Patent Application
20140028203
This application claims the benefit of Taiwan patent application No. 101127426, filed on Jul. 30, 2012, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an LED driver circuit and more particularly to a high efficiency AC LED driver circuit.
2. Description of Related Art
Electrical transmission is usually in AC nowadays, because AC electrical transmission is more efficient than DC electrical transmission. A voltage of the AC power transmitted from a power plant to each family is 110V or 220V. However, the voltage of the AC power received by users is usually not that ideal but has some error. In general, an error range of the AC power is +/−10%. For example, a tolerance range of an 110V AC power is between 99V and 122V.
LEDs are common lighting appliances nowadays. Compared to conventional incandescent bulbs, LEDs have advantages of higher luminous efficiency and lower power consumption. However, LEDs can only be conducted in a one-way circuit such that LEDs cannot be connected to a conventional AC outlet. Therefore, an AC LED driver circuit is invented. With reference to
a rectifier unit 60 having an input terminal and an output terminal; wherein the input terminal is connected to an AC power AC/IN and converts the AC power AC/IN into a pulsating DC power outputted by the output terminal;
an LED unit 61 having multiple LED sources and connected to the output terminal of the rectifier unit 60 to form a power loop;
a voltage controlled transistor 62 having a control terminal and connected in series with the power loop; wherein the voltage controlled transistor controls currents flowing in the power loop;
a current detection unit 63 connected in series with the power loop to obtain a loop current value of the power loop; and
a control unit 64 having a built-in reference current value, electrically connected to the current detection unit 63 through a low-frequency filter and electrically connected to the control terminal of the voltage controlled transistor 62; wherein the control unit 64 obtains the loop current value from the current detection unit 63, the control unit 64 compares the loop current value with the reference current value, and then feedback controls the loop current of the power loop based on a comparison result of the loop current value and the reference current value through the voltage controlled transistor 62.
In conclusion, a user can control the loop current flowing through the LED unit 61 by setting or adjusting the reference current value of the control unit 64 to further control an output power and a luminance of the LED unit 61 by the loop current.
However, the voltage of the AC power AC/IN outputted by the power plant is not stable; thus, a means of stabilizing the loop current is adopted in a conventional AC LED driver circuit to prevent same products from having difference degrees of luminance due to the instability or error of the AC power AC/IN. For example, if a voltage between two ends of the LED unit 61 is 80V and a power of 12.8 W is needed to achieve a desired luminance, the user just sets the reference current value as 160 mA to fix the loop current at 160 mA to further achieve an objective of fixing the output power of the LED unit 61 at 12.8 W.
With reference to
To investigate the reason, according to the power equation (input power Pin=output power Pout+lost power Plose) and the efficiency equation (efficiency η=output power Pout/input power Pin), the main reason of the decrease of the efficiency of the conventional AC LED driver circuit is that the output power of the LED unit 61 is not increased with the increasing of the input power Pin, that is, the lost power Plose is increased with the input power Pin. Therefore, a better solution must be provided to solve the above-mentioned problem.
The main objective of the invention is to provide a high efficiency AC LED driver circuit.
The LED driver circuit comprises:
a rectifier unit having an input terminal and an output terminal; wherein the input terminal is connected to an AC power and the rectifier unit converts the AC power into a pulsating DC power outputted by the output terminal;
an LED light string connected to the rectifier unit and having multiple LED units connected in series; wherein each LED unit has an anode terminal and a cathode terminal;
multiple voltage controlled transistors respectively and electrically connected to the cathode terminals of the LED units to form multiple hierarchical shunt circuits; wherein each voltage controlled transistor has a control terminal;
a current detection unit electrically connected to the voltage controlled transistors, and forming a power loop with the rectifier unit, the LED light string and the voltage controlled transistors; wherein the current detection unit is used to detect a current flowing through the power loop, and the current flowing through the power loop is a sum of currents flowing through the shunt circuits; and
a power efficiency control unit electrically connected to the current detection unit, series nodes between the LED units, and the control terminals of the voltage controlled transistors; wherein the power efficiency control unit obtains a voltage drop of each series node between the LED units, and then adjusts current intensity of a current flowing through each shunt circuit based on a voltage drop of each LED unit.
When the AC power increases, the power efficiency control unit adjusts a current flowing through each shunt circuit by each voltage controlled transistor to distribute an increased lost power Plose of each voltage controlled transistor caused by the increase of the voltage of the AC power to each LED unit, and each LED unit consumes the lost power Plose such that the lost power Plose is converted to the output power Pout. Therefore, lost power Plose of each voltage controlled transistor is decreased and output power Pout of each LED unit is increased to achieve the objective of increasing the whole efficiency of the LED driver circuit.
With reference to
a rectifier unit 10 having an input terminal and an output terminal; wherein the input terminal is connected to an AC power AC/IN and the rectifier unit 10 converts the AC power AC/IN into a pulsating DC power outputted by the output terminal; in a preferred embodiment, the rectifier unit 10 is a full-wave rectifier circuit or a half-wave rectifier circuit;
an LED light string 20 connected to the rectifier unit 10 and having multiple LED units 21 connected in series; wherein each LED unit 21 has an anode terminal and a cathode terminal; in a preferred embodiment, each LED unit 21 has multiple LED sources, each LED source is connected in series, parallel or series-parallel with another LED source in a same LED unit 21;
multiple voltage controlled transistors 30 respectively and electrically connected to the cathode terminals of LED units 21 and forming multiple hierarchical shunt circuits; wherein each voltage controlled transistor 30 has a control terminal; in a preferred embodiment, each of the voltage controlled transistors 30 is a MOSFET, a JFET or a BJT, and the control terminal is a gate of the above-mentioned transistors;
a current detection unit 40 electrically connected to the voltage controlled transistors 30, and forming a power loop with the rectifier unit 10, the LED light string 20 and the voltage controlled transistors 30; wherein the current detection unit 40 is used to detect a current flowing through the power loop; the current flowing through the power loop is a sum of currents flowing through the shunt circuits; in a preferred embodiment, the current detection unit 40 is a detection resistor; and
a power efficiency control unit 50 electrically connected to the current detection unit 40, series nodes between the LED units 21, and the control terminals of the voltage controlled transistors 30; wherein the power efficiency control unit 50 obtains a voltage drop of each series node between the LED units 21, and then adjusts current intensity of a current flowing through each shunt circuit based on a voltage drop of each LED unit 21; in a preferred embodiment, the power efficiency control unit 50 is electrically connected to the current detection unit 40 through a low-frequency filter 51 and the low-frequency filter 51 is a analog filter or a digital filter; the digital filter can be a down-sampling filter.
When a user uses the LED driver circuit, the user first conducts a first shunt circuit of the power efficiency control unit 50. When voltage drops between the LED units 21 are increased with increase of voltage of the AC power AC/IN, the user gradually decreases a current flowing through the first shunt circuit and gradually increases a current flowing through a second shunt circuit. When the voltage of the AC power AC/IN is decreased such that the voltage drops between the LED units 21 are decreased, the user gradually decreases the current flowing through a lower shunt circuit and gradually increases the current flowing through an upper shunt circuit.
With Further reference to
Therefore, when the voltage of the AC power AC/IN is increased, the power efficiency control unit 50 adjusts a current flowing through each shunt circuit by each voltage controlled transistor to distribute an increased lost power Plose of each voltage controlled transistor 30 caused by the increase of the voltage of the AC power AC/IN to each LED unit 21, and each LED unit 21 consumes the lost power Plose such that the lost power Plose is converted to the output power Pout. Therefore, lost power Plose of each voltage controlled transistor 30 is decreased and output power Pout of each LED unit 21 is increased to achieve the objective of increasing the whole efficiency of the LED driver circuit.
In addition, with reference to
According to the above description, when power of the multiple LED units 21 is increased with increase of the AC power AC/IN, the power efficiency control unit 50 gradually adjusts current intensity of a current flowing through each shunt circuit by each voltage controlled transistor 30 to decrease the loop current, that is, the original input power Pin prior to the increase of the AC power AC/IN is maintained after the AC power AC/IN is increased. Therefore, the original output power Pout prior to the increase of the AC power AC/IN is also maintained after the AC power AC/IN is increased.
Hence, when the input power Pin is temporarily increased due to the increase of the AC power AC/IN, the LED driver circuit decreases the loop current to maintain the original input power Pin after the AC power AC/IN is increased. The LED driver circuit further adjusts a current flowing through each shunt circuit to maintain the original output power Pout after the AC power AC/IN is increased. When the input power Pin and the output power Pout are both unchanged, the efficiency of the LED driver circuit must not be changed.
In conclusion, the LED driver circuit solves a problem of decreased efficiency and further keeps the efficiency at a high point.
| Number | Date | Country | Kind |
|---|---|---|---|
| 101127426 | Jul 2012 | TW | national |
