Here is a calculator for transistor base resistor values. Its IMPORTANT that you read the following.
Calculate the current you need to pass through the transistor when its on, that is your collector current.
The current gain, beta, Hfe, is a value you can find in the datasheet for the specific transistor.
Supply voltage is the voltage that you use to drive the base of the transistor with.
Voltage drop is the Vbe(sat) value, you will get this from the datasheet looking at the graph for Vbe and Vce(sat) vs. collector current.
To insure to turn the transistor fully on, you can double the value for collector current, which will result in a base resistor value half of what this calculator gives you.
The example values are for a BC547 transistor.
Hi great little calculator. I am having trouble finding Vbe(sat) for a BD244 in the data-sheet http://www.datasheetcatalog.org/datasheet/motorola/BD244C.pdf
And it states two different Hfe values, would it be ok if you took a look?
I want to drive the transistor using an SG3525 chip and I want to ideally have it passing about 2 amps (for a gate drive transformer).
Thanks.
Hey Alex
If you look at “Figure 8. DC Current Gain” in the datasheet you can see a DC current vs Hfe curve, at 2 Ampere its 50 gain.
Kind regards
Mads