Joshua asked in Science & MathematicsEngineering · 3 months ago

# Can someone verify if the following circuit is correct?

I need to build a circuit that lights up only 1 LED bulb in the first switch position, off in the middle (second) switch position and light up all 3 LED bulbs in the third switch position. Is following circuit correct? If so, what type of diode should I use in place of D1. Any suggestions or changes are welcome but as I am not an expert, kindly keep the suggestions simple. Thanks in advance!

Relevance
• 1 month ago

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• Dixon
Lv 7
3 months ago

Yes the wiring is fine but like the other answer says, there must be resistors to limit the current if they are not part of the LED assembly. I would suggest that the circuit could be drawn to make the action bit more obvious by having the voltages generally drop going down the page. Also,  just a subtle  thing but if you want the 3 LEDs to be well matched in brightness you could add another coupe of diodes so they all see the same voltage and current when all on. If you were really bothered you could even add another diode into the line from the switch when only L1 is on, so that the brightness of L1 is identical in both cases. Or it may be that if you have LED units with internal circuitry, then all that might be taken care of anyway. A 1N4001 is a sort of default choice for experimenting and perfectly fine here.

• 3 months ago

first of all you need resistors in series with each LED, unless those you have have internal resistors or circuitry and are rated at 12 volts.

R value depends on current spec. If these are 3 volt 100 mA LEDS, R = (12-3)/0.1 = 90 Ω, with power of 1 watt (double this).

yes the circuit is correct.

diode depends on the specs on the LEDs. If they are 100 mA each, you need a diode good for that, 100 ma, with a reverse voltage spec >12 volts. Usual practice is to double both of those.

Some common diodes: A 1N4001 diode is good for 50 volts and 1 amp. A 1N5400 50 volts and 3 amps. A 1N914 200 mA and 100 volts.