Transistor BC547 Datasheet !

[neptune]

hi, i am listing certain points given in this datasheet
correct me on any point that you feel is wrong.

http://www.datasheetcatalog.org/datasheet/philips/BC546_547_3.pdf

1> Vcbo - collector base voltage - max 50V - it is the max. permissable voltage across collector and base
2> Vceo - collector emitter voltage - max 45V - it is max. permissible voltage across collector and emitter

Q> why is Vcbo > Vceo it should be other way round ?
3> Vebo - emitter base voltage - 6V - it is max. permissible voltage accross base and emitter
4> Ic - collector current DC - 100mA max - it is max current that can flow through collector

Q> So, Transistor can drive only 5 red LED max each 20mA ?
5> Icm - peak collector current - 200mA max - what is this ?
6> Ibm - peak base current - 200ma max - what is this ?

 

[carbonzit]

Peak current is the maximum allowable for short duration pulses (unfortunately, not specified on the datasheet). Collector current is the maximum continuous (DC) current. Keep in mind that these are "absolute maximum" ratings, so you should stay well below them, or expect transistor failure. So 4 20mA LEDs would be more like it. (You can, of course, drive more LEDs than this if they're in series, not parallel.)

(I had the Fairchild version of this datasheet, which doesn't even list the peak ratings that Philips has.)

 

[audioguru]

You should always use the datasheet from the original manufacturer that usually has more details.
Philips invented the BC107 in a metal case then made the BC547 in a plastic case. Fairchild simply copies it.

The max emitter-base voltage is 7V because it is a reverse voltage. Transistors usually have the base-emitter with a forward voltage, not a reverse voltage. The reverse-biased emitter-base junction has avalanche breakdown (like a zener diode) at about 7V.

 

[crutschow]

,,,,,,
Q> why is Vcbo > Vceo it should be other way round ?

Why to you think that?

Vcbo is the maximum voltage before the collector-base diode junction breaks down with the emitter open.

Vceo is the maximum transistor voltage before the collector-emitter breaks down with the base open. The reason it is less then Vcbo is that as you approach the breakdown voltage, the leakage current from the collector-base junction will start to increase. This current has no place to go in the base region expect to be amplified by the beta of the transistor. This increases the collector current, causing it to reach the breakdown current value sooner.

 

[neptune]

Vcbo is the maximum voltage before the collector-base diode junction breaks down with the emitter open.

how is Vcbo measured , by putting +ve side voltage on collector or base ?

The reason it is less the Vcbo is that as you approach the breakdown voltage, the leakage current from the collector-base junction will start to increase. This current has no place to go in the base region expect to be amplified by the beta of the transistor.

if base is left open while measuring the Vceo then what will happen ? will the current still be amplified by beta of the transistor ?

 

[audioguru]

how is Vcbo measured , by putting +ve side voltage on collector or base?

The collector to base junction is always revese-biased.

if base is left open while measuring the Vceo then what will happen ? will the current still be amplified by beta of the transistor ?

Of course the transistor will amplify the collector-base leakage current.

 

[neptune]

BC547 transistor datasheet - 2

hi again,
I am listing some more points given in this datasheet that i dont understand
correct me on any point that you feel is wrong.

http://www.datasheetcatalog.org/datasheet/philips/BC546_547_3.pdf

1> Icbo - collector cutt off current - 15nA max - Is this max. reverse bias current which can flow when transistor is operating normally? they applied 30V Vcb , why didnt they applied 40V Vcb ?
2> Iebo - emitter cutt off current - 100nA max - Is this the max. reverse bias current that can flow in emitter ? but why is emitter base juction reverse biased ?
3> Vce sat - collector emitter saturation voltage - 250mV max - This is the voltage between the collector and emitter when both the base-emitter and base-collector junctions are forward-biased.? when increase in base current no longer increase collector current, where is this point located in transistor characterstic graph ?what is the need of Vce SAT. ?
4> Vbe sat - base emitter saturation voltage - 250mV max - Is it max. voltage achievable when base emitter junction is forward biased ?
5> Vbe - base emmitter voltage - 700mV max - what is this ?

 

[carbonzit]

Should have stayed in that other thread. Now we have two threads to watch. Twice as confusing.

 

[neptune]

who joined these two threads

 

[ericgibbs]

I did, its confusing and pointless to start a new thread while a current thread, on the same topic, is being replied too.

 

[crutschow]

hi again,
I am listing some more points given in this datasheet that i don't understand
correct me on any point that you feel is wrong.

http://www.datasheetcatalog.org/datasheet/philips/BC546_547_3.pdf

1> Icbo - collector cut off current - 15nA max - Is this max. reverse bias current which can flow when transistor is operating normally? they applied 30V Vcb , why didn't they applied 40V Vcb ?
Ans.: They spec the leakage current at a typical operating voltage, The test voltage value is somewhat arbitrary.

2> Iebo - emitter cutt off current - 100nA max - Is this the max. reverse bias current that can flow in emitter ? but why is emitter base junction reverse biased ?
Ans.: This is the leakage current when the transistor is off and the base-emitter junction is reverse biased. In some high-speed switching circuits the base-emitter junction is reverse-biased to speed up the turn-off from a saturated "on" condition.

3> Vce sat - collector emitter saturation voltage - 250mV max - This is the voltage between the collector and emitter when both the base-emitter and base-collector junctions are forward-biased.? when increase in base current no longer increase collector current, where is this point located in transistor characteristic graph ?what is the need of Vce SAT. ?
Ans.: The saturation voltage is the "on" voltage of the transistor.
That value is not shown on any of the graphs in the referenced data sheet. It can be seen on a typical transistor characteristic curve of collector current verus base current.
It is important to know this value when using the transistor as a switch. It's a measure of how good a switch it is.

4> Vbe sat - base emitter saturation voltage - 250mV max - Is it max. voltage achievable when base emitter junction is forward biased ?
Ans.; You have the wrong value. It is 700mv to 900mV. That is the base-emitter voltage when the collector-emitter junction is saturated (on).

5> Vbe - base emitter voltage - 700mV max - what is this ?
Ans.: That is the base-emitter voltage when the transistor is operating in the normal region, such as in a AC amp, but not saturated.

Answers in quote in blue.

 

[carbonzit]

1> Icbo - collector cut off current - 15nA max - Is this max. reverse bias current which can flow when transistor is operating normally? they applied 30V Vcb , why didn't they applied 40V Vcb ?

Ans.: They spec the leakage current at a typical operating voltage, The test voltage value is somewhat arbitrary.

2> Iebo - emitter cutt off current - 100nA max - Is this the max. reverse bias current that can flow in emitter ? but why is emitter base junction reverse biased ?

Ans.: This is the leakage current when the transistor is off and the base-emitter junction is reverse biased. In some high-speed switching circuits the base-emitter junction is reverse-biased to speed up the turn-off from a saturated "on" condition.

So why isn't this spec'ed as "leakage current" rather than "cutoff current'? I would have thought cutoff current would be that current flowing when the device is just at cutoff. Is this the same thing as leakage current?

 

[crutschow]

So why isn't this spec'ed as "leakage current" rather than "cutoff current'? I would have thought cutoff current would be that current flowing when the device is just at cutoff. Is this the same thing as leakage current?

It's the same. It's called leakage current since it's the current that "leaks" through a reverse biased junction (ideally, of course, it would be zero). Cutoff is the operating condition of the transistor when the cutoff (leakage) current is measured.

 

[neptune]

Vce sat - The saturation voltage is the "on" voltage of the transistor.
That value is not shown on any of the graphs in the referenced data sheet. It can be seen on a typical transistor characteristic curve of collector current verus base current.
It is important to know this value when using the transistor as a switch. It's a measure of how good a switch it is.

1>so if this the ON voltage of tranisistor then it should be given value such as Vce sat min 250mV instead of max, that means min. voltage required by device to turn itself ON ?
2> why havent they given min. collector current that can flow in transistor ?
3> there is a second graph shown in datasheet Hfe vs Ic , does it mean gain of transistor changes when Ic value changes ? and what is that Vce=5V ?
4> why havent they given transistor characterstic which is between Ic and Vce graph in there data sheet ?

Vbe sat - That is the base-emitter voltage when the collector-emitter junction is saturated (on).

when collector-emitter junction is on (saturated) then base-emitter region must be forward biased, so min. voltage drop would be 0.7V , then what is this 700-900 mV ?

Vbe - That is the base-emitter voltage when the transistor is operating in the normal region, such as in a AC amp, but not saturated.

then which region ? is it forward or reverse voltage ?

It's the same. It's called leakage current since it's the current that "leaks" through a reverse biased junction (ideally, of course, it would be zero). Cutoff is the operating condition of the transistor when the cutoff (leakage) current is measured.

I dont get it, there are 2 diffent types of current 1-leakage current when transistor is cutt off region and 2- is reverse bias current , when transistor is in which region ? cutt off,SAT or active region
where are they specified ?

 

[audioguru]

Transistors are not identical even if they have the same part number. A range of saturation voltages are spec'd on the datasheet when the collector current is 10mA and the base current is 0.5mA. Some good transistors have a low saturation voltage (spec'd "typical" 90mV on the datasheet) and other weak transistors have a high one (spec'd max 250mV). When you turn on a transistor then you want its saturation voltage to be low.
The base-emitter forward voltage is also shown as a range of voltages because transistors are not identical.

 

[crutschow]

1>so if this the ON voltage of transistor then it should be given value such as Vce sat min 250mV instead of max, that means min. voltage required by device to turn itself ON ?
2> why haven't they given min. collector current that can flow in transistor ?
3> there is a second graph shown in datasheet Hfe vs Ic , does it mean gain of transistor changes when Ic value changes ? and what is that Vce=5V ?
4> why haven't they given transistor characteristic which is between Ic and Vce graph in there data sheet ?

when collector-emitter junction is on (saturated) then base-emitter region must be forward biased, so min. voltage drop would be 0.7V , then what is this 700-900 mV ?

then which region ? is it forward or reverse voltage ?

I don't get it, there are 2 different types of current 1-leakage current when transistor is cutt off region and 2- is reverse bias current , when transistor is in which region ? cutt off,SAT or active region
where are they specified ?

1>The Vce sat is the voltage across the transistor when it is "on" acting as a switch. The maximum (worst-case) value of that is of interest so that is what is given.

2>The don't give the min collector flow since it obviously can be zero. Why would there be a minimum?

3>Yes the gain of a transistor varies with collector current. They show the gain at 5V since that is a typical operating voltage when using the transistor as an amplifier (not a switch).

4>Don't understand your question. A lot of data sheets have incomplete information due to cost cutting from the manufacturer.

Normally a transistor is operated with the collector-base junction reverse-biased and the base-emitter junction forward-biased. For a NPN transistor this would mean positive voltages on both the collector and emitter. Reverse that for a PNP.

All cutoff (leakage) currents are specified with the transistor off.

I do believe you need to read a tutorial on how transistors operate. You seem to have only a vague understanding of that.

 

[neptune]

Normally a transistor is operated with the collector-base junction reverse-biased and the base-emitter junction forward-biased. For a NPN transistor this would mean positive voltages on both the collector and emitter. Reverse that for a PNP.

1> when collector-emitter junction is on (saturated) then base-emitter region must be forward biased, so min. voltage drop would be 0.7V then what is this 700-900 mV ?

2>The don't give the min collector flow since it obviously can be zero. Why would there be a minimum?

2> if we see then we see cutt off region , which has 3 parameters Ib,Ic and Vce , i was asking why they didnt gave value Ic or Ib ? is this because all transistors are different so these three values would be different !

I do believe you need to read a tutorial on how transistors operate. You seem to have only a vague understanding of that.

i fully understand how transistor works, but data given in datasheet seems to not corelate with what values we really need !

 

[crutschow]

1> when collector-emitter junction is on (saturated) then base-emitter region must be forward biased, so min. voltage drop would be 0.7V then what is this 700-900 mV ?


2> if we see then we see cutt off region , which has 3 parameters Ib,Ic and Vce , i was asking why they didn't gave value Ic or Ib ? is this because all transistors are different so these three values would be different !

1> Vbe (sat) varies over the range of 700-900mV for different transistors due to manufacturing tolerances.

2< Cutoff (cutt off) simply means the transistor is off. Thus Ic and Ib are zero or equal to the cutoff leakage current (which is specified in the data sheet). What did you think cutoff meant?

 

[neptune]

1> Vbe (sat) varies over the range of 700-900mV for different transistors due to manufacturing tolerances.

it says that this value is MAX. . how is it possible when in forward biased condition it is min. 0.7 volt drop ? why do we need to measure Vbe(sat) , what is its use ?
Rest all items have become clear to me.. how do i thumbs you up ?

 

[crutschow]

it says that this value is MAX. . how is it possible when in forward biased condition it is min. 0.7 volt drop ? why do we need to measure Vbe(sat) , what is its use ?

When saturated, the value of Vbe can vary from 700-900mV. I don't understand why you have a problem with that. 0.7V is a nominal value for Vbe when the transistor is on but not saturated. You do understand the difference between the transistor being on, as when being used as an AC amp, and saturated on, as when being used as a switch?

You need to know the value of Vbe(sat) so you can calculate the proper value of the base bias resistor to get the desired base current from the input control voltage value you are using.