Minor Stepper Driver Modification

Hi!

I am soldering my stuff on a own proto pcb and have a very tiny wire soldered to the allegro stepppr driver IC's.

Since a stepper needs 1,68A, can i also use a 1K resistor and a parallel PNP and NPN triac connected to the stepper to avoid my wires to melt?



Greetings
user

Edited 2 time(s). Last edit at 07/05/2010 09:23AM by user82.

No

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> No


can you tell me why?

are the triacs too slow, does the voltage need to be regulated?

Edited 1 time(s). Last edit at 07/06/2010 07:25AM by user82.

I assume you don't mean "triac" but "transistor" as there are no such things as NPN and PNP triacs. You also can't wire NPN and PNP transistors in parallel, you would just get two pairs of back to back diodes in series, not a useful circuit.

Each pin of the chip is driven by two MOSFETs each with its own gate drive signal. They switch at different points in the cycle to control the current and perform synchronous rectification. The current can flow both ways through either transistor as they are FETs. You cannot control two external transistors to do the same job because you only have one signal coming from the chip but you need two.

Also 1K would not pass enough base current for a typical power transistor passing 1.65A.

If you get rid of the resistor and wire the transistors as emitter followers and add two Schottky diodes per motor output you might get something that works, but not very well. You would lose about 2V drive and would have added 8 power transistors and diodes.

Keep it simple, use thicker wire, it doesn't need to be very thick as long as it is short so the heat is conducted away from it. The chips are SOICs so the pins are quite widely spaced. PCB tracks are very thin vertically so you don't need a very big wire to have the same cross section.

Edited 1 time(s). Last edit at 07/06/2010 08:25AM by nophead.

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[www.hydraraptor.blogspot.com]

well i would lower the current from the IC with the resistor(be it 1k or maybe 100Ohms) and then activate a transistor with it,
that should give the needed Amp's to drive the stepper

the wires on the picture immedialtely burn with 4A, do you think two of those or three can handle 1.7A?

The SOIC is not that good to solder in my oppionion is the problem

Edited 1 time(s). Last edit at 07/06/2010 08:25AM by user82.

What picture?

If you use an emitter follower configuration you don't need a resistor to limit the base current.

If you use common emitter configuration then you do but the circuit would be inverting and you would need four resistors to avoid both transistors being on at the same time when both of the MOSFETs are off. You would also have problems with shoot through currents due to transistors turning off slower than they turn on causing some brief overlap where both are on.

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[www.hydraraptor.blogspot.com]

i was talking about the start post image.

i will try my setup but it might really not work properly