How to Conect PIC with High power Circuit (Graound Consider)

[trento]

Hi dear all

I would like to ask you about the connection of the PIC

I use the 16F877A in AC motor control application so I use it with the H-bridge converter I, pleas tell me how I connect the PIC to this High power Circuit to protect the PIC from the high voltage and how I have to supply it to make it work properly.

Regards

[arunb]

Hi,

The best method is to use opto-isolators. This will completely isolate the low power side from the high power side. You could also consider using darlington pairs, there is an CMOS IC, ULN 2803 that is used to control relays or stepper motors. I have used this very succesfully to control stepper motors at 24 V DC.

thanks
arunb

[trento]

Thank you for you response

I would like to ask you to attachand the Circuit schamatic diagram conection,especialy the source and ground conection of the PIC with the high voltage Circuit

regards

[Ttelmah]

Arunb, has given you some pointers on where to start, but don't expect people on this forum (most of whom have work to do for a living), to post complete circuit solutions.
Now in fact your question does not give enough detail for a reasonable answer. You say 'AC motor control', but not what voltage is involved (mains?), what power levels are involved (there is a significant difference between 'controlling' a 10W synchronous motor, and a 5KW three-phase motor), what 'control' is required (on an AC motor, you could require ramped accelerations, decelerations, braking, etc. etc., or just simple 'stop/start), what sort of quantities are involved (the 'best' solution for a 'one off', will differ from that needed in a production enviroment involving millions of units), and if this is a production device, what safety standards will have to be met. The basic 'rules'will be the same in each case (couple digital signals, using either transformers, or opto-couplers), but the sort of control involved, and the parts count, will vary massively.
If (for instance), you just require to 'switch' a motor safely, then look at a SSR. These are available off the shelf with logic inputs, and snubber networks (which will be necessary to kill the tendency for an inductive load to produce huge voltage spkes when switched off), built in. If you want really complex speed control, look at 3 phase inverter modules (from companies like Honeywell, Mitsubishi etc.), which will be cheaper than building a solution yourself, and will usually offer RS232 serial control. However if this is to be a unit with a large production 'run', and fully custom, then get the data sheets for some of the motor control IC's, which will usually have 'examples' showing how to interface them to micro controllers.

Best Wishes

[trento]

Now in fact your question does not give enough detail for a reasonable answer. You say 'AC motor control'(single phase Induction motor), what voltage is involved (mains?) 220v , what power levels are involved (0.37 Kw (there is a significant difference between 'controlling' a 10W synchronous motor, and a 5KW three-phase motor) I know that, if this is a production device, what safety standards will have to be met. The basic 'rules'will be the same in each case (couple digital signals, using either transformers, or opto-couplers), If (for instance), you just require to 'switch' a motor safely, then look at a SSR. These are available off the shelf with logic inputs, and snubber networks (which will be necessary to kill the tendency for an inductive load to produce huge voltage spkes when switched off), built in I mean just how I supply them and how I conected togathar . However if this is to be a unit with a large production 'run', and fully custom, then get the data sheets for some of the motor control IC's there is some thing wrong on the data sheet they always did not give the full information I traid but I couldnot get the result, which will usually have 'examples' showing how to interface them to micro controllers. I just want him to send the diagram I thinkit will be just copy paste or attach file or send link I think it will not take so much time .

anyway thank you for ur help

[Ttelmah]

Except that he is talking about control of DCmotors...
You still have not said what sort of 'control' is needed, but I'd suspect that if this is simple 'on/off', then a SSR is the 'answer'. These comprise basically an opto-coupler, feeding a MOSFET, or a TRIAC. The more sophisticated types, add a snubber network, and the control for zero-voltage switching, to limit RF. Go and look at the CryDom site, and possibly at the ASO242, which is a zero-voltage version, with 2A continuous, 3A 'peak' rating.

Best Wishes

[trento]

Dear sir

I want just the conetion just conection,between microcontroler and the isolator and the drive which is (full H-bridge single phase) to make the PIC work properly I traid in our lab to conect as the data sheet said but it was not work for your informatin I use (IR2110)as gate drive and I use the H-bridge circuit as drive because the main application of PIC is controling motor so this is why I put this question in your user fourme because I believe that there is someone faced this problem last time ,so he can told me the practical soloution.the main problem is how to conect all the component ground togathar and how you should supply them for corect arangment. hoppfully I will get a soloution and give it to some after me asking about it.the problem is not easy as you think before I put this qouestion I read the component data sheet and I traid my self in my lab olso I search some artical but I can not do it i spend 20 days for this, so please help me

regards

[SherpaDoug]

I suggest you contact the applications engineers at International Rectifier (www.irf.com) and ask them how to use their IR2110 chip or to suggest an alternative for your application. You are talking about a fairly high power high voltage system with lots of opportunity for people to get hurt. This is worth putting some real engineering time into.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[treitmey]

Listen to SherpaDoug. Don't kill someone with this circuit!

[kender]

Check out also the Analod ADuM series of magnetic isolators. They come in SIOC and take half the board space of the optos. Additionally, if the number of channels is three or more, they end up being cheaper then optos.

[Ttelmah]

The IR2110, is a great way of driving a high voltage DC H-Bridge.
You should read the MicroChip application notes AN984, and AN967, which show how a bridge driver has to be arranged and driven to drive an AC motor. Seriously, most normal single phase AC motors cannot be reversed with an H-Bridge, since they contain a capacitor start, or shaded pole system, to create the phase shifted fields needed to start a rotation. You need to actually access the second internal phase widing, and control this relative to the signal on the other winding, to reverse such a motor. It is usually easier to use a DC motor for this reason (you will find most 'reversable' consumer electronics, is rectifying the incoming mains, and using a DC motor).
Logic level opto-couplers are then used to couple the control signals from the PIC to the bridge drive, to give the isolation required for most applications.

Best Wishes

[MikeValencia]

[neil]

We are talking about controlling an AC motor with an H-bridge from a PIC. This can only mean that the PIC is going to be doing the job of an inverter right? As far as I know, a single phase induction motor will not like being driven from a quasi-square wave source, so the little PIC is going to have to do sinewave modulation. Can they do this? I would have thought this is either a job for a DSP, or a custom hardware design. This kind of design is a complete profession in itself, requiring expert knowledge.
What is the design for? Is it commercial, or educational?

As for the grounding question, if you use optical or magnetic isolation, the grounds can be completely separate.