When using inductor less than 100uH the circuit doesn't work at all and because of that sometimes i need to use like 200uH inductor and the current draw is very small like 80mA -- 8 LEDsHave you used the exact inductor specified ? Does the 5 volt spply drop in voltage ? What output current are you drawing ?
Les.
Except that the output won't be a regulated 12V since there is then no feedback.everything turns good
You are right -- do you have any idea why it won't go up to 12 volt when i put in the feedback and it only goes up to 8 volt insteadExcept that the output won't be a regulated 12V since there is then no feedback.
My first guess is that one of the resistors is the wrong value. My second guess would be that you have a subtle miswire.You are right -- do you have any idea why it won't go up to 12 volt when i put in the feedback and it only goes up to 8 volt instead
I measured exactly the value of the resistor using a multimeter on the feedback 10.7K (+-) and also 1.24K (+-) andMy first guess is that one of the resistors is the wrong value. My second guess would be that you have a subtle miswire.
Actually i have another step up circuit using LM2577 IC and it works exactly as expected...in comparison the output effect between LM2577 and LT1172 using 5 volt is way so much different. And LT1172 is very weak...i try find all sort of ways to change connection including diode, inductor, resistor, capacitor...seems nothing changed while the LM2577 is pretty easy and work very very well - not much all sort of tweaking...but i want to get the LT1172 to work so that i can compare their performance..They are compensation components to ensure stability, to cater for varying loads. Instability may account for why you were only getting an apparent 8V output. I say 'apparent' because a digital multimeter on a DC Volts range requires a steady input to give an accurate reading.
Now i can see clearly maybe the inductor value need higher test on 100uH gives 9.6 volt with load...increase to 240uH increase to 10.5 volt so maybe need higher like 300uH or 470uHI tested again maybe i am closer to the answer...without load it generate 11.7 volt but when load 8 volt LED is being used the voltage drop down to 8 volt...can anyone advise where do you think i should tweak this time
by Duane Benson
by Jake Hertz