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User talk:Daveb: Difference between revisions
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== 20V, 30V or 60V diode bridge. == | == 20V, 30V or 60V diode bridge. == | ||
From what I read yesterday, the voltage drop of a schottky diode is a function of the junction temp, the current passed, the reverse voltage barrier, and the size of the diode junction (which I guess becomes cost). | From what I read yesterday, the voltage drop of a schottky diode is a function of the junction temp, the current passed, the reverse voltage barrier, and the size of the diode junction (which I guess becomes cost). | ||
There is this | There is this [http://uk.farnell.com/vishay-formerly-i-r/vs-95sq015/diode-schottky-9a-15v/dp/506795 £3.19 diode 9A/15V] that has a Vf for 1A at 25C less than 250mV. If you could heat the junction to 100C it would be about .1V!! AT 100mA it is less than 200mV Vf. | ||
Since the voltage out of the dynamo is essentially a function of the road speed, it could be quite high | Since the voltage out of the dynamo is essentially a function of the road speed, it could be quite high. leading to my difficulties in finding low Vf diodes.. | ||
If I put a pair of zener diodes across the output of the dynamo - before the rectifier, then the rest of the circuit is limited to only that voltage, and the diodes in the bridge recifier are limited to half of that. | If I put a pair of zener diodes across the output of the dynamo - before the rectifier, then the rest of the circuit is limited to only that voltage, and the diodes in the bridge recifier are limited to half of that. | ||
I am not sure if 20V or 30V is the right target voltage for the rectifier. Higher voltages get more complex, as larger logic level MOSFETs seem to need 5.5 to 4.5V gate voltages rather than 2.5V. Also, low-drop-out v-reg that will take > 30V as input are rare | I am not sure if 20V or 30V is the right target voltage for the rectifier. Higher voltages get more complex, as larger logic level MOSFETs seem to need 5.5 to 4.5V gate voltages rather than 3V, 2.5V or even 1.8V. Also, low-drop-out v-reg that will take > 30V as input are rare. | ||
I am leaning towards 20V (or 18V to split the diff between LEDs and specs). | |||
