Hey Guys,

I have a question around this, the PWM signal is it a 2.5v pwm ?
I am about to repair a heap of strings of these and the main CPU that drives it has blown up, so i would like to rig up a test circuit to do so before replacing the motherboard.

Was just going to use an Arduino with a level shifter on it to change the voltage if required.
Note the level shifter diagram has 12V as i stole it from google i would make this 2.5v if i am reading the data sheet correctly.

Thanks Guys

 

NO! NO!! The Vin, if you are driving it with a duty cycle is with an open collector transistor PULLING DOWN to less than 0.2 volts. And a PWM frequency below 500Hz.
If you are going to feed it a DC level to control the intensity, the range is from 0.3 volts up to almost 2.5 volts.

And with no pin numbers on the drawing it is actually a guess. Where did the drawing come from???

 

Just got the drawing from the internet, what would be a more appropriate pwm circuit ?
I cannot just use the ardunio as its pwm is 5V and i believe from reading the sheet the PWM must not exceed 2.5V or is this an incorrect assumption ?

 

As MisterBill2 explained you just need to pull the pin down with an open collector/drain transistor.

To do this simply drive a N-type transistor from your Arduino and place the collector/drain output to the VSET pin without any pullup.

 

Oh wow the penny just dropped......
When Vset is floating the circuit is on and the current is set by the resistor between VIN & ISENSE.
Pulling lower then 0.2 V turns the circuit off and if i want to control the circuit via a voltage the max voltage is 2.% V is that correct?

 

Correct.

 

Correct.

Okay SO i will need to invert the output by adding a second transistor or a hex invertor as 100% duty cycle on the NPN would result in it being pulled low correct ?

 

It's more practical to invert the signal in code, or internal hardware in the Arduino.

But yea, otherwise you would have to invert the signal using some sort of external hardware.

 

It's more practical to invert the signal in code, or internal hardware in the Arduino.

But yea, otherwise you would have to invert the signal using some sort of external hardware.

Had no idea this was possible excellent thank you