Sensor Led Driver – Adaptive Current, Voltage, and Threshold Control
The latest sensor led driver has a range of features to suit specific applications. These include adaptive current, voltage, and threshold control to provide a highly accurate and efficient LED illumination system.
A sensor-led driver is a self-contained power supply that provides outputs matched to the electrical characteristics of the LED(s). It typically lists its specifications on the device, with one output current rating and a voltage range that varies based on the wattage of the LED.
Adaptive Current Control Circuit
The adaptive current control circuit, which is used by the sensor led driver, aims to adapt the current supplied to each individual LED channel according to the quality of the signal being received at the photo detector. To provide an optimal level of current, the circuit quantizes the sensed current by the ADC 313 to one of a set of possible programmable currents and stores the quantized current in the DAC 307 as the corresponding current In for each channel.
The current sensed by the DAC 313 is then sent to the LDO 304 via a feedback loop. LDO 304 compares Vref to Vsense, and if Vref is higher than Vsense, it increases the gate voltage applied to pass transistor QL, which increases the current flow through sense resistor RS and LED string 302 until it stabilizes at the programmed current level set by Vref.
When the current is below the programmed current, the op-amp 306 decreases the gate voltage applied to pass transistor QL, and current through RS drops until it stabilizes at Vref. At this point, the output of op-amp 306 is passed to the PD, which determines the output of the circuit and generates an analogue dimming signal.
This circuit can drive the LEDs within a wide input voltage range from 12 to 40 V. It has a high system efficiency and a fast response. In addition, it features a full-range analogue dimming and high-frequency pulse-width modulation (PWM) dimming methods with high linearity in wide range and excellent contrast ratios.
The circuit also features a low power dissipation and a high efficiency, as well as an accurate current and a low switching frequency variation quantity. Moreover, it can easily be integrated into a low-cost and small chip design. The circuit is suitable for use in a wide variety of applications. Especially, it is capable of driving several series-connected LEDs and can be a useful solution for controlling and monitoring the illumination intensity in medical diagnostic devices.
Adaptive Voltage Control Circuit
A sensor led driver with adaptive voltage control consists of multiple linear current regulators and a preregulator that has an output voltage that is automatically self-adjusted to the lowest value that is required to maintain the desired string current. This allows the driver to operate at minimal power dissipation and minimizes losses in the linear current regulators that are used to drive each LED string.
In this way, power loss is minimized and the overall efficiency of the driver is maximized. The preregulator also provides a low input voltage to the linear current regulators that are used to control current flow through each LED string.
The circuit can be designed to accommodate a large number of LED strings with a variety of forward voltage drops. The circuit can also be designed to support a wide range of power-supply voltages.
Another benefit of the circuit is that it can be used to share the current for multiple LED channels within the same unit. The current sharing can be achieved by regulating the current across each LED channel using the SCC module.
Moreover, the current-sharing performance of the system can be optimised for a number of different application situations. For example, the power loss in a single-channel system can be minimized if a higher number of MOSFETs are used. The power loss for a four-channel system can be optimized by using eight MOSFETs.
In addition, the system can be optimised for a wide variety of operating conditions and energy demands sensor led driver by adjusting the PWM duty cycle. This can be done by adjusting the current level of each LED string and determining a PWM duty cycle that is appropriate for the specific type of operating condition.
Further, the system can be optimised for generating high dimming performance by adjusting the PWM duty cycle and selecting an output level that is suited for the task at hand. The output level selected can be based on the desired dimming intensity, the number of available LED strings, or the desired dimming duration.
The circuit can be programmed to adjust the current level of each LED string using a combination of control signal 314, DAC 307 and Vboost. Initially, DAC 307 is set to its maximum possible level; then the voltage boost is increased by the luminance controller until all LED strings operate at or above a predefined master current level Iset (e.g., 40 mA). This approach reduces the number of individual current levels to a smaller number that are suitable for a particular application.
Adaptive Threshold Control Circuit
A sensor led driver is a device that controls the output voltage of an LED string based on the current flow through a sensing resistor. The input signal from the sensing resistor is compared to the reference voltage in a feedback loop, and a controller that operates in a linear region of the closed loop control system adjusts the output voltage until the current flowing through the resistor matches the reference voltage.
Adaptive thresholding is a type of thresholding that changes the threshold value dynamically over an image. This technique is useful for separating the dark and light regions of an image. It also helps in converting an image from grayscale to binary.
In adaptive thresholding, the image is first divided into smaller regions and the threshold value for these regions is calculated. Then, the values of pixels in each of these regions are assigned a value if they exceed a certain threshold.
The threshold values are determined based on the local mean intensity (first-order statistics) of the neighbourhood pixels. The blocksize of each pixel neighbourhood is also considered.
This method allows for more robust detection in highly variable lighting conditions, such as those found in industrial applications. It also provides better sensitivity to dc and EMI than conventional thresholding algorithms.
Another important advantage of adaptive thresholding is its ability to detect and segment images with varying illumination. This means that the image can be processed even in areas with a high probability of having an unstable power supply or low lighting.
Similarly, the adaptive thresholding algorithm also provides good EMC performance, which is important for a sensitive electronic device like a sensor led driver that may be operated in an electromagnetic environment. This is especially true if a large number of other electronic devices are located near the LED driver.
A threshold detector is a circuit that provides hysteresis. This means that it generates a logic one for each crossing of the threshold, and a zero for each non-crossing. This is done to allow a predetermined percentage of the incoming waveform to cross over the threshold.
Adaptive Output Voltage Control Circuit
Adaptive output voltage control (AVP) is used to regulate the output of a power supply according to the equation Vref=Vmax-IrefRo where Ro is the desired output impedance. This approach can be used to adjust the output of a power supply to reduce how many capacitors are required in the device.
A voltage regulator is designed to adjust the output voltage of a power supply over time, based on changes in the load. In AVP control, the output voltage of the regulator decreases with the increase in the output current, and vice versa. This technique can reduce how many output capacitors are required in the regulator, which may save circuit board area and cost.
The digital controller circuitry 100 uses this idea to change the adaptive output voltage reference value by a small step amount over a period of time, so that it maintains the sensor led driver power supply within a substantially constant output impedance range. In addition, the digital controller circuitry 100 controls the output current associated with the output voltage 180 to be limited to a peak current reference value that varies proportionally with respect to the adaptive output voltage reference value.
This allows the digital controller circuitry 100 to quickly switch between mode settings that reflect how much current is needed to supply an appropriate amount of power to a dynamic load. When the output voltage 180 begins to change rapidly, the digital controller circuitry 100 implements larger steps in its adjustment of the adaptive output voltage reference value so that it can catch up with the change in the output voltage 180 more quickly.
For example, if the output voltage 180 changes from 12 to 40 V, the digital controller circuitry 100 switches the adaptive output voltage reference value from a first lower step to a second higher step, so that it can catch up with the change. This increases the responsiveness of the power supply to provide current to the dynamic load.
This is important for the stability of the LED driver. The LED driver is sensitive to the forward voltage drop across each LED in each string 102. If the forward voltage drop is less than a certain amount, the LED driver can fail to operate properly. The sensor led driver can detect this failure and turn off the failed LED channel. This prevents LEDs in the LED strings from overheating and reducing the system efficiency.
