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Topic: TM1803 question - if the data sheet says 5V why doesn't 12V fry the chip? (Read 1 time) previous topic - next topic

wsanders

I have a question about the TM1803 - looking at the data sheet is says the maximum Vdd is either 5 or 7V (depending on the data sheet :0). A lot of the cheapo LED strips you buy have 3 LED in series connected to each chip, and the circuit is powered with 12V.

Why doesn't this fry the chip? Or is the data sheet wrong?

The data sheets for the TM1804, TH1809 says "working voltage" up to 24V so I suspect the data sheets are wrong and that the whole line of TM chips will work fine on 12V. Or else the designers are shipping LED strips that will burn out quickly from running the TM1803 over specs?

(Radio Shack is clearing our their 1M 30-LED 1803-based strips for $7, which is why I ask. 3 LEDs in series for each chip, but they are very bright and it's not a bad deal for $7.....)

TIA w

(Links to datasheets; https://www.google.com/search?q=tm1803+datasheet+pdf&ie=utf-8)

CrossRoads

Link to a datasheet?
3 LEDs, and usually a current limit resistor too.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Chagrin

I can't read that datasheet (Chinese) but I see it's a three channel, linear, sinking, LED driver. The 24V refers to the voltage that can be fed through the LEDs; the 5V-7V voltage is the logic voltage (DI, DO, etc. pins).

This is really not much different than using a transistor with an Arduino to switch a higher-than-5V voltage, except here it's happening all inside the chip. You'll see this same type of multi-voltage arrangement on motor driver chips or other LED chips; the TLC5940, for example, allows 17V drive for the LEDs.

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