BA6144 bargraph LED driver without resistors? - Page 1
Forum section: electronics / beginners

author: dentaku
author_rank: Frequent Contributor
timestamp: March 04, 2015, 03:24:38 am
content: I got 5 of these BA6144 LED bargraph drivers and some fun little rectangular LEDs to go with them from an old stereo.It's very easy to use but...In the datasheethttp://pdf.datasheetcatalog.com/datasheets/50/233589_DS.pdfIt says "has constant-current outputs, so it can directly drive the LEDs without variations in LED current due to supply voltage fluctuations." AND the example circuits in the .pdf don't show any resistors on the LEDs.Question: I've only tested one so far and I've used resistors on each LED but because it has constant current outpts (MAX 18.5mA) can I really omit the resistors?I see that this Youtube video shows it working fine without resistors so I'm assuming the answer is yes but I just want to make sure.

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 04, 2015, 03:36:23 am
content: You have not revealed what voltage you are using to operate the chip.You have also not revealed what current your LEDs want.The data sheet (which you cited) pretty much answers your questions.QuoteFigure 4 clearly shows using the chip WITH resistors.

author: dentaku
author_rank: Frequent Contributor
timestamp: March 04, 2015, 01:26:21 pm
content: Quote from: Richard Crowley on March 04, 2015, 03:36:23 amI saw Figure 4 which is why I used resistors on each LED when testing this and I have been using it at 9V but I'm more likely to use it at 5V. These LEDs look fine anywhere between 10 and 16mA. I've found that most regular old LEDs I've ever used never need more than 10mA to be bright enough for general use.In fact, it's Figure 4 that got me wondering about this.I guess the better question would be...Why is the example circuit,Figure 2 running at 12V, not showing resistors connected to each LED when Figure 4 shows using at least 240ohm resistors when VCC=12V.

author: Zero999
author_rank: Super Contributor
timestamp: March 04, 2015, 02:02:04 pm
content: Resistors are required at higher currents and voltage to keep the power dissipation of the IC below a safe level. At high forward currents and supply voltages, the IC has to drop a fairly high voltage at a high current, causing it to over heat. The resistors in series with the LEDs drop some of the voltage and dissipate the power exteranlly.

author: dentaku
author_rank: Frequent Contributor
timestamp: March 04, 2015, 03:21:56 pm
content: Quote from: Hero999 on March 04, 2015, 02:02:04 pmOK, so the resistors are not being used like you normally would see current limiting resistors on LEDs to protect the LED itself but it's more to avoid overheating the BA6144 like it says under NOTE: on page three of the datasheet.I just found the board I salvaged these ICs from and the LEDs don't haveindividualresistors connected to them, the anodes are all connected together and they have a 100ohm 1W resistor leading to them just like the top half of Figure 2 in the datasheet.The underside of the board is actually discoloured where the resistor sits so it was definitely dissipating some heat.The resistor to the first LED bar has the worse discolouring and it gets better as you move up through the other 4 so you can see that the lower frequency band was using more power than the lesser used meter that show the level of the highest frequencies.