Most of the DSP chips designed for motor drive that I've looked into -- ADI, Freescale, TI -- do this.
Dunno about discrete chips, though.
Most of the DSP chips designed for motor drive that I've looked into -- ADI, Freescale, TI -- do this.
Dunno about discrete chips, though.
-- Tim Wescott Wescott Design Services
A DSP may be the most simple and inexpensive solution for your problem, but only if your problem is big enough to justify having a processor sitting on your board.
What the PWM circuits in the motor drive DSPs provide is all the "smarts" -- settable PWM frequency, duty cycle, & vector drive math for that little bit of extra overhead on a 3-phase brushless system. Their output is just logic level, so you still have to provide all the power electronics but your power circuit can be as dumb as a post -- you only need enough stuff to turn the FETs on and off fast, not all the timing &c.
Take a look at a datasheet, or some whitepapers, and see.
-- Tim Wescott Wescott Design Services
Oh, I'm stupid.
Some of the more sophisticated switching regulators provide all the deadband & timing stuff, and sometimes even FET switching. There's no reason you have to use them to actually regulate, unless you want to.
I'm trying to remember the part number, but I've seen this sort of thing used for 4-quadrant switching amplifiers with full H bridges. All of the smarts were analog and on the regulator controller, with the regulator connected either directly to the FET gates or through snubber circuits.
But there were some interesting snubber circuits, which would still be required even with a DSP solution. Something about shoot-through, and FETs that would scatter bits of chip package all over the lab...
-- Tim Wescott Wescott Design Services
Check out the HIP4080A, by Intersil. It doesn't include the oscillator, but it has everything else including programmable dead time on the top and bottom FETs. You could use anything from a 555 on up for the oscillator (and if you're clever about where you put the PNP you can even get a linear ramp from a 555).
-- Tim Wescott Wescott Design Services
I'm fond of the HIP4080A and HIP4081A parts. Intersil has app notes showing how to implement a PWM controller from the '4080, using its comparator, but I prefer the '4081 with an external PWM generator. For example, with a phase-shift PWM modulator for the H-bridge FETs.
-- Thanks, - Win
Is there a PWM chip that can properly drive an H bridge? (with dead time, fast on and off times etc)?
thanks
i
Thanks. You are suggesting something very interesting. I looked at motor drive chips yesterday and was a little confused. Are they also good for power switching applications?
Again, I am looking for some easy solution that would have frequency and duty cycle settable, and would drive an H bridge. I can do that either with one oscillator chip and two half bridge gate drivers, or, possibly, with something else.
If you have a suggestion for something simple and inexpensive, it will be greatly appreciated.
Thanks!
i
I have seen several chips like that, with easily settable frequency and duty cycle.
I have not seen one like that, and, frankly, that's exactly what I am looking for.
So, I could find a chip that would switch IGBTs in a full bridge, and also have settable frequency and duty cycle (using pots or some such), I would be in heaven.
The trouble is, no one knows if there is such a chip, people say all kinds of smart things, I spent a couple of hours looking, and did not find anything.
If you could recall the part number, I would be eternally grateful.
Sure, no doubt about that. That's not really a problem. I am looking for a simple gate driver solution, but snubber circuits would be separate.
So, again, if you can recall the part #, that would be wonderful and most appreciated.
I will be driving toshiba IGBTs. I received them (4 on a heatsink) last night. I was already able to drive them with a wavetek 171, and see them conduct current when turned ON and not conduct when turned off. I watched wavetek's on my oscilloscope and it was a fun evening.
iI
I see. That's unfortunate, but looks like it's the reality that I can deal with.
I like IR21094 as a gate driver, and also MAX038 as the signal generator. Both are DIP based. The only issue that I see, for now (which may not be a big deal) is that MAX038 produces +- 1 volt, and IR21094 needs 5 or so volts to turn the bridge sides on and off. So I need to amplify MAX038's output a little bit. That can probably be done with an appropriate transistor or some such.
So, I would use MAX038 driving two IR21094 gate drivers.
MAX038 has its frequency and duty cycle separately settable with pots.
Does this plan make sense to you?
i
It certainly looks very nice. I like the fact that it is a full bridge driver. I just printed out its datasheet and will read it on the way home.
Thanks!
i
Sounds very nice. Seems like you know what you are talking about.
What PWM generator would you suggest (preferably DIP), using similar power supply voltage and working from 50-1000 Hz at least, and providing duty cycle control, at least 15-85%, etc.
Thank you!
i
The actual FET / IGBT gate driver ( and level shifter ) is typically a separate IC from the control chip.
Probably can't be done well in one package due to different processes required I expect.
Graham
separate
required I
accurate, high-frequency
external components. The
There is no reason other than seeing that it could somehow do what I need. If you have a better suggestion, I will appreciate.
Would you have a specific chip that you could suggest?
thanks
i
separate
required I
I don't understand why you want to use a Max038.
The MAX038 is a high-frequency, precision function generator producing accurate, high-frequency triangle, sawtooth, sine, square, and pulse waveforms with a minimum of external components. The output frequency can be controlled over a frequency range of 0.1Hz to 20MHz
Why not use a classic PWM controller ?
Graham
accurate, high-frequency
external components. The
Pooh, I found a very simple chip XR2206, it is not perfect because duty cycle and frequency are not independently selected, but it is simple.
i
Wtf do you mean by "duty cycle"? Looks to me like the job of the output inverter is just to smartly reverse current to the arc at a certain (low) frequency, and the primary inverter is tasked with actually controlling the arc current. The IRF app note even suggests a slight negative "duty cycle"-- forcing a small amount ( a few hundred ns) of cross-conduction in the bridge.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com
If you wire a 555 as an astable multivibrator and put a comparator on the trigger input, the duty cycle out of the comparator will vary as you change it's threshold voltage. You can adjust the frequency of the 555 with a single pot, and the threshold voltage with a separate pot. At those frequencies things will even be somewhat consistent.
-- Tim Wescott Wescott Design Services
IIRC the 3525 has two open-collector outputs which can be paralleled to get nearly 100% duty cycle (I know the LM3524 can, because I have the data book open to that page).
If you're driving an H bridge for electronically switched polarity, and if you're clever, you could get square-wave AC out of the thing by clever application of your '3524.
-- Tim Wescott Wescott Design Services
Or a PIC with a couple of buttons, a beeper and an LCD. But then he'll have so much fun with the operator's interface that he'll never get to the power electronics.
I'd go with the 555 and a 393, myself, but then I've been reading too many of Jeorg's posts.
-- Tim Wescott Wescott Design Services
Shoot-through connects the two power supply rails together, leading to high currents in the switches and some rather dramatic behavior (wear safety goggles).
Catch diodes would probably be more appropriate, and are routine in this sort of application.
-- Tim Wescott Wescott Design Services
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