# US 2012/0249014 A1 · Circuit for leakage-current elimination in led t8 fluorescent tube

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- Number: US 2012/0249014 A1
- Document ID: US20120249014A1
- Status: Published application
- Kind: A1
- Application number: 13/075,177
- Filed: 2011-03-29
- Published: 2012-10-04
- Earliest claimed: 2011-03-29
- Assignees: Gre Alpha Electronics Ltd.
- Inventors: Milan Mei
- Web page: https://patentgrep.com/patent/US20120249014A1

## CPC

- H05B 45/325: Pulse-width modulation [PWM]
- H05B 45/3578: Emulating the electrical or functional characteristics of discharge lamps
- Y02B 20/30: Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS

## Abstract

An electric-shock protection circuit that incorporates a PWM start-up control circuit for controlling the start-up of the PWM controller IC. When an electric-shock current test is conducted, the PWM start-up control circuit prevents the starting up of this PWM controller IC. This circuit is realized by resistors, capacitors and switches. In order to achieve protection, the switches perform an operation that different electric paths are activated for a supply voltage condition of around 90-149Vac and another condition of around 150-264Vac. The circuit disclosed in this invention: can be used in the electric-shock current test with a wide range of supply voltage; can ensure that the peak value of the shock current is lower than the safety threshold for human bodies; and can solve the problem encountered in carrying out the test of Standard UL935 where one end of the LED light tube is connected to the electric grid.

## Claims

### Claim 1

A pulse-width-modulation (PWM) start-up control circuit for controlling start-up of a PWM controller IC comprising:
a protection circuit to prevent operational start-up of the PWM controller IC when conducting an electric-shock current test;
wherein the protection circuit comprises:
one or more resistors,
one or more capacitors, and
one or more switches;
the one or more switches are configured to activate a first electric path when a first supply voltage condition of 90-149Vac is presented and a second electric path when a second supply voltage condition of 150-264Vac is presented.

### Claim 2 (depends on 1)

The PWM start-up control circuit of claim 1, wherein the protection circuit comprises:
a resistor,
a transistor, and
a diode;
such that a collector of the transistor is connected to an anode of the diode;
an emitter of the transistor is connected to the resistor; and
a base of the transistor is connected to a voltage detection circuit that detects a voltage level of an electric grid.

### Claim 3 (depends on 1)

The PWM start-up control circuit of claim 1, further comprising a start-up capacitor for the PWM controller IC.

### Claim 4 (depends on 3)

The PWM start-up control circuit of claim 3, wherein capacitance of the start-up capacitor is within 4.7-15 μF.

### Claim 5 (depends on 1)

The PWM start-up control circuit of claim 1, wherein the PWM start-up control circuit is configured for a lighting fixture that employs a T8 LED light tube.

### Claim 6 (depends on 1)

The PWM start-up control circuit of claim 1, wherein the protection circuit further comprises:
an EMI filter,
an AC/DC rectifier,
a DC/AC converter, and
the PWM controller IC; and
input ports of the EMI filter are connected to a AC power supply; output ports of the EMI filter are connected to the AC/DC rectifier; and
when conducting an electric-shock current test, the PWM start-up control circuit is serially connected, via the DC/AC converter, to an equivalent resistor of a human body.

### Claim 7 (depends on 6)

The PWM start-up control circuit of claim 6, wherein total input capacitance of the EMI filter is less than 0.08 μF.

### Claim 8 (depends on 2)

The PWM start-up control circuit of claim 2, wherein the protection circuit further comprises:
an EMI filter,
an AC/DC rectifier,
a DC/AC converter, and
the PWM controller IC; and
input ports of the EMI filter are connected to a AC power supply; output ports of the EMI filter are connected to the AC/DC rectifier; and
when conducting an electric-shock current test, the PWM start-up control circuit is serially connected, via the DC/AC converter, to an equivalent resistor of a human body.

### Claim 9 (depends on 8)

The PWM start-up control circuit of claim 8, wherein total input capacitance of the EMI filter is less than 0.08 μF.