the change of voltage with load current

W

whay

New Member
Good afternoon~
First, thank you for taking the time to read my post.
I'm not very professional.So ,Please give me some more time to describe my question.
I made a power switch by using MOS, I added triode --S8050NPN to control it in the pre-circuit. The led is act as load in my circuit diagram. I don’t understand that why the voltage drop to 0.5V when the load current is bout 1A,and when 2A,it’s 1.2V? Is there any wrong in the circuit? Any idea? Can you?
Any help would be greatly appreciated!:)
Regards
You can see the following picture:
12a.png
 
... In the first place this circuit is much more complicated than necessary to drive an LED, that can be done with just the transistor drive stage
that gates the mosfet. Assuming you really do want that mosfet, in order to drive higher power levels, (almost) everything looks good except
the lack of current limiting for the LED. o_O

My SPICE emulation shows 2.5 mA across the transistor and 2.72 mA driving it, so far so good.
But 470K is too high for driving that MOSFET at only 0.02 uA. I suggest changing that value to 47K which drives the gate with .05 mA.
Also, as is, you're applying 1.89 amps to that LED which would smoke it in an instant. I suggest adding a 150 ohm limiting resister for 10.8 mA.

Lack of proper gate saturation driving the MOSFET is likely why you're getting those readings.
Note: I didn't set up constant current parameters to run this (I prefer it that way) so I didn't get "voltage sags".
Not knowing anything more specific regarding the supply voltages and current limits, that's my analysis of what you've got. ;)
 
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