Author Topic: LED driver current sense cant find resistor  (Read 1041 times)

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Offline smileTopic starter

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LED driver current sense cant find resistor
« on: September 23, 2023, 12:22:36 pm »
Hello,

I have LED flood light, the driver is BP3319MB
Data sheet https://www.alldatasheet.com/datasheet-pdf/pdf/1141562/BPS/BP3319MB.html

There is CS pin to set current level.
However in my PCB there are more then one resitor connected to CS pin. So I cant find it. help.

Copy paste image URL to see full size version.



« Last Edit: September 23, 2023, 12:28:03 pm by smile »
 

Online RJSV

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Re: LED driver current sense cant find resistor
« Reply #1 on: September 24, 2023, 03:53:21 am »
Wild Guess; (before I go read the spec).
   I'm thinking that could be SEVERAL separate resistor loads, for controlling one at a time.
Such as for selection between Dim, Medium, and Bright.  In that case you would likely observe a separate surface mount transistor for each resistor,...with only one of them selected at a time.

   Maybe try (power off) measure the resistances; my guess would be something like:
   (R1) at 500 ohm (dim)
   (R2) at 330 ohm (medium)
   (R3) at 100 ohm ((brightest)
 

Offline MarkS

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Re: LED driver current sense cant find resistor
« Reply #2 on: September 24, 2023, 01:59:55 pm »
Wild Guess; (before I go read the spec).
   I'm thinking that could be SEVERAL separate resistor loads, for controlling one at a time.
Such as for selection between Dim, Medium, and Bright.  In that case you would likely observe a separate surface mount transistor for each resistor,...with only one of them selected at a time.

   Maybe try (power off) measure the resistances; my guess would be something like:
   (R1) at 500 ohm (dim)
   (R2) at 330 ohm (medium)
   (R3) at 100 ohm ((brightest)

If you trace the circuit, it consists of R1, R2, R13, R14, R15, R16 and D2 and seems to be connected back to the IC through R13. I understand smile's confusion!

« Last Edit: September 24, 2023, 02:08:00 pm by MarkS »
 
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Offline smileTopic starter

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Re: LED driver current sense cant find resistor
« Reply #3 on: September 25, 2023, 11:59:08 am »
Quote
   Maybe try (power off) measure the resistances; my guess would be something like:
   (R1) at 500 ohm (dim)
   (R2) at 330 ohm (medium)
   (R3) at 100 ohm ((brightest)

The light has only one mode, not 3. So Why all the resitors?

Here is the other side of PCB



 

Offline MarkS

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Re: LED driver current sense cant find resistor
« Reply #4 on: September 25, 2023, 03:20:17 pm »
I wish I could help, but that circuit makes zero sense! I'm waiting for someone to come along and explain it myself.
 

Offline TimNJ

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Re: LED driver current sense cant find resistor
« Reply #5 on: September 27, 2023, 02:06:05 am »
R1 and R2 are the current sense resistors. 1.6ohm and 620mOhm in parallel. Of course, they need to be relatively low value. They are split presumably to spread power dissipation and to trim/fine tune the current.

R16 is 1K in series with the CS pin, presumably helps protect the pin from spikes/surges.

R15 is a 10K gentle pull down across gate source of the MOSFET to try to prevent the MOSFET from turning on when it should not be.

R13, R14, D2 are the gate drive components.
 
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