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something confusing me with LED

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baby_1

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Hello
the 120 resistor it is connected to a pin of micro (pic18f452) when i set it high( set 5 volt at the resistor terminal) it works fine
79_1346156028.jpg

but when i changed the 1kohm situation at the collector of bdx53 led won't work!!!!!
83_1346156028.jpg


i tested it by BC337 and BDx53 and two led but it doesn't work at the second circuit.why?!!!!
 

You've obviously hooked something up wrong. It makes no difference which way you do this.
 

Measure from both ends of R2 and D1 and the Q2 collector. You should have 9 V, ~1.6 V, ~1.6 V, 0V and 0V. This won't be the case though, because you've connected something wrong.
 

Hello Sloth
VBE=2
V(resistor 120ohm)=3.1 ~ 3.2
VCE~=1.5
 

Hi,

VCE seems high. How about the R2 and D1 ends? I think something is not connected there.
 

Vbe is way high. Should be about 0.6V. Something bad happened to your components.
 

Vbe is way high. Should be about 0.6V. Something bad happened to your components.
Click to expand...
BDX53 is a darlington. Vbe of 1.2 to 1.4 is O.K.
 

baby_1 said:
Hello
the 120 resistor it is connected to a pin of micro (pic18f452) when i set it high( set 5 volt at the resistor terminal) it works fine
but when i changed the 1kohm situation at the collector of bdx53 led won't work!!!!!


i tested it by BC337 and BDx53 and two led but it doesn't work at the second circuit.why?!!!!
Click to expand...

did you do both simulation & actual testing?
 

No need. He already got it to work in a similar arrangement. I think he killed a part.
 

Joeisi said:
No need. He already got it to work in a similar arrangement. I think he killed a part.
Click to expand...

ah i see.
to add, initial study must be done to ensure proper connections and setup. :)
 

LED's act as load .then what is the collector current ?
LED's Current ?
 

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