What is the maximum base current for a BJT NPN transistor and how can I find it?

[atwork123]

in BJT transistors how can I find the maximum base current?

Do we have maximum voltage limitation for base of transistor? consider a resistor between input and base of transistor.

I want to use a transistor that its input range is from 3 to 30 volts and its output is 5 volts. how can i do it with BJT NPN?

 

[Bob S]

Hi atwork-
BJT npn's don't like high voltages (over a volt or so), but do like current. Depending on the hfe of the transistor, the base current can be anywhere from 1/100 to 1/10 of the collector current. A darlington transistor can also be used. What range of power supply voltages and output currents are you talking about?
Bob S

 

[vk6kro]

I want to use a transistor that its input range is from 3 to 30 volts and its output is 5 volts. how can i do it with BJT NPN?

Are you looking for a 5 volt regulator?

The common one is the 7805. This accepts an input voltage in the range of 7 volts to 37 volts and gives a steady output of 5 volts. Maximum current if mounted on a heatsink is about 1 amp.
These are available quite cheaply at electronic stores or online.
It is easy to use. It just has 3 wires. Input, Ground and Output.
It contains transistors but is really an integrated circuit.

BJT transistor data can be found on Google and they always list the maximum base current.