Title of Invention

A FULLY PROTECTED BUCK CONVERTER

Abstract A -fully protected buck converter comprising an input end -for receiving d.c, power from a sources an output end -for connecting the load thereto; a first comparator for comparing the output with a voltage; a dual current transformer circuit for sensing the load currents a second comparator for comparing the current sensed by the said dual transformer circuit with a reference currents switching means for being activated by the said comparators, to switch off- power from the said source whenever the output voltage reaches a first value higher than the rated output voltage value OR the load current reaches a -first value higher than the rated load current values and to switch on power whenever the output voltage reaches a second value lower than the rated output voltage value AND the load current reaches a second value just above the rated load current value-
Full Text This invention relates to a fully protected DUCK converter.
In the known buck converter popularly known as the ripple regulator, whenever the output voltage reaches a value higher than the rated value, power is switched off, until the output voltage falls to another value, when power is again switched on.
The known buck converter, however, has no provision for protection against shortcircuit conditions, when destructive currents flow. There are of course hysteretic current controllers, which are safe, but they require a minimum load.
This invention proposes a buck converter which is simple in its construction and which provides protection ■for short-circuit conditions as well.
The fully protected buck converter, according to this invention, comprises an input end for receiving a.c. power from a source; an output end for connecting the load thereto; a first comparator for comparing the

output voltage with a reference voltage; a dual current transformer circuit for sensing the load current; a second comparator for comparing the current sensed by the said dual transformer circuit with a reference current; switching means for being activated by the said comparators, to switch off power from the said source whenever the output voltage reaches a first value higher than the rated output voltage value OR the load current reaches a first value higher than the rated load current value: and to switch on power whenever the output voltage reaches a second value lower than the rated output voltage value AND the load current reaches a second value just above the rated load current value.
This invention will now be described with reference to the accompanying drawings which illustrate,
in Fig.l the circuit of the known buck converter (ripple regulator)
and
Fig.2 lustrates, by way of example, one of possible

embodiments of the buck regulator according to this invention.
Referring to Fig.l when the switch SW is on, the output voltage Vo increases with time. Comparator Al through switch control SC switches SW off when Vo reaches an upper limit Voh. The voltage now drops with time and the said comparator switches SW on when the voltage falls to Vol. The output voltage thus remains within these limits. This circuit allows operation under no load conditions also; however, under short circuit conditions destructive currents will flow. As already stated above, there airs hysteretic current controllers which Are safe, but these require a minimum load for operation.
Referring to Fig.2 of the drawings, besides the voltage Vo, the load current IL is also sensed. A voltage analogous to IL appears across R2. When Vo reaches Voh OR when IL reaches ILH, switch SW is switched,off. It is only when Vo falls to Vol AND IL falls to a lower limit ILL, switch SW is switched on. ILL is selected to be just above the rated current and ILH is aerated than

ILL. Under normal operating and open circuit conditions, current sense has no effect on circuit operation. When the output is shorted (or when the converter starts with no charge in capacitor C) switch SW is switched on and off such that IL ramps up to ILH and decays to ILL cyclically.
Cl and CT2 are identical unidirectional pulse type transformers. When Is flows in the direction shown in Fig.2 diode D3 conducts and an analogous voltage of the current Is is developed across R2. Rl is much larger than R2.
At the end of such a forward current pulse, rapid recovery of the current transformer core occurs because D3 blocks and the secondary fly back resistance is high,
CT2 works similarly, for Id. The voltage across R2 is analogous to the sum of the currents Is and Id which is equal to the load current IL. Hence comparator A2 senses the current IL.
The terms and expressions in this specification are of

description and not of limitation there being no intention in the use of such terms and expressions of excluding any equivalents of the features illustrated and described, but it is understood that various other embodiments of the converter proposed herein are possible without departing from the scope and ambit of this invention.



We Claims
l.A fully protected buck converter comprising an input end for receiving d.c. power from a source; an output end for connecting the load thereto; a first comparator for comparing the output voltage with a reference voltage; a dual current transformer circuit for sensing the load current; a second comparator for comparing the current sensed by the said dual transformer circuit with a reference current; switching means for being activated by the said comparators, to switch off power from the said source whenever the output voltage reaches a first value higher than the rated output voltage value OR the load current reaches a first value higher than the rated load current value; and to switch on power whenever the output voltage reaches a second value lower than the rated output voltage value AND the load current reaches a second value just above the rated load current value.
2.A buck converter as claimed in Claim 1 wherein the two current transformer circuits respectively sense two

parts o-f the load current, the outputs of the said circuits being the analogous values of the respective parts.
3.A fully protected buck converter substantially as herein described with reference to, and as illustrated in, the accompanying drawings.

Documents:

2134-mas-1996 abstract.pdf

2134-mas-1996 claims.pdf

2134-mas-1996 correspondence -others.pdf

2134-mas-1996 correspondence -po.pdf

2134-mas-1996 description (complete).pdf

2134-mas-1996 drawings.pdf

2134-mas-1996 form-1.pdf

2134-mas-1996 form-26.pdf


Patent Number 198235
Indian Patent Application Number 2134/MAS/1996
PG Journal Number 30/2009
Publication Date 24-Jul-2009
Grant Date
Date of Filing 29-Nov-1996
Name of Patentee INDIAN INSTITUTE OF TECHNOLOGY
Applicant Address IIT PO, CHENNAI - 600036.
Inventors:
# Inventor's Name Inventor's Address
1 DR. SUNDARAM SANTHAKUMAR INDIAN INSTITUTE OF TECHNOLOGY, IIT PO, CHENNAI- 600036.
PCT International Classification Number H02H9/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA