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Author Topic: TRANSISTOR SELECTION QUESTION  (Read 4933 times)

magnetman12003

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TRANSISTOR SELECTION QUESTION
« on: May 27, 2016, 11:02:03 PM »
I am making a project that requires a single NPN transistor. Wish to power the transistor with 12 volts without using a large resistor connected to its base.

What transistor can have a ""BASE"" voltage of ""!2 volts"" applied ''DIRECTLY'' to its base without burning up the transistor?  In most cases there is some large value of resistor there.  Transistor would have to be a motor switching type.  The faster the better.   Need part numbers.

citfta

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Re: TRANSISTOR SELECTION QUESTION
« Reply #1 on: May 28, 2016, 04:31:05 AM »
Hi magnetman12003,

I have seen several posts by you on this and other forums where you are asking questions that indicate you don't really have a good understanding about electronics.   I would like to respectfully suggest that you take the time to study some of the free online electronics classes.  If you are serious about working or experimenting in this hobby then a good understanding is a must.  You will only frustrate yourself trying to make things work when you don't understand what you are doing.

For instance to answer your own question in this thread you can go online and look for info about the different types of transistors.  I am pretty sure you will find there are NO npn transistors you can apply 12 volts to the base and not burn out the transistor.  However there are other types like Mosfets that can take 12 volts to the gate.  Do you even know why the resistor is going to the base?  And why do you think you need to remove it?

Respectfully,
Carroll

magnetman12003

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Re: TRANSISTOR SELECTION QUESTION
« Reply #2 on: May 31, 2016, 03:01:15 AM »
Hi magnetman12003,

I have seen several posts by you on this and other forums where you are asking questions that indicate you don't really have a good understanding about electronics.   I would like to respectfully suggest that you take the time to study some of the free online electronics classes.  If you are serious about working or experimenting in this hobby then a good understanding is a must.  You will only frustrate yourself trying to make things work when you don't understand what you are doing.

For instance to answer your own question in this thread you can go online and look for info about the different types of transistors.  I am pretty sure you will find there are NO npn transistors you can apply 12 volts to the base and not burn out the transistor.  However there are other types like Mosfets that can take 12 volts to the gate.  Do you even know why the resistor is going to the base?  And why do you think you need to remove it?

Respectfully,
Carroll
Do you think a FJP5554 transistor available from Mouser can be used without a resistor in the base circuit.
The VEBO is 15 volts?

magnetman12003

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Re: TRANSISTOR SELECTION QUESTION
« Reply #3 on: May 31, 2016, 05:45:49 AM »
Hi magnetman12003,

I have seen several posts by you on this and other forums where you are asking questions that indicate you don't really have a good understanding about electronics.   I would like to respectfully suggest that you take the time to study some of the free online electronics classes.  If you are serious about working or experimenting in this hobby then a good understanding is a must.  You will only frustrate yourself trying to make things work when you don't understand what you are doing.

For instance to answer your own question in this thread you can go online and look for info about the different types of transistors.  I am pretty sure you will find there are NO npn transistors you can apply 12 volts to the base and not burn out the transistor.  However there are other types like Mosfets that can take 12 volts to the gate.  Do you even know why the resistor is going to the base?  And why do you think you need to remove it?

Respectfully,
Carroll

I have already made a self sustaining setup that charges a single 12 volt battery powering it.  My problem is I don't have quite enough current to fully  charge my single 12 volt 1.2 AH battery. Thus only a 5 straight hour run time.  That's why the questions about any current robbing resistor connected to the base of the transistor.  I am not well trained in transistor selection but can put any circuit diagram together very quickly.  My hope is to find a very simple Tesla  pancake type circuit that is very efficient as far as current flow and build it in hopes I can boost the current.  With that accomplished I will have at least a self sustaining runner with the run battery being charged at the same time.

pomodoro

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Re: TRANSISTOR SELECTION QUESTION
« Reply #4 on: May 31, 2016, 10:50:44 AM »
The base resistor, uses practically no power if you make it large enough.  Look for darlington NPN  power transistors to make it even less of an issue.  MOSFETS and IGBT are best avoided as they have a large capacitance which uses up some current. A TIP122 is a popular generic one one I use, 100V, 5A (8A Peak),current gain of 1000  beware of the the built in diode, it may not suit your needs. There are plenty of others which may be better for your design I don't know what your circuit is like.

magnetman12003

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Re: TRANSISTOR SELECTION QUESTION
« Reply #5 on: May 31, 2016, 08:15:32 PM »
The base resistor, uses practically no power if you make it large enough.  Look for darlington NPN  power transistors to make it even less of an issue.  MOSFETS and IGBT are best avoided as they have a large capacitance which uses up some current. A TIP122 is a popular generic one one I use, 100V, 5A (8A Peak),current gain of 1000  beware of the the built in diode, it may not suit your needs. There are plenty of others which may be better for your design I don't know what your circuit is like.

Hi ,
So far my circuit is like what's in the below video. What other transistor arrangement should give me a lot more current and do away with the 5 watt power robbing resistor?  I noticed those that made this circuit complained about transistor overheating.  If I could get the second or pickup pancake to put out enough current to charge a 12 volt 1.2 AH battery I will have made a self runner using an additional charging circuit   Will post all after completed.  A small diagram would be a great help as I can put that together in a jiffy.

https://www.youtube.com/watch?v=4UmVLfFNx7U

pomodoro

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Re: TRANSISTOR SELECTION QUESTION
« Reply #6 on: June 01, 2016, 10:43:09 AM »
Looks like a blocking oscillator.  If the TIP35C has not blown up, then you can use a similar rating darlington. The 35C only has a gain of about 25.  Try a TIP150 with a gain >100 at high current. Handles 400V, =4x the TIP35C. Its a darlington without the built in protection diode, which I assume you don't want.  Use the same resistor, to check but then increase its value to the highest that works. If transistor heats up too much then its not getting enough current through the base to saturate and acts like a resistor.
I have not  built any of these so I'm just answering your generic question.