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Can You Put a Diode in Series with the LED?
Floyd asks readers:
“I’ve not tried this but am wondering if anyone has put a diode in series with the LED. I think it would convert the power to DC but would probably require some tinkering to get the current correct. Just a thought without practical experience.”
4 Responses to Can You Put a Diode in Series with the LED?
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The LED is a diode, so power already only passes in one direction. To limit the current, it is necessary to put a resistor in series, but if you want to convert AC to DC, you could use a bridge rectifier (basically 4 diodes), although this would produce higher voltage at the LED.
A 1000 ohm 1/4 watt resistor will drop 12volts DC to the correct voltage for a LED. If you are using AC, you can put a single diode in series with a LED but you will also need a small Electrolytic Capacitor to smooth the current. The + of the Capacitor goes to the point where the Cathode of the diode attaches to the + of the LED. The – of the capacitor goes to the – of the LED. A capacitor of anywhere from 47 uF up to 1000uF at 25 volts working will do the job. The larger the capacitor the higher the voltage that will reach the LED. eg 12 volts AC going through a diode with a 1000uF capacitor attached will give 15 or more volts DC. The voltage will drop as the load increases ie if you run a powerful DC motor from this arrangement the voltage may drop as low as 9 volts DC. A LED will only use a small amount of current so there will be no noticeable voltage drop. Normally a 9volt AC supply will deliver 12 DC with this arrangement. Without the capacitor the LED will flicker and may have a short life expectancy. If you use a higher voltage you will need a 1500 Ohm resistor.
i have two mth and one lionel engines and in want and have to run them on a one direction only these are o gauge engines can you please tell what i need to run them all i one direction thanks cliff
Yes you can put a diode in series with an LED, as long as it is the same way round, It will “Convert” AC to DC to a limited extent though the LED is itself a diode. If you fit them cathode to cathode they will not conduct. However the diode will drop the voltage approx 0.7 volts depending on the precise make etc so you will need to adjust the voltage. Usually you change the resistor, I use a variable voltage power unit. Sorry to say this but the figures above for resistance are approximate at best as Model Railway 12 volts can be anything from 11 to 20 volts.Computer 12 volts is 12 volts and Automobile 12 volts is usually 13.8 to 14.2 volts.