Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Using MOSFET Body diodes on an H-Bridge

Status
Not open for further replies.

fastcomponents

Newbie level 5
Joined
Dec 16, 2005
Messages
8
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,413
Hi,

we're currently designing a servo controller for these motors that we've started getting made up https://www.fastcomponents.co.uk/product_info.php?products_id=56. The idea is to make a 'servo beater' for robotics applications, retailing at $15 - $20. Basic specs to include a variety of gearboxes (and nominal RPM outputs 40 ~ 250RPM), quadranture encoding, RSXXX, I2C, SPI, PWM, analogue, arbitrary (absolute & relative) positioning commands, arbitrary torque output commands, temperature overload control / feedback... etc.

To keep the cost down, I wondered if we could use the body diodes of the MOSFETs instead of using schottky diodes. Currently in our prototype we're using 2 P-channel (topside) FDFS2P103 (fairchild), and 2 N-channel (lowside) FDFS6N303 (fairchild). But in a S08 package they take a lot of space on the miniature board. Therefore ideally we could use some S023 MOSFETS, and use the body diode.

Quick specs - motor stall current is about 1.5A. Supply voltage is 4-6v, pwm switching is variable between 2 and 8khz to minimise audio noise approaching discontinuous operation, and switching loss at higher power levels.

I wonder if the body diode would be fast enough at these switching speeds?

Any ideas for alternative MOSFETS? Unit will be fitted with miniature heatsink to aid dissipation, and the aim is to mount the board on top of the motor casing (yes it is small!!!)

Thanks, Tom.

Fast Components - the best way to buy components!
https://www.fastcomponents.co.uk
 

scottieman

Full Member level 2
Joined
Aug 8, 2005
Messages
136
Helped
12
Reputation
24
Reaction score
1
Trophy points
1,298
Location
On Top of Silicon
Activity points
2,629
fastcomponents said:
Hi,

Quick specs - motor stall current is about 1.5A. Supply voltage is 4-6v, pwm switching is variable between 2 and 8khz to minimise audio noise approaching discontinuous operation, and switching loss at higher power levels.

First, I haven't checked the specification of the MOSFET (both N and P) you are using. Based on the switching frequency 2 - 8kHz you mentioned, the body diode should be relative fast enough, since in power electronics, we are normally operating the switching power converter in 20 - 100kHz.

Scottie
 

fastcomponents

Newbie level 5
Joined
Dec 16, 2005
Messages
8
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,413
Ok thanks :). I was also looking at using a FDC6401N https://www.fairchildsemi.com/ds/FD/FDC6401N.pdf, since it's dual mosfets in a tiny SuperSOT-6 package :)

The drain-source diode for the above is rated at a max Is of 0.8A. Any ideas how one goes about determining whether this would be able to handle the reverse EMF spike from the motor?

Tom.
 

scottieman

Full Member level 2
Joined
Aug 8, 2005
Messages
136
Helped
12
Reputation
24
Reaction score
1
Trophy points
1,298
Location
On Top of Silicon
Activity points
2,629
fastcomponents said:
Ok thanks :). I was also looking at using a FDC6401N https://www.fairchildsemi.com/ds/FD/FDC6401N.pdf, since it's dual mosfets in a tiny SuperSOT-6 package :)

The drain-source diode for the above is rated at a max Is of 0.8A. Any ideas how one goes about determining whether this would be able to handle the reverse EMF spike from the motor?

Tom.

If the max. current flow through your motor is more than 0.8A, than the diode associated with that MOS will have problem.

Scottie
 
Last edited by a moderator:

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top