K
Ken Smith
- Jan 1, 1970
- 0
Winfield Hill said:One problem in designing such a power supply is the short-circuit
current-limiting aspect of the design. BJT's have a horrible 2nd-
breakdown effect that will greatly exacerbate your design problems.
A type 861 triode doesn't have a 2nd breakdown problem.
I recommend that you use high-voltage MOSFETs as pass elements, and
avoid the issue.
With care, you can float all the smarts of the regulator circuit at the
source voltage of the FET. Since this is mains powered, a very small
transformer can be used to make a floating 12V to run the regulator
circuit.
High V
!
!!-
Gate----------!!-
!!-
!
I sense --------+
!
/
\
/
\ Vfloat
------------------------+---------------- To load
----------------------------------------- GND
******************
VRef -/\/\-----+-->!--- overcurrent/
!
!
!
!
GND -/\/\/\/--+-!+\
! >----+-/\/\/-+--- Gate
--!-/ ! !
! ! V
+-/\/\--!!- ---
! !
\ Over Current/
/
\
/
!
Vfloat
*************************
-------+----------- Over current/
!/ c !
ISense ---+---------------! !
! !\ e !
! ! !
! Vref2 !
! -\/\/--!!--------+
! ! !
-/\/\-+--!-\ !
! >-----------
Vref2--!+/