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Help designing a dual H-Bridge controller

Help designing a dual H-Bridge controller

Help designing a dual H-Bridge controller

(OP)
I am trying to build a circuit to control 2 H-bridges. The H-bridges outputs must be 90 degrees out of phase with each other. I was thinking about using a sg3524 signal to control one H-Bridge and using the same signal as an input to 2 556 timers acting as a delay and trigger signal to the other H-bridge. The H-Bridges will be driving coils. I don't believe I have the skills to use a microcontroller unless I am thinking it is more complicated than it is. If anyone has any ideas as to how I can control this setup more effectively please give me some guidance.

Chad

RE: Help designing a dual H-Bridge controller

Why not use two 3524. Anything but a 555!!!!

RE: Help designing a dual H-Bridge controller

(OP)
How do I ensure that the 3524s stay 90 degrees out of phase?

RE: Help designing a dual H-Bridge controller

The brute force and ignorance solution is to start with a 4x version of the control signal and divide by 4, and decode the output quadrature signals

TTFN

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RE: Help designing a dual H-Bridge controller

I've got to ask.  Is it possible that the 90 degree requirement refers to the relationship of the current through the coils?  If the coils are at right angles, the current drive often has the relatioship of sine in one coil and cosine in the other coil so that a magnetic vector can be rotated.

RE: Help designing a dual H-Bridge controller

(OP)
Thanks for the response. I am performing an experiment on magnetic field interaction. I need the first B field to be at full north while the second B field is at neutral.

RE: Help designing a dual H-Bridge controller

http://focus.ti.com/lit/an/slua143/slua143.pdf
Figure 22 page 3-61. Did something similar a while ago.
I used 2 uc3846 chips and a flip/flop to an external
clock. The f/f gives a square wave 180 out. The resultant
outputs out of the chips where 90 degrees out.
Should work the same for a uc3524 chip.
Now, I would agree with itsmoked and use a micro.

RE: Help designing a dual H-Bridge controller

Since you are doing an experiment, I'd sugest that you purchase amplifiers to drive current into the coils.  Varedan

http://varedan.com/

makes some nice linear current mode amplifiers that can be factory configured to drive voice coils.  Linear means no PWM switching noise.  The current is proportional to the command signal and is bidirectional.  You would also need a servo chassis to power the amplifiers.

RE: Help designing a dual H-Bridge controller

(OP)
Once again, thanks for taking the time to give me some guidance on the best way to tackle this problem. Unfortunately, I think it will take me quite a while to learn how to use a microcontroller (I dont even know any computer languages). I will continue to study the ideas that you guys have provided.

Thanks again
Chad

RE: Help designing a dual H-Bridge controller

Lay hands on one of those Stamps and you will find that some are trivial to program.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Help designing a dual H-Bridge controller

I would create an independent clock at twice the frequency of either H-brige, divide it by two with a flip-flop, then reshape them into two pulses. Send these to the synchronous clock inputs to the PWM IC.

Now you've got your 90 out-of-phase.

RE: Help designing a dual H-Bridge controller

Yes and how do you prevent shoot-thru due to turn off delay?

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Help designing a dual H-Bridge controller

It's odd that people are suggesting a micro to produce two simple pulse trains. Most of the PWM IC application notes will show you how to sycn them with a clock. Producing two staggered clocks would just take a few parts. Your two H-bridges will run independently from the two clocks.

RE: Help designing a dual H-Bridge controller

You haven't answered the previous question about preventing DC shoot-through when the off-going switches are still conducting as the on-coming switches begin to conduct. You can't just use a pair of antiphase square wave drives - there has to be a short 'dead time' when all gate drives are 'off' to allow the off-going switches to reach a blocking state before the other pair switch on. Following your advice will lead to DC shoot-through and destruction of the switches.
 

----------------------------------
  
If we learn from our mistakes I'm getting a great education!

RE: Help designing a dual H-Bridge controller

Scotty, using off-the-shelf H-bridge gate drivers solves this problem, most of them have built-in dead-time circuits.

Regards,

Benta.

RE: Help designing a dual H-Bridge controller

I know - that's why the comment about antiphase squarewaves to drive the gates seems strange! On re-reading I think I know what hgldr is getting at - using a quadrature pair of squarewaves to synchronise two driver ICs which take care of the dead time etc for each bridge.
 
 

----------------------------------
  
If we learn from our mistakes I'm getting a great education!

RE: Help designing a dual H-Bridge controller

About the two staggered clocks. The leading edge of each square wave would go into a simple pulse forming circuit, about 500ns width would do. These are what are sent to each PWM IC sync input, not square waves.
For an IC like the 3524 The sycn pulse current would be sent to the ramp capactior and must be higher than the ramp-discharge current. This isn't specified in some IC's so it has to be high to make sure it works. I'd use a 3525 PWM instead of the 3524. The sync methods are specified and more straigtforward.

RE: Help designing a dual H-Bridge controller

Thanks hgldr.
 

RE: Help designing a dual H-Bridge controller

Use a TL494 or equivalent.  Adjustable timing, adjustable
dead time, bi-phase outputs, dual feedback inputs, etc.

<als>

RE: Help designing a dual H-Bridge controller

It seems to me you have a solution in the sg5324. You are asking for a secondary function from your primary solution. I think this could be to implemented with analog signal processing.
A reasonable copy of the pwm with 90 deg. phase delay would be to send the signal through a single pole low pass filter. The pole would be designed at the frequency of pwm giving you 45 deg. of phase and then sending it through another single LPF just like the first to pick up the other 45 deg. Paying attention to the impedance input so as not to tap off to much current from the sg5324 and the necessary gain to get back the 6 dB dropped by filter.
 This would require a single chip with a couple of op amp on a single chip some resistors and capcitors.  A potentiometer or two to vary where the pole actually ends up and viola a 90 deg. phase shift of the sg5324 output. Anyone disagree.

Best Regards

RE: Help designing a dual H-Bridge controller

Digital is easier and more precise, especially if this a variable frequency application.
 

----------------------------------
  
If we learn from our mistakes I'm getting a great education!

RE: Help designing a dual H-Bridge controller

I also agree on digital control.  You can sense coil currents through and opamp and the micro A/D input. The micro triggers one coil when the other's current is at its max: a perfect quadrature.    Also, it prevents shoot-through as said before.

Good luck with it!

Regards,
Gonzalo
 

RE: Help designing a dual H-Bridge controller

Easiest way to do this is to start off with a clock running at four times the required frequency.

Feed that into a pair of flip flops, but they need to be connected in a special way. Google "twisted ring counter" or "Johnson counter".  That will give you four output phases arranged in exact 90 degree phase quadrature.

Take any two of these phases that have a 90 degree relationship, and drive a pair of the commercial H bridge driver chips. Some of these drivers have the feature of adding dead time, so the upper and lower drive signals do not overlap.

RE: Help designing a dual H-Bridge controller

The 3524 may have overlapping quadrature outputs under certain fault conditions.  I've seen several power supplies fail because of that.  They released the 3525 to address the issue.

I don't know what are your voltage and current requirements, but to have a quickly working driver section here is an integrated H-bridge chip that is very good and virtually foolproof.  It takes care of shoot-thru itself.  ST Micro model VNH2SP30E.  It is good up to 30 amps.  I had a good success with it in an automotive application.

RE: Help designing a dual H-Bridge controller

That's sweet felixc!!
I only ever see under 10A ones mostly ~5A.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Help designing a dual H-Bridge controller

Yeah, that part was my hero last year.  It is used for the car seat adjustment motors.  The customer wanted a given design, and it ended up needing twice the current that I designed, after a good margin from their initial requirement.  And with its great (I mean low) Rdson, it runs cool.  I don't have STMicro in such a good esteem, but for this part they made it great.

RE: Help designing a dual H-Bridge controller

Quote:

how do you prevent shoot-thru due to turn off delay?
One simple way to deal with it is to put an inductance in series with the supply. The brief time during which both switches are on just results in a manageable current increase which stores energy in the inductor and this energy is immediately relased when one of the switches goes off. In many cases it is the easiest and simplest way to deal with the problem.

RE: Help designing a dual H-Bridge controller

(OP)
GS3,

That seems to be a brilliant yet simple solution to the problem of shoot through. I was not familiar with this method. Do you happen to know an easy method to determine what is the appropriate inductance to use but also not really interfere with the maximum power available to the H bridge?

Chad

RE: Help designing a dual H-Bridge controller

Just going a bit further with what GS3 said:

Please note that a bigger inductance will keep the shoot-thru current low for longer time, though it will also rise the voltage spikes if the clamp diode protections of your H-bridge aren't fast enough.

Also pay attention when choosing filter caps. and PWM frequency, to prevent ringing and resonance issues.

Good Luck!
Gonzalo

RE: Help designing a dual H-Bridge controller

Quote:

Do you happen to know an easy method to determine what is the appropriate inductance to use but also not really interfere with the maximum power available to the H bridge?

Chad, sorry I had not seen your post until now.

I have seen this method of putting an inductance in series used very widely in smaller electronics like inverters for fluorescent lights etc. It is simple and cheap but maybe in larger things it might make sense to use other methods if the inductance becomes too big and can be replaced by a different design of the controlling circuit.

I suppose the characteristics of the inductor would have to be studied and determined by the specific circuit. You would need to determine not only the inductance but resistance and other parameters, including cost.

RE: Help designing a dual H-Bridge controller

Chad, one way of approaching this would be to design it as for a "turn on snubber circuit".

These consist of a series inductor, usually along with a diode and a resistor to dissipate the stored energy in the inductor.

 

RE: Help designing a dual H-Bridge controller

The fewer parts, the better.  Each new part is just another point of failure.
With the good IC solutions suggested earlier. I guess you're done winky smile

Good Luck!

RE: Help designing a dual H-Bridge controller

The shoot-thru is taken care of in most integrated chip solutions.
 

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