What BJT specification do I need to look at for switching time? - Electronic Circuits Projects Diagrams Free

FusionITR · 9th July 2006, 10:21 PM

What specification in the datasheet list the time it takes for the collector current to change in reaction to a change in the base current? Ive looked at mulitple datasheets for different transistors and I dont see this time specificed, altough it does matter.

For example, this is my sample circuit:

This is what the output is using a 2N2222 transistor:

This is what the output looks like using a MPSA05 transistor:

Obviously using the MPSA05 transistor, it doesnt react fast enough to the base current going to zero to change the collector current to zero before the base current goes back up.

What specification on a datasheet do I need to look at in general to see if a transistors switching time is good enough for whatever I happen to be working on?

Thanks.

Hero999 · 9th July 2006, 10:34 PM

What frequency are you using?

You could try a higher frequency unitl like the BF199 or a small MOSFET like 2N7000.

FusionITR · 9th July 2006, 10:37 PM

The frequency is 15.63Khz but the duty cycle is like 90% so the switching time is very fast compared to the frequency.

Hero999 · 9th July 2006, 10:46 PM

Look on page 5 of the datasheet.

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9th July 2006, 10:21 PM	(permalink)
FusionITR	What BJT specification do I need to look at for switching time? What specification in the datasheet list the time it takes for the collector current to change in reaction to a change in the base current? Ive looked at mulitple datasheets for different transistors and I dont see this time specificed, altough it does matter. For example, this is my sample circuit: This is what the output is using a 2N2222 transistor: This is what the output looks like using a MPSA05 transistor: Obviously using the MPSA05 transistor, it doesnt react fast enough to the base current going to zero to change the collector current to zero before the base current goes back up. What specification on a datasheet do I need to look at in general to see if a transistors switching time is good enough for whatever I happen to be working on? Thanks.

9th July 2006, 10:34 PM	(permalink)
Hero999	What frequency are you using? You could try a higher frequency unitl like the BF199 or a small MOSFET like 2N7000. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.

9th July 2006, 10:37 PM	(permalink)
FusionITR	The frequency is 15.63Khz but the duty cycle is like 90% so the switching time is very fast compared to the frequency.