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Topic: simple power supply question!! (Read 193 times) previous topic - next topic

karthyk

So i have a 5v 1.5 amp power supply can i power my 74hc574d and 74hc138 directly from the power supplyy? or will it burn the chip? sorry if this is a very basic question, but i dont know where else to ask.

thanks,
karthy

larryd

#1
Jan 17, 2021, 12:51 am Last Edit: Jan 17, 2021, 12:52 am by larryd
Yes, a 5VDC power supply is what you need.


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aarg

Quote
i dont know where else to ask
You don't really need to ask anywhere. The manufacturers of these things almost always put the data sheets on line. You can Google those.
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

karthyk

No i mean i know 5V is what i need but i am talking about the current here the power supply is rated at 1.5 amps is it too much? or will the chip draw current as much as it needs

DVDdoug

5V is constant and the 1.5A current rating is the maximum allowed.    If nothing is connected no current flows.   With just a couple of small logic chips, a few milliamps will flow.     If you try to power something like motors that require too much current the voltage will drop and the power supply might burn-out.

Most "things" work that way...   The voltage is (approximately) constant (or at least independent of the load) and the current depends on the resistance of the load (Ohm's Law).   We don't always know the resistance and the resistance can change if you turn-on an LED or motor, etc.    But the important thing is that the current depends on the load.

It's the same thing with power in your house...    There is always voltage at the power outlet (120VAC here in the U.S.) but current only flows with something is plugged-in and turned-on.    A small light bulb takes less current than a toaster or hair drier, and if you plug-in two hair driers you'll blow a circuit breaker (and the voltage goes to zero).

aarg

No i mean i know 5V is what i need but i am talking about the current here the power supply is rated at 1.5 amps is it too much? or will the chip draw current as much as it needs
Supply currents are also specified in almost every data sheet.
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

karthyk

ye like you said it is specified in datesheet it says max 100ma does that mean i have to some how reduce the 1.5 amps to 100ma? if  so how i only have some 100 ohm resistors lying around. i dont want to burn the chip 

larryd

#7
Jan 17, 2021, 04:39 am Last Edit: Jan 17, 2021, 04:46 am by larryd
You need to study some basic electronics.

Start by Googling 'Ohms Law'.




The amount of current a load takes is determined by the internal components that make up your load.

The I.C.s in question are made from transistors, resistors etc.

When you apply 5v to the I.C. power pins the internal components will take 100mA maximum.




If you had a 5v 'power supply' that was rated at 500 Amps you could still attach these I.C.s without any damage.

Just don't short the power supply's +5v and 0v terminals !    :smiley-roll-sweat:



No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

Paul__B

ye like you said it is specified in datesheet it says max 100ma does that mean i have to some how reduce the 1.5 amps to 100ma?
You did not understand what DVDdoug explained?

I am not in America, but on my power point (outlet) here it states "250 V, 10 A" which is 10 Amps.  The supply voltage is actually about 240 Volts.

So I have plugged in my Ikea 3 W LED lamp which will require about 0.0125 Amps.

Does this mean the power point forces it to take 10 Amps at 240 Volts which is 2400 Watts instead of three?  That is of course, the power of a common radiator!


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