Hi All,
I'm improving a circuit for a dynamo, which is to feed the AC into a USB 5v output. The dynamo has a wide range, theoretically anything up to 100v is possible, but at lower speeds it'll generate about 6v. As bicycle speeds are generally all over the place, it can differ quite widely. I know that I've had over 50v downhill at speed.
Why this matters, is at lower speeds the voltage is crucial to getting enough wattage out to the USB. Previously I've used a standard bridge, with a 1.1v drop, a 24v darlington regulator and then the switch mode buck.
I'm trying to improve lower speed efficiency, at the expensive of higher speed by replacing the 1.1v bridge with mosfets. This means I'm limited to 20v unless I add in more resistors and zeners, but the switch mode can only handle a maximum of 24v anyway. So, my thinking now is a 18v zener/darlington on protection and then the fets should be safe. Does the x1.41 factor still apply here?
Please take a look at the circuit and see if I've made any errors. I'm completely new to PCB design (you'll notice I haven't figured out how to switch the P-FETS around yet).
Many thanks!
Andrew
I'm improving a circuit for a dynamo, which is to feed the AC into a USB 5v output. The dynamo has a wide range, theoretically anything up to 100v is possible, but at lower speeds it'll generate about 6v. As bicycle speeds are generally all over the place, it can differ quite widely. I know that I've had over 50v downhill at speed.
Why this matters, is at lower speeds the voltage is crucial to getting enough wattage out to the USB. Previously I've used a standard bridge, with a 1.1v drop, a 24v darlington regulator and then the switch mode buck.
I'm trying to improve lower speed efficiency, at the expensive of higher speed by replacing the 1.1v bridge with mosfets. This means I'm limited to 20v unless I add in more resistors and zeners, but the switch mode can only handle a maximum of 24v anyway. So, my thinking now is a 18v zener/darlington on protection and then the fets should be safe. Does the x1.41 factor still apply here?
Please take a look at the circuit and see if I've made any errors. I'm completely new to PCB design (you'll notice I haven't figured out how to switch the P-FETS around yet).
Many thanks!
Andrew
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