FIELD OF INVENTION
The present invention relates to a smart lighting driver for measurement of input power and method thereof. The present invention more particularly relates a system and method for predictive input power calculation in smart lighting driver. 5
BACKGROUND AND PRIOR ART
Several kind of AC metering systems have been proposed and used in the prior arts, which typically calculates the input power by measuring the voltage, current, 10 phase, power factor values which are digitalized by very high speed ADC’s to get phase difference between V and I with RMS values to get input power by using the formula P = V*I*cosՓ.
In several other prior arts, methods using current transformers and shunt 15 operations to predict the input power are disclosed. However, for these methods, much faster microcontroller is needed to sample AC waveforms at faster rate which leads to extra very complex electronic circuit.
JP2014026737 (A) discloses a lighting device, a luminaire using the same and an 20 illumination system capable of precisely calculating the input power even when the characteristics of the light source load are not uniform and the ambient temperature of the light source load varies. This invention uses the lighting device wherein the input power estimating unit estimates the input power with a constant value of a circuit loss to be corrected regardless of an input voltage and a lighting 25 state of the light source load.
EP2434844 (A2) discloses measurement of input power without using a current transformer and obtains input power with sufficient accuracy even if there is a change in the ambient temperature of a light source load. A detection resistor is 30
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connected in series to a switching element of a power conversion circuit and detects a current flowing in the switching element. By using a power setting value outputted from a power setting part so as to determine a size of power supplied to a discharge lamp and a current detection value corresponding to an output of the detection resistor, a power calculation part obtains input power through correction 5 of a fluctuation of a current detection value caused by a change in the ambient temperature of the discharge lamp. However, the invention detects current flowing in the switching element.
JP2010277731 (A) discloses a compact lighting device simplifying a circuit for 10 calculating input power and realizing cost reduction as well as a lighting fixture, and also to provide an illuminating system using the same. This invention calculates input power by sensing output voltage, output current and input switching current.
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Patent No. 9,042,127 discloses a method can be used for controlling the switching operation of a switching power converter that includes a semiconductor switch coupled in series to an inductor. The switching power converter consumes an input current from a power supply and provides an output current to a load. In each switching cycle a switch-on time instant is detected for the semiconductor 20 switch. The semiconductor switch is closed thus enabling, at the detected switch-on time instant, the input current passing through the semiconductor switch. The semiconductor switch is opened after a desired on-time, during which the input current rises from zero to a peak value, has passed. A time interval is detected, in which the instantaneous output current is not zero. The invention claims to auto 25 calibrate the output current and controls the dimming for the LED system by using a switching power converter to control the input current (switching current) from a power supply and provides an output current to a load.
US20120112735 discloses an electronic apparatus including a power supply unit, 30 a current value calculator, and an input power value calculator. The current value
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calculator is configured to calculate a current value on a power supply cable led out from the power supply unit based on a voltage between two ends of the power supply cable and a resistance value of the power supply cable. The input power value calculator is configured to calculate an input power value of the power supply unit based on the current value on the power supply cable calculated by the 5 current value calculator and an input/output characteristic (efficiency) of the power supply unit. In LED driver, efficiency is a function of output voltage. This invention calculates efficiency based on current.
US20160254748 discloses a switched power converter includes a power stage. 10 The power stage includes a sensor for sensing an output current to obtain a sensed output current, a sensor for sensing an output voltage to obtain a sensed output voltage, and a sensor for sensing an input voltage to obtain a sensed input voltage. The power converter further includes a look-up table or mathematical relationship implementation for deriving an efficiency measure of the power converter from 15 the sensed input voltage, the sensed output voltage and the sensed output current by relating an energy taken by a load and an energy delivered by the input voltage for a specific period of time. This invention is calculating efficiency of power converter in specified time in a DC/DC converter.
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US20150054494 discloses a power supply detecting circuit including a first voltage detecting module configured to detect an input voltage of a power supply module; a micro control unit (MCU) connected to the first voltage detecting module; a display module connected to the MCU; a second voltage detecting module configured to detect an output voltage of the power supply module; and a 25 current detecting module configured to detect an output current of the power supply module. The MCU is capable of comparing the detected input voltage, the detected output voltage, and the detected output current of the power supply module with corresponding predetermined parameters and calculating an output power of the power supply module. This invention is measuring AC input power. 30 However, the AC signals directly need complex and fast circuits.
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US20130113458 determines the type of an LED power driver (i.e., a magnetic transformer or an electronic transformer) by manipulating the AC voltage produced by the power driver so that it may be analyzed and the type of power driver reliably determined. In various embodiments, a system for detecting an AC 5 power supply type includes a circuit for monitoring a negative half or a positive half of an output voltage of the AC power supply and an analyzer for determining the AC power supply type based at least in part on a presence or absence of an envelope in the monitored output voltage. This invention is determining type of power supply i.e. AC or DC power supply of an LED driver. 10
Thus, in view of the above prior arts, it is clear that prior arts need complex and fast circuits for the prediction of input power.
Hence the present invention aims to predict the input power of smart LED drivers 15 with much simple circuitry and avoiding complex True RMS AC measurement and hence provides low component count and lower cost circuit for input power measurement.
OBJECTS OF THE INVENTION 20
The principal objective of the present invention is to predict the input power of smart LED drivers with much simple circuitry and avoiding complex True RMS AC measurement.
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Another object of the present invention is to predict the input power by estimating circuit loss a function of average rectified input AC voltage and output power.
Yet another object of the present invention is to not use any switching current to measure the output power, rather using the average rectified input AC voltage by a 30
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simple DC measurement of input and output parameters which reduces the need of complex AC/switching signal power measurement.
Yet another object of the present invention is topredict input AC power by sensing output voltage, output current and average rectified DC voltage of input AC 5 without the use of input switching current which makes the AC power prediction simpler by sensing only DC signals and hence, simplifies the circuit.
Yet another object of the present invention is to focus on predicting input power characteristics by using parameters like average rectified input AC, output 10 voltage, output current and output power.
Yet another object of the present invention is to calculate efficiency as a function of output voltage, current and input voltage which is more accurate.
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Another object of the present invention is to predict input AC power by measuring DC parameter.
Yet another object of the present invention is to read DC equivalent signals from output and input to predict input AC power. 20
Yet another object of the present invention is to provide low component count andlower cost circuit for input power measurement.
Still another object of the present invention is to measure DC output current which 25 is less complicated measurement, hence more cost effective method.
Still another object of the present invention is to predict AC power of an AC input LED driver.
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SUMMARY OF THE INVENTION
In accordance with the said objectives, the present invention provides an alternate and novel method for predicting the input power in smart LED drivers without involving complex AC power measurement technique. Smart LED driver already 5 has the information of output parameters (output voltage and output current) which can be used to predict input power, if correct efficiency is known. Efficiency is a function of output power and input voltage; hence by measuring the input voltage, one can predict input power without complexity of AC power measurement. The present invention uses a simple DC measurement of output and 10 average rectified input AC to predict AC power eradicating the need of complex AC power measurement and reducing the number of components used, which in turn reduces the size and cost of the PCB. Smart LED AC/DC driver predicts the input power by average rectified input AC and DC output measurement.
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BRIEF DESCRIPTION OF THE DRAWINGS
It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered for 20 limiting of its scope, for the invention may admit to other equally effective embodiments.
Figure 1 shows block diagram of smart lighting driver for predicting input power; 25
Figure 2 shows overall efficiency predicted by a predictive efficiency calculator;
Figure 3 shows input power predicted by realizing the ratio of output power and efficiency;
Figure 4 shows graph of overall efficiency line coefficient (Kline) with respect to input line; 30
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Figure 5 shows graph of efficiency power co-efficient (Kload) as a function of power.
DETAIL DESCRIPTION OF THE INVENTION
Accordingly the present invention provides an alternate and novel method for 5 predicting the input power in smart LED drivers without involving complex AC power measurement technique.
Referring to the figure 1, smart lighting driver (100) for predicting input power according to the present invention has a single/ multistage power converter (5), an 10 input rectifier (10), an input signal averager unit (15), High Voltage Isolated SMPS unit (20), level converter (25), current sensing amplifier (30), primary digital circuit (35), secondary digital circuit (40), optical isolated data transfer unit (45) and voltage divider circuit (50).
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The input AC power is converted to rectified DC voltage through High voltage Isolated SMPS. The current at the output side is sensed through a current sense device (55). The current sense amplifier (30) amplifies the current signal to a desired level to be read by digital circuit. The voltage at the secondary side is converted to the desired DC voltage level by a voltage divider (50) to be read by 20 secondary digital circuit (40).The sensed current and the sensed voltage at the output side goes as an input to the secondary digital circuit (40). The input AC power is rectified using input signal rectifier (10) and averaged with an input signal averaging circuit (15) and goes as an input to the level converter (25) where it gets converted to the desired DC, and in turn serves as an input voltage signal to 25 the primary side to the primary digital circuit (35).
Since, this is an optical isolated circuit, the primary side sensing is achieved by using a primary digital circuit (35) and the data is optically transmitted to the secondary digital circuit (40) using an isolator (45). The secondary digital circuit 30
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(40) receives the input side parameters (input voltage) from the isolator (45) as well as output side parameters (output voltage, output current). The overall computation power lies within the secondary digital circuit (40). The input power prediction is conducted by the claimed algorithm which resides in secondary digital circuit (40). 5
The design consists of driver mounted with a control card which has the microcontroller at the output side. Smart AC/DC driver referred here is an AC/DC converter which has DC at the output. Smart LED AC/DC drivers whose AC power is to be measured is connected with a DC load whose voltage and current is 10 measured by a microcontroller sitting on the output side of the driver. The concept to predict the input power is realized by a general formula which is defined as – the input power is calculated as the ratio of output power to the efficiency (ƞ),
P input = P output / ƞ. 15
The overall efficiency is a function of three parameters as mentioned below:-
Ƞ = ƞ typical*ƞ line*ƞ power
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Where ƞ typical is the typical efficiency of the given smart LED AC/DC converter, ƞlineis the efficiency multiplier which is a function of input voltage. ƞ power is the efficiency multiplier which is a function of output power. The overall efficiency is predicted by a predictive efficiency calculator as shown in figure 2and supported 25 by figure4.After predicting the overall efficiency, the input power is predicted by realizing the ratio of output power and efficiency as shown in figure 3 and figure 5.
Some observation has been done at different input voltages and it is concluded 30 that the predicted input power is very close to actual input power, as mentioned in table (1). Hence, this method is practically used for predicting input power.
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Table 1- Parameters observed at 50% dimming at different voltages
V input I input V output I output P output Actual Predicted
power power
150 0.421 56.275 0.97384 54.977 62.8 64.8 5
240 0.277 56.275 0.97384 54.977 63.63 63.845
280 0.247 56.275 0.97384 54.977 64.15 63.96

WE CLAIM
1. A smart lighting driver (100) for predicting input power comprising of:
a single/ multistage power converter (5);
an input rectifier (10); 5
an input signal averager unit (15);
High Voltage Isolated SMPS unit (20);
level converter (25);
current sensing amplifier (30);
primary digital circuit (35); 10
secondary digital circuit (40);
optical isolated data transfer unit (45); and
voltage divider circuit (50).
2. The smart lighting driver (100) as claimed in claim1 wherein the smart lighting 15 driver (100) has microcontroller at the output side.
3. The smart lighting driver (100) as claimed in claim1 wherein smart AC/DC driver is an AC/DC converter having DC at the output.
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4. A method for predicting the input AC power in Smart LED drivers by sensing output voltage, output current and average rectified DC voltage of input AC without involving complex AC Power measurement technique.
5. The method for predicting the input AC power as claimed in claim 4 wherein 25 the input AC power is converted to rectified DC voltage through High voltage Isolated SMPS (20).
6. The method for predicting the input AC power as claimed in claim 4 wherein the input AC power is rectified using said input signal rectifier (10); 30
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averaged with an input signal averaging circuit (15);
goes as an input to the level converter (25) where it gets converted to the
desired DC; and
serves as an input voltage signal to the primary side to the primary digital
circuit (5 35).
7. The method for predicting the input AC power as claimed in claim 4 wherein
the primary side sensing is achieved by using said primary digital circuit (35)
and the data is optically transmitted to said secondary digital circuit (40) using
10 said optical isolated data transfer unit (45).
8. The method for predicting the input AC power as claimed in claim 4 wherein
said secondary digital circuit (40) receives the input side parameters selected
from input voltage or the like from said optical isolated data transfer unit (45)
15 as well as output side parameters selected from output voltage, output current
or the like.
9. The method for predicting the input AC power as claimed in claim4 wherein
20 the input power is calculated as the ratio of output power to the efficiency (ƞ),
P RinputR = P RoutputR / ƞ
wherein, the overall efficiency Ƞ = ƞ RtypicalR*ƞ RlineR*ƞ Rpower
Where ƞ Rtypical Ris the typical efficiency of the given smart LED AC/DC converter,
ƞRline Ris the efficiency multiplier which is a function of input voltage and ƞ RpowerR is
25 the efficiency multiplier which is a function of output power.