FIELD OF THE INVENTION
The present invention relates to a multi-modulation mode LED (Light Emitting Diode) driving circuit, particularly to a LED driving circuit, which can modulate the period and energy level of driving power.
BACKGROUND OF THE INVENTION
Refer to FIG. 1, the conventional power control technology, such as the dimming control, usually adopts an ON-OFF Interval modulation method, wherein the ratio of an ON interval and an OFF interval is modulated to vary the energy output. It is the most frequently-used method. In the above-mentioned method, there is an EDR (Excitation Dynamical Ratio) defined as
and the traditional EDR is
The above-mentioned equation will attain an EDR of infinity, and the effect of the infinite EDR can be explained with the following analogy example: a steel wire is bent by 90 degrees, and restored to be a straight wire, and then bent by 90 degrees again; after the above-mentioned steps are repeated many times, the steel wire will be fractured finally; if the steel wire is bent by only 10 degrees, much more times of bending is required to fracture the steel wire. Similarly, when LED works in two extremities, it will age faster. Therefore, the conventional power control technology of too high an EDR greatly affects the lifetime of LED.
SUMMARY OF THE INVENTION
The primary objective of the present invention is to overcome the above-mentioned problem. In the present invention, a gradient amplitude is used in a turn-on interval TON to control an inverter lest too high an EDR appear. Thereby, the inverter and LED can be effectively controlled to prevent LED from aging fast.
To achieve the above-mentioned objective, the present invention discloses a multi-modulation mode LED driving circuit, which controls an inverter to perform energy conversion to drive at least one LED. The driving circuit of the present invention is modulated by a timing control signal containing an on time and a standby time. In the present invention, a varying-amplitude modulation energy is added to the standby time. In the present invention, the start and end of the on time respectively have a gradually-ascending interval and a gradually-descending interval, and/or the start and end of the standby time respectively have a gradually-descending interval and a gradually-ascending interval. In the present invention, two or more different cycles are mixed to generate high-reliability and wide-dynamical range modulation modes, which can make an energy conversion unit and a rear-end LED group operate in reliable ranges of some performance characteristics.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing the waveform output by a conventional power modulation/control circuit.
FIG. 2 is a block diagram schematically showing the circuit according to the present invention.
FIG. 3 to FIG. 7 are diagrams showing the waveforms of different-mode timing control signals according to different preferred embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Below, the technical contents of the present invention will be described in detail in cooperation with the drawings.
The present invention discloses a multi-modulation mode LED driving circuit, which controls an inverter to perform energy conversion to drive at least one LED. Refer to FIG. 2, a block diagram schematically showing the architecture of the present invention. The driving circuit of the present invention at least comprises: a power source 1, an energy ratio synthesis/control unit 2, a switching unit 3, an energy conversion unit 4 and an LED group 5. The power source 1 provides power. The energy ratio synthesis/control unit 2 receives a total-energy control signal 6, such as a signal indicating that the total energy is modulated from 10% to 100%, and generates a timing control signal TON/TSB containing an ON-Time TON and a Standby-Time TSB, wherein the sum of TON and TSB is exactly Ttotal in FIG. 1, and Ttotal is the time interval of two timing cycles. The timing control signal TON/TSB enables the switching unit 3 to modulate the energy sent to the energy conversion unit 4. The energy ratio synthesis/control unit 2 generates the timing control signal TON/TSB according to the total-energy control signal 6 received in the input thereof. The present invention is characterized in that the energy ratio synthesis/control unit 2 controls the switching unit 3 to add a gradually varying-amplitude modulation energy in the Standby-Time TSB to generate a new EDR. In the start and end of the ON-Time TON/Standby-Time TSB, the timing control signal TON/TSB have a gradually ascending interval and a gradually descending interval. Mixing two or more different cycles can generate high-reliability and wide-dynamical range modulation modes, which can effectively control some special energy conversion units 4 and make the energy conversion unit 4 and the rear-end LED group 5 operate in the reliable ranges of some performance characteristics. Refer to FIG. 3 for an embodiment of the present invention. In FIG. 3, a non-zero energy intensity E2 is maintained in the Standby-Time TSB, which can provide a standby mode function to greatly improve the modulation range of the LED driving circuit and maintain the overall operation of the energy conversion unit 4 not completely stopping. Thereby, the perceptible noise is inhibited. Further, via the different energy intensities in the ON-Time TON and Standby-Time TSB, the energy conversion unit 4 and the LED group 5 are effectively controlled, and the LED group 5 is effectively excited. When the amplitude of the output energy is to be changed, the duty width of the timing control signal TON/TSB is changed, but the frequency of the timing control signal TON/TSB is maintained. Thus, the bandpass-featured energy conversion unit 4 can work at a point of maximum efficiency. Changing the duty width can change the voltage that the energy conversion unit 4 outputs to the LED group 5 and can attain a regulation control function, which makes the product more reliable and efficient.
In a preferred embodiment is adopted a constant-frequency and varying duty width mode, wherein the frequency is maintained unchanged, but the duty width (i.e. the lengths of the ON-Time TON and Standby-Time TSB) is changed. As the frequency is fixed (fON=fSB), the bandpass-featured energy conversion unit 4 can still operate at a point of maximum efficiency (usually in a better frequency range). Changing the duty width makes the energy conversion unit 4 output a smaller-amplitude square-wave voltage to vary the voltage driving the LED group 5 and thus attain a regulation controlling function. Alternatively, a varying-frequency (fON≠fSB) and constant duty width mode, or a varying-frequency and varying duty width, may also be adopted.
Refer to FIG. 4. In another preferred embodiment, a Stop-Time TS with a zero energy intensity (ES=0) is added into the Standby-Time TSB. Therefore, the present invention can achieve the same effect via various combinations of duty cycles of multiple modulation modes.
Refer to FIG. 5 for a variation of the embodiment shown in FIG. 3. In FIG. 5, a gradually-ascending interval TON-up and a gradually-descending interval TON-down are respectively added to the start and end of the ON-Time TON and used to prevent the energy transition between E1 and E2 lest the EDR (E1/E2) being too high, wherein E1 is the energy intensity in the ON-Time TON, and E2 is the energy intensity in the Standby-Time TSB. Refer to FIG. 6 for a variation of the embodiment shown in FIG. 4. In FIG. 6, a gradually-ascending interval TON-up and a gradually-descending interval TON-down are respectively added to the start and end of the ON-Time TON, and a gradually-descending interval TSB-down and a gradually-ascending interval TSB-up are respectively added to the start and end of Standby-Time TSB.
Refer to FIG. 7 for another preferred embodiment of the present invention. In FIG. 7, a gradually-descending interval TSB-down and a gradually-ascending interval TSB-up are respectively added to the start and end of Standby-Time TSB, to prevent the energy transition between E1 and E2 lest the EDR (E1/E2) being too high.
In the present invention, a varying-amplitude modulation energy E2 is added to the Stop-Time TS, and thus
The total energy intensity is
wherein Ttotal is the time interval of two timings.
The power sent to the LED group 5 is still maintained the same; therefore, a power regulation function is attained. Compared to the infinite EDR in the conventional technology, EDR has been greatly reduced in the present invention, and the aging of the LED group 5 is also decelerated.
The present invention can maintain the original dynamical peak energy and modulate the total energy simultaneously. Therefore, the present invention can expand the range of dynamical energy modulation without affecting the lifetime of the LED group 5, wherein the control signal may be of a constant-frequency and varying-duty width mode, a varying frequency and constant duty width mode, or a varying-frequency and varying duty width mode.
Refer to FIG. 5 again. The extended buffer interface timing control signal contains the gradually-descending interval TON-down and the gradually-ascending interval TON-up and they may have characteristics of constant frequency, varying frequency, constant duty width or varying duty width. The extended buffer interface timing control signal of the present invention can improve the energy transition between E1 and E2 lest EDR (E1/E2) be too high. The total energy in Ttotal—the time interval of two timings or the burst period can be calculated from the following equation:
wherein TON and TSB are the time intervals for allocating energy, and E(TFI)×TFI+E(TRI)×TRI is the energy in the gradually-ascending intervals TON-up and TSB-up, and the gradually-descending intervals TON-down and TSB-down.
The preferred embodiments described above are only to exemplify the present invention but not to limit the scope of the present invention. Therefore, any equivalent modification or variation according to the spirit of the present invention is to be also included within the scope of the present invention.
Patent Grant
7755302
