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# Current in IC chip Answered

Hello,

It's a bit stupid to ask (I think), but essential to me. From all schematic I readed over intructables I never saw anything or anybody that cared for that.

If a IC have a maximum and minimum current to respect ie: 6mA to 10mA, do we even care? Do I need to limit the current somehow? As I said, every schematic I readed never added any resistor or talked about anything relate to limiting the current on the VCC for the integrated circuit.

I'm currently building a device that use one 555 timer IC in astable and a few others IC and they are all connected in parralel to the power suply.

Thanks

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## Discussions

It is possible to fry a chip, in the sense of electronic damage.  From my limited knowledge I think circuit protection is part of the design of integrated chips.  On a microscopic level they do mimic transistors, resistors and capacitors and even fuse-like or thermal cutoff circuits with overload protection.  You can also damage a chip from too much heat when you solder one of the legs.  Hopefully something else in the circuit fails first rather than the chip going up in smoke.

so it'S all protected and I should connect it directly to the power suply as long as I don't exceed the maximum voltage?

A real electronics person will need to confirm this but I think the load or "drain on the batteries" caused by the IC will only draw as much current as needed.  You would still have to watch out not to hook up a car battery directly to an IC chip.

why not? Just kidding.

Yeah, but I think you are right.
To determine the current you need to know the Voltage and the resistance.

If the datasheet tell something similar to: at 15 volt max current is 200mA, that mean they already considered the resistance.
Well, I think.

Hello There!

I wanted to know the parameter that gives the maximum current drawn by the IC (with load). Is Q current equal to operating current? what if operating current range is not given in datasheet. For example I have a power amplifier (2A) which is designed to operate at 1.2A, how to determine the supply current drawn by IC.

NOT a stupid question...

A) Current drawn by the IC itself during operation?
B) Current sourcing/sinking on the IC's outputs?

A--Connect any device up to it's correctly-specified voltage, and it will draw just as much current as it should draw.  A 5V IC generally will draw much less current than a 5V relay--both are 5V, but each has a different current draw. Current draw is a function of the device itself.

Raise the voltage above the spec'ed values, and that voltage drives more current through the device--often frying it.

If your power supply has the current capacity to supply all your IC's, then you can safely connect them all to it. They will not draw more current then they need. Only if the voltage is too high will it force more current flow.

B-- The outputs on ICs typically are transistors, and they're usually designed to interface with specific "logic families" -- TTL, CMOS, etc.

ICs work well together within logic families; the outputs are carefully designed to handle the required current.  But even within the families, there are rules and chip I/O ports are certainly NOT fail-safe in every combination...

Note that ICs with high-impedance inputs (like CMOS) draw very little current at those inputs--so an output that can safely supply 10mA can provide MUCH more current than is required.

The problems with current sourcing develop when you're trying drive external devices (LEDs, motors, etc...) If more current capabilities are needed, just add an external transistor or driver IC.

Oh thanks, you saved me.

I'm using CMOS IC's from the 4000serie, I was told their work perfectly together.

Cool. Watch out for static electricity when handling CMOS chips...

There are still dangers when connecting CMOS (or TTL) outputs together (on a "Bus", for instance.) If you have several outputs going HI, and one going LO, the HI pins can supply more current than the single LO pin can handle.

Use logic gates instead of a common bus... (if you must use a bus, look into "tri-state" logic... there are CMOS tri-state ICs.)

Yeah, using logic.

I didn't knew they were static sensitive until recently. I almost never touched them and I dont recall having a static burst or anything, ouf.

Also using socket so I dont worry about melting the parts.