This is a micro switch which can be attached to devices on an RC car or drone which takes a UART port / PIN IO to turn on or off VTX, camera, other devices by an input by RC transmitter..
Cannot order this online so thinking to get parts and build one..
Tried searching for part numbers on internet but cannot find datasheets, can anyone help what is the big component “J27 FQT5P10” transistor i think, and the small part named LO
Can anyone help?

Mod:Lightened your image.E

 

Hi,
Look here.
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https://www.mouser.co.uk/ProductDetail/ON-Semiconductor-Fairchild/FQT5P10?qs=uJsByDR%2B4V3wn7FuCL0yfQ==

And here
http://www.s-manuals.com/smd/lo

 

Just after posting i found the datasheet, can anyone help me with understanding the function of “LO” transistor’s collector pin connected to Gate of mosfet,
Both Source and Gate of the Mosfet are connected to Input voltage Source directly while Gate via resistor
What is happening here when the transistor’s base pin gets signal from FC pad, how thr mosfet gets turned on to Drain the + batt voltage
I hope you get what am i asking

 

hi kay,
Post the datasheet you have received.

Your Source/Gate connect sounds incorrect.

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There is no datasheet, i am just looking at the picture i posted in very first post of this thread, looking onto the PCB traces directly and assuming it to be one sided circuit only..

 

hi,
OK,
Look at this marked up image,
also
this quick LTSpice test circuit [ the circuit component values are not the same as your PCB'] its a basic circuit.

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This is what i figured out from the image, can you help me now?

 

This is what i figured out from the image, can you help me now?

hi,
Not sure what you mean by can you help me now?

I thought I was already helping you.

What else would you like help with.?

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yes i meant could you help me explaining the phenomenon taking the drawn schematic into consideration..
I want to know the behaviour of this circuit.
Lets say the FC pad goes high i.e. <=3.3v ,which is connecting to the base pin of the transistor, now what is happening at the MOSFET gate activating its drain pin..
My question is whether the Gate of mosfet is being grounded via collector of transistor, i mean how the circuit gets complete..

 

hi
As you say the Gate is pulled to 0V via the transistor, this turns the P MOSFET On.

The FET is acting as a Power On Switch
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If your schematic is correct, yes the bjt is grounding the MOSFET gate when FC is high, bringing VTX high.

 

hi kay,
As this clip shows the resistors for the NPN Base drive, one of the resistors drives the LED.
Choose a suitable value that will provide approx 10mA to the LED. [ the top resistor]

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hi
As you say the Gate is pulled to 0V via the transistor, this turns the P MOSFET On.

The FET is acting as a Power On Switch
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Yes agreed but why gate is also connected to BATT+ via resistor

 

hi,
So that the NPN transistor can control the Gate voltage On/Off
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hi kay,
This circuit shows what could happen if you do not add that resistor, R1 from Gate to Vbatt.
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hi,
So that the NPN transistor can control the Gate voltage On/Off
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View attachment 240885

Thanks alot Eric for all your answers, i just have one confusion now..
what i understood from your reply is that VTX + would not get full 12v but still positive Batt+ voltage coming and passing through R1 is also being grounded when transistor switches on, when FC pad goes high..
Wouldn’t the heat-up in this case..
If not so what are the suggested values for this resistor, batt+ voltage can be around 5-28v

 

hi kay,
What is your battery voltage and the drive voltage on FC and how much current does the load on VTX require.?

Update:
This should answer your query.

 

hi kay,
What is your battery voltage and the drive voltage on FC and how much current does the load on VTX require.?

Update:
This should answer your query.

The VTX draws around 600mA to 1000mA and FC pad i am not sure but i guess it would be around +3.3v to toggle this switch
Battery voltage is 16.8V

 

hi kay,
What is your battery voltage and the drive voltage on FC and how much current does the load on VTX require.?

Update:
This should answer your query.

also in your above schematic, R4 and R2 are in series while if we look at the circuit board , Fc pad should go to R4 and R2 parallel and then from R4 to Transistor and R2 to LED

 

hi,
This is what I see from the Images you have posted, You have the PCB in front of you.!

If you can clearly see the resistors and LED connected in the way you state, then do it that way.!

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