Large Currents vs Small Currents

[electronicsLearner77]

I want to know is it possible to distinguish between large currents and small currents. For example beyond certain Amps (ex. 1 Amp) it is called large current and below this it is small current etc? Is there is any such definition?

 

[Nanren888]

It depends on the context.
.
For one cracker, three slices of cheese is a lot. If I sell cheese professionally, wholesale, 50kg is a smal amount of cheese.
.
With some degrees, there is a distinction high current = power electronics or power engineering/distribution, and low current = analog, digital, microprocessors, ...
.
A 555 timer output will deliver 300mA which is a lot of current if everything else about will only source or sink a few mA.
Battery chargers might deliver 25Amps or more which is a lot compared to smaller bench supplies.
.
What's your context?

 

[electronicsLearner77]

Thank you for the reply. I was reviewing the transistor types a. General-purpose / Small - Signal transistors b. Power transistors c. RF Transistors. In this context i wanted to understand the current limits.

 

[Nanren888]

Maybe work backwards. Look up the ones of interest. Note the currents they list as absolute maximum and whether the description is "high current" or not.

 

[Audioguru]

.
A 555 timer output will deliver 300mA.

No. The datasheet says 200mA.



[fixed quote error ]

 

[bertus]

Hello,

For the bipolair version the absolute maximum current is 225 mA:


For the CMOS version it is much lower:


Bertus

 

[bertus]

Hello,

Take a look at the ranges of mosfet operating currents.
A small 2N7000 can only handle 0.35 A.
A large IRF3205 can manage about 100 A.

Bertus

 

[Audioguru]

The datasheet for the LM555 and uA555 show spec's stopping at 200mA where the maximum voltage drop is very high at 2.5V and the graphs showing typical ones stop at 100mA.

I believe that Mosfets have a high gate to source capacitance and very low on-resistance because they are made with thousands of paralleled Mosfets cells on the chip. The 2N7000 datasheet says it has high cell density.

 

[electronicsLearner77]

Hello,
Take a look at the ranges of mosfet operating currents.
A large IRF3205 can manage about 100 A.
Bertus

I saw the data sheet of IRF3205, i think the 100 A you are referring to is the below one


My doubt is it is such a huge current and it will flow through the IC, if l look at the image of the transistor

it looks very small, how does it handle so much current? I am not sure if the question makes any sense.

 

[Audioguru]

Note #5 in the datasheet says its case has a max drain current rating of 75A. I doubt the little pins will survive 75A.

 

[electronicsLearner77]

Note #5 in the datasheet says its case has a max drain current rating of 75A. I doubt the little pins will survive 75A.

Then how to understand all these data sheets, are they mistakes? Then how do i design a system?

 

[Harald Kapp]

This is the note from the datasheet:

Calculated continuous current based on maximum allowable
junction temperature. Package limitation current is 75A.

(emphasis by me)

What this means is:

1. You need to read the datasheet carefully and completely.
2. The transistor die is capable of 100 A. The limit is imposed by the housing. Theoretically one could put this die into another case and get the full 100 A. But it is not very likely that this will happen.

A note on the side: Electrical characteristics are, as noted, at room temperature (25 °C). When a component dissipates a non-negligible amount of power you need to to take into account the derating, usually shown in curves following the tables. The useful range of many parameters is typically much smaller than the typical values in the tables suggest at first glance.
Also some parameters may be achievable with additional measures only, e.g. heatsinks, forced cooling etc.
Even when considering the derating curves, it is always a good idea to leave some margin between the actual use case and the limits. This will improve reliability and longevity of your circuit.

 

[Audioguru]

I have never tried to do welding so I cannot think of anything else that I would make that uses the extremely high DC current of 100A.

 

[Harald Kapp]

The 12 V side of an inverter for use in a car? Not seldom rated at 1 kW or higher which makes the primary side current close to 100 A at 12 V.

 

[Audioguru]

I do not know anybody who uses a powerful alternator so that they live all the time in their car. I guess it is connected directly to the battery and does not cause the cigar-lighter fuse to blow.

 

[davenn]

I do not know anybody who uses a powerful alternator so that they live all the time in their car.

eg. construction site workers --- in my telecom van, so many years ago, I had a 1500W inverter for running electric drills and other hand power tools etc

eg. camping -- running fridge/freezers and other camping gear

I guess it is connected directly to the battery

Yes, definitely, with very heavy gauge cables