DIY H-bridge

[medved]

Hi

I am trying to implement DC brush motor control by using Atmel microcontroler (providing PWM) and mosfets.
Because microcontroler cant provide enought current for fast and full switching of mosfets, i am going to use mofset-driver to assure fast switchnig of mosfets.

Here is my question:
In H-bridge circuit, two (of four)mosfets have to be switched simultaneously, which could be a problem for DIY circuit, so could the same be achieved by PWM switching only one mosfet WHILE the other mosfet is permanently ON (at least while motor is turning in one direction)?
Are there also comercially available H-bridges supposed to work that way(fast switching only one mosfet)?

[JBV]

I'm have built a H-bridge for my induction heater! I will use 2 IR2104 Gate Drivers. Check out the pdf for the driver!

[pastera]

You only need to switch one to modulate the current. You probably don't want to switch the two lower or upper switches on together as this would cause a braking action.
The circuit will need good freewheeling capacity to work correctly, however. You can't rely on body diode conduction unless the FET is specified for it.

Aaron

[kreutz]

Read the following article for the answer to your question.

[samco]

I have been playing around with a ir2111 half bridge driver to make a full bridge with 2. Have had good luck so far.

sam

[sswitaj]

Have you looked at the LMD18200 H-bridge from National Smiconductor?

I designed a couple of them into a small motor contol project this summer, they were much easier for the manufacturing guys than discrete parts, and they worked great at reasonable power levels.

[ericdwilso]

Sam,

I am looking to build a servo CNC gantry mill. Thinking of using the MESA card with EMC2 (EMC2 for sure)...
I read that you got your H-Bridge circuit to work... Mind sharing the design?

Eric

[Warpspeed]

Pastera definitely has the right idea here.

With an H bridge, two diagonal FETs need to be completely off. One FET needs to be permanently hard on, and the fourth FET PWM'd. That will give a variable speed in one direction.

For braking just turn on EITHER both upper or both lower FETs. The inbuilt reverse diodes in the FETs will take care of the back EMF action.

There is absolutely no need to PWM two FETs simultaneously.

[samco]

Sorry - I overlooked this tread.
http://www.electronicsam.com/images/...vostart/schem/
http://www.electronicsam.com/images/...start/mess.JPG
http://www.electronicsam.com/images/...art/almost.JPG

lets call it revision .01 The componants where picked for their package size - not what was actually used.

Here is the short list.

FDH44N50 N - MOSFET transistors 500V / 44A for the power mosfets.
RURG5060 Ultra Fast Diodes 600V 50A for the free wheeling diodes
IR2111 for the half bridge driver.
MUR120RLGOSCT-ND DIODE ULTRA FAST 1A 200V AXIAL for the boot strap.
LM340T-15-ND 15volt regulator
TLP2530-ND PHOTOCOUPLER DUAL 6N135 8-DIP
.1uf caps and
iirc 10uf electrolytics.
The big cap is 1200uf I think at 350volts (I think)

Couple things
- when there isnt any pwm signal applied to the bridge - both lower mosfets are on. (braking)
- I had a lot of help from a emc developer that does high power circuits for his real job.
- there is no current limiting yet.
- you should find lower Rds mosfets.
- if your going to run higher than 100v you need higer voltage boot strap diodes.
- this cannot have 100% duty cycle pwm signal other wise the boots strap doesn't get charged.
- use at your own risk (of cource)
- great care was made to have a short power circuit loop - to help get rid of stray inductance.

sam

Originally Posted by ericdwilso Sam, I am looking to build a servo CNC gantry mill. Thinking of using the MESA card with EMC2 (EMC2 for sure)... I read that you got your H-Bridge circuit to work... Mind sharing the design? Eric

[samco]

Also - the mesa board right now does only pwm+dir and my bridge does pwm+pwm. (known as up/down) so you will need a few extra logic chips to turn the pwm+dir out of the mesa board to pwm+pwm.

I think at some point they will have an up/down option on the mesa board - I keep mentioning it anyways.

sam

[NC Cams]

An H bridge involves a tiny bit more than simply turning on opposite diagonals. You MUST prevent a thing called "shoot through" from occurring.

THis is where the same side of the bridge fets are simultaneously going thru enhancement/depletion mode and current "shoots through" to ground as if a dead short occurs.

This is where and why proper fet drivers and interlock logic is CRITICAL to the function of an H bridge, ESPECAILLY, as you switch at higher and higher frequencies. Inductive spikes, too, become a real problem as you build and collapse the field in a motor, especially a stepper with a bridge.

You can get by with some pretty simple stuff when you use an H bridge to run a motor at 50-60 hz (common R/C servos). However, start switching at 20-30khz and you start getting into some serious inductive and/or gate enhancement/depletion issues.

Do some serious PWM'd H bridge driver investigations before you simply put some logic gates in front of some fets. We learned that lesson the expen$ive way.

[samco]

that is why I went with the ir2111 - it does all that for me.

taken from the datasheet....

Floating channel designed for bootstrap operation Fully operational to +600V Tolerant to negative transient voltage dV/dt immune Gate drive supply range from 10 to 20V Undervoltage lockout for both channels CMOS Schmitt-triggered inputs with pull-down Matched propagation delay for both channels Internally set deadtime High side output in phase with input

sam