How Can I Boost the Base Current in a BJT-Driven DC Motor Circuit?

[medosoft]

How to increase the current?!

I'm designing a drive circuit for a 12V DC motor
I'm using a (2N3055 BJT) as a switch to control the output, and I'm using a (74121 monostable oneshot) to control the BJT switch.
So, the output of the 74121 is fed into the base of the BJT.

Here is the schematics for my circuit
http://img594.imageshack.us/img594/7411/etpcircuit.jpg


According to the datasheet of the BJT, β=100. Which means that the current supplied to the base should be at least 1/100 of the current that is supposed to run through the collector. The motor needs about (2-3) Amps to run at a proper speed, meaning that the base current should be at least (20 - 30 mA).
The problem is that the output current of the 74121 ranges from (4 - 16 mA).

Is there anyway to increase the current?
I can sacrifice some of the voltage

 

[uart]

You could add a base drive circuit like in the attachment.


Or you could just replace the 2n3055A with a suitable n channel logic level mosfet and you wouldn't need any auxiliary drive components.

 

[gnurf]

I'll just throw this out here: http://www.coilgun.info/theoryinductors/inductivekickback.htm

 

[jim hardy]

indeed the good ol' 3055 is not the greatest for current gain. hfe may drop to more like 10 in the Ic=amperes range.

TTL sinks better than it sources so your design is needing a tweak or two

uart's MOSFET is one solution, so is his darlington

a 555 in between the '121 and the '3055 is another, but the 555 inverts so use the '121's Qnot output.
Tie TRIG and THRESH together and 555 becomes a schmitt trigger buffer with substantial drive capability. That's a handy trick .

glad you're experimenting , it's the best teacher.

old jim

 

[alphysicist]

for more current, perhaps by using a different transistor with a higher β value, or by using a Darlington pair configuration. Another option could be to use a transistor with a lower voltage drop, such as a MOSFET, which would allow for more current to flow through the circuit. Additionally, adjusting the resistor values in the circuit could also help increase the current. It may also be worth considering using a different type of driver circuit altogether, such as a H-bridge or a motor driver chip, which are specifically designed for controlling motors and can handle higher currents. Ultimately, the best approach would depend on the specific requirements and limitations of the project.