driverled
I am testing below LED Driver Circuitry on breadboard using LM3410X.
Input Specs:
Vin & DMM = 5V,
L = 20 uH
R=2 Ohm
Only thing is I have'nt connected LED ( I am testing with 10k resistor as dummy load)
But somehow I am getting 4.86 V at o/p ( across 10K load resistor )
Can anybody help me to figure out. Do I need to connect LED string?
Thanks in advance. 🙂
Few things to check:
If you still can't find the issue, can you post an image of your board layout (pics/gerber) and measured voltages if possible.
You could do a sort of modified high-side PWM controlled joule thief for each of the LEDs, with each having an independent PWM controlling the power though the LED.
Simple version might look something like this...
simulate this circuit – Schematic created using CircuitLab
This is different from a normal joule thief in that...
The chopping is done via PWM rather than feedback. This lets you control the power though the LED.
The LED is connected to the high side rather than ground. This means you will need more kick in the inductor to get the LED up to minimum voltage, but has the advantage that there is no leakage current though the LED when the PWM is off.
Note that there is not a straight relationship between PWM and brightness here. When PWM is off, LED is off and no current flows. As you increase PWM duty cycle, you will hit a minimum current needed to light the LED. Then as you increase more, you will get brighter and brighter LED until you hit a maximum. Past the maximum the LED will start getting dimmer and you will start killing the battery, so stop increasing the PWM duty cycle when you get to the maximum brightness.
This circuit should have very low quiescent current- basically whatever the leakage current of the transistor is.
Best Answer
So you have set a current of 95mA using R1 = 2\$\Omega\$ (190mV typical reference) and are thusexpecting a voltage of 950V (95mA * 10K) at the output.. this will can damage the chip.
Put some LEDs on there (more than 5V drop!- three or more white/blue LEDs) and see if it still works. You may have fried the chip. See the zener OVP circuit suggestion from the datasheet:
1MHz+ (this one is 1.6MHz) switching supplies require good breadboarding techniques so you may have other problems even if the chip is functioning properly. In particular the critical loop areas must be kept small. See the typical layout in the datasheet for guidance.