Products > Test Equipment
Hantek CC-65 AC/DC Current Probe Teardown and Testing
<< < (24/33) > >>
mickab:
Indeed this is a typo error for the OPA195. ;)

In first place U4 was an OPA2350 but the response wasn't great due to the poor capability of driving capacitive load.
C15 represent the C-Load and is needed for noise attenuation.

Good observations Mechatrommer ;) the OPA2350 can't work at 9V but the regulator of the clamp is set at 7V.
I think we can replace all op amp with OPA2192. This will need some simulation and testing but it is possible. ;)
Tell me if you're interested.  :D
Mechatrommer:

--- Quote from: mickab on November 14, 2020, 08:51:27 am ---In first place U4 was an OPA2350 but the response wasn't great due to the poor capability of driving capacitive load.
C15 represent the C-Load and is needed for noise attenuation.

--- End quote ---
but there is R18 1Kohm separating them. this is a bit surprise for me. maybe i will figure out how to reduce noise from that output later.


--- Quote from: mickab on November 14, 2020, 08:51:27 am ---Good observations Mechatrommer ;) the OPA2350 can't work at 9V but the regulator of the clamp is set at 7V.
I think we can replace all op amp with OPA2192. This will need some simulation and testing but it is possible. ;)
Tell me if you're interested.  :D

--- End quote ---
yes interested. as i'm going to order some parts from lcsc, i will add few parts for this mod as well (save shipping cost). but i can only find OPA2350 and another opamp that can get supply from ±12V, but 15MHz GBW only, i wont name it as its limited supply so i dont want somebody to outrun me  >:D (its 2-3X the OPA2350 price anyway) if really the bottleneck is in opamp BW, i'm suspecting U3 will need high BW since its in sort of high gain differential (instrumentation) mode from schematics you guys provided. i cant figure out what gain, but lets say gain 10, OPA2350 38MHz GBW still can give 3MHz+ BW, so i think its a wise choice. where the rest of opamps are mostly for Voffset correction i guess. if my eye and mind is correct U4-1 is only gain 4 differencing opamp, so 15MHz GBW opamp still can give 15/4 = 3MHz+ BW. unfortunately, i cant make order for OPA2192 since lcsc doesnt stock this opamp, i will try with whats available in lcsc first. ordering separately from digikey for this particular mod will result in shipping cost damage on my side. cheers.
mawyatt:

--- Quote from: mickab on November 11, 2020, 03:21:32 am ---Hello,

I'm currently searching a solution to increase the bandwidth of the clamp. The hall effect sensor seems to response up to 3MHz but the mod is design for +/- 1Mhz (Power supply design)
My first glance on this topic was very helpful. ;D

I have simulated the signal conditioning stage of the hall-effect sensor on Spice with a rudimentary model. An OPA2350 is used for U3 (high speed, low noise, single supply...) and a OPA2192 (high C-Load capacity) for the output stage.
The simulation is based on the schematic "cc-65-CLAMP.pdf" wich seems right except the capacitor value. I correct some cap value with few measurements. The correction is into the .pdf.

Push to the limit we can obtain 2.3MHz with +/- 170° phase shift and -3dB (see picture)

I will make a comparison soon with a new clamp vs modified.  ;)

--- End quote ---

Interesting modifications, thanks for posting. I have a couple questions:

1) Since R18 isolates the output capacitance due to the load, is the added 22pf is to help stabilize U4-1?

2) Shouldn't another 22pf like capacitor be added across R20 to balance the differential amplifier?

3) With R18 isolating the capacitive loading to U4-1, then just about any good op-amp can be used that has rail to rail I/O at +- 3V rails and sufficient BW. The 22pf added capacitance may need to be changed depending on the op-amp selected.

4) With the leakage in C4 and R269 bleed resistor, wonder if another type cap and larger resistor value could work? Or removing R269 and placing back to back low leakage diodes (CB junction of bipolar) might work better drift-wise? If the drift is dominated by the Hall Effect sensor then this wouldn't matter.

5) What did you find in relative BW before and after the mods, maybe you could post images showing such if it's not too much trouble?

Anyway, great work and many thanks for showing :-+

Best,
masterx81:
Bought one of this, as soon as it arrives, i'll do the mods. Thanks for sharing! Nice result!
I've readed on other threads that this clamp have a lot of noise, but i see only ~1mv of noise (around 10ma), seem quite good.
maxspb69:
Today I made all the modifications exactly according to the mickab 's description. The result is in the pictures below.

  1 - original device,
2 - modified device.

Test conditions: 6Vp-p amp, 50Ω load, 3 turns of wire on  hantek cc-65.

The band has expanded to up to 2.4MHz (-3dB).
If only to remove the amplitude jumps in the 1.0-2.5MHz range, the frequency response would be generally very beautiful! But this jumps within 1db are quite acceptable, I think...

(I think I can save a lot on the Micsig CP2100B current probe purchase  ;)) 

Thank a lot for the detailed instructions!
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod