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[split] EEG EM Basic Circuits
#1
Hi solarlab,

I was looking into the H-bridge and how to use it, but it is completely new to me and most videos (if not all) are regarding their use with DC motors. And all of it is confusing to me as hell, even the datasheets.

The H-bridge can only make positive voltage right? From 0V to whatever Vs? There is no negative voltage coming from the H-bridge?
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#2
(02-01-2024, 07:31 AM)kloakez Wrote: Hi solarlab,

I was looking into the H-bridge and how to use it, but it is completely new to me and most videos (if not all) are regarding their use with DC motors. And all of it is confusing to me as hell, even the datasheets.

The H-bridge can only make positive voltage right? From 0V to whatever Vs? There is no negative voltage coming from the H-bridge?

I know you asked Solarlab, but I am extremely familiar with that exact modem H-bridge as I have over 50 of them. And work with them almost daily.

Yes they can flip polarity at pretty decent frequency. They basically need the logic voltage (5V) from a microcontroller (Arduino or the likes). Then they have 2 enable pins and 2 PWM pins- 1 that control each output wire.

For most basic transformer / induction like setups, we will power both enable pins with 5V to always keep them on.

So say you feed 12V into the input power.  If you fire 5V on to PWM 1 pin and 0 volts on PWM pin 2,  Output 1 becomes Hot 12V and Output 2 becomes  ground.  Then simply switch power feeding PWM pins, so PWM2 has 5V and PWM has 0 volts.  Then the output DC polarity flips.

They can support pretty high frequency.  20-30 Khz is usually not a problem.  

There are also more advanced tasks they can do when we realize the possibilities of the enable pins. Some of my projects use 9 H bridges at once, where 1 H bridge grounds into another and so forth. 

They are basically like a DPDT Solid State Relay that can operate a much higher frequencies and not wear down the contacts. 

If you get one, I can help you with the basic setup, wiring, coding for the arduino
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#3
Thanks Jim, I really appreciate it. I will get the H-bridge you recommended and some Arduino and I'll report back after they arrive.

In the meantime I am designing some bobbins for the coils. I plan on forming 3 cores out of 4 blocks of sendust blocks each (I have 14 of them in total) and one electrical steel core (C-shaped pair) that arrived earlier this week. When I print the bobbins, I'll do some simulations to determine the number of coil turns.
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#4
Hi solarlab,

What about back emf ?
Don't we have to deal with that.

feb_
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#5
Hi Kloakez & Jim,

Hopefully Jim answered your inquiry. Thanks Jim...

Here's a simplified overview version of the Full H-Bridge operation. This fellow explains it much 
better than I would be able to!

Pay attention to the last part where this fellow explains "shoot-thru" and the need for a brief
pause between switching directions to avoid excess bridge mosfet heating, etc. You can really
waist a lot of power if the timing is off even a very slight little bit!

What is an H-Bridge?
https://www.youtube.com/watch?v=3N_4VpzmKY0

Note that the Motor is replaced by the "N S Coils." This allows the coil current to change direction
as the H-Bridge operates, thus creating the "N-S" action toggling them back and forth; similar to 
very rapidly changing the motor direction.

SL


Hi Feb,

Maybe you could expand your question a bit about BEMF and what effect you think this
might have on the circuit. 

I ask since there are a variety of interpretations of BEMF depending on an individual's
perceptions.

Thanks,

SL
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#6
That part at the end about break through is the most important part
That noise that they teach you to get rid of
Is what everyone is looking for
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#7
Another little "gotcha" is good programmers will get the delays correct in their code
but generally don't pay attention to the part's data sheet.

What happens is the device data sheet propagation delays (ton/toff) are not considered
(the rise and fall times inside the chip can be quite different sometimes) thus the device
runs warm (hot) and no one can figure out why. A skilled Scope user can usually spot
the problem but it can be a bit tricky, especially near the thresholds.

Most MOSFETS should run somewhat cool if your only using them for switching. Modern
Fets have a pretty good rds on (low internal resistance [drain to source] when ON).
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#8
Another thing to consider when choosing the right MOSFET is that a lower RDS(on) generally means that the MOSFET can handle a larger current because the gate is physically larger. This comes at the expense of having a greater gate charge Q(g), which means that the switching times will be slower. A MOSFETs switching speed basically comes down to how fast you can charge and discharge the gate.

Using a MOSFET with lowest RDS(on) isn't always the best choice. My opinion is that you should choose a MOSFET which is capable of switching the expected current plus some safety factor. Using a MOSFET capable of handling more than 1.5x your max. expected amperage is a waste in terms of switching performance (td(on), tr, td(off), tf) and also switching losses.

Here's an application note that goes into more detail: Power MOSFET Basics: Understanding Gate Charge and Using it to Assess Switching Performance
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#9
Hi solarlab,

A protection something like this.
So you don't burn the MOSFETs.

   
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#10
Hi Fellows,

NOTE: The EEG EM Basic thread has been "split" into "EEG EM Basic" where the discussion hopefully will
focus around the "EE_TFG" theory and physical build type information. That is, the mechanics of the design.

A Second Thread "EEG EM Basic Circuit" hopefully is where "circuit implementions" relating to the EE_TFG
such as Microprocessor, H-Bridge, and related circuits will be the focus. Related general Electronic Circuit 
Designs can be posted here. Much of this information is important so this "split" should make it more easily
accessed.

Mixing the EE_TFG concept with general circuit design and development would quickly fray the discussions 
and mask the some of the important features of each subject.

Several of the Circuit related posts have been moved to the "EEG EM Basic Circuit" split branch.

Regards,

SL

PS - Not sure how this "split" thing works, but we shall see! Guests cannot see images in the messages. Please register at the forum by clicking here to see images.
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