[helow]

hey

there are two circuits using same transistor but one of them do not have diodes. i read

bout these diodes as following:

"The diodes are a feature typical of circuits that handle magnetic coils, that is inductive

circuits. In this context, the motor windings are the inductive element. Capacitors provide

a means for the storage of electrical charge, inductors provide a means for storage of

electrical current. The driving current causes a magnetic field to be built up in the coil.

As soon as the drive is removed, the magnetic field collapses and causes the inductor to

release its stored current. Semiconductors are particularly sensitive to these currents

(they briefly become conductors and then become permanent nonconductors!). The diodes

provide a mechanism to safely shunt these currents away and, thus, protect the transistors

and the computer."

but in second circuit there is not diodes. why. how much important to use these diodes. if

not to use diodes then which are general measures to protect the transistors from being

burnt as described in above sentence.

and there are some detail about connections of wire:

"You should also note that ground for the transistors must be made common between the

parallel port (say at pin 25) and the motor power supply. An additional wire with an

alligator clip can be used to provide access to the ground for the motor power supply. So,

on the motor side of the circuit we have six wires, one for each coil, one for ground and

one for the motor voltage on the shunt diodes. The motor (positive) voltage supply is

provided through the common coils."

how the motor coil's conman wire and the four diodes wires will be used.
and also tell me about connection of motor with circuit which has not diodes.





http://www.forth.org/fd/Step.html

[H500]

You have to use diodes or your transistors will be destroyed. A better approach is to use a FET. They have built in diodes.

[LZ1TWB]

Hi,

TIP120/121/122 have built-in protection diodes, look at the datasheet PDF and you will see them. That's why there is a schematic without diodes. I always tend to use external ones, that are usually faster than the build-in.

The higher the supply voltage, the inductance of the motor or the switching speed - the higher is the inductive spike generated, hence more heat in the diodes.

You seem to be driving the output transistors directly from the parallel port. The grounds are connected, so the current could flow from base so emitter and turn the transistor on.

Todor