transistor bias / saturation

[MrDEB]

This is a different application

Sorry for the misunderstanding.
I am going by the measurments that another member informed me of.

With no resistance only 2 of the 3 segments light up. At 61 ohms they all work and just to see I stuck another 82 ohms in series and they also all worked with no change in brightness. I think too much voltage saturates the sequencer circuit, but resisters are built in to the led circuit. The 3.5 amps is wrong. I had my meter on a/c. I checked it with the 61 ohms at 13.5v and read 13.125mA dc peak.

Using several different simulation programs
none seem to agree.
One site stated that with a 100ohm relay coil, a 2n2222 transistor,
6Vcc, hfe =100 using the output of a cmos ic
it stated that a 1800-2000 ohm base resistor to achieve saturation.
Tried same figures in **broken link removed**
using both simulations on that site.
Then input same into TINA and a different set of figures.
Am trying to understand how to caculate saturation. I think its when the collector voltage is near the emitter voltage (.7v or less) but the base needs to have a small amount of voltage (.7v) and control of the current to the base to achieve saturation.
formula I found is Rb = .2 X Rl x hfe
again sorry for the misunderstanding.

 

[audioguru]

Nearly all transistor datasheets say that the base current must be 1/10th the collector current to guarantee a low saturation voltage.
hFE is used when the transistor is not saturated.

 

[MrDEB]

Thanks

I entered and rechecked cals and yes it works in the simulations
THANKS again
I show 16ma collector and 1.65 on the base
do these figures hold true for darlingtons as well? 1/10
and the formula Rb=.2 X Rl X hfe

 

[audioguru]

do these figures hold true for darlingtons as well? 1/10
and the formula Rb=.2 X Rl X hfe

Of course not. A darlington is two transistors. Look at the datasheet. The TIP120 saturates well when its base current is 1/250th of the collector current.

The formula you found is wrong. hFE is not used for a switching saturating transistor. The base current should be 1/10th the collecor current and Ohm's Law is used to calculate the base resistor value.