dc-motor drive circuit(darlington TIP 122)

Thread Starter

h.d

Joined Oct 22, 2007
150
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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Murod

Joined Dec 24, 2005
30
Yes you can use TIP122, but I think using IRFZ48N Power Mosfet is much cheaper, since it capable handling of 40A+, need only a single TO220 packaged component.
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beenthere

Joined Apr 20, 2004
15,808
Your circuit won't work, as ther are no current limiting resistors between the inverters and the darlington bases. With a potertial of 20 amp currents, the logic inverters may not sullpy enough current to drive the darlingtons into saturation.

Life is easier if you go away from transistors and use FET's or IGBT's instead. Many IGBT's are rated up at 80 amps for lots of overhead.
 

Thread Starter

h.d

Joined Oct 22, 2007
150
Your circuit won't work, as ther are no current limiting resistors between the inverters and the darlington bases. With a potertial of 20 amp currents, the logic inverters may not sullpy enough current to drive the darlingtons into saturation.

Life is easier if you go away from transistors and use FET's or IGBT's instead. Many IGBT's are rated up at 80 amps for lots of overhead.
ya.. i know that i can use IGBT
but i discuss the ability of using darligton transistors in that way
in other hand i put that circuit to show the way of using the transistors .surely its need limiting resistors..
& thnks for replay
 

Thread Starter

h.d

Joined Oct 22, 2007
150
Yes you can use TIP122, but I think using IRFZ48N Power Mosfet is much cheaper, since it capable handling of 40A+, need only a single TO220 packaged component.
-----------------------------------------------------------------
http://www.softhardzone.com :high quality free-wares, electronic design and software programming tutorials.
thank u
i will see the data sheet of IRFZ48N
 

thingmaker3

Joined May 16, 2005
5,073
The biggest problem with using BJTs in parallel is their temperature coefficient. If a BJT starts to conduct too much, it gets warmer, and conducts even more. Whichever BJT happens to be conducting most will tend to burn up first. Then the others will burn up each in turn.

FETs, on the other hand, conduct less when they heat up. This lets them perform just fine when in parallel.
 

Thread Starter

h.d

Joined Oct 22, 2007
150
i see thats agreement for the problem of heating in FET's so i think the MOSFET is the right element for the high current.

thanks for all.:)
 
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