Detection circuit and LED tube including the same

1. A voltage detection circuit, comprising:

an impedance coupled between inputs of an LED tube;

a voltage detector configured to detect a voltage across the impedance;

a voltage threshold circuit configured to provide a threshold voltage;

a first control circuit configured to compare an input voltage across the inputs of the tube to the threshold voltage, and to control the voltage detector to detect the voltage across the impedance when the input voltage is less than the threshold voltage; and

a second control circuit configured to enable the voltage detector when the voltage threshold circuit is charged to a starting voltage;

wherein the voltage threshold circuit comprises a first capacitor and the detection circuit comprises,

a first charging loop configured to charge the first capacitor to reach the starting voltage; and

the first control circuit further comprises a transistor adapted to connect the impedance between the input voltage and a power ground, and the transistor is adapted to be turned on to begin the detection and is adapted to be turned off when not detection.

2. The detection circuit according to claim 1 , wherein the threshold voltage is not greater than 30 volts.

3. The detection circuit according to claim 1 , wherein the first control circuit is configured to compare the input voltage with the starting voltage that acts as the threshold voltage, and to control the voltage detector to detect the voltage across the impedance when the input voltage is less than the starting voltage, wherein the first control circuit is adapted to decouple the impedance from the inputs before the detection and to couple the impedance between the input during the detection.

4. The detection circuit according to claim 1 , wherein the first charging loop is configured to set a time required for an initial charge of the first capacitor to reach the starting voltage as:

from 90 milliseconds when the input voltage is 230 volts; to

260 milliseconds when the input voltage is 90 volts.

5. The detection circuit according to claim 4 , wherein the detection circuit comprises a first discharging loop configured to discharge the first capacitor when the voltage detector starts detection.

6. The detection circuit according to claim 5 , wherein the first discharging loop is configured to set the time for discharging the first capacitor to be less than the starting voltage as less than 1 millisecond, and

the first charging loop is configured to set the time range required for recharging the discharged first capacitor to reach the starting voltage as:

from 50 milliseconds when the input voltage is 230 volts; to

200 milliseconds when the input voltage is 90 volts.

7. The detection circuit according to claim 1 , wherein the voltage detector is configured to detect the voltage across the impedance to determine whether a further impedance, apart from the LED tube, is linked to the impedance connected across the inputs of the LED tube; whereby, when the voltage is greater than a first threshold, the voltage detector determines the absence of the further impedance apart from the LED tube; and whereby, when the voltage is less than the first threshold, the voltage detector determines the presence of the further impedance apart from the LED tube.

8. The detection circuit according to claim 1 , further comprising a rectifier bridge, wherein the voltage threshold circuit, the first control circuit and the impedance are configured to:

connect to an output of the rectifier bridge to receive an input voltage of full-wave rectification; or

connect to an input of the rectifier bridge to receive an input voltage of half-wave rectification.

9. The detection circuit according to claim 1 , at least partially implemented in an integrated circuit.

10. An LED tube, comprising the detection circuit for the tube in claim 1 , wherein the LED tube is connected to a mains supply;

the LED tube further comprising an LED light source and an LED driving circuit for driving the LED light source,

wherein the detection circuit initiates the LED driving circuit when the voltage across the impedance is detected to be greater than a first threshold.

11. The LED tube according to claim 10 , wherein the LED light source and the LED driving circuit are in a series connection, and the series connection is in parallel with the detection circuit, especially in parallel with the impedance of the detection circuit.

12. A voltage detection circuit, comprising:

an impedance coupled between inputs of an LED tube;

a voltage detector configured to detect a voltage across the impedance;

a voltage threshold circuit configured to provide a threshold voltage;

a first control circuit configured to compare an input voltage across the inputs of the tube to the threshold voltage, and to control the voltage detector to detect the voltage across the impedance when the input voltage is less than the threshold voltage; and a timing circuit configured to enable the voltage threshold circuit and the first control circuit before timing expires, and to disable the voltage threshold circuit and the first control circuit when timing is expired;

wherein the timing circuit comprises a second capacitor, a second charging loop configured to charge the second capacitor, and a voltage limit element, wherein the timing circuit is configured to enable the voltage threshold circuit and the first control circuit when the voltage of the second capacitor is lower than a threshold of the voltage limit element.

13. The detection circuit according to claim 12 , wherein the timing ranges:

from 275 milliseconds when the input voltage is 230 volts; to

800 milliseconds when the input voltage is 90 volts.

14. The detection circuit according to claim 12 , wherein the timing circuit further comprises a second discharging loop configured to discharge the second capacitor when the circuit is not connected to the input voltage.