Could you name one?No problem use a logic n_mosfet it will go in saturation above the 2V.
http://www.ti.com/lsds/ti/power-man...nsistor-products.page#p2419=Yes&p2748=0.82;10
Could you name one?No problem use a logic n_mosfet it will go in saturation above the 2V.
http://www.ti.com/lsds/ti/power-man...nsistor-products.page#p2419=Yes&p2748=0.82;10
Actually I was the one who first mentioned the LM317 and electronic (as opposed to resistive) current control generally. But then BramLabs came back saying he'd considered it and that the LM317 needs a large capacitor (I'm dubious) and you said there'd be too much voltage drop, which is harder to answer. I don't think the LM317 is the way to go here.The two subjects are not mutually exclusive.
Keeping in mind I have another imaginary unspecified circuit that can sink or source billions of amps without any voltage drop at all...
It is the TS who stated his intent to use an LM317 as his constant current source. That would not be my first choice for this application and I stated my reasons for this.
Oh i know that circuit. It's called current limiter. Okay sir, thank you for your idea !I hope that this will give some idea.
Okay sir, big thanks for your help !Your calculations is fine, you need to adjust the values of power dissipation, in the situation of 100% duty cycle, the watts of resistor will be as 5 times of calculation, but you used the pwm here, so maybe you can take 2 or 3 times to try
You mean the "two-transistor controller" is a current limiter ?Actually I was the one who first mentioned the LM317 and electronic (as opposed to resistive) current control generally. But then BramLabs came back saying he'd considered it and that the LM317 needs a large capacitor (I'm dubious) and you said there'd be too much voltage drop, which is harder to answer. I don't think the LM317 is the way to go here.
However, the two-transistor controller still seems to me like the best approach. I said that it could double as a switch for the processor to control the circuit, and I just realized that it also makes all this talk about saturation behavior irrelevant--the power transistor would be in its linear region anyway, so you don't need to figure anything out, as long as you can meet the worst-case specs. Though with only 20mA of load current, there's no need for much base drive.
It is much easier to use 6 leds in both series.let's say i'm going to use 6 LED and 5 LED.
I'm not sure why you didn't use the 3.2V(or 3.0V) Red Led?Red LED needs Vf = 2,1V, If = 20mA
The schematic is more complicated than necessary: it can be done with two transistors / mosfets.I hope that this will give some idea.
As i already attached in my first post as a thread starter, i'm using SMD 5050 RGB LED.I'm not sure why you didn't use the 3.2V(or 3.0V) Red Led?
So, you mean a circuit like this sir ?Yes, when I first mentioned it I said "a constant-current circuit in place of the resistor and transistor. You could use the 2-transistor type" which I thought explained it. If you need to look it up, it's in any number of places:
https://en.wikipedia.org/wiki/Current_limiting
Look under the heading "Single power-supply circuits". And what do you know, it says "Due to its simplicity, this circuit is sometimes used as a current source for high-power LEDs"!
To provide a switching function, you'd want to drive R1 from a processor pin, not directly off the power supply.
Okay sir, i'll try it later ^^The schematic is more complicated than necessary: it can be done with two transistors / mosfets.
1) put the two transistors current sink to the bottom, and connect the led string to its collector / drain;
2) find the resistor that connects the collector of one transistor to the base of the other transistor and reroute it to your mcu pin.
3) when the mcu pin goes high, the led is turned on at a set current level; when the mcu goes off, the led is turned off.
Oh yeah sir, i want to make a difference approach. I'm using a 5 Volt supply that can gives current up to 1 A.Yes, when I first mentioned it I said "a constant-current circuit in place of the resistor and transistor. You could use the 2-transistor type" which I thought explained it. If you need to look it up, it's in any number of places:
https://en.wikipedia.org/wiki/Current_limiting
Look under the heading "Single power-supply circuits". And what do you know, it says "Due to its simplicity, this circuit is sometimes used as a current source for high-power LEDs"!
To provide a switching function, you'd want to drive R1 from a processor pin, not directly off the power supply.
If you want to run the LEDs in parallel, you'll need to put a resistor in series with each LED, and then hook those 11 series combos up in parallel.
If you simply connect the LEDs in parallel without corresponding resistors, more current will flow through some LEDs than others. This can lead to premature LED failure and cascading failures.
Oh yeah i forgot sir.
Okay sir, i get your point and the 'logical approach'.O BramLabs, please reconsider. Your shift to a 5V supply makes the circuit much less fun, and there's no point in using electronic current control. You'll need one resistor per LED, and each one will simply control the current through that part of the circuit. You only need one transistor, and it has to switch the current for 11 LEDs in parallel, not a single string of them in series. That would mean you do need to think about saturation current etc, but you can deal with that by using a logic MOSFET instead. The efficiency of your overall circuit will be a lot less, because now each LED will get less than half the voltage from the supply, and the rest will be lost as heat. How can this be an improvement? If you stick with this design, I'm not going to help any more.
p.s. The answer to the question "So, you mean a circuit like this sir?" is yes. But my answer to "So, my circuit would be like this" is "No, don't do it".
It's okay sir to use 10 or 12 or 13 or 14. But at least 9 LED. ahahaha...What's the reason to caused you to used 11 leds and not 10 or 12?
I see and be careful of the light of leds, they could be hurt your eyes and never recover, so don't see them directly.It's okay sir to use 10 or 12 or 13 or 14. But at least 9 LED. ahahaha...
I just need to make sure the brightness is enough for a single room in the house.
Wahahahahaha..... roger that sir !I see and be careful of the light of leds, they could be hurt your eyes and never recover, so don't see them directly.
As you can see on my first post, i'm using SMD 5050 RGB type of LED. And i think it's possible to control R,G and B separately using this IC.If these RGB LEDs are the type with a common cathode or a common anode and separate R, G, and B pins, wouldn't it be impossible to connect them in series in a way that allows controlling the R, G, and B separately?