Voltage comparator with variable voltage input. How?!
Hullo,
I think that the subject I chose is not the most appropriate but I couldn't find a better one.
Anyway, I am designing my first "serious" circuit. I will use it to manage the power from a bicycle dynamo (permanent magnet generator?). I want it to switch from the dynamo to a backup battery when the output of the dynamo is not sufficient to drive a high power led.
First of all, I will use a full wave bridge to get a DC output.
Then, I was thinking of using a relay followed by a comparator with a fixed voltage reference.
To help you help me,
At 8km/h no load the output voltage is 15V.
At 8km/h with load the output voltage is 8V.
At 12km/h no load the output voltage is 17V.
At 12km/h with load the output voltage is 10V.
Let's say I set the threshold level of the comparator to 10V.
Under 10V, the battery is employed.
The problem:
The bicycle is still (0km/h)
[The comparator sees 0V from the dynamo and switches to the battery.
No problem here.]
The bicycle accelerates to e.g 8km/h and maintains this speed
[The dynamo has no load and its voltage is 15V, the comparator+relay switches to the dynamo. Now the dynamo is under load and its voltage drops to 8V, the comparator+relay now switches to the battery. The dynamo has no load and its voltage rises to 15V, the comparator+relay switches to the dynamo.
That is the problem I am facing. If my logic is correct, this oscillation will keep happening as long as my speed is below 12km/h.]
The bicycle accelerates to e.g 15km/h and maintains this speed
[The dynamo's output is above the threshold level, the comparator+relay switches to the dynamo. The dynamo's output WITH load is still above the threshold level.
No problem here.]
The bicycle decelerates to 8km/h and maintains this speed
[Like before, the same problem with the oscillation occurs.]
The bicycle decelerates to 0km/h and stays still
[The comparator sees 0V from the dynamo and switches to the battery.
No problem here.]
In conclusion, the problem is when the bicycle's speed is 0km/h
I hope that my question is clear because english is not my native language.
If something is not clear or wrong please point it out.
I think that the subject I chose is not the most appropriate but I couldn't find a better one.
Anyway, I am designing my first "serious" circuit. I will use it to manage the power from a bicycle dynamo (permanent magnet generator?). I want it to switch from the dynamo to a backup battery when the output of the dynamo is not sufficient to drive a high power led.
First of all, I will use a full wave bridge to get a DC output.
Then, I was thinking of using a relay followed by a comparator with a fixed voltage reference.
To help you help me,
At 8km/h no load the output voltage is 15V.
At 8km/h with load the output voltage is 8V.
At 12km/h no load the output voltage is 17V.
At 12km/h with load the output voltage is 10V.
Let's say I set the threshold level of the comparator to 10V.
Under 10V, the battery is employed.
The problem:
The bicycle is still (0km/h)
[The comparator sees 0V from the dynamo and switches to the battery.
No problem here.]
The bicycle accelerates to e.g 8km/h and maintains this speed
[The dynamo has no load and its voltage is 15V, the comparator+relay switches to the dynamo. Now the dynamo is under load and its voltage drops to 8V, the comparator+relay now switches to the battery. The dynamo has no load and its voltage rises to 15V, the comparator+relay switches to the dynamo.
That is the problem I am facing. If my logic is correct, this oscillation will keep happening as long as my speed is below 12km/h.]
The bicycle accelerates to e.g 15km/h and maintains this speed
[The dynamo's output is above the threshold level, the comparator+relay switches to the dynamo. The dynamo's output WITH load is still above the threshold level.
No problem here.]
The bicycle decelerates to 8km/h and maintains this speed
[Like before, the same problem with the oscillation occurs.]
The bicycle decelerates to 0km/h and stays still
[The comparator sees 0V from the dynamo and switches to the battery.
No problem here.]
In conclusion, the problem is when the bicycle's speed is 0km/h
I hope that my question is clear because english is not my native language.
If something is not clear or wrong please point it out.
Replies
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jellochaosI was thinking of using an additional circuit that will sense the frequency of the AC output of the dynamo to make the switch.
But this would add more components to the circuit adding to the complexity and most importantly, it will introduce more losses.
I am aiming for the most efficient circuit possible.
You are reading an archived discussion.
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