- #1
nlaham
- 44
- 0
I had a few questions about circuits. I am a mechanical engineer so I don't have very much knowledge in electrical theory, just basic stuff, but I have been working on some basic circuit design and could use some help.
I have three questions really.
So I have a 3.7V battery on a device that normally charges with a 5V USB source (I think it draws around 1 amp to charge). There are of course 2 pins on the device to provide power to charge. There are also power out pins for a 3.3V accessory, however I tried to draw current from this and it seems to cap out at around 300mA. I was trying to actually draw a lot more, somewhere around 2 amps, but there must be some sort of current limiter. The voltage dropped to about 0.6V when I did this. Am I correct in assuming something is limiting the current? I am guessing normally if the current was too much for a circuit and wiring, the circuit would burn up, but is it true this particular circuit has some sort of device to limit the current so that is protects the circuit? Wouldn't I normally be able to draw unlimited current until the circuit burns up in a simple circuit.
Anyway, my question is, how can the device put over 1 amp of current through the charging pins, but it won't let me draw more than 300mA from the other pins? It seems if the charging circuit can handle all of that current, why can't the power output give me the same? Maybe it can in theory, but they limit the current for other reasons, so as to not drain the battery so quickly or something.
Last question, can I draw power off the charging pins? Couldn't these pins just act as a power source since I am charging with them. I mean normally if I give 5V to 3.7V battery, I will be charging, but what if I just attach an LED or something to those same charging pins. Will the LED light up? Kind of confused on this, how charging is accomplish and if that makes any sense.
Thanks,
Nick
I have three questions really.
So I have a 3.7V battery on a device that normally charges with a 5V USB source (I think it draws around 1 amp to charge). There are of course 2 pins on the device to provide power to charge. There are also power out pins for a 3.3V accessory, however I tried to draw current from this and it seems to cap out at around 300mA. I was trying to actually draw a lot more, somewhere around 2 amps, but there must be some sort of current limiter. The voltage dropped to about 0.6V when I did this. Am I correct in assuming something is limiting the current? I am guessing normally if the current was too much for a circuit and wiring, the circuit would burn up, but is it true this particular circuit has some sort of device to limit the current so that is protects the circuit? Wouldn't I normally be able to draw unlimited current until the circuit burns up in a simple circuit.
Anyway, my question is, how can the device put over 1 amp of current through the charging pins, but it won't let me draw more than 300mA from the other pins? It seems if the charging circuit can handle all of that current, why can't the power output give me the same? Maybe it can in theory, but they limit the current for other reasons, so as to not drain the battery so quickly or something.
Last question, can I draw power off the charging pins? Couldn't these pins just act as a power source since I am charging with them. I mean normally if I give 5V to 3.7V battery, I will be charging, but what if I just attach an LED or something to those same charging pins. Will the LED light up? Kind of confused on this, how charging is accomplish and if that makes any sense.
Thanks,
Nick