Z
z_neep
Guest
Hi all. I've been away from electronics for quite some years but I have a reasonable understanding of things still.
I am working on a toy that will contain 20 LEDs that are spec'd 20mA / 3.3V. The power source are 3.7V rechargeable li-ion batteries of at least 350mAh.
I have wired up the LEDs in parallel as well as the batteries on two separate strings. One reason for keeping the batteries in parallel is so I can charge them all at the same time using the same wire. There is a switch between the two wire pairs to turn on the lights. Each LED has its own resistor. The problem now is that when the battery discharges the voltage drops (to under 3V towards the end), and the LEDs will shine less bright or go off completely.
I have heard this can be fixed using a step-up / boost converter or a current source that can keep the voltage up whilst drawing more current from the batteries, so that they are used until completely empty. My question is what should I buy to achieve this with?
The toy needs to stay as light as possible and there isn't much space either so I'm looking for a solution using an IC that can do this without too many other components. I've been looking at the MAX1674 step-up converter but it seems really awkward to solder and I'm not sure it's the right chip yet.
Has anyone here done a project like this before, or can you give me some hints in the right direction? I'd be driving the LEDs between 15 and 20mA, so the total output current would be under 400mA.
Thanks!
Paul
I am working on a toy that will contain 20 LEDs that are spec'd 20mA / 3.3V. The power source are 3.7V rechargeable li-ion batteries of at least 350mAh.
I have wired up the LEDs in parallel as well as the batteries on two separate strings. One reason for keeping the batteries in parallel is so I can charge them all at the same time using the same wire. There is a switch between the two wire pairs to turn on the lights. Each LED has its own resistor. The problem now is that when the battery discharges the voltage drops (to under 3V towards the end), and the LEDs will shine less bright or go off completely.
I have heard this can be fixed using a step-up / boost converter or a current source that can keep the voltage up whilst drawing more current from the batteries, so that they are used until completely empty. My question is what should I buy to achieve this with?
The toy needs to stay as light as possible and there isn't much space either so I'm looking for a solution using an IC that can do this without too many other components. I've been looking at the MAX1674 step-up converter but it seems really awkward to solder and I'm not sure it's the right chip yet.
Has anyone here done a project like this before, or can you give me some hints in the right direction? I'd be driving the LEDs between 15 and 20mA, so the total output current would be under 400mA.
Thanks!
Paul
