Voltage Regulator, Battery resistance, current

AI Thread Summary
A voltage regulator maintains a constant output voltage regardless of variations in input voltage, as long as the input remains within acceptable limits. In this case, both 9V and 12V inputs will yield a steady 5V output. The charging current into the battery will not increase with a higher input voltage because the battery's internal resistance remains constant. Any excess voltage is dissipated as heat by the regulator, which does not affect the output current unless the load changes. Therefore, the output current from the voltage regulator is determined by the load rather than the input voltage.
ramonegumpert
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Dear Experts

Lets say I have a power source of 9 volts.
A 5v output voltage regulator is connected to this power supply.
So, input 9 volts, output is regulated to 5volts constant.
the output pin is connected to a battery with has a constant internal resistance.

Does this mean, because the resistance of battery and the charging voltage is constant, the charging current going into the battery will not increase even when the power source is increased say from 9 volts to 12 volts?

So, my question is can a voltage regulator giving constant 5 volt output charge with higher current when the source voltage is increased?

Thanks for reading.

Best regards
Ramone
 
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The point of the voltage regulator is to provide a constant output (i.e. regulate the output to within certain tolerances) over a range of input voltages. So, even with a 12 volt input, the output of the regulator is still 5 V, (assuming that both 9 V and 12 V are within the range of acceptable inputs for your regulator). So, regardless of input voltage, it's still 5 V at the output, which means that the same thing will happen when you connect the thing to a battery in both cases.

A voltage regulator steps down voltage by basically wasting power. So, with a higher voltage input, more energy will be wasted as heat in order to step down to 5 V. That's about it.
 
Hello Cepheid

Thank you for your response.
To finalise, the output current from voltage regulator cannot be increased as the battery resistance is constant.

regards
Ramone
 
ramonegumpert said:
Hello Cepheid

Thank you for your response.
To finalise, the output current from voltage regulator cannot be increased as the battery resistance is constant.

regards
Ramone

That's correct for your example, but it's potentially misleading.

If the load needs 100mA, the regulator gives it 5 volts at 100mA. If the load changes, the regulator current follows it (within design limits.) You can double the voltage going into the regulator, but if the load doesn't change, the current doesn't change.

As cepheid said, the higher voltage is simply dissipated as heat by the voltage regulator.

(Of course, like all electrical circuits, if you supply higher than its rated voltage, bad things tend to happen.)

ETA: Look at the information panel on some power supplies -- such as the charger for your phone. Mine says:
Input: 100-240v, 50/60Hz, 0.1A
Output: 5.9v DC, 375mA​
You can see that a wide range of input voltage has no effect on the output.
 
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Thank you very much Mr Pantaz :)
 
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