Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Source Current & Sink Current of MIC

Not open for further replies.


Full Member level 2
Mar 4, 2007
Reaction score
Trophy points
Activity points
pic source current

hi to all

can anybody tell me what are the Sink Current and Source Currrent?.../

also what is the value of Sink Current and Source current of each port of AT89C51..

is it differ from MIC to MIC?

Popatlal Panjarawala

AT89c51 is having very less source current. u cannot drive led, seven segment directly u have to use drivers. Source and sink current vary for controller to controller. PIC microcontrollers will sink and source 20 mA. U can directly drive the leds, lcds with PIC microcontroller

Sourcing is where the current is flowing out of the device. Sinking is when current is flowing into the device. The 74LS logic family can source a lot more current (15 - 25 mA typically) and only siink 0.4 mA. And that is why spec sheets usually have the sinking current as negative. 74HCT bus devices like a 74hc374 latch can source and sink 25 - 35 mA. Basically, if you hooked an LED and 470 Ohm resistor from the output of a 74LS type buffer and put the LED to ground it would source the current needed when you put the ouput high. But if you inverted the circuit, and put the LED and resistor from 5 Volts on one end and put the other end to that same LS output and turned the LED on by driving the output low, you would fry the 74LS becasue it couldn[t sink that much (about 17mA )current. The HC, HCT, ACT and other 74 logic chips would handle both circuits. So, know your chips and the variations of the chip when it comes to sinking and sourcing. As was said in the previous post, pic can source and sink 20 mA and I believe the new designs can handle about 25 mA (not positive) and I wouldn't doubt that the earlier pic devices don't handle as much, but again, always look at your spec sheet to be sure.
As per datasheet for HD74LS273P Iol = 8 mA and Ioh = -0.4mA.
That means you can sink 8 mA but source only 0.4 mA.

Not open for further replies.

Part and Inventory Search

Welcome to