Help designing a dual H-Bridge controller

[chadj2]

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

 

[xray]

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

 

[ScottyUK]

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


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

 

[GonzaloEE]

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

 

[Warpspeed]

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.

 

[felixc]

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.

 

[itsmoked]

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

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[felixc]

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.

 

[GS3]

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.

 

[chadj2]

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

 

[GonzaloEE]

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

 

[GS3]

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.

 

[Warpspeed]

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.

 

[GonzaloEE]

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 ;-)

Good Luck!

 

[felixc]

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