Hi! I am new to electronics, please don't judge my misknowledge.
I am using a power multiplexer (TPS2113A) to switch between two power sources (5V 1A cable and usb VBUS), the output of the multiplexer gives 5V and up to 1.25A. This output will then go to a linear voltage regulator (LD1117#33) to drop it to 3.3V but here is the problem, I am not finding any information about the input current of the voltage regulator (if it makes sense?!). I only found the output current that can go up to 800mA. Can you please tell me if the input current makes sense and if yes, should I change the regulator or add a resistance to drop the current? thank you!

 

hi LG,
Welcome to AAC,
The Input current will only be few mAmps above the current you are actually supplying to the 3.3v Load.
E

 

hi LG,
Welcome to AAC,
The Input current will only be few mAmps above the current you are actually supplying to 3.3v Load.
E

Thank you for replying, but I did not understand, is it acceptable to give the voltage regulator 1.25A ? if yes, how much is it going to give in the output (the datasheet says that the maximum output current is 800mA

 

Hi,
Consider your required 3.3v load current was say 500mA.
The Input current to LD1117 would be approx 510mA.

If your 3.3V load required only 100mA, then the Input current would be approx 110mA.

You don't set the input current to the LD1117.

Do you follow OK.
E


Update: post the circuit you are powering with the 3.3V

 

If you try drawing more than the rated maximum 800mA from the regulator output it will go into self-protect mode and limit the current as per the datasheet.

 

Hi! I am new to electronics, please don't judge my misknowledge.
I am using a power multiplexer (TPS2113A) to switch between two power sources (5V 1A cable and usb VBUS), the output of the multiplexer gives 5V and up to 1.25A. This output will then go to a linear voltage regulator (LD1117#33) to drop it to 3.3V but here is the problem, I am not finding any information about the input current of the voltage regulator (if it makes sense?!). I only found the output current that can go up to 800mA. Can you please tell me if the input current makes sense and if yes, should I change the regulator or add a resistance to drop the current? thank you!View attachment 298110

Why do you have resistor R15 in your circuit. It is only shown in the datasheet as a test load, and isn't needed in your application. It's wasting about 100 mA of current unnecessarily!

 

Why do you have resistor R15 in your circuit. It is only shown in the datasheet as a test load, and isn't needed in your application. It's wasting about 100 mA of current unnecessarily!

My bad, thank you for pointing out!

 

Hi LG,
Please, post the actual circuit you are powering with the 3.3V
E

 

Though what delivers power to your regulator may be capable of supplying 2.5 amps, the regulator will only draw the current required by its load. The "2.5 amps" is the available current, not necessarily what will be supplied.

 

Though what delivers power to your regulator may be capable of supplying 2.5 amps, the regulator will only draw the current required by its load. The "2.5 amps" is the available current, not necessarily what will be supplied.

Thank you very much, I understand now

 

Hi LG,
Please, post the actual circuit you are powering with the 3.3V
E

Hi! Sorry for the late reply, I am powering an stm32f407 based pcb. should I post the whole schematics?