LED's AC trany

[jonnyg2k6]

I have some garden lights (non LED) running off a 12v AC transformer that would normally be used for Haolgen lighting, 60va 12v AC etc etc. This work great, but I now want to add some LED's.

Can I use this 12ac feed to also power the 3 x 3.3v 20ma Blue LED's (designed to run off 12v dc) if I place a suitable resister in the circuit?? my main concern is the DC and AC bit!?! (

 

[Stoday]

All you need is a cheap rectifier diode and one 390Ω 1/4W resistor per LED.

You can buy a 1N4004 diode for 16p and a 0.6W resistor for 17p from Maplin

 

[esar]

All you need is a cheap rectifier diode and one 390Ω 1/4W resistor per LED.

Is it worth bothering with the diode? The LED is one already.

 

[jonnyg2k6]

Hay thats great!! Many thanks for the reply.

So I would put the Diode on one of the 12v ac out puts and then a resistor on each LED and then wire in parallel?

P.S Does it matter which side of the LED the resister go?

 

[esar]

Hay thats great!! Many thanks for the reply.

So I would put the Diode on one of the 12v ac out puts and then a resistor on each LED and then wire in parallel?

P.S Does it matter which side of the LED the resister go?

Yes, that's right, diode can go on either output of the transformer and resistors can go either side of the LED's. Then just wire up the resistor/LED pairs in parallel.

 

[jonnyg2k6]

Many thanks all!!

 

[electronicsuk]

All you need is a cheap rectifier diode and one 390Ω 1/4W resistor per LED.

Is it worth bothering with the diode? The LED is one already.

Yes, it is worth it, as most LEDs have a very limited maximum reverse voltage.

 

[esar]

All you need is a cheap rectifier diode and one 390Ω 1/4W resistor per LED.

Is it worth bothering with the diode? The LED is one already.

Yes, it is worth it, as most LEDs have a very limited maximum reverse voltage.

Thanks, that makes sense, just checked a couple of data sheets and 5V seems to be the norm.

 

[ericmark]

All you need is a cheap rectifier diode and one 390Ω 1/4W resistor per LED.

Is it worth bothering with the diode? The LED is one already.

Yes the threshold voltage for LED is very low