EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: KOR on October 31, 2021, 12:12:50 pm
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I got the schematic of the attached sensing cirquit. I know that from Vout+ high current pulses with multiple kHz frequencys are comming the connector is a bnc connector.
But overall my limited knowledge about electronics just can't figure out why a high pulsing current path is cut open and a tiny 0805 1k resistor is put in its way. The PCB trace which is blocked by the resistor is 60 mil.
Sry I don't have much more information other than it is a sensing cirquit of a EDM spark generator.
Thank you for your help.
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There is most likely a heavy-duty low-value resistor across R34 that actually measures the current through the electrode. The 1 K SMT resistor is likely there to do something sensible if the wires to the current sense resistor go open.
Jon
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after checking all the traces and finding none I measured the little bugger it is 0.1Ohm. (Silkscreen says 1k) So I guess it is a current sensing resistor. It still seems to me pretty high in value since such a tiny resistor can't be more than 0.5W which would be 2.2A at most. Ok it is a pulsed current so one could probably drive it with a higher current but still it seems way to weak.
I am still completly confused what this cirquit actually does. Is there a way to simulate the cirquit So I can find out what is actually happening? Or can someone explain it to me like I am a five year old :)
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Current sensing on the high side, the transistors are there to make a current mirror, turning the voltage drop across the sense resistor R34 into a current, which is converted to a voltage proportional to the current in R37. the capacitor is there to filter out noise, and the current generated is, to a large part, independant of the actual applied voltage, so the measured value is current only.
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after checking all the traces and finding none I measured the little bugger it is 0.1Ohm. (Silkscreen says 1k) So I guess it is a current sensing resistor. It still seems to me pretty high in value since such a tiny resistor can't be more than 0.5W which would be 2.2A at most. Ok it is a pulsed current so one could probably drive it with a higher current but still it seems way to weak.
I am still completly confused what this cirquit actually does. Is there a way to simulate the cirquit So I can find out what is actually happening? Or can someone explain it to me like I am a five year old :)
Measuring low-value resistors is very hard. Most meters are good to +/- a couple Ohms at best.
And, in-circuit, even less accurate.
Is this wire EDM or sinker? Wire EDM runs at much lower current.
Jon
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Thank you guys. I know that it is hard to measure low values of resistance thats why i desoldered the resistor. :)
@jon: it is a sinker.