Calculate current requirement of a circuit

Hi,

I'm designing a circuit board for a particular application. I have all components and ICs placed properly. I'm stuck at the part of designing power supply.
Circuit needs 3.3V but I don't know how to calculate its current requirement...can anyone help me in this?

Thank you.

you can look up the datasheets of every component. Check for POWER CONSUMPTION (mW or W). In case of a load, just simply multiply current (mA or A) by voltage (VDC).
Once you have calculated all power consumption, just divide it by 3.3V, and the result is current you need. It is recommended to increase theorical value by 1.25.

Best regards.

- - - Updated - - -

you can look up the datasheets of every component. Check for POWER CONSUMPTION (mW or W). In case of a load, just simply multiply current (mA or A) by voltage (VDC).
Once you have calculated all power consumption, just divide it by 3.3V, and the result is current you need. It is recommended to increase theorical value by 1.25.

Best regards.

chuzkin said:

you can look up the datasheets of every component. Check for POWER CONSUMPTION (mW or W). In case of a load, just simply multiply current (mA or A) by voltage (VDC).
Once you have calculated all power consumption, just divide it by 3.3V, and the result is current you need. It is recommended to increase theorical value by 1.25.

Best regards.

- - - Updated - - -

you can look up the datasheets of every component. Check for POWER CONSUMPTION (mW or W). In case of a load, just simply multiply current (mA or A) by voltage (VDC).
Once you have calculated all power consumption, just divide it by 3.3V, and the result is current you need. It is recommended to increase theorical value by 1.25.

Best regards.

Click to expand...

Thank you Chuzkin. Your answer really helped me a lot.
I have some more doubts..It will be really helpful if you guide me with these.
My circuit has an ASIC, micro-controller and some signal conditioning circuitry. Power dissipation given in the datasheet of ASIC and micro-controller is 10mW and 1.5W respectively. So m I supposed to add these powers to get total power consumption of the circuit?
And how to find out power dissipation by signal conditioning circuitry which has few resistors,capacitors and diodes ?

Thank you.

Dear AnujaM

It will be better if you post a schematic page. But, in case of conditioning circuit, what you can do is calculate current through very component like resistors and inductive loads. Then multiply it by the voltage drop in that component and finally sum all results.
Power dissipation in transistors (if they are acting like switches, saturation zone) are not significant.

Hope it helps.

AnujaM said:

Hi,

I'm designing a circuit board for a particular application. I have all components and ICs placed properly. I'm stuck at the part of designing power supply.
Circuit needs 3.3V but I don't know how to calculate its current requirement...can anyone help me in this?

Thank you.

Click to expand...

If this circuit is finished and working, best way is to monitor current with ampermeter or ampermeter logger (EEPROM,SD,...) in real environment of usage, based on this data you should see peak current and normal needed current for your circuit, and according to that you will design appropriate power supply.

A 1A voltage regulator like LD1117-3.3 can run many types of simple circuits.
Seldom do we calculate to the exact ampere.

If you have a lab bench power supply, monitor the current drawn when you operate your circuit. Take the max reading. Design or get a voltage 3.3V which can supply higher than the max reading. Normally I will double the rating. If my circuit uses 0.1A, I will get one that can supply more than 0.2A. Taking the current reading is important if you are aware that your circuit is going to draw more than the usual amount of current.

Some people may think that supply more current can damage the circuit. No, it don't work this way. The higher current rating means that the power supply is capable of supplying it. The actual amount of current being drawn will still depend on the load, which is your circuit.

You will be used to the amount of current a typical circuit is going to draw after working with more circuits.

AnujaM said:

Hi,

I'm designing a circuit board for a particular application. I have all components and ICs placed properly. I'm stuck at the part of designing power supply.
Circuit needs 3.3V but I don't know how to calculate its current requirement...can anyone help me in this?

Thank you.

Click to expand...

hi
you can serie a small resistor at input then voltage drop resistor divide resistor equal total current

Dear hamid.abbaszadeh.

It is a good idea, but you should have an idea of current in order to select a correct resistor because of power disipation. Remember any resistor value in ohm have different power dissipation (most common 1/4 watt, 1/2W, 1W, etc).

Best regards.