- Wed Mar 23, 2011 1:07 pm
#123595
OK very simple requirement yet I am struggling to think of an elegant solution with the smallest footprint possible.
I have 4 LEDs in parallel, basic blue with approx 3.2 Vf. I need to switch them on from a 1.6V trigger source.
The trigger can have very little current drawn from it so ideally less than 500nA max.
A standard transistor with 0.3mV Vce was ok and could drive the LEDs with 0.3V loss without too much notice. But the DC gain was then too low for full drive too, so wasn't suitable.
I have then thought of a darlington pair, but the Vce lowest I can find is 0.8V which is far too much drop over the LEDs.
My first thought is to find a darlington pair with a 0.3V Vce if one even exists? Failing that, I am either looking for a solution that is no larger than a SOT-23 due to space limits, or failing that, ignoring space limits I would create a separate board that buffers the 1.6V source to then connect to the buffer instead, so what would be the best thing to do that - perhaps an op-amp unity gain?
I have 4 LEDs in parallel, basic blue with approx 3.2 Vf. I need to switch them on from a 1.6V trigger source.
The trigger can have very little current drawn from it so ideally less than 500nA max.
A standard transistor with 0.3mV Vce was ok and could drive the LEDs with 0.3V loss without too much notice. But the DC gain was then too low for full drive too, so wasn't suitable.
I have then thought of a darlington pair, but the Vce lowest I can find is 0.8V which is far too much drop over the LEDs.
My first thought is to find a darlington pair with a 0.3V Vce if one even exists? Failing that, I am either looking for a solution that is no larger than a SOT-23 due to space limits, or failing that, ignoring space limits I would create a separate board that buffers the 1.6V source to then connect to the buffer instead, so what would be the best thing to do that - perhaps an op-amp unity gain?