Hello....
Every time when i work with transistors, fets, LED circuits, i am facing problems with current limiting resistors or biasing resistors.
This time i want to get it clear.
How to select a proper resistor when using with these components.??
I am attaching some pictures.
when using LEDs: for 12v supply R=1K; for 5v supply R=330 ohm.
When using transistors: from 12v analog IC, base resistor =1K
from 5V microcontroller, resistor = 330 or 220 ohm
when using optocouplers: diode side 1K for 12v, 330 for 5v
transistor side 1K for 12v for any mosfet.
99 percent i'll get positive results.
but sometimes not. Here is an example.
Consider the LDR circuit shown in the attachment. the output leds are responding to the LDR status. but not driving the relay. Tested with 741 and 358 also.
can anybody give me some suggestions.??
Every time when i work with transistors, fets, LED circuits, i am facing problems with current limiting resistors or biasing resistors.
This time i want to get it clear.
How to select a proper resistor when using with these components.??
I am attaching some pictures.
when using LEDs: for 12v supply R=1K; for 5v supply R=330 ohm.
When using transistors: from 12v analog IC, base resistor =1K
from 5V microcontroller, resistor = 330 or 220 ohm
when using optocouplers: diode side 1K for 12v, 330 for 5v
transistor side 1K for 12v for any mosfet.
99 percent i'll get positive results.
but sometimes not. Here is an example.
Consider the LDR circuit shown in the attachment. the output leds are responding to the LDR status. but not driving the relay. Tested with 741 and 358 also.
can anybody give me some suggestions.??
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