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After much pulling of hair I realized my circuit didn't work because my signal generator was capacitor coupled.
I need the measurement to be AC coupled OR reject any DC that the signal may be riding on. How can I accomplish this ?
I agree with FvM that a large value cap across the 10M is better than a resistive shunt. If you need capacitive coupled measurements (reject DC) then this approach is good.
It's also a good idea to put a fast clamp (low leakage) or a simple RC to slow down transients. Your frequency is fixed...
Thanks for all the suggestions. I ended up using a primary oscillator (555 type) to operate a mosfet switch on the XFMR primary so I can pick the frequency. This made things a lot more straight forward and the application is working so far.
Thanks again all...
Thank you both for the response. Out of curiosity I threw a large (2uF) cap from B to E and the result was a fairly sharp high amplitude square wave at about 200Hz. I was excited till the secondary opened up. Good thing I have a box of these transformers.
I was going for very low parts count...
I would like to slow this circuit down to about 1-2KHz. At present it's about 38KHz with the transformer I have.
Is there a simple way to do this with a single capacitor ?
Are you certain the other cap isn't charging with a slope ? Perhaps looking at the waveform with more horizontal resolution will show whats going on. Every sharp edged pulse I have seen have some slope to it, just might be faster than your equipment. Unless your simulating this with Spice...
Ok, not so confused anymore... They must tie together via the supply GND of the difference amps. I'm guessing a classic diff amp with 4 resistors on front end acting as a divider to the diff inputs. These would all tie to op amp grounds via the non feedback resistors (if that makes sense)...
Rise time usually refers to the time is takes to go from 10% to 90% of peak voltage (assuming little overshoot). Probably not that important for your problem unless you have multiple gates that depend on accurate timing between each other.
If your looking for a specific terminology used in...
I have an instrument with (3) 2 terminal inputs. Each labeled U- U+ (3 channels)
All inputs measure 4 megohms and any terminal measures 4 megohms between.
With meter across chan 1 (U- U+) and I short chan 1 U- to chan 2 U- resistance drops to 3 megohms.
When I additionally short all U-...
Thank you for all the great information and suggestions.. I did fix the problem and it was not the capacitor.. I had wrongly put a series
current limiting resistor in series with the IRF540 gate. Once I lowered this the circuit worked great... Woops..
Thanks for the explanation LvW - The datasheet was very clear that I needed the range of ESR but I did not listen. It also recommends using a resistor in series to account for a low ESR part.
I'm still not entirely certain it failed due to low ESR cap but I'm replace and try again. Betwixt you...
I'm using the LM2941 with the recommended minimum 22uF. Datasheet says the the ESR is critical (.01-5ohms).
I used a tantalum and used no resistance in series and the regulator died (After much use though) Seems the 1.27V reff is now .9V
My question: Why is this value so critical and how do I...
Well so far I can't make this "probe" flat past 8 or 9MHz.. Perhaps the series resistance (277 OHM) is too high. Critically damped ? I have not inserted any inductance yet as suggested by the excellent document FvM linked - Great stuff thanks.. I'm uneasy about a discreet inductor as I need...
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