I'm working on this switching Step Up converter for an RGB LED.
Input = 5V,2A+ (smartphone wall wart)
Output = 7-15V Variable,300mA Max
RGB LED is a 10 W Module and takes 300mA max. There are 3 LED in Series for each color.Each color has a different forward voltage to reach 300mA.
Brightness control is a1 KHZ PWM.
This is for US home/hobby use.
Circuit
100KHz OSC,Fairly simple Boost supply.Has bout 60 ma Current ripple that remains constant through the PWM range.
The LM339 on Left is a 100Khz Oscillator. The LM339 on the right is set as a Current Limit Trip,which starts the process by going high. This allows oscillator pulses to drive the MOSFET gate which boosts Vsupply and turn on the LED.
When LED Current reaches 300mA ,the voltage across 0.6 Ohm current sampling resistor goes beyond the 0.18V to switch comparator low ,which turns off the MOSFET . The PWM input (Brightness) is ANDed with Oscillator . So ,Brightness control is via POV and Color Accuracy is maintained as LED Current is 0 or (close to) 300 mA.
I need comments/review on this design . It passes my sanity check and LTSpice Sniff Tests ,but I might be missing something(OC protection to be added,for ex.)
P.S :
>This project is my first rodeo with LTSpice. Usually I Just "buy and build/design on paper".
>I know there are IC's that do this better,faster ,and cheaper (Supertex HV99XX/Clones etc.).
>I was initially sampling MOSFET Current in the Fast loop (for I Limit Trip) , but correlating it with LED current was not linear .I switched to slow loop sampling in the Led which worked better.
Update - Hysteritic Mode in Post 4