felezjoo PI(the best pulse induction metal detector that I made until now)

[Detectorist#1]

Hi Aadu,
Number 1 haves too big Coss and maybe too big Cgs.
Number 3 haves too big Rds.
Number 2 is more suitable - use it for this project. For this transistor no need for additional diode in the drain.

[Aadu]

Thank you very much for the informative answer. I have three options to choose from, which are very different.
1.mosfet 60r360q 600v, Coss 715pf, tr 41ns, Rds 0.36, qg 19nc.
2.mosfet SDP 7NA40 400V, Coss 120pf, tr75ns, Rds 0.82, qg 34nc.
3.mosfet KNB2D0N60D 600v, Coss 46pf, tr 60ns, Rds 3.8, qg 10.9nc.
Which one is better?

[Detectorist#1]

Yes, these parameters affects the detector but N-ch MOSFETs with Uds=500V and Id =5A to 8A have very similar Rds and Coss parameters. Parameter trr of MOSFETs is less than 100ns and no problem for PI designs.

ST - IRF840_Uds=500V_Id=8A_Rds=0.85R_Coss=131pF at 25V_TO-220
Vishay - IRF840_Uds=500V_Id=8A_Rds=0.85R_Coss=155pF at 25V_TO-220
Infineon - IPA50R800CE_Uds=500V_Id=7.6A_Rds=0.72R_Coss=250pF at 25V_TO-220
ST - STP9NK50Z_Uds=500V_Id=7.2A_Rds=0.72R_Coss=125pF_TO-220

Also, it is easy to reduce the influence of Coss by serially connecting on the DRAIN of MOSFET diode like MR260 or MUR460 (any fast diode with Trr<70ns, U>500V and I>2A)

[Aadu]

Mosfets has different Rds, Coss, tr. Do these parameters affect the detector

[Detectorist#1]

Hi Aadu,
Any 500V N-ch MOSFET for 5A to 8A drain current in TO-220 case is suitable for this project.

[Aadu]

Hello. Does anyone know which mosfet parameters are best for felezjoo. I don't have the original irf 840

[van0014]

Yes, 3.2v and 3.7v are common average voltages. In practice, you should be getting 4.2v per cell fully charged, and 3v per cell empty. Though some datasheets suggest 2.5v empty, I won’t advise it. They also don’t like to be fully charged, and shouldn’t be left above 4v unless you’re ready to use them. I’ve gone through many batteries, and looked into ways to increase their life

[Tanrjrj]

18650 cells usually range from 3v - 4.2v, or as low as 2.5v. Their average or nominal voltage is the 3.2v value, but it’s usually higher when it’s fully charged. But note that the voltage can’t accurately tell you how much charge the cell has

Hi van, maybe because there are two types of battery one is with 3.2v and 3.7v thanks for your idea

[van0014]

Hi you say 18650 in 3.2v each that would only be at 9.6v

18650 cells usually range from 3v - 4.2v, or as low as 2.5v. Their average or nominal voltage is the 3.2v value, but it’s usually higher when it’s fully charged. But note that the voltage can’t accurately tell you how much charge the cell has

[Tanrjrj]

Hi all,,,,,I don't know if this will help anyone but I have 2 x working Felezjoo's and for both I use 3 x 18650 batteries with a DC Adjustable XL6009 Step up step down converter and they work fine and give me about 6 hours detecting time. The 3 x 18650 give me 12v but I adjust the step up converter to 18v and it's been fine,,,no overheating or any other problems. Hope it helps someone. Marty

Hi you say 18650 in 3.2v each that would only be at 9.6v

[van0014]

A suitable replacement alternative is TLE2071A

[Emersonpaz]

I also made this metal detector. I can't get Lf357 anywhere here. I soldered Lm318 to test and it works poorly. But where to order an original Lf357 op-amp when there are so many fakes on the market?

https://www.aliexpress.com/item/4001274026922.html?spm=a2g0o.store_pc_allItems_or_groupList.0.0.357f7416zvilKc&pdp_npi=4%40dis%21BRL%21R%24%2046%2C00%21R%24%2045%2C50%21%21%217.92%217.83%21%402101c67a17498143139257594eedf2%2110000015562416596%21sh%21BR%210%21X&_gl=1*64dzr0*_gcl_aw*R0NMLjE3NDk4MTQxMTYuRUFJYUlRb2JDaE1JOXFlY3dxWHVqUU1WVjFCSUFCMFJuQ3RQRUFBWUFTQUFFZ0pkel9EX0J3RQ..*_gcl_au*NTkxNzUwOTQ4LjE3NDk4MTQxMDk.*_ga*NTU3NDUxMjQuMTc0OTgxNDExMA..*_ga_VED1YSGNC7*czE3NDk4MTQxMDkkbzEkZzEkdDE3NDk4MTQzMjYkajE3JGwwJGgw

[kipi]

I also made this metal detector. I can't get Lf357 anywhere here. I soldered Lm318 to test and it works poorly. But where to order an original Lf357 op-amp when there are so many fakes on the market?

[mmlove2007]

[Boadil]

The versatility of the circuit is incredible, and how we can make changes to how it works just by modifying the chip's program...it's a shame we don't have the source code to tweak things.