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Picotest Injector Teardowns

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16bitanalogue:

--- Quote from: Jay_Diddy_B on April 12, 2020, 10:58:48 am ---
--- Quote from: 16bitanalogue on April 10, 2020, 08:10:18 pm ---Picotest J2112A High Current Injector
Price: $1,995
BOM:
I will need to go back and measure the components. I lost that information. It is also difficult to see the part number on the SOIC8 - I want to recall it was an op-amp of some kind.



--- End quote ---

The pictures that were included are actually the J2111A

I was having difficulty getting the component values, that I can read in the photograph, in the model agree with the datasheet performance.



--- End quote ---

Oops! I couldn't remember which version since it has been several months. The performance is really close to the datasheet, so I would move forward with what you have. In the future, I can update with actual measured values and track down the op-amp that is being used. It may be moot, but I'll be happy to do it.

According to the User's Manual for the Signal Injectors, the J2111A is bi-directional; i.e., it can only SINK current up to 100mA with positive and negative voltages. Where as the J2112A can SINK up to 1A with positive voltages only.

16bitanalogue:

--- Quote from: Jay_Diddy_B on April 12, 2020, 04:30:16 pm ---

The board is 100mm x 100mm

The plan is to use Keystone 575-4 for the connections.

Comments?

Jay_Diddy_B

--- End quote ---

I am personally partial to Keystone 7006 and 7007, but for low cost purposes the 575-4 are good.

2-layer, FR4, 1oz copper top pour.

Wolfgang:

--- Quote from: 16bitanalogue on April 12, 2020, 10:14:17 pm ---
--- Quote from: Jay_Diddy_B on April 12, 2020, 10:58:48 am ---
--- Quote from: 16bitanalogue on April 10, 2020, 08:10:18 pm ---Picotest J2112A High Current Injector
Price: $1,995
BOM:
I will need to go back and measure the components. I lost that information. It is also difficult to see the part number on the SOIC8 - I want to recall it was an op-amp of some kind.



--- End quote ---

The pictures that were included are actually the J2111A

I was having difficulty getting the component values, that I can read in the photograph, in the model agree with the datasheet performance.



--- End quote ---

Oops! I couldn't remember which version since it has been several months. The performance is really close to the datasheet, so I would move forward with what you have. In the future, I can update with actual measured values and track down the op-amp that is being used. It may be moot, but I'll be happy to do it.

According to the User's Manual for the Signal Injectors, the J2111A is bi-directional; i.e., it can only SINK current up to 100mA with positive and negative voltages. Where as the J2112A can SINK up to 1A with positive voltages only.

--- End quote ---

When trying to build your own, watch for two pitfalls:

- The part has a dead zone at small voltages where the current drawn is completely incorrrect, even if the sense resistor says its OK.
- Have a look at the transistor datasheets. They will die if you draw max. current (dynamic plus offset) at 40V. If you want to keep
  this spec, you need better transistors and better cooling.

Jay_Diddy_B:

--- Quote from: Wolfgang on April 13, 2020, 12:13:11 am ---When trying to build your own, watch for two pitfalls:

- The part has a dead zone at small voltages where the current drawn is completely incorrrect, even if the sense resistor says its OK.
- Have a look at the transistor datasheets. They will die if you draw max. current (dynamic plus offset) at 40V. If you want to keep
  this spec, you need better transistors and better cooling.



--- End quote ---

Wolfgang,

Thank you for the guidance. The cooling for the transistors is certainly inadequate for 3W of dissipation.


And yes there is a dead band where the devices doesn't work properly.



My interest in building these is to find out what they can do.


Regards,
Jay_Diddy_B

Jay_Diddy_B:
Hi,

Further to my last reply, the manual that can be found here:

https://www.picotest.com/support.html

On page 44 it says the maximum input voltage is DC +  AC is 5V

5V x 74mA = 375mW

This is consistent with the transistor selection and mounting method.

Regards,
Jay_Diddy_B

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