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UD2.5 Alternative Comparator

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zzz_julian_zzz

Sun Apr 20 2014, 10:45AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Hi to All,

In the UD 2.5 gave us by Eric (Goodchild Engineering) and Steve ward (thanks to them!) we basically see a TL3116 ultra-fast comparator to provide a square wave output after the RL burden w/c is used to advance the signal that is coming from the CT and from the bridge. Question is, "how fast do we really need the comparator to be used on this application? on its datasheet

its says that the propagation delay is ~10ns. What will happen if we replace this TL3116 comparator to a much slower device like the MCP6562

that has 40ns propagation delay? Will the 30ns difference be a big impact on the performance of the driver? Note that the MCP6562 has only 1 output and requires an inverting buffer (74hc14 that has ~7ns propagation delays) to get the 180 degree shift signal vs the TL3116 which has already two complementary output. I'm asking because in my country we don't have these TL3116 chip, only the MCP6562 are available. This driver is to drive 60n60s full-bridge config and a resonant coil of about 450khz (a QCW) .. will this comparator up to the task?? thanks in advance.

HV Enthusiast

Sun Apr 20 2014, 12:58PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

If you send me your mailing address, I'd be happy to mail you out some free comparators at no charge.

Steve Conner

Mon Apr 21 2014, 08:44AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The phase lead will compensate for delays in the comparator too. 30ns of a difference is negligible compared to turn-on delays in the IGBTs etc.

zzz_julian_zzz

Mon Apr 21 2014, 11:04AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

To EVR:

WOW

Thank you EVR! You are generous indeed!

To Steve Conner:

thanks to you too.. the coil I will be using is resonating at about 450khz (QCW DRSSTC), and the IGBT (FGH40N60SMD) i will be using is also fast, and that has switching speed of td(on)=16ns; trise=28ns; td(off)=120ns; tfall=17ns although these values are in the range of ~25 deg celcius and ~40 Amp load. That's what keeps me worrying on the comparator and other logic delays as well. Plus, the final buffer stage to be used is like this one (below) this was from Dr. KV as an alternate discrete components driver of the P/N output FETS of the original UD2.5... Basically it will be using a small fet to provide 24v from 5v(coming from the logic IC) - (level shifter) to the base of the transistor that will then drive the heavy gates of the P/N fets. hopefully it wont add more delays to the system ;) Do you think?

HV Enthusiast

Mon Apr 21 2014, 12:37PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

No problem. Glad to help out a fellow coiler! Received your PM and address and will mail out the parts today!

Steve Conner

Mon Apr 21 2014, 01:02PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The driver circuit posted will have about 100-200ns of delay.

zzz_julian_zzz

Tue Apr 22 2014, 01:20AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

To Dan:

Thanks Dan, got your message! More power to you and to the coiling community!

Steve Conner wrote ...

The driver circuit posted will have about 100-200ns of delay.

hi Steve, Thank you.. I agree with that, last night i plugged a 250khz square signal on this driver, I'm seeing a ~230ns Time-on delay and the rise&fall time aren't so snappy and square, and then I tried adding a 0.1uf between the two gates of FETS and a diode and pull up resistor to the P channel FET gate, but the result was worse. It made the rise time waveform more "curve" rather than the original circuit.. do you have any other solutions on what I'm experiencing,

OR

All of this worrying about delays, propagation, rise time, fall time of my driver can be compensated by a RL Phase Lead Compensator circuit? Please enlighten me.. Thank you.

Steve Conner

Tue Apr 22 2014, 10:45AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

zzz_julian_zzz wrote ...

All of this worrying about delays, propagation, rise time, fall time of my driver can be compensated by a RL Phase Lead Compensator circuit? Please enlighten me.. Thank you.

Yes! In fact I already pointed this out.

zzz_julian_zzz

Wed Apr 23 2014, 01:20AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Steve Conner wrote ...

Yes! In fact I already pointed this out.

Haha! Thanks for clearing that out Steve

zzz_julian_zzz

Fri May 09 2014, 02:43PM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

hi EVR,

Got your free comparators! Thank you so much! :)

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