HELP Choosing a design for first digital PI build

[eduardo1979]

Yes, this indicates that my assumption that overvoltage is the cause of the white smoke on the BSS139 is correct.

You were right.

[eduardo1979]

I got it to work using DN3535 mosfets. My circuit uses a 180v snubber circuit, so the assumption of overvoltage is probably correct. The transistors were running warm. This blocker circuit works the best out of the ones that I have used. By the way ML didn't invent this current limiter. See fig4 in attached pdf. Photos of the add on blocker pcb and scope shot.

Hi Altra. Could you please attach the diagram again, as the PDF file you're referring to doesn't exist?

[Altra]

Hi Eduardo, I can see the pdf in my post. I have had problems with attachments on the forum lately. Here it is again

[eduardo1979]

Hi Altra. Now it works.
Thank you very much.

[Altra]

This is the test circuit with snubber

[algan]

Thank you, Altra, I'm thinking of testing it on Surf Master to see how it will work, and according to your tests, is the signal felt deeper with this circuit than with the resistor, and how much, for example, for a coin with a 28 cm mono antenna?

[Altra]

Hello, I have no idea how deep your detector will go with changes. My experience is earlier sampling and a quieter pre-amp. Good for low conductivity targets. For high conductor coins it may not show much improvement.?

[eduardo1979]

Thank you, Altra, I'm thinking of testing it on Surf Master to see how it will work, and according to your tests, is the signal felt deeper with this circuit than with the resistor, and how much, for example, for a coin with a 28 cm mono antenna?

Here's the variant for P-type and N-type MOSFETs. It's a schematic that Altra published a while ago.
That can help if you want to reduce the voltage to 180V and avoid overheating the MOSFET.

[algan]

Here's the variant for P-type and N-type MOSFETs. It's a schematic that Altra published a while ago.
That can help if you want to reduce the voltage to 180V and avoid overheating the MOSFET.

Thanks eduardo1979 I haven't tested snubber yet, it will be interesting to see what the result is.

[eduardo1979]

Hi Altra.
I have two questions about the snubbers shown in the two attached files. Which one is correct? I see that in one case, the 47uF capacitor is connected to GND (B+), and in the other, it's connected to B-. I also notice that in one case, the snubber is in parallel with the MOSFET, and in the other, it's in parallel with the inductor. Could you clarify these points for me, please?
Regards.

[Altra]

Hi Altra.
I have two questions about the snubbers shown in the two attached files. Which one is correct? I see that in one case, the 47uF capacitor is connected to GND (B+), and in the other, it's connected to B-. I also notice that in one case, the snubber is in parallel with the MOSFET, and in the other, it's in parallel with the inductor. Could you clarify these points for me, please?
Regards.

Hello Eduardo, it will work either way. But the correct connection would be across the coil or snubber connected to coil ground. This goes for the P or N configuration.

[eduardo1979]

Okay. Thank you very much for the clarification.