All Questions
10
questions
2
votes
1
answer
188
views
Turn on/off a LED using a D-FF and a transistor
I'm trying to control a LED using some microcontroller and I designed a circuit using a D-FF and a transistor to handle it. It looks like this:
So I can control when to turn it on or of by simply ...
- 21
2
votes
4
answers
339
views
What is the correct maximum value for resistor R₁?
How do I calculate the maximum value of resistor R1 if the following values are known:
VDD = 5 V
inverter CMOS CD4069UB
IIL = IIH = 0 mA
VOH = 4.95 V
VOL = 0.5 V
IOH = IOL = 0.6 mA
VD = 1 V
maximum ...
- 121
5
votes
3
answers
1k
views
Bi-colour LED resistor value
I am trying to calculate a suitable resistor to give about 2mA to the a bi-colour LED in the following configuration:
simulate this circuit – Schematic created using CircuitLab
The LED package ...
- 99
7
votes
2
answers
701
views
Current limiting resistors
I notice that in Ben Eater's project for the 74 series logic chip computer, which my son and I are building, sometimes he uses current limiting resistors on LEDs on the pins of some chips, and on ...
- 193
0
votes
1
answer
3k
views
Digitally-controlled 0-10A constant current source for driving LEDs
I'm looking to build a circuit to drive single high-power LEDs. The circuit will be controlled from a series of TTL pins: one for enable/disable, and ~4-6 to set brightness via current.
The LEDs ...
1
vote
3
answers
804
views
TTL logic level: how does a NOT gate check logic level?
This is a TTL logic level checker circuit. The highlighted blue area is a checker pin. Voltage at the checker pin is 0.65 V, so this must be logic 0, the LOW LED will on.
But the input of the first ...
- 11
1
vote
2
answers
202
views
More advice desired on my Model Railroad Building light controller circuit
Building is built in O Scale (1/48) and has 40 rooms that are lighted independently (masked out from each other with walls) Rooms are lighted with White LEDs. The rooms will light one at a time (but ...
- 15
1
vote
1
answer
2k
views
Optimal method for multiple MOSFETs for LED driving with a shared power rail
I have three LEDs (RGB), with the following forward voltages and current:
red 2.25 V @ 0.35 A
green 3.3 V @ 0.35 A
blue 3.1V @ 0.35 A
I plan on using three (3) RFP30N06LE MOSFETs in parallel @ 0.35 ...
- 11
4
votes
1
answer
3k
views
Increase 74LS TTL gate's output current to drive multiple high-power LEDs
If have several 1 watt LEDs that I want to drive off of a TTL gate's ouput. What can I do to increase a 74LS TTL logic chip's output fan-out (current) to be able to produce a true 5 V output that is ...
6
votes
1
answer
3k
views
Should I calculate a resistor value for driving indicator LEDs from TTL outputs?
Traditionally I have always used a \$1\:\mathrm{k\Omega}\$ resistor as a current limiting resistor for driving an LED direct from a TTL (or 5V CMOS) output. I can't remember how I came by this value -...
- 56.3k