Mosfet reverse polarity, voltage drop down

[baloubass]

Hello guys, i'm trying to design a power filtering with a reverse polarity protection using a mosfet as the old and very good RG article.

Mosfet:
https://www.infineon.com/dgdl/irfr9024npbf.pdf?fileId=5546d462533600a401535635f91d2132

For the test i make a veroboard and use a reverb circuit based on the btdr3h.

-Output power supply voltage: 9.42v.
-Voltage at V+ and VB+ with anything connected: 9.42V
-Voltage at V+ and VB+ with the circuit connected: 8.05v

1)Does anyone can explain me why the voltage down at 8.05v please?
2)Does this voltage down can affect the circuit operation?
3)Do you gus have a suggestion to not have this voltage loss?
Thank you so much.

[antonis]

Μπαλούμπα, nobody biases either p or n channel  MosFet with its Gate to GND in case of he wish for low R_D(on)..

[baloubass]

Μπαλούμπα, nobody biases either p or n channel  MosFet with its Gate to GND in case of he wish for low R_D(on)..

Bad english sorry, van you explain please?

[antonis]

Μπαλούμπα, nobody biases either p or n channel  MosFet with its Gate to GND in case of he wish for low R_D(on)..

Bad english sorry, van you explain please?

Bad quote too..

Anyway, a p-channel MosFet needs a negative Gate-Source voltage bias to work in its "saturation" (no channel variable resistance) region..

[R.G.]

In your schematic, the drain and source of the mosfet are reversed from what they should be.

[baloubass]

In your schematic, the drain and source of the mosfet are reversed from what they should be.

Ok i have mirror it in fact?

[baloubass]

[/quote]
Bad quote too..

Anyway, a p-channel MosFet needs a negative Gate-Source voltage bias to work in its "saturation" (no channel variable resistance) region..
[/quote]
😂😂 French T9 to write in english not help me.
What i have to do? Apply a voltage on the gate viaba resistor ?

[antonis]

Maybe, by declaring your nationality, some forum member could help you in written..

[baloubass]

Maybe, by declaring your nationality, some forum member could help you in written..

Done, and what i have to do, apply a voltage via a voltage divider

[antonis]

Do what R.G. noticed..
> the drain and source of the mosfet are reversed from what they should be.<

Drain should face R4 & Source face +9V..

[jubal81]

[baloubass]

Thank for the video.

Do what R.G. noticed..
> the drain and source of the mosfet are reversed from what they should be.<

Drain should face R4 & Source face +9V..

In your schematic, the drain and source of the mosfet are reversed from what they should be.

Ok i will reverse the thing tomorrow. But i dont understand, because in all schematic i have seen, the +9v connect to the "D" and the circuit to the "S" pin according Drain(in), Source(out). i don't understand what i'm do wrong.

[antonis]

Your schematic has some flaws, like LED cathode pointing to +9V instead of GND, so plz verify first all "proper" polarities..

[baloubass]

Your schematic has some flaws, like LED cathode pointing to +9V instead of GND, so plz verify first all "proper" polarities..

Ok, i just write this schematic to make this post, for people see my global idea. I'm not take time etc... just for power section. So i don't think the reverse led on the schematic are   the source of my problem. On the veroboard i just put the power section.

[baloubass]

The reason I lost my voltage came from the RC filter I wanted to do. When i loaded the the voltage down at R4 in relation with the current.
Does anyone have a way to make a filter without loss voltage?

[baloubass]

Thank R.G.
find the answer in an old post about balance between :
-RC filter voltage loss due to the current load.
-Desired frequency cut off.
-Space in the box.

See here (answer 19):https://www.diystompboxes.com/smfforum/index.php?topic=80063.0

[antonis]

-Voltage at V+ and VB+ with the circuit connected: 8.05v

Judging from your schematic, in case of voltage drop due to low-pass filter resistors, V+ & VB SHOULDN'T exhibit identical voltage drop..!!
(unless, of course, VB output provides zero current..)

[baloubass]

-Voltage at V+ and VB+ with the circuit connected: 8.05v

Judging from your schematic, in case of voltage drop due to low-pass filter resistors, V+ & VB SHOULDN'T exhibit identical voltage drop..!!
(unless, of course, VB output provides zero current..)

VB+ are connected only on the buffer section with just a 5088, the current are ridiculous.
V+ are connected with the other section contain the belton brick with lot of current.

I had checked with an overdrive circuit and the voltage loss something around 0.7v, less current than the belton.
I have swapped the "D", "S" connnection same thing with voltage down but lost the reverse polarity protection.

I reduce R4 24r to 4.7r and the voltage up around 9,35v or something like that.
I think i have to calculate a new RC filter around the 4.7r and play with the "uf value" to down the cutoff frequency, in relation with the space and capacitor size.

What cutoff frequency can be considered as good?
With 660uf and 4.7r = 51hz for the LC (R4+C1,C2).
        33nf and 4.7r= around -35db at 20khz for the HC (R2+C3).
Does i need to reduce the LC filter or it's look good at this value? i have no reference to judge if it's a good value.

[antonis]

R2 + C3 is just another LOW pass filter is series with R4 + C1,C2..
(placing a second pole and, IMHO, loading enough preceding one..)

IMHO, again, R2 + C3 is useless, taking into account VB feeds a buffer with "ridiculus" current..

Without a complete circuit schematic, we can't tell for sure neither for HPF placement/configuration nor for its cut-off frequency..

P.S.
For current consuming circuits it should be a good idea to "split" positive supply rail (more than one V+) and place an individual LPF before each one...
(to keep low shunt cap value..)

[baloubass]

P.S.
For current consuming circuits it should be a good idea to "split" positive supply rail (more than one V+) and place an individual LPF before each one...
(to keep low shunt cap value..)

I don't understand this last suggestion.
Ok to form an high pass filter, i have to put R2 after C3.
I'm looking to create a filtering with the LC for the V+, and add a HC for the buffer section.
Maybe i have to make  a LC and a HC with one V+ for the all of the circuit.