Amplify PIR 3.3V?

[almamater]

Hello Everyone!

I want to make a simple circuit but now i have one question\problem. I want to control one LedStrip (40Leds \ ~450mA current consumption) with one sensor PIR like this one and control one 5mm LED at same time, when LEDstrip is ON the LED is OFF and vice versa.

This PIR have 3.3V (Hight) at the Output Pin when motion is detected

So, i made this circuit and works very well with my ATX power supply (for simulate the 3.3V input):


But now when i test with the PIR Output the circuit don't work, probably i have to amplify some how the 3.3V from the sensor, can you please help me with this? Probably i must put another transistor between the PIR and this circuit (BD139).. but what the best way to do it?

Thank you.

[Terry Bites]

Most of these little PIRs can only source 100uA or less from their output.
The BD139 has a beta of ~20 so you will barely turn it on.
Change it for a logic level mosfet. For example an NTR4501NT1G, it will handle 2A with very low drive requirements.

[cavac]

Something like this should work, at least i think it should without actually building the circuit:

[Zero999]

Something like this should work, at least i think it should without actually building the circuit:

The MOSFET's drain and source connections are reversed and why use two BJTs, when one will do?

[cavac]

The MOSFET's drain and source connections are reversed

Whoops. 

Copied the MOSFET design from a recently finished project. Switched the pins on my PCB around after an ElectroBOOM moment but i guess i forgot to update my hand-drawn schematic. Well, uhm, it's good thing that the error popped up here in discussion, i would probably have just copied the design for my next project... and looked in wonderment at another smoking crater in the midst of my PCB...

The MOSFET's drain and source connections are reversed and why use two BJTs, when one will do?

Terry Bites mentioned that the PIR can only source a tiny current, so i figured i'd better double up on those transistor to get better amplification of that tiny signal.

[Zero999]

MOSFETs have a truly massive, almost infinite, current gain. One BJT is sufficient. The only reason to add more is to improve the switching speed, which isn't necessary in this instance.

[cavac]

Thanks!

[almamater]

Thanks for the responses!! I will try and test the suggestions