sth_dinesh
Newbie level 1
- Joined
- Jun 28, 2011
- Messages
- 1
- Helped
- 0
- Reputation
- 0
- Reaction score
- 0
- Trophy points
- 1,281
- Activity points
- 1,291
I am trying to construct a 16x64 led matrix display board for which I am using stp16dp05 as the LED matrix driver IC. I have connected the anodes of the LEDs in rows and the cathodes of the LEDs are connected to the output pins of 4 stp16dp05 ICs. I have casacded these ICs.
I have not been able to control the current through the LEDs by adjusting R-ext as mentioned in the datasheet. When I use only single stp I am able to control the current to 50ma using R-ext through each led but when I cascade the ICs, the current through individual LEDs drops to almost half of the set value. For eg if I set the current value to around 50 ma using R-ext, I get around 50 ma when I use single stp, but when I cascade the ICs, the current through each LED drops to around 20 ma. I do not understand what is the problem here?
Each of the 16 rows are connected to the collector of TIP127 and scanned using PIC18F microcontroller.
I have not been able to control the current through the LEDs by adjusting R-ext as mentioned in the datasheet. When I use only single stp I am able to control the current to 50ma using R-ext through each led but when I cascade the ICs, the current through individual LEDs drops to almost half of the set value. For eg if I set the current value to around 50 ma using R-ext, I get around 50 ma when I use single stp, but when I cascade the ICs, the current through each LED drops to around 20 ma. I do not understand what is the problem here?
Each of the 16 rows are connected to the collector of TIP127 and scanned using PIC18F microcontroller.
