i am currently building this HV9910B led driver. The typical application looks like the diagram below.
I wanted to build an application that can dim when the surrounding is dark. So , for the first trial i built a 555 timer circuit with 2 diodes with the circuit looks like the diagram below. i connect collector leg output to the led driver(HV9910B) PWM pin. i also replace R1 of the 555 timer circuit with LDR. The pulse width is sent to PWM pin and it does dim when i cover the ldr. i know that it is because when Ton the switch keep on switching and when toff it doesnt switch so then average power decreases, the problem is that the frequency also changes when duty cycle changes and i realize that just by using 555 timer it can already dim the led. so i decided not to use PWM pin and connect the led driver PWM pin to VDD(HIGH) and start manipulating the RT(oscillator pin). I used a 1M POT as the datasheet says it needs at least 226k resistor and max 1M resistor and i realize by changing the RT the frequency changes and so does the LED . But the problem with it is that i dont understand how it works. I know that impedance of inductor is 2pi*f*L but that is applicable for sine wave only, the oscillator give out pulse to the mosfet and cause it switch at high frequency. so how does changing this switching frequency cause led to dim?
I wanted to build an application that can dim when the surrounding is dark. So , for the first trial i built a 555 timer circuit with 2 diodes with the circuit looks like the diagram below. i connect collector leg output to the led driver(HV9910B) PWM pin. i also replace R1 of the 555 timer circuit with LDR. The pulse width is sent to PWM pin and it does dim when i cover the ldr. i know that it is because when Ton the switch keep on switching and when toff it doesnt switch so then average power decreases, the problem is that the frequency also changes when duty cycle changes and i realize that just by using 555 timer it can already dim the led. so i decided not to use PWM pin and connect the led driver PWM pin to VDD(HIGH) and start manipulating the RT(oscillator pin). I used a 1M POT as the datasheet says it needs at least 226k resistor and max 1M resistor and i realize by changing the RT the frequency changes and so does the LED . But the problem with it is that i dont understand how it works. I know that impedance of inductor is 2pi*f*L but that is applicable for sine wave only, the oscillator give out pulse to the mosfet and cause it switch at high frequency. so how does changing this switching frequency cause led to dim?