9
votes
Accepted
Would reverse voltage kill the optocoupler over long time period?
The anti parallel arrangement of the diodes ensures the voltage across the opto's input is clamped on each half cycle.
During each half cycle, one of the anti-parallel diodes conducts, and whilst it's ...
- 38k
6
votes
Circuit that turns two LEDs off/on depending on switch
From another thread, here is a non-standard approach that works very well. SW1 can be replaced with a small n-channel MOSFET such as a 2N7000, or a small NPN transistor with a base resistor.
When the ...
- 22k
6
votes
Is this schematic ready to be made into a circuit?
In addition to what Kuba has said:
your LED connector seems to be used for getting 12 V supply into the system – but where do you connect your power supply's ground? That's equally important, and ...
- 98.2k
4
votes
Is this schematic ready to be made into a circuit?
There may be other problems, but let’s start with the basics:
Power supply input connector is missing - where 12V is fed into the circuit.
Missing is the bulk decoupling capacitor for the 12V supply....
4
votes
Would reverse voltage kill the optocoupler over long time period?
No, there will be no damage as there can never be enough reverse voltage to damage the reverse biased LED because one diode must then be forwars biased.
This is why the data shet does not even mention ...
- 164k
4
votes
Would reverse voltage kill the optocoupler over long time period?
The LEDs should protect each other. One is always forward biased, which means the voltage across it is never going to be more than 1.4V according to the datasheet (should be even less as it is defined ...
- 937
4
votes
Why doesn't 5 V PWM (50% duty cycle) burn my 2.5 V rated LED?
The LED should burn out, but it seems your MCU or whatever chip that is outputing the PWM has so large source impedance that it can't burn the LED.
MCU IO pins and other IO pins from chips are rather ...
- 164k
4
votes
Guidelines for using downward-facing LEDs
Yes, I have used 1206 size SMD LEDs this way.
The pad geometry I used was 1.0 x 1.8 mm, 3.556 mm (140 mil) pad distance center to center. The drill diameter of the hole in the center was 2.3 mm.
So ...
- 7,815
3
votes
Circuit that turns two LEDs off/on depending on switch
It should be obvious that one of the LEDs can be controlled directly by the switch. For the other LED, you need a simple inverter circuit. The simplest is to use a transistor to short it out.
...
- 176k
3
votes
How can I turn on LEDs one by one with increase in speed of a DC motor?
As always with electronics, there are different possible solutions. Since you're doing the PWM with an NE555, I guess you don't want to use a microcontroller just for the LED bar. We won't talk about ...
- 3,624
2
votes
Accepted
Circuit that turns two LEDs off/on depending on switch
When the red is on, you have Vbe from Q3 and Vce from Q_no_number which seems to be enough to turn Q2 on in the simulator.
Swapping the green LED and its resistor raises the emitter voltage of Q2 by 2 ...
- 2,036
2
votes
Circuit that turns two LEDs off/on depending on switch
Basic idea
If two voltage-stabilizing nonlinear elements (e.g., diodes) with different threshold voltages are connected in parallel, the current will be diverted through the element with the lower ...
- 18.2k
2
votes
Circuit that turns two LEDs off/on depending on switch
Here's another few ways of doing it. In the top circuit R1 is optional in a breadboard, it just reduces the leakage in the transistors. The switch is not called upon to switch the LED current, rather ...
1
vote
Circuit that turns two LEDs off/on depending on switch
So let me take you through how to analyze the problem before solving it.
As you can see this is a digital 1,0 type problem; the first thing you can do here is draw a truth table (doesn't matter how ...
1
vote
Circuit that turns two LEDs off/on depending on switch
Based on TINA-TI simulation if the switch is open:
The collector-Emitter current (RED LED transistor) is almost zero and its based voltages is also not enough to make the transistor on, but the the ...
- 948
1
vote
How can I turn on LEDs one by one with increase in speed of a DC motor?
Here's an approach using jellybean parts- one or two quad op-amps and some resistors plus a filter capacitor. An LM3914 would simplify things (they're officially 'in the process of being discontinued' ...
Only top scored, non community-wiki answers of a minimum length are eligible