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DC output current in a Datasheet

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Please read the title of the table, it says "Absolute maximum ratings", the individual outputs are rated to supply at least 6mA so the 35mA is for the whole package. The note under the table explains that exceeding 35mA may damage the device. It isn't intended to be a current driver, it's just a simple logic device designed to feed the inputs of other logic devices.


Brian.
 
betwixt said:
Please read the title of the table, it says "Absolute maximum ratings", the individual outputs are rated to supply at least 6mA so the 35mA is for the whole package. The note under the table explains that exceeding 35mA may damage the device. It isn't intended to be a current driver, it's just a simple logic device designed to feed the inputs of other logic devices.


Brian.
Click to expand...


I see, thanks you.
I want to use this chip to drive 8LEDs which is 20mA each. This is the LED cube sch on the internet. 4072693764_e4598492ec_o.jpg
How could it work? on ebay, most of LED i found rate at 20mA.
 

Connect your LED's so the chip is sinking current to turn them on. Do not source current from driver I.C.

The N-ch output drivers will have lower resistance then the P-ch pull up so N-ch pull down will usually provide greater current capability.
 
Do not confuse the ratings of an LED with the current you intend it to pass. The rating is the maximum allowed but you can use any current up to that. A typical LED will visibly glow with currents as low as 0.1mA, you choose the current up to the limit allowed.

I repeat my comment though, the '595 is NOT an LED driver IC although I see many references to it being one. For best results you should add a driver stage after the '595, you will then get more consistent results and probably brighter LEDs as well.

Brian.
 
One single or two outputs of the 74HC595 can drive LEDs with more than 20mA with a 5V supply. But the maximum allowed current for all outputs continuously is 70mA.

All 74HCxxx and microcontrollers have these output ratings. The lower current spec's on the datasheets are for low voltage drop logic but LEDs have a much higher voltage drop so the output current is much higher.

Cmos outputs are fairly symmetrical so they sink or source almost the same amount of current.
 
From datasheet: Q0-...-Q7 maximal current is 35mA and Q7s is 25mA.
But I think this device able to drive some leds or a 7 segment display. :)
 

jamespond said:
From datasheet: Q0-...-Q7 maximal current is 35mA and Q7s is 25mA.
But I think this device able to drive some leds or a 7 segment display. :)
Click to expand...
The chip inside a 74HCxxx logic IC is tiny so its total continuous maximum allowed current is 70mA.
Then it can drive up to 10mA into 7 segments but without a decimal LED.
 

A STP16CP05 may be a good choice for LED driver.
 


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