OpenServo.com

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

Now that I'm waiting for my PCBs and components for OpenServo 2.0 to arrive, I've turned my attention to designing an H-Bridge with MOSFETs that can handle more current.

A few weeks ago Andy pointed me to an interesting MOSFET. The IRF7309 which is available in large numbers and has a fairly low price of less than a dollar in single unit quantities from DigiKey. A datasheet can be found at the following URL:

http://www.irf.com/product-info/datasheets/data/irf7309.pdf

I wanted to get other's opinions on this MOSFET and whether it can be driven by the OpenServo interfaces from the ATmega8/168 MCUs. I have minimal analog design experience and any feedback would be very helpful.

The chips contains both the N-Channel and P-Channel MOSFET in an SOIC-8 package. I already designed an OpenServo 2.0 derived PCB layout for this package. It seems a fairly common package which is good.

Below is a list of similar MOSFETs from other manufacturers in the same SOIC-8 package that may be interesting to look at as well. However, they may be harder to get a hold of.

-Mike

AO4606 ALPHA & OMEGA SEMICONDUCTOR
AO4607 ALPHA & OMEGA SEMICONDUCTOR
APM4536 ANPEC
APM4542 ANPEC
APM9930/C ANPEC
APM9932/C ANPEC
FDS8958A FAIRCHILD
IRF7317 I.R.
IRF7319 I.R.
IRF7389 I.R.
BSO215C INFINEON
UPA1792 NEC
FW313 SANYO
Si4539ADY VISHAY
Si4539DY VISHAY
Si4544DY VISHAY
Si4558DY VISHAY
Si9801DY VISHAY
Si9939DY VISHAY
ZXMC3A16DN8 ZETEX
STS7C4F30L STMicroelectronics

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

Looking deeper into this I came across this PIC driven H-Bridge circuit that utilizes the IRF7309 MOSFET.

http://www.propix.hu/examples/HBridge.pdf

Looks more promising.

-Mike

mikewardlow · Joined: 16 Mar 2006 Posts: 42

www.atomicmods.com worth looking at

4562 FET

These are the FETs that we stack on Mini-Zs and XMOD Gen1s to allow a greater current draw from the batteries to the motor. The stock FETs, allow just over 2 amps of usable current. These 4562 FETs allow about 7 amps of usable current! So when they are stacked 2x2, your FETs will be capable of passing 14 amps of current.
? Includes: 1) 4562 FET
? Application Notes: Although the tutorial is very detailed, this modification should be reserved for those possessing moderate-to-advanced soldering skills. Also, this item is sold under the ""You fry, you buy"" policy...meaning if you fry the FETs, you buy new ones. We have installed several hundred FETs on our bench and have yet to receive a DOA.
? Tutorial Link Stacked FET Installation
? For Use With: XMOD Gen1, Mini-Z MR-01, MR-02, MR-015, MR-010, Monster & Overland
? Weight: .08 grams
? Shipping: Normally ships within 1 day

mikewardlow · Joined: 16 Mar 2006 Posts: 42

http://www.atomicmods.com/custom.aspx?id=18

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

I think the following is the 4562 FET you are referring to:

http://www.vishay.com/docs/70717/70717.pdf

Like the other parts this is the same SOIC-8 package as the other MOSFETs and I believe it should work fine in the PCB layout I created for these packages.

I'm not seeing the Si4562DY stocked by DigiKey. The price from AtomicMODs is $2.95 which is pretty steep for this kind of chip. Any other sources?

-Mike

mikewardlow · Joined: 16 Mar 2006 Posts: 42

I think mouser carries them...price is probably about the same though...

ginge · Posted: Sun Mar 26, 2006 5:41 pm Post subject:

The IRF7309 is very common in Europe, and has been used by our onsite design team before.

I have noticed that the schematic in the diagram does not have external flyback diodes, and would seem to rely on the internal diodes.

The guys in the design department here see no reason why not having the external diodes would be a problem, unless there are high speed transitions between directions. It is not seen to be a problem on designs with PID algorithms, which in the most part take care of these transitions.

The current Openservo designs use similar FETS with the internal diodes. Would the removal of the external diodes be significant when driving such small motors?

Any thoughts?

Barry

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

Barry, I'm working on a redesign of the PCB with the IFR7309 now without the external flyback diodes (to save space). I really don't have experience or knowledge to say one way or the other, but the information from your design guys make sense. When I examine a few commercial RC servos with discrete MOSFETs I don't see a use of external flyback diodes. I'm going to proceed to leave them off for now and build a prototype to do testing with.

Anyone elses thoughts on this would be useful.

-Mike

mikewardlow · Joined: 16 Mar 2006 Posts: 42

Just found TC4421/22 and others on microchip website...
interesting.....

TC4421/22 9amp 18 volt 8pin ssoc/dfn/dip
TC4429 6amp 10 volt "" ""

TC4428 dual 1.5 Amp but only in 8 pin dip ??

mikewardlow · Joined: 16 Mar 2006 Posts: 42

Looks like you might be able to use 1 chip TC4423/24/25
3A max current dual driver...@ 0.91 cents . see link

http://telcom-semi.com/ParamChartSearch/chart.aspx?mid=11&lang=en&branchID=9010

which translates to microchip

mikewardlow · Joined: 16 Mar 2006 Posts: 42

Heck looks like possibility of big reduction in parts...

1 cpu
1 TC442x
1 large electrolytic
4 ? diodes
2 motor noise suppress caps ??

ginge · Posted: Sun Mar 26, 2006 11:21 pm Post subject:

Looks interesting.

Have you found any application notes or examples relating to driving a motor directly?

Barry

mikewardlow · Joined: 16 Mar 2006 Posts: 42

Have found no appnotes......

did find a website[David Cook]

http://www.robotroom.com/HBridge.html

mikewardlow · Joined: 16 Mar 2006 Posts: 42

After viewing the website... the output resistance may be too hi
.....dratz.....

mikewardlow · Joined: 16 Mar 2006 Posts: 42

Although, if it can be otained in surface mount , it might be easier to
implement for fet driving..../ just a thought..