I am designing a linear step-down regulator using a PNP pass transistor. The output of the regulator is good at no load.
When I connect my regulator to a battery supply, leave it for 2 seconds and then I connect my load (say a 12 V DC motor or a microcontroller), it works good.
But when I attach my load to the circuit and then supply power, my output drops to almost 0 V.
Here is my regulator circuit...
There is a problem in my design. I am trying to analyse it. It would be appreciated if someone could help me.
Above one is a reference image from Texas Instruments.
Input supply (battery) = 40-50 v
Output volt (for controller) = 12 v (500 ma approx)
I connected the input for 7805 in source side by using a transistor to get a constant supply as shown in the image. Now my circuit works better.But pnp transistor heats quite a lot by connecting load. Since it's a low dropout regulator, why it heats much.