LDR question

[rutledj]

I'm rather new to playing with LDR's. Can someone tell me what the typical voltage should be across the LED for a VTL5C1? If I'm reading the datasheet correctly I'm thinking a 5v supply is sufficient.

http://www.alliedelec.com/Images/Produc ... 219695.pdf


Thanks,
Rut

[John_P_WI]

5v should get you there, like any LED make sure you bias it appropriately. Biasing and controlling the current is more important than the voltage.

[DonMoose]

5v should get you there, like any LED make sure you bias it appropriately. Biasing and controlling the current is more important than the voltage.

The key is the Vf range - in the part you posted, Vf.min is 1.65.
With Vsupply = 5, you need a resistor that keeps you below the If.max of 40mA with a voltage across it of (5 - 1.65)V =3.35V

3.35/.04 = 83.75 ohms - I'd go with at least 91, probably 110, even 120 to maximize LED life.

Hope this helps!

[beasleybodyshop]

I'm rather new to playing with LDR's. Can someone tell me what the typical voltage should be across the LED for a VTL5C1? If I'm reading the datasheet correctly I'm thinking a 5v supply is sufficient.

http://www.alliedelec.com/Images/Produc ... 219695.pdf


Thanks,
Rut

are you repairing a blackface vibrato issue or building a pedal?

[rutledj]

Actually just looking to do some channel switching. I notice mesa and soldano both use them extensively.

[roberto]

LDRs are fine, but if you have just to switch channels, you should go for relays.

Anyway you will find the resistance of the LDR at every current.
By memory, that one should have around 2.2M at 0mA and something like 100R at 40mA.

[rutledj]

[quote="roberto"]LDRs are fine, but if you have just to switch channels, you should go for relays.

So why do so many amp manufactures still use them for channel switching instead of relays? I assumed it was an easy way to avoid the pop when the relay switched.

[roberto]

To avoid pops just pulldown the relay.
Most part of the builders use relays.