hi,
in my project a want to design drive & control speed circuit for dc-motor
(1.5 hp,24 v)
PWM is the tech. that i will use to control the motor speed because i need smooth variation in speed, the PWM signal is taken from PIC.
in that circuit i want to use the darlington transistor (TIP 122)(up to 5 A)
dc-motor current may rise to 20 A, so i want to ask if i can use the TIP 122
in the way which obtaind in the graph.
and thnks....

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You need emitter resistors to balance the load across the transistors, and the circuit is generally lacking other parts as well - however, I suspect you are wildly out in your estimate of the current handling required!. You need to consider start-up surge and stall requirements.

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for up to 20A i can garentee that the TIP 122 wont survive. i've worked a lot with those transistors.. they can miraculously survive currents up to 15A for very short periods of time...

by the way i have a couple of schematics and projects for motor control using TIP transistors in my website.. the guys around here helped me a lot to boost the performance of my H-Bridge...

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Ibrahim Kamal
check my electronics and robotics page: http://www.ikalogic.com/

 

u mean that darligton (TIP 122) cant used to acheive 20 A?
also we put 4-5 transistors in parallel that will divide the current..

 

that would be biiiig mistake... never put Bipolar Junction Transistors in parralel.. the current wont be divided the way you think.. you can do this with Field Effect Transistors, but not BJT

__________________
Ibrahim Kamal
check my electronics and robotics page: http://www.ikalogic.com/

 

Sort of. The circuit given doesn't quite operate them in saturation (for better or worse) and has independent base bias for each transistor. Current sharing is poor, but does exist. This circuit can be improved, as suggested by Nigel, with emitter resistors. You only need about 150 mV (30 milliohms) in each emitter to achieve this improvement. Be sure that the heat sink is adequate.

 

ok.. i know that's my cicuit not complete but am aims to know if the way of using the darlingtons in that cicuit is exist or not?
the motor need about 20 A, i can use power MOSFET or IGBT
which can handle highn currents (its need driver).
but i want to know if the using if darligtons in that way(connection parallel)
is true or not?
and if its can handle that current for long time or not?

 

How many times do you need the same answer? - try reading my first post in this thread!.

As for a 'long time', that depends on the heatsinking arrangements, and on the accuracy of your requirements.

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http://www.winpicprog.co.uk

 

am read what u r wrote
& dont need to re it
am only obtain whats the problem that i discuss it.....
that what u must note from my post..

 

Then use a MOSFET rather than wasting your time with silly darlingtons and emmitter resistors.

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Awesome. You should teach.

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com

 

i want to teach
and its my goal
(am need the knowledge evry where)

 

Where do you live?

(dont move there to teach your children)

Wht aer uour reasons...
fer teachierng?

__________________
MechTronics

World of Warcraft is a disease

 

know we leave the problem of discusion
and discusse how can i teach.......hehe

 

also thanks for evry one posted....
and sorry if my accent is bad..