary controller of claim 5 , wherein the data cable interface is a Universal Serial Cable (USB) interface.

7. The secondary controller of claim 5 , wherein the data cable interface is a Lightning cable interface.

Assignees

• Dialog Semiconductor Inc
• Dialog Semiconductor Uk Ltd

Inventors

• Zhang Xiaoyong
• Kronmuller Frank
• Zhang Jiandong
• Chen Lijie
• Wang Honglai
• Chen Yimin

Classifications

• H02M3/33507

  with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence) · CPC title

• H02H3/044

  Checking correct functioning of protective arrangements, e.g. by simulating a fault (for differential current circuit breakers H02H3/335) · CPC title

• H02H7/1213

  for DC-DC converters · 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