I have an Akai vintage tuner/amp which I've refurbished. The panel was originally illuminated by 3 globes. My multimeter shows each globe received 13 volts AC. I replaced them with 2 arrays of LED's designed for 12 volts DC. In addition, I added another small resistor before each of the two arrays. Works beautifully! Problem is, I was advised against using LED's by the supplier as they were not designed for AC current - what is the consequence?
Well, LEDs, being diodes, conduct only in 1 direction. Their reverse breakdown voltages are probably not too high, so you risk destroying them. Just put a small rectifier diode in series with them, plus a small cap in parallel, to make a simple half-wave rectifier and you'll be good to go. Such parts won't cost you almost anything.
Never had a problem is not the same thing as good idea.
If you run an LED on 13VAC and each LED has a reverse rating of 5v, it may well survive anyway - ratings are not hard lines. But I wouldn;t specify that in any design.
For the penny a diode costs, why think of reasons not to be prudent?
The opposite polarity parallel arrangement means the forward drop of each LED limits the reverse potential either can see.
If you run an LED on 13VAC and each LED has a reverse rating of 5v, it may well survive anyway - ratings are not hard lines. But I wouldn;t specify that in any design.
For the penny a diode costs, why think of reasons not to be prudent?
The opposite polarity parallel arrangement means the forward drop of each LED limits the reverse potential either can see.
Hmm,I just replaced the burnt out bulbs in my Sansui TU-717 with white LED's. IIRC they run from a 'raw' ~8Vac supply. I just used two white LED's in 'anti-parallel' with a suitable dropping resistor,and haven't had any problems yet.
This way the voltage across the reverse biased LED is clamped to the forward voltage of the LED that's conducting on that cycle. Perhaps not ideal,but it's worked well for me before.
Usually when using a single LED on raw AC,I just put a small diode in anti-parallel with the LED,to clamp the reverse voltage to ~0.7V,well within tolerance for any LED I've come across.It will burn a bit more power in the dropping resistor on the 'unused cycle' (when the diode conducts) but it's never been an issue so far.
This way the voltage across the reverse biased LED is clamped to the forward voltage of the LED that's conducting on that cycle. Perhaps not ideal,but it's worked well for me before.
Usually when using a single LED on raw AC,I just put a small diode in anti-parallel with the LED,to clamp the reverse voltage to ~0.7V,well within tolerance for any LED I've come across.It will burn a bit more power in the dropping resistor on the 'unused cycle' (when the diode conducts) but it's never been an issue so far.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.