Hello,
'cause it's my first post, a big hello to everyone here!
I hope you won't throw me out after my first silly questions!
I'm looking for a constant current source with a low voltage drop!
The application:
Power comes from a bike's dynamo. Voltage is AC at frequencies roughly between 30Hz and 100Hz.
Voltage can vary (at max.) between 4.2V (climbing a hill) and 7.5V (normally less, but depends on dynamo and frontlight's current draw).
The thing I want to power are two red LEDs in series, normally they are 2V each. They'll get between 10 and 20mA.
So now I need a supply with a very low drop-out, to get a satisfactory current even at 4,2V.
Also, I'd like it to be simple! The circuit on the image is not that bad, it gives me (trusting LTSPice) 4,4mA per Diode at 4.2V and 9,8mA at 7,5V.
It's not that bad, but I'd like the current difference between high and low volatge to be lower.
Also, I imagine to use that circuit 2 times, one for each AC leg. Ok, I'll probably add a capacitor in order to reduce the flickering, but I don't have much space. I'll decide on the caps when I see the circuit in action.
I'd be very glad for any suggestions!
Dominique
'cause it's my first post, a big hello to everyone here!
I hope you won't throw me out after my first silly questions!
I'm looking for a constant current source with a low voltage drop!
The application:
Power comes from a bike's dynamo. Voltage is AC at frequencies roughly between 30Hz and 100Hz.
Voltage can vary (at max.) between 4.2V (climbing a hill) and 7.5V (normally less, but depends on dynamo and frontlight's current draw).
The thing I want to power are two red LEDs in series, normally they are 2V each. They'll get between 10 and 20mA.
So now I need a supply with a very low drop-out, to get a satisfactory current even at 4,2V.
Also, I'd like it to be simple! The circuit on the image is not that bad, it gives me (trusting LTSPice) 4,4mA per Diode at 4.2V and 9,8mA at 7,5V.
It's not that bad, but I'd like the current difference between high and low volatge to be lower.
Also, I imagine to use that circuit 2 times, one for each AC leg. Ok, I'll probably add a capacitor in order to reduce the flickering, but I don't have much space. I'll decide on the caps when I see the circuit in action.
I'd be very glad for any suggestions!
Dominique