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Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Aragorn wrote ...
Ah fair enough, that makes sense.
Though I'm sure i've seen single gate drive transformers wound with ethernet cable driving a full bridge in my browsing/researching (needless to say i cant find it again!)?
Does it depend on the drive current requirements of the IGBT used?
Yes, individuals do it both ways.
It will depend on the IGBTs / MOSFETs being used (i.e. how much gate load there is), the ferrite core being used, as well as the switching frequency and voltage.
Having two output channels just provides that much more flexibility.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Aragorn wrote ...
Ah fair enough, that makes sense.
Though I'm sure i've seen single gate drive transformers wound with ethernet cable driving a full bridge in my browsing/researching (needless to say i cant find it again!)?
Does it depend on the drive current requirements of the IGBT used?
Yes you are correct, you can also parallel the driver sections on a single GDT (two primaries). I did this on my large DRSSTC when I was using a single DRSSTC to drive 4 CM600s
Registered Member #22717
Joined: Thu Jun 06 2013, 11:37AM
Location: Upstate NY
Posts: 3
In testing my UD2.5 build I experienced a number of failures of the 9V regulator. I'm still a bit uncertain as to why I was having failures, but C1 had a cold solder joint and was not connected and may very well have been the issue allowing unfiltered AC to "kill" 9V the regulator. This in turn caused the 9V regulator to fail shorted and pass 24V+ into the driver... BANG!
In the process of testing I used all of the available 9V regulators. So I looked more closely at the parts on the 9V buss. Here's where the question comes in. Why is a 9V regulator used? All of the parts can tolerate 15V or more. Given that I have access to 12V regulators at work I elected to make the substitution.
Here's my reasoning as to why the 12V part might be more a more suitable choice. The delta V between the AC supply and 12V is smaller hence less heating due to power dissipation. The 12V part barely gets warm (I have a good sized heat sink on the 3 regulators) compared to the 9V part.
Any thoughts? Am I missing anything.
I haven't yet tested with the secondary in place, I have done my testing at work so far and I did not want to be sending all sorts of RF into the mains if something went wrong.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
I bet that you are using the fairchild Vregs. Chances are you are also not using a 20Vac transformer.
What is probably happening is that you are exceeding the Vreg input voltage on the 9V reg and that is why you are killing them. The voltage ceiling on the fairchild regs (for regs under 15V) is typically 30V.
The 5V is protected behind the 9V and the 24V is usually rated up to 35V or 40V.
Switching from a 9V to a 12V is not a bad idea to help with thermal performance because of the lower dV, matter in fact I like that idea a lot and intend to give it a try myself. However it will not fix your exploding Vreg issue because the 12V regs still have the same max voltage ceiling as the 9V regs.
Find your self a 20Vac xformer (20Vac * 1.414 = ~28Vdc) Just below the ceiling for the regs but still able to supply 24V. Chances are you are probably using a 25Vac (~35Vdc)
Good call on the 12V reg I may just add that into the next revision! From my initial check I don't see any issue with switching it out and getting some better performance. It should be a drop in replacement from the 9Vreg.
Best Regards, Eric
P.S. I have had the same issue as you in the past with the older UD2.0 Good luck on the fix!
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
teravolt wrote ...
just turn the regulators around 90 deg so you can mount a heat sync to them if needed
The regs are already turned 90, and as I said the issue is not heating, it's overvoltage on the input. This particular failure is also very common with fairchild Vregs.
Registered Member #22717
Joined: Thu Jun 06 2013, 11:37AM
Location: Upstate NY
Posts: 3
Goodchild wrote ...
I bet that you are using the fairchild Vregs. Chances are you are also not using a 20Vac transformer.
20 VAC flat pack toroidal transformer (if18-20), measured AC output unloaded at 24.5V. DC input to the 9V regulator was 26.5VDC with the transformer loaded at 350mA which was the measured draw from the UD2.5 on a DC supply. The whole circuit was tested and working correctly on a DC supply prior to putting the transformer in.
It looks like the fairchild Reg was the issue. I looked through all our designs at work, we don't use a single fairchild Reg in any of our circuits, that might be why!
The 12V part I'm using now has a 35V max Vin so life should be good from here. As a fix I had considered splitting the input feed to the 9V regulator and using one half of the transformer output. I didn't want to hack up the board to do that, plus working with a known good design also meant I was probably "doing something wrong".
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
What you say about Fairchild may be correct but the dissipation of those regs are about 1 or 2 watts with out a heat sync so when a stranger connects them to there transformer they may think it is ok to connect them to the 20vac transformer. First of all 20vac is 20/.707=28.28vdc at the capacitor with no load and with about 26 with a load. second of all as jmorlockny states all transformers were not born alike. I have had some of those 20vac transformers up to 25vac and if you do the math it probably will exceeded most specs.
I had the same problem generating the 20vdc for my drivers and I fixed it with a simple peace of bent aluminum. I am not trying to read you a sermon I just think they should be more robust for less experienced builders outside the laboratory.
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Universal DRSSTC Driver V2.5 (Sold Out)
