Datasheet NSI50350AD (ON Semiconductor) - 6
| Fabricante | ON Semiconductor |
| Descripción | Constant Current Regulator & LED Driver 50 V, 350 mA +- 10%, 11 W Package |
| Páginas / Página | 9 / 6 — NSI50350ADT4G. Other Currents. Figure 12. Figure 10. Dimming using PWM. … |
| Formato / tamaño de archivo | PDF / 255 Kb |
| Idioma del documento | Inglés |
NSI50350ADT4G. Other Currents. Figure 12. Figure 10. Dimming using PWM. Figure 13. Luminous Emmitance vs. Duty Cycle. Reducing EMI
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NSI50350ADT4G Other Currents
generate audible sound. Dimming is achieved by turning the The adjustable CCR can be placed in parallel with any LEDs on and off for a portion of a single cycle. This on/off other CCR to obtain a desired current. The adjustable CCR cycle is called the Duty cycle (D) and is expressed by the provides the ability to adjust the current as LED efficiency amount of time the LEDs are on (Ton) divided by the total increases to obtain the same light output (Figure 10). time of an on/off cycle (Ts) (Figure 12).
Figure 12.
The current through the LEDs is constant during the period they are turned on resulting in the light being consistent with no shift in chromaticity (color). The brightness is in proportion to the percentage of time that the LEDs are turned on. Figure 13 is a typical response of Luminance vs Duty Cycle. 6000
Figure 10.
5000
Dimming using PWM
4000 The dimming of an LED string can be easily achieved by placing a BJT in series with the CCR (Figure 11). 3000 2000 ILLUMINANCE (lx) 1000 Lux Linear 00 10 20 30 40 50 60 70 80 90 100 DUTY CYCLE (%)
Figure 13. Luminous Emmitance vs. Duty Cycle Reducing EMI
Designers creating circuits switching medium to high currents need to be concerned about Electromagnetic Interference (EMI). The LEDs and the CCR switch extremely fast, less than 100 nanoseconds. To help eliminate EMI, a capacitor can be added to the circuit across R2. (Figure 11) This will cause the slope on the rising and falling edge on the current through the circuit to be extended. The
Figure 11.
slope of the CCR on/off current can be controlled by the The method of pulsing the current through the LEDs is values of R1 and C1. known as Pulse Width Modulation (PWM) and has become The selected delay / slope will impact the frequency that the preferred method of changing the light level. LEDs being is selected to operate the dimming circuit. The longer the a silicon device, turn on and off rapidly in response to the delay, the lower the frequency will be. The delay time should current through them being turned on and off. The switching not be less than a 10:1 ratio of the minimum on time. The time is in the order of 100 nanoseconds, this equates to a frequency is also impacted by the resolution and dimming maximum frequency of 10 MHz, and applications will steps that are required. With a delay of 1.5 microseconds on typically operate from a 100 Hz to 100 kHz. Below 100 Hz the rise and the fall edges, the minimum on time would be the human eye will detect a flicker from the light emitted 30 microseconds. If the design called for a resolution of 100 from the LEDs. Between 500 Hz and 20 kHz the circuit may dimming steps, then a total duty cycle time (Ts) of 3 milliseconds or a frequency of 333 Hz will be required.
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NSI50350ADT4G Other Currents
generate audible sound. Dimming is achieved by turning the The adjustable CCR can be placed in parallel with any LEDs on and off for a portion of a single cycle. This on/off other CCR to obtain a desired current. The adjustable CCR cycle is called the Duty cycle (D) and is expressed by the provides the ability to adjust the current as LED efficiency amount of time the LEDs are on (Ton) divided by the total increases to obtain the same light output (Figure 10). time of an on/off cycle (Ts) (Figure 12).
Figure 12.
The current through the LEDs is constant during the period they are turned on resulting in the light being consistent with no shift in chromaticity (color). The brightness is in proportion to the percentage of time that the LEDs are turned on. Figure 13 is a typical response of Luminance vs Duty Cycle. 6000
Figure 10.
5000
Dimming using PWM
4000 The dimming of an LED string can be easily achieved by placing a BJT in series with the CCR (Figure 11). 3000 2000 ILLUMINANCE (lx) 1000 Lux Linear 00 10 20 30 40 50 60 70 80 90 100 DUTY CYCLE (%)
Figure 13. Luminous Emmitance vs. Duty Cycle Reducing EMI
Designers creating circuits switching medium to high currents need to be concerned about Electromagnetic Interference (EMI). The LEDs and the CCR switch extremely fast, less than 100 nanoseconds. To help eliminate EMI, a capacitor can be added to the circuit across R2. (Figure 11) This will cause the slope on the rising and falling edge on the current through the circuit to be extended. The
Figure 11.
slope of the CCR on/off current can be controlled by the The method of pulsing the current through the LEDs is values of R1 and C1. known as Pulse Width Modulation (PWM) and has become The selected delay / slope will impact the frequency that the preferred method of changing the light level. LEDs being is selected to operate the dimming circuit. The longer the a silicon device, turn on and off rapidly in response to the delay, the lower the frequency will be. The delay time should current through them being turned on and off. The switching not be less than a 10:1 ratio of the minimum on time. The time is in the order of 100 nanoseconds, this equates to a frequency is also impacted by the resolution and dimming maximum frequency of 10 MHz, and applications will steps that are required. With a delay of 1.5 microseconds on typically operate from a 100 Hz to 100 kHz. Below 100 Hz the rise and the fall edges, the minimum on time would be the human eye will detect a flicker from the light emitted 30 microseconds. If the design called for a resolution of 100 from the LEDs. Between 500 Hz and 20 kHz the circuit may dimming steps, then a total duty cycle time (Ts) of 3 milliseconds or a frequency of 333 Hz will be required.
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