scsinet
Active Member
Quote:
Originally Posted by 2Quills http:///t/386777/led-s-are-the-best/100#post_3410869
Crazy things running through my mind. Resistors would seem as though they should be a MUST have for running parallel strings after this discussion. Would you feel the same for a single series string?
The vast majority of these diy builds that I see aren't using resistors for single series and that ones that are running parallel strings are simply using the 1ohm/5w resistors as recommended on one of the diy supply sites. And they are using those same resistors on a wide range of build sizes as a simple way to test voltage drop across strings. If you look at the pdf.'s on these drivers they have a minimum and a maximum voltage requirement.
But in the case of the ELN drivers that the O.P. is using for instance...you could run 8-12 leds at 3.5v in series. So why isn't a resistor need to run either or? Or should it be and people just aren't doing that?
Should I be looking into current mirrors vs resistors or both? Are my questions annoying you yet? lol You don't have to answere them. I just enjoy the fact that I feel like I'm actually learning something here. And appreciate the input.
We have been having a discussion on the use of resistors as a current limiting because I was under the assumption that you were running an ordinary off the shelf 48v power supply. LED drivers are not ordinary power supplies. Where ordinary power supplies regulate the amount of voltage, and will put out whatever current (within their design limits) is necessary to maintain that voltage, LED drivers put out a constant current. An LED driver is matched to the current ratings for an LED, so you can run any number of LEDS (provided you stay within the design limits of the driver) and it will work just fine.
So, in the event you are using a by-design LED driver, a resistor may well be unnecesary.
When powering multiple parallel strings, a means must exist to ensure that current is evenly dividied amonst the parallel strings. This is becuase unlike ordinary light bulbs and most other things, semiconductors do not share current nicely in parallel configurations. The small resistor does that. In this case, the 1 ohm resistor is not really for current limiting, but for current distribution.
I don't know how the resistor helps you measure the voltage drop across the strings. What it will help you do is measure the current. Normally, to measure current, a circuit has to be broken open and the meter inserted into the current path to measure. By putting a known resistance into the line that only negligably affects the circuit otherwise, you can measure the voltage across it, and using ohm's law, calculate the current flow. 1 ohm is commonly used for this and many other similar applications because from a design perspective, 1 ohm is so little that it will likely not effect the rest of the circuit significantly and because 1 volt across 1 ohm equals 1 amp, so by measuring across a 1 ohm series resistor, a 1.43 volt reading indicates 1.43 amps are flowing.
Originally Posted by 2Quills http:///t/386777/led-s-are-the-best/100#post_3410869
Crazy things running through my mind. Resistors would seem as though they should be a MUST have for running parallel strings after this discussion. Would you feel the same for a single series string?
The vast majority of these diy builds that I see aren't using resistors for single series and that ones that are running parallel strings are simply using the 1ohm/5w resistors as recommended on one of the diy supply sites. And they are using those same resistors on a wide range of build sizes as a simple way to test voltage drop across strings. If you look at the pdf.'s on these drivers they have a minimum and a maximum voltage requirement.
But in the case of the ELN drivers that the O.P. is using for instance...you could run 8-12 leds at 3.5v in series. So why isn't a resistor need to run either or? Or should it be and people just aren't doing that?
Should I be looking into current mirrors vs resistors or both? Are my questions annoying you yet? lol You don't have to answere them. I just enjoy the fact that I feel like I'm actually learning something here. And appreciate the input.
We have been having a discussion on the use of resistors as a current limiting because I was under the assumption that you were running an ordinary off the shelf 48v power supply. LED drivers are not ordinary power supplies. Where ordinary power supplies regulate the amount of voltage, and will put out whatever current (within their design limits) is necessary to maintain that voltage, LED drivers put out a constant current. An LED driver is matched to the current ratings for an LED, so you can run any number of LEDS (provided you stay within the design limits of the driver) and it will work just fine.
So, in the event you are using a by-design LED driver, a resistor may well be unnecesary.
When powering multiple parallel strings, a means must exist to ensure that current is evenly dividied amonst the parallel strings. This is becuase unlike ordinary light bulbs and most other things, semiconductors do not share current nicely in parallel configurations. The small resistor does that. In this case, the 1 ohm resistor is not really for current limiting, but for current distribution.
I don't know how the resistor helps you measure the voltage drop across the strings. What it will help you do is measure the current. Normally, to measure current, a circuit has to be broken open and the meter inserted into the current path to measure. By putting a known resistance into the line that only negligably affects the circuit otherwise, you can measure the voltage across it, and using ohm's law, calculate the current flow. 1 ohm is commonly used for this and many other similar applications because from a design perspective, 1 ohm is so little that it will likely not effect the rest of the circuit significantly and because 1 volt across 1 ohm equals 1 amp, so by measuring across a 1 ohm series resistor, a 1.43 volt reading indicates 1.43 amps are flowing.
