Help reading schematic

[51dueller]

I'm having a little trouble reading this schematic mostly with the FDC6420C mosfets. I know there are only 4 (says in parts required) and are 6 pin. I just don't know which ones get paired up. I'm used to more of automotive wiring diagrams.

Also on the BAT54S diodes, are these 3 pin? If so would someone have a full part number as I already have 2 pin ones.

Thanks

[mackrackit]

Welcome to the forum.

http://www.fairchildsemi.com/ds/FD/FDC6420C.pdf
http://www.fairchildsemi.com/ds/BA/BAT54.pdf

The FETs are paired N and P. The diodes are three pins. The data sheets show all of that.

Automotive type???

[Acetronics2]

Automotive type???

Hi, Dave

Automotive type electrical SCHEMES ...

sure they're somewhat different ...

Alain

[aratti]

Also on the BAT54S diodes, are these 3 pin? If so would someone have a full part number as I already have 2 pin ones.

Any schottky diode of 500 mA 30 volts will be ok as a replacement.

Every FDC6420C should be regarded as half bridge. It incorporate both the N & P channels mosfet.

The circuit function is a driver for a bi-polar stepper motor with 12 volts @ 2 Amps max per winding.

Cheers

Al.

[51dueller]

As an automotive service technician, just more used to their type of wiring diagrams. They just don't show a single component in two parts. Mostly just a box or dotted line around it to show you which module your looking at.

For the mosfets I'm just not sure which gets paired up. For example does Q3:A go with Q5:B or is it Q6:B?

I'm beginning to wonder if I accidentally got the wrong diodes shipped to me. I ordered BAT54SCT-ND SOT23-3 from Digikey and got a two pin diode with 2002 written on top.

I'm reconstructing an instrument cluster to fit into my classic truck cause aftermarket metric guages are almost non existant and I want all 6 guages. I'm going to be using Fraen AMD 6405-1512 stepper motors (5v 22ma).

[cncmachineguy]

Wow, have to thank all of you. I bet I have read that app note 3 or 4 times in the past. Problem was, when I read it I wasn't looking for a bi-polar drive. Now for the past 5 months I have been putting together a 6 axis drive for 2A bi-polar/uni-polar steppers. I settled on a uni drive for convineance and price. This is a worthwhile drive circuit, deserving much deeper look.

So far, it looks to be both cost effective and manufacturable!

So again, thanks! Now as I develop this further, should I start a new thread or continue this one?

[mackrackit]

An "A" gets paired with a "B" or N with a P.
Sounds like they may have shipped the wrong diode. SOT23-3 with two pins?

[mackrackit]

should I start a new thread or continue this one?

Start a new one.

[cncmachineguy]

I'm going to be using Fraen AMD 6405-1512 stepper motors (5v 22ma).

I'm not sure how far down this road you are, but this circuit is way bigger then you need for this motor. Now of course it should work, but there are smaller simpler solutions if you are intrested.

[Acetronics2]

As an automotive service technician,
...
I'm reconstructing an instrument cluster to fit into my classic truck cause aftermarket metric guages are almost non existant and I want all 6 guages. I'm going to be using Fraen AMD 6405-1512 stepper motors (5v 22ma).

Hi, 51

a look here ???

http://www.sportdevices.com/ignition/tacho.htm

Ok, not bipolar stepper ... but minor mod.



Alain

[51dueller]

I'm not sure how far down this road you are, but this circuit is way bigger then you need for this motor. Now of course it should work, but there are smaller simpler solutions if you are intrested.

I'm still in the preliminary stages of building a test circuit. I know I could use a L293D to drive it but it won't have the resolution as this setup. The L293D can only handle up to a 5 khz signal where as the circuit above can go 31.2 khz. The ECCP of the pic16f684 using pwm can microstep the motor providing an extremely smooth and accurate rotation. Microstepping the motors I have will rotate 0.083 degrees a step.

If you know of a single chip driver that can equal the resolution of the above circuit, I'm very much interested.

[Acetronics2]

I'm still in the preliminary stages of building a test circuit. I know I could use a L293D to drive it but it won't have the resolution as this setup. The L293D can only handle up to a 5 khz signal where as the circuit above can go 31.2 khz. The ECCP of the pic16f684 using pwm can microstep the motor providing an extremely smooth and accurate rotation. Microstepping the motors I have will rotate 0.083 degrees a step.

If you know of a single chip driver that can equal the resolution of the above circuit, I'm very much interested.

Hi, 51

a quick calculation will show with a 250 mm dia Gauge ( BIG Truck ...eh ! ), a half degree resolution is enough !!!

that is half the needle width ...

AND that is your motor FULL STEP resolution ... BTW.

so, 1/4 or 1/8 Microstepping will widely fit ... see Allegro 3967 driver, All in one ...

But you do it your way, of course !

Alain

[cncmachineguy]

The L293D can only handle up to a 5 khz signal where as the circuit above can go 31.2 khz.

How fast will your input signal be?

The ECCP of the pic16f684 using pwm can microstep the motor providing an extremely smooth and accurate rotation. Microstepping the motors I have will rotate 0.083 degrees a step.

Microsteping is a term referring to modulating the current to each coil of a step motor in an effort to gain step resulotion. That is all microstepping describes. The circuit above appears to microstep to 1/8 step. It may be 1/16, but I don't think so. So what does 1/8 step mean? a full step is the amount of movement when 1 coil is energized. So 1/8 step is just that: full step/8. Taking the statement from the datasheet as you have "Microstepping the motors will rotate 0.083 degrees a step". You left out a very important part of that statement. The data sheet says microstepping at a rate of 12 steps per degree! Full step for your motor is .5 deg per step. So the microstepping they refer to is 1/6 step. All this just to say Using above circuit at full microstep mode, will really be .0625 deg per step.

If you know of a single chip driver that can equal the resolution of the above circuit, I'm very much interested.

I agree with Alain above. But before I did that, without telling anyone, I would try to direct drive it some how in full or half step .Afterall its only 22mA. But I also don't mind leting the magic smoke out

[mackrackit]

More info/stuff to read
http://www.picbasic.co.uk/forum/showthread.php?t=101
http://www.picbasic.co.uk/forum/content.php?r=39

[cncmachineguy]

As it turns out, you could drive the motor direct from the tc44xx chips. They are designed to be able to do this. May have to do some fiddiling with things but much easier then messing with those fets

[51dueller]

I've started a new topic in the General Section as I don't want to clutter up this section.
http://www.picbasic.co.uk/forum/show...4649#post94649