Electronics > Beginners
transistors
Jwillis:
--- Quote from: Circlotron on August 15, 2019, 05:57:26 am ---
--- Quote from: Jwillis on August 15, 2019, 05:24:12 am ---for simplification yours has a "Gain" of 110 to 800. Which is to say that the current passing from collector to emitter is 110 to 800 times the current at the base.
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Not trying to be pedantic, but with a gain of 110-800 a *change* of base current causes a *change* of collector current that is 110-800 times as great as the base current change. Or was that allowed for in your simplification?
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Your absolutely correct.Any knowledge is good knowledge.Thanks for pointing that out.
--- Quote from: queennikki1972 on August 15, 2019, 12:36:39 pm ---So I tried the flashing light circuit on page 104 of Getting started in electronics. Unfortunately the only 100k variable resistor i had was used pull from old stuff and was a little flaky. It did flash properly for a minute so it must have been ok. I will order more parts and keep doing the same circuit until i figure out what im doing wrong. I will also try more expensive parts from digikey as well.
I do have one of the component testers as well. And the parts test ok before using.
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If your could provide that circuit diagram then someone here good walk you through it and mark the pins to where they go .Even a photo of a sketch is a great help.Some of us don't have that book.
Electronics is not an exact science. All components will have a tolerance and as for resistors they can be as much as 5% out for ones with a gold band and 10% for silver band. Even the most common ones from Ebay Have a 1% tolerance .This means that the higher the rated Resistance the more deviation your going to get. For example a 100k 5% resistor can be as high as 5000 ohms out and a 100k 1% resistor can be as high as 1000 ohms out .This is not a problem with simple circuits .There are precision components available but are far to expensive and unnecessary unless you plan on launching a probe to some distant planet.Even Transistors are never perfect.
Remember, there is no such thing as a stupid question.It's only stupid when you stop asking questions and think you know it all.
queennikki1972:
For those needing it here the page and its the bottom right circuit.
queennikki1972:
I assume you could use a red led with this circuit? Even though it calls for some odd ball #222 bulb
ledtester:
--- Quote from: queennikki1972 on August 15, 2019, 03:10:22 pm ---I assume you could use a red led with this circuit? Even though it calls for some odd ball #222 bulb
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Sure - as always, though, put some sort of current limiting resistor in line.
Audioguru again:
In this thread, people have been talking about hFE and beta being over 100 times for a BC547, but the hFE and beta are only used when the transistor is a linear amplifier that always has lots of C to E voltage and not when it is used as a saturated switch. The flashing light circuit uses both transistors as saturated switches and the datasheet for most little transistors shows that the base current should be 1/10th to 1/20th of the collector current.
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