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Regarding Current and Voltage Sensing for Micro-EDM Application

Mayank Srivastava
Prodigy 40 points
Other Parts Discussed in Thread: DRV421, DRV425, AMC1100, TIDA-00795, INA300, INA168, INA138

My application is intended towards drilling holes by the help of Spark (it is known as Electric Discharge Machining). I am using DC Power Supply of 300V, 10A range and the -ve terminal of which I am switching using MOSFET circuit, which then gets connected to the tool and workpiece is connected to +ve terminal of a power supply. As soon as we bring the two electrodes (tool & workpiece) close to each other, sparks occurs. So I need to sense the current and voltage that changes during spark / short circuit, using some Sensing Modules having voltage and current range we have.

Kindly suggest the better solution.

Also i need to buy better Switching MOSFET Modules which can switch high DC Voltages upto 300V upto 1 microsecond or even better.  

Also, Protection Circuits for this application, to prevent high flow of current during Short-circuiting and Arcing, which may protect other electronic elements from getting damaged; also needs to be placed.

  • 0
    TI__Genius 14825 points

    Mayank,

    Are you saying that you will see very fast transients up to 300V when you activate the FET?  Our shunt based solutions currently only go up to around 80V in high side configuration, so you would be limited to a low side configuration where the shunt is placed between the load and ground.  Would this work for you?

    There are other options, the AMC1100 isolated amplifier will support a shunt solution up to 300V (or more), and we also have some magnetic sensing options that are isolated as well (DRV421 and DRV425, for example).

    This application looks to me very much like an arc welding application, so maybe you could gain some insight from our welding system design web pages.  This may help answer your other questions about MOSFETs and protection circuits.  Let us know if that doesn't help you so we can find the right material to get you going, or hook you up with the right people to help you with your design.

  • 0 in reply to Jason Bridgmon
    Prodigy 40 points

    Hi Jason

    In our application, we are not looking for any isolated amplifier or shunt based IC. Actually, we are using MOSFETs as a switch. SO our basic concern is that while sparking ,sometimes tool and workpiece come in contact with each other causing short problem. So in that case, the current will rise and voltage drop will be there. So how to handle this problem as increase in current is damaging the MOSFET.

     Thus we need to measure / sense the current and voltage too during the case of sparking & shorting, which can handle values of upto 300V.

  • 0 in reply to Mayank Srivastava
    TI__Genius 14825 points
    Mayank,
    So you need some kind of protection IC or circuit to protect the FETs, like an e-fuse? Have you taken a look at TIDA-00795 which uses the INA300 in a shunt-based setup to be a resettable trip switch?
  • 0 in reply to Jason Bridgmon
    TI__Expert 5705 points

    Hello Mayank,

    Correct me if I've misinterpreted your description but I think the attached circuit will help you monitor both the wide-band current and voltage signals at the output of your 300V source.

    The current sense circuit is described in detail in this application note. The INA138 or INA168 can be used in this circuit for their high bandwidths (800kHz typical in gain of 1 configuration) and should get you close to your target requirement.

    For voltage measurement you will have to attenuate the common-mode signal to fit within the input CM range of the op amp that you select. We have a wide range of op amps suitable for various supply voltage constraints. So what other supply voltages does your system have besides the 300V supply?

    Best Regards,

    Harsha

  • 0 in reply to Harsha Munikoti
    TI__Expert 5705 points

    Hi Mayank,

    Just wanted to check back with you on whether you were able to find a solution to your problem. We are here to help if you need further support.

    Best Regards,

    Harsha