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Old 3rd October 2004, 10:15 PM   #71
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Hi Chris,

My problem is that I get this error message when I start the schematic editor, so I can not go to the simulation. But my company bought this version when WindowsNT4 came out and never upgraded.

Best regards,

Jaka Racman
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Old 4th October 2004, 12:18 AM   #72
JohnW is offline JohnW  Hong Kong
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Hi Chris,

I would just use a Diode pump from the lower Gate drive supply & resistors say 22K to 47K from VDD to the upper driver supply, and a similar resistor from upper driver “floating Gnd” to VSS, with a Zener diode to limit the resultant voltage across the upper driver supply to say 12V.

This will charge up the upper driver supply regardless if the OPS is switching or not. You would have to add a short Ton Delay before the OPS started switching (say 5 Sec) on power up to allow the upper rail supply to “charge up” though the resistor paths. Not a bad thing anyway, allows the input circuits (buffers) to settle on power up.

If you use your method, I would add a resistor from upper drivers “floating Gnd” to VSS, this guarantees that the upper driver supply charges up without a Load connected.

John
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Old 4th October 2004, 05:12 AM   #73
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Quote:
Originally posted by JohnW
Hi Chris,

I would just use a Diode pump from the lower Gate drive supply & resistors say 22K to 47K from VDD to the upper driver supply, and a similar resistor from upper driver “floating Gnd” to VSS, with a Zener diode to limit the resultant voltage across the upper driver supply to say 12V.

This will charge up the upper driver supply regardless if the OPS is switching or not. You would have to add a short Ton Delay before the OPS started switching (say 5 Sec) on power up to allow the upper rail supply to “charge up” though the resistor paths. Not a bad thing anyway, allows the input circuits (buffers) to settle on power up.

If you use your method, I would add a resistor from upper drivers “floating Gnd” to VSS, this guarantees that the upper driver supply charges up without a Load connected.

John
Hi,

Thanks for the tips, as always, more than helpful and it's very appreciated.

Your method of precharge is great, beats the hell out of what I found in the IR app note which didn't seem to work well at all.

I've done the bootstrap thing with my proto-amp already so I'm just trying something new, someone out there might appreciate seeing an H bridge with full floating supplies realized in such a simple manner as well.

Really, if you search online for bridge info the most you find is app note related = this is how it's done with our chip. I find that so limitting, it's nice to see how to do it discretly and open up a few options. All the app notes make it sound like the only way to do it is with a charge pump+bootstrap.. bah.. as though the extra high side supply is impossible to achieve otherwise. Seems kind of simple to me now, don't even need extra windings around the secondaries.

Regarding the delay, I'm tempted to leave the input/comparator portion powered all the time and use the "enable" as an on switch, with added delay as well, just in case it were ever plugged in turned on, which I've tried a few times with the bootstrap circuit btw, it worked, but yeh it's not very bright.

Hmmm, what if, for the dual regulator version, instead of tying a pull down to VSS I tied it to earth ground? Should have the same effect and it wouldn't introduce any type of balance/offset problem , might also allow the use of a smaller resistor as it would have alot less voltage across it. Would that work ok?

Hi Jaka Racman,

I've found with cadence that error can show up at any time, just a small edit to the schematic, change of a value, wire, even something so simple as scrolling can bring it on. I've had it happen while trying to save, while closing it, while clicking on simulate, it is a very inconsistent error.

Once it locks the file I can open the program up, start a new project, or open other old projects, but trying to open up the one that it crashed with brings up that same error as before and closes the entire program, so there's no schematic editor for it.

While working in schematic editor typically before it crashes like that it starts responding very poorly, almost not at all, so I can usually see the crash comming.

It was interesting to know you get the very same error with a different simulator, perhaps it's not a cadence issue.

All in all I'm still happy with pspice but I won't ever be so ignorant as to not try new things.

I need to spend more time with LTspice eventually, perhaps the next project.

I know Ispice is known to be one of the more accurate simulators out there, and since simetrix uses a different method of simulating, have you compared the two for accuracy at all?

Regards
Chris
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Old 4th October 2004, 07:39 AM   #74
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Hi Chris,
since Ispice is based on Berkley 3F3 (3F4?) engine and Pspice on 2G6 one, I hardly think that problems we are experiencing are due to the simulating engine. Ispice actually consists of different programs for schematic entry and simulating engine and it is best to close one while other is running. ICAPS launcher makes that easy. I can really not compare Simetrix and Ispice at this time, beeing this a one day experience compared to a 10 years one (I started with a DOS version). But I was pleasantly surprised at well thought of user interface and speed of simulation.

Regarding driver, I fully agree with John. I thought that this solution was already implemented, since it is the only logical one. But maybe small diode in series with upper resistor might be in place. Otherwise bootstrap capacitor could discharge through upper resistor when amplifier is driven into clipping. But because of the long time constant that is not strictly necessary.

Best regards,

Jaka Racman
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Old 4th October 2004, 08:04 AM   #75
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Hi,

Why is the bootstrap the only logical one? I think such a simple auxiliary supply is a most viable option.

I'd originally done the H bridge with bootstrap supplies and it simulated really ugly at start up for the first few switches = smoked bridge in reality.

Of course I made no attempt to simulate a delay at turn on, as I knew was required.

Basically, I'm of the train of thought that auxiliary supplies are more robust, and that's what wins it for me.

Aside from having a component or two less, which I don't view as a very big deal, does it have any other advantages?

Thanks
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Old 4th October 2004, 08:45 AM   #76
JohnW is offline JohnW  Hong Kong
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Hi Chris,

Best way to “Mute” the modulator is to switch the current source.

From my neck of the woods – cost is KING! Although nobody has ever called me Cheap when it comes to decoupling caps! – In fact there seems to be some suspicion in the industry that I own stocks in Cap. Companies

John
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Old 4th October 2004, 12:00 PM   #77
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Hi,

Sad news is I won't be able to test the auxiliary supplies as I found another burnt transistor from the first test and it leaves me short.

So I'm taking the transistors from the supplies to patch the rest of the circuit up, and going back to the bootstrap method. I guess at times one extra transistor means alot to me too

I now see the light about tying down to VSS to create a virtual ground, it can only help balance things out. It doesn't simulate worth a darn though but there is no delay in the simulation , I've no problem dismissing spice in this case.

I'll use 10K's though, I'm only working with 15V rails. So I guess I'll have a better bootstrap than I did before.

Anyway I appreciate the help, it's been informative, and I like having options

Cheers
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Old 6th October 2004, 11:04 AM   #78
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Quote:
Originally posted by JohnW
Hi Chris,

I meant to post earlier, but I’ve a had very busy week.

Why don’t you just use a diode from the bottom FET driver supply to form a charge pump to the top supply? Then you only need one transistor. If you are worried about the diode voltage drop, then supply each driver from a diode.

Also, you’re going to need something much bigger for the regulator transistor – something in a TO220 case.

John

Hello,

Just bringing this up now as I was thinking it over, tried a few simulations with it.

Ideally both upper and lower driver voltages would be identical, but you're right with the bootstrap technique there is that extra diode drop. I can't see how adding a diode to the supply of the lower driver helps, it just brings the whole network down by another diode drop. Have I missed something, or is that perhaps a good reason for dual floating supplies?

Thanks
Chris
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Old 6th October 2004, 11:21 AM   #79
JohnW is offline JohnW  Hong Kong
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Hi Chirs,

It just depends where you put your diodes

Don't kick yourself - but something like this

John
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File Type: pdf charge pump etc.pdf (23.4 KB, 402 views)
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Old 6th October 2004, 11:53 AM   #80
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Hi John,

fffffffffffffff..... of course it's going to work if you do it that way


Heh, that's where I put it alright, I however neglected to move the take off for the bootstrap to the right side of it I think, kind of foolish of me.

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