I'm designing a simple 15V to 5V DC voltage feadback mode non SMPS regulator.

I'm using E13007E2 power NPN switch mode transistor. And to drive that transistor I'm using C945 another transistor.

This is my schematic diagram of the circuit.

enter image description here

It gives 4.5V output when it's not loaded. But when it's loaded and after some time the C945 had gone. It's 2 junctions are open now. c945 is to shunt just only 6mA. Why it can't handle 6mA?

Any idea how could I calculate the operating points precisely?

  • \$\begingroup\$ I hope you didn't really apply 200V -- that would have done it! \$\endgroup\$
    – Dave Tweed
    Oct 19, 2012 at 17:38
  • \$\begingroup\$ sorry , that for only simulation. See the edited new picture. \$\endgroup\$ Oct 19, 2012 at 17:43
  • 1
    \$\begingroup\$ I honestly can't think of any reason that the transistor would have failed as a result of that circuit design. Perhaps it was "just its time." :-) Can you provide any other details about your setup and what you're trying to accomplish? \$\endgroup\$
    – Dave Tweed
    Oct 19, 2012 at 22:41
  • \$\begingroup\$ @DaveTweed I want to build a 15v to 5v Dc2DC converter. Fortunately I got another C945 Tr-1. it also work some long and gone. \$\endgroup\$ Oct 20, 2012 at 5:17
  • 1
    \$\begingroup\$ Is there any chance you've misunderstood which pin is which on either of the transistors? \$\endgroup\$
    – Dave Tweed
    Oct 20, 2012 at 14:54

1 Answer 1


Circuit Lab has simulations
Series Voltage Regulator
Link to the above circuit
They did not have your parts number in their library.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.