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  • Users: Kepco
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  1. Kepco

    Cantilever beam reinforcement question

    Hi, While doing some work around the building to repair dry rot we came across this beam that was sandwiched between 1 1/8 ply board and bolted together to the beam. After we took the ply out we noticed the cantilver part of beam was held by only the plyboard and bolts. My contractor put these...
  2. Kepco

    USB 2.0 Strange Signal Issue

    Thanks VEIBLL and IRstuff. You guys are certainly correct on the point that this a grounding issue. But let me first answer the questions. How long is the cable (shown on the right side)? (K) The cable is 6 feet long. Are there other power or signal wires contained in the same cable? (K)...
  3. Kepco

    USB 2.0 Strange Signal Issue

    Hi, We are working with a USB2.0 design that has attached circuit block diagram. The USB2.0 is working intermittently. USB 1.0 works fine. We have ruled out a few things now. We are doing eye pattern under various scenarios and trying to see what is causing the issue. We are reading eye pattern...
  4. Kepco

    HDMI redriver circuit

    Thanks iop95 for your comments. See response below. What is bandwidth of scope used to see U3 output? (We are using the 2GHz scope. The signal frequency is 742MHz. It is not ideal but it is good enough to show input side eye diagram on U3. Those are very clean eye patterns.) Why used 16V cap...
  5. Kepco

    HDMI redriver circuit

    Hi , Attached is an HDMI (1.485gbps) redriver/retimer circuit. It takes in DP++(DDI) input and produces HDMI signals going to connector. We are trying to troubleshoot this circuit. We are seeing some lines on the monitor. When scoped the output HDMI signal is about 3Vpp. This voltage should not...
  6. Kepco

    Reverse Polarity Protection

    Transient protection is Vicor's recommendation. The bridge is what they are recommending for reverse polarity protection. But the voltage loss/power loss in the bridge is not desirable. The MOSFET needed for this job needs to handle only 100V and this fit the budget from all the specs needed...
  7. Kepco

    Reverse Polarity Protection

    Guys, Can you comment on the downside of the attached circuit comparing to other methods of reverse polarity protection? I do not want to use bridge or diode for power dissipation reasons ( parallel reverse bias diode will blow the fuse so that is also not an option). This circuit will see...
  8. Kepco

    Zeroization implementation

    Very good points. Unfortunately this system has an embedded OS. The system power source should have battery back up in case power is out to implement this feature. Thanks.
  9. Kepco

    Zeroization implementation

    This could be an option. The Zeroization pin on a system board connector when detected by the software as grounded, all the software stored in the flash memory of the system is wiped off. Thx for the input.
  10. Kepco

    Zeroization implementation

    Hi Guys, What will be the best way to provide Zeroization option for a system without using an external (Covered) switch? Zeroization pin when grounded clears all the software on the system. Some systems have implementation that takes external 12V pulse with isolated GND to trigger the internal...
  11. Kepco

    Strange Voltage Drop

    "reduce R6325 and R6326 by minim a order. " This was it. Changing the divider current to 1mA did the trick. Original value was 1.5uA then changed to 5uA with not difference. So new values of U6325=3.3K and U6326=1K provides current of 1.2mA and it worked. Thanks a lot iop995 and all who took...
  12. Kepco

    Strange Voltage Drop

    Hi Guys, Here is a circuit that is two part. Top part is 48V ( Telecom -48V) monitoring circuit. This circuit converts 48V to a low isolated voltage (~1.6V) 48V_MNTR. Also the 12V that power U26 is from same 48V going through a DC to DC (48V,4.5A to 12V) converter. Bottom part is a 15V...
  13. Kepco

    AC mains circuit : safety related question

    Thanks Dave. I will try going through 60950 again to see I find something directly related. I have posted this thread link on UL forum also.
  14. Kepco

    UL60950 Related Question

    Hi Folks, I am reposing this thread from Circuit Design . Can anybody with UL expertise comment on this? http://www.eng-tips.com/viewthread.cfm?qid=341737 Thanks
  15. Kepco

    AC mains circuit : safety related question

    The attached example circuit from UL safety rated fuse resistor app note shows UL rated fuse and a regular resistor ( I believe) and replaced with one UL rated fuse/resistor as shown. Is this assumption correct that a regular resistor with UL fuse will be...
  16. Kepco

    AC mains circuit : safety related question

    Thanks for the response. Yes, this is a power monitoring circuit interfaced to a micro to monitor the AC input. You are correct that UL is about fire and safety and therefore thought of isolation between primary and secondary circuits might be important. A user might come in contact with...
  17. Kepco

    AC mains circuit : safety related question

    Hi Folks, In the attached application note figure 12 - Page 7, is there a need to select a safety approved (UL) resistor Rx/2 for any type of safety certification purposes? The IC HCPL-3700 is already providing safety rated optical isolation between 110/220V mains input and 5V logic output. Any...
  18. Kepco

    Simple Redundant AC Input Circuit Issue

    Skogsgurra,can you shed some light on using relay interlocking with a work around to the arcing? The switchover time cannot exceed the hold time of the PSUs, which is 20ms. The current relay has 20ms max make time and 10ms max break time. Also the neutral on top source and bottom source may not...
  19. Kepco

    Simple Redundant AC Input Circuit Issue

    Excellent suggestion regarding arcing. There is a big pop when this happens confirming that belief. Using a three pole does not solve the problem because it seems that the arc create a short of long enough duration when breaking from AC1 to PSUs that when PSUs connects to AC2 by second pole...
  20. Kepco

    Simple Redundant AC Input Circuit Issue

    That was absolutely correct. I screwed up on the setting of the probe. Now, the probe is 100A max and I am measuring about 300A and then the probe saturates. So I guess now the reason why the fuse is blowing can be seen on the scope shot as attached. CH1 being AC1=208V CH2=208V and CH3=AC1 line...

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