Methods and devices for detecting the input voltage and discharging the residuevoltage

Patent metadata

Field	Value
Publication number	US-2016164428-A1
Application number	US-201514670918-A
Country	US
Kind code	A1
Filing date	Mar 27, 2015
Priority date	Dec 3, 2014
Publication date	Jun 9, 2016
Grant date	—

Abstract

The present invention relates to power conversion systems, specifically, it relates to a device for detecting the DC voltage rectified from the AC power supply voltage in an AC-DC converter, primarily used to determine whether the DC input voltage is under a brown-out level and to monitor whether the AC power supply is removed and to discharge the residue DC voltage generated in a high frequency filter capacitor, which is used to filter high frequency noise signals of the AC power supply, during the removal of the AC power.

First claim

1 . A device for detecting input voltages and discharging residue voltages, comprising:
a detection unit receiving a rectified DC input voltage, and according to fluctuations of the input voltage, generating a detection voltage signal having different logic levels; a triangle signal generator having a first capacitor, wherein in any one cycle of the input voltage at a moment the detection voltage signal changes from a first state to a second state, the first capacitor begins to charge, and in a following consecutive cycle of said any one cycle at a moment the detection voltage signal changes from the second state to the first state, the first capacitor begins to discharge; a reset signal generator having a second capacitor, wherein the second capacitor charges synchronously with the first capacitor and begins to discharge in the following consecutive cycle at a moment the detection voltage signal changes from the first state to the second state g, wherein the reset signal generator compares a varying voltage of the first capacitor and a varying voltage of the second capacitor and according to a comparison result triggers generation of a reset signal; an AC power removal and brown-out status determination unit comprising a counter, wherein within a preset period when the counter does not receive a first state reset signal and the voltage of the first capacitor is not lower than the voltage of the second capacitor, the AC power removal and brown-out status determination unit generates a brown-out detection signal indicating the input voltage at brown-out status; and when the voltage of the first capacitor is lower than the voltage of the second capacitor within the preset period, the AC power removal and brown-out status determination unit generates a power removal signal indicating the removal of the AC power supply.

2 . The device of claim 1 , wherein, in the detection unit an anode of a Zener diode is connected to a drain of a junction field effect transistor (JFET), and the input voltage is applied to a cathode of the Zener diode, thereby generating detection voltage signal at a source of the junction field effect transistor.

3 . The device of claim 2 , wherein when the input voltage exceeds a breakdown voltage of the Zener diode, the detection unit generates the detection voltage signal of the first state having a high logic level, and when the input voltage is lower than the breakdown voltage of the Zener diode, the detection unit generates the detection voltage signal of the second state having a low logic level.

4 . The device of claim 2 further comprising:
a rectifier circuit having a high frequency filter capacitor connected across two input terminals of the rectifier circuit, wherein an AC power supplied to the two input terminals is rectified through the rectifier circuit to produce the DC input voltage; and
a discharge branch having a switch connected between the source of the junction field effect transistor and ground; wherein during the AC power removal, a high level power removal signal is produced, which turns on the switch of the discharge branch to discharge the residue voltage of the high-frequency filter capacitor.

5 . The device of claim 2 , wherein:
during the AC power removal, a residue voltage of the AC power is discharged to a set safety level voltage V BRR _ DC ; during brown-out state, an effective value of the input voltage is V BO _ RMS and a duty cycle of the detection voltage signal at the first state is D BO ; during startup, the effective value of the input voltage is V BI _ RMS and the duty cycle of the detection voltage signal at the first state is D BI ; and after the first and the second capacitors complete charging synchronously for a same period of time, a maximum voltage of the second capacitor is V CLM , and a maximum voltage of the first capacitor is V CTM satisfy the equation:

V
CLM

V
CTM

=

1
-

1

(

D
BI

1
-

D
BI

)

·

(

1

D
BO

-
1

)

;

Where

D
BO

=

1
-

1
90



sin

-
1



(

V

BRR

_

DC

2



V

BO

_

RMS

)

,


and

D
BI

=

1
-

1
90



sin

-
1

Assignees

• Alpha & Omega Semiconductor

Inventors

• Chen Yu-Ming
• Liu Chih-Yuan
• Huang Pei-Lun

Classifications

• H02M1/32 Primary

  Means for protecting converters other than automatic disconnection · CPC title

• G01R19/22 Primary

  using conversion of AC into DC · CPC title

• G01R19/0007

  Frequency selective voltage or current level measuring (measuring frequency G01R23/00; testing attenuation in line transmission systems H04B3/48; monitoring testing in transmission systems H04B17/00) · CPC title

• H02M7/04 Primary

  by static converters · CPC title

• H02M1/322

  Means for rapidly discharging a capacitor of the converter for protecting electrical components or for preventing electrical shock · CPC title