ok, these are hopefully somewhat easy questions. I'm fairly new in electronics so I'm always afraid of my own calculations and what I've learned by reading. It's easy to mix things up, I thank everyone for any help ahead of time.
First question,
I'm replacing a 21W 12v lamp with a resistor (I know this will be a very large resistor), These are my calculations, am I correct?
21W
12v
21W/12v = 1.75 A
then
12v/1.75A = 6.86 Ω
so the resistor should be >= 21W and 6.86Ω
The closest I could find was 50W and 6.81Ω, which will work, right? It would be pulling 1.762A instead of 1.75A, close enough for a lamp.
ok, that was the only question I think I could completely answer myself.
Second question,
The correct base resistor for the transistor always confused me. Online, I always see a 1KΩ resistor used, so is my assumption correct that you can always use a 1KΩ base resistor to fully saturate the transistor? Does the entire circuit need to use the same voltage for this to work or will it work regardless? Such as if the device in the image below used 12v, and the 5v logic from the IC was the same, would it still work properly? I've read so many different things on them, im completely confused.
I have used transistors in the past with the 1KΩ resistor trick, but I just wanted to be sure I was doing it right.
Third and final MONSTER question.
I may need to create a separate thread for this one.
I really appreciate you sticking with me thus far.
This is a zener diode regulator question (you'll see)
I'm driving rows of LEDs from an IC. I'm using an unstable 12v source voltage (12v - 14.5v) which is fine for the IC as it works off 5v so I'll just use a regulator but I was hopping to use the least amount of transistors to power the LEDs
There are 5 LEDs in each row, and 16 rows. The rows are divided into four sets. Each set will turn on independently of each other. There will never be more than one set on. Below is an image of what i'm talking about. Color coded for each set.
So my problem is the power. I can figure out what size resistor to use so I don't burn out the LEDs but I don't know how to supply power to them.
as stated above, power is 12v - 14v fluctuating. I wanted to use a zener regulator circuit but if there's something better, i'll listen.
Each LED is 20ma, 2.1v forward voltage. So each row will require 100mA. As there will never be more than 4 rows on at a time, the max current draw is 440mA (400 + 10% added for safety). voltage will need to be 10.5v as they'll be running 5 in series. Would it be possible to source 10.5v with a zener circuit? I've read that your source voltage must be 2v higher than your desired output. This would put me 1.5v below below my source which wouldn't work.
Do I have any chance? lol
I don't mind running multiple regulating circuits, or even individual for each set if I have to as I realize there is alot of current going thru. But I really don't want to have to break the rows of 5 up [if possible of course] (easy to solder if in a row, I don't want wires hopping everywhere).
Thank you everyone for all the help! I really, truly appreciate it. I hope I made this as clear as I could, I've been making images and collecting data for the last three hours, I tried to make this as simple as I could.
Thanks again.
First question,
I'm replacing a 21W 12v lamp with a resistor (I know this will be a very large resistor), These are my calculations, am I correct?
21W
12v
21W/12v = 1.75 A
then
12v/1.75A = 6.86 Ω
so the resistor should be >= 21W and 6.86Ω
The closest I could find was 50W and 6.81Ω, which will work, right? It would be pulling 1.762A instead of 1.75A, close enough for a lamp.
ok, that was the only question I think I could completely answer myself.
Second question,
The correct base resistor for the transistor always confused me. Online, I always see a 1KΩ resistor used, so is my assumption correct that you can always use a 1KΩ base resistor to fully saturate the transistor? Does the entire circuit need to use the same voltage for this to work or will it work regardless? Such as if the device in the image below used 12v, and the 5v logic from the IC was the same, would it still work properly? I've read so many different things on them, im completely confused.
I have used transistors in the past with the 1KΩ resistor trick, but I just wanted to be sure I was doing it right.
Third and final MONSTER question.
I may need to create a separate thread for this one.
I really appreciate you sticking with me thus far.
This is a zener diode regulator question (you'll see)
I'm driving rows of LEDs from an IC. I'm using an unstable 12v source voltage (12v - 14.5v) which is fine for the IC as it works off 5v so I'll just use a regulator but I was hopping to use the least amount of transistors to power the LEDs
There are 5 LEDs in each row, and 16 rows. The rows are divided into four sets. Each set will turn on independently of each other. There will never be more than one set on. Below is an image of what i'm talking about. Color coded for each set.
So my problem is the power. I can figure out what size resistor to use so I don't burn out the LEDs but I don't know how to supply power to them.
as stated above, power is 12v - 14v fluctuating. I wanted to use a zener regulator circuit but if there's something better, i'll listen.
Each LED is 20ma, 2.1v forward voltage. So each row will require 100mA. As there will never be more than 4 rows on at a time, the max current draw is 440mA (400 + 10% added for safety). voltage will need to be 10.5v as they'll be running 5 in series. Would it be possible to source 10.5v with a zener circuit? I've read that your source voltage must be 2v higher than your desired output. This would put me 1.5v below below my source which wouldn't work.
Do I have any chance? lol
I don't mind running multiple regulating circuits, or even individual for each set if I have to as I realize there is alot of current going thru. But I really don't want to have to break the rows of 5 up [if possible of course] (easy to solder if in a row, I don't want wires hopping everywhere).
Thank you everyone for all the help! I really, truly appreciate it. I hope I made this as clear as I could, I've been making images and collecting data for the last three hours, I tried to make this as simple as I could.
Thanks again.