EMCO HV converter not being switched

[GoKid]

HI folks,

Because of space requirements I changed out an existing PSU supplying an FET push-pull driver for a transducer to a Q-Series EMCO HV DC converter (Q05-5). The component is operating correctly but the push-pull network doesn't seem to be switching. My push-pull netowrk uses Int'l Rect. N & P FETs rated for 150v and 200v respectively. The DC conv. output is stable at 140v. What is the problem? I just changed the source voltage to the PP network.

http://www.emcohighvoltage.com/

Thanks in advance

 

[itsmoked]

You have an oscilloscope? What does it show?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[GoKid]

On o-scope the push-pull network output (pre transducer load) is the exact same 40KHz burst as the 5Vpp microprocessor signal used to drive the push-pull network except it is 0.6vpp . It instead should be 140 Vpp.

 

[itsmoked]

I'm not real comfortable with my understanding of your layout. Barring a schematic I can only guess about.

If this system worked fine before you changed supplies have you hooked up the grounds correctly between the 'new supply' and your existing hardware?

You description sounds like you flat have no power going to the FETs.

What does the o-scope show for the FET gate signals?



Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

A couple of other thoughts:

140V output on a 150V FET is marginal - add in a di/dt induced voltage spike and you'll exceed the switch rating. Even if it is working now doesn't guarantee it will last. FET's with a 600V or 800V rating are a commodity item because they're used in mains-fed SMPS designs all over the world, so they don't command much premium in price.

Is this a pure push-pull design or is there some dead time between the two switches? DC bus shoot-through is the usual outcome of pure push-pull.

----------------------------------

I don't suffer from insanity. I enjoy it...

 

[itsmoked]

Very good point Scotty. I thought the 150V was waaaaaay to close to acceptable and was going to mention it but forgot... I swear!!

The output you are stating GoKid is something you might see capacitively coupled through dead FETs.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MacGyverS2000]

I fried one of our boards last week ($15k a pop) by hooking a bad emulator to it. Both 1.8V and 3.3V supplies died, both supplied by the same chip. Our hardware guy replaced the chip several times, but no luck. If a particular pin was unsoldered we saw parts of the board come back up, so I traced it back... the upper FET was fried. Replaced that and all was hunkey dorey.

I'm voting for fried FET on this one...


Dan - Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

What board costs fifteen thousand dollars??

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MacGyverS2000]

It was a 20+ layer VME board... two 'C67xx DSPs, a Virtex2000E FPGA, and numerous other parts. The PCI version is even tighter, I'm amazed at the layout of that board... almost every signal has to jump to another layer the moment it comes out of a chip just to get somewhere.


Dan - Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

Goodness! Sounds like the board we used to make at HP, 24 layers about 24" by 16" all in gold. Was for a mini computer that didn't have an integrated processor. I framed a defective one and hung it on my wall.

I thought you made automotive gizmos Dan? That sounds a little excessive for a dash light controller. Have you ever heard of a 555?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MacGyverS2000]

Automotive gizmos are just my alter ego (i.e., my personal business)... the 8 to 5 thing sees me as an embedded DSP engineer. We make video tracking systems for the military and large commercial venues, I'm currently in the process of porting our current codebase over to TI's DSP/BIOS RTOS. Been highly frustrated the last several weeks... works with the emulator plugged in, but won't boot on its own. I'll get it eventually, I'm sure I'm just missing something simple in the boot code when I transferred over to the RTOS.

Besides, I don't need no stinkin' 555s around here... I use the all-powerful PIC Twice the power at twice the price!

I'm curious to see the OP's comments once he logs back on...


Dan - Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

Thanks Dan. Sounds like fun. Sept when the esoteric tools choke.

I had a National Semi emulator the size of a place mat that was for their 800 series 4bit processors. I designed a temp logger that you could just plug into any printer with a parallel port and would spontaneously print out a formatted sheet of the temp recordings. We were leasing the emulator. One of our techs borrowed the lab supply that was required to run it. (5V)

Without ever telling me, he brought it back, reinstalled it and left.

I came in later and fired it up. It smoked! The tech had set it to 15V for his task.


Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MacGyverS2000]

Yikes. I had been at this job several months when something similar happened (taking out yet another $15k board!). One of our <ahem> previous hardware engineers decided to use a non-keyed power supply plug for the lab setup... hey, HE knew which way it plugged in! Not even a pin 1 marking.

So here I come, be-boppin' along in the lab getting ready to test a board. The plug slides right in, I think nothing of it, and crank 'er up. Why don't I have video? <sniff sniff> Is something burning? Uh-ohhhhhhh.

The head cheese heard about it, walked in and looked it over, said a few things that would make a sailor blush, then started looking for someone to blame. The second cheese in command looked at me, chastised me for plugging it in backwards and claimed it would have to have been forced in to get it in backwards. "Here, I'll show you!", he says, and grabs the plug... as it slid right in backwards with no resistance

The plug was replaced with the next parts order, and for the several days until the new plug came in there was white-out on pin 1 ;-) The following week the hardware engineer was replaced, too.

Dan - Owner

http://www.Hi-TecDesigns.com