DIFF : OPEN_DRAIN and OPEN_SOURCE

[tok47]

Hi ALL,

Can anyone show me how to differentiate OPEN_DRAIN type output buffer and OPEN_SOURCE type output buffer?

Why sometimes we use OPEN_DRAIN type buffer but sometime OPEN_SOURCE type buffer?

Thanks


rdgs
tok

 

[Kral]

tok47,
Open drain circuits are used in applications where you want to sink current from the load. For example to turn on a LED, you can connect the LED (thru a resistor) to an external voltage source. An open drain connected to the led cathode would allow you to "sink" the current from the extrnal voltage source thru the LED. This topology has the advantage that the LED supply voltage can be different from the Vdd voltage of the IC.
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With an open source, you would connect the source to the anode of the LED (through a resistor) to ground. In this arrangement, you are "sourcing" (supplying) the current to the the LED from the IC that contains the open source FET.
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I hope thsi helps,
Kral

 

[huojinsi]

Kral's explanation is just good!