Lecture 15 Isolated DC-DC converters

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Dale Banks
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1 ELEC440/940 Lecure 15 olae C-C converer Ofen, he oupu C volage fro a C-C converer u be iolae fro he inpu AC upply. C power upplie for appliance an equipen are goo exaple. i avanageou o have he iolaion ranforer on he C ie, where he wiching frequency i high. 1. olaion Tranforer iolaion a he AC ie i bulky.. Muliple Oupu Muliple iolae oupu poible uing one high frequency core. 3. egulaion (PWM uy cycle -conrol) can ake avanage of he ranforer raio. C ie ranforer allow eign flexibiliy by aking he range of ore uiable. i 1 i 1 v 1 1 v i 1 i 1 v 1 / 1 / ; L l1 i 1 i L l L 1 : v ieal Lecure 15 Flyback converer 1 F. ahan

olaion Tranforer iolaion a he AC ie i bulky.. Muliple Oupu Muliple iolae oupu poible uing one high frequency core. 3.

2 ELEC440/940 Figure 15.1(a) Lecure 15 Flyback converer F. ahan

3 ELEC440/940 i 1 i L 1 : v eal Figure 15.1 (b) B B Wihou B r Wih airgap H Figure 15. The airgap reuce he B r, which i he B when fall o zero. Thi iniie he nubber coponen which woul ree he core flux. Operaion wih flux ree increae he range of variaion of he flux in he core hereby increaing he uiliaion of he ranforer (or reucing i ize). Uniirecional core exciaion Flyback (buck-boo erive) an Forwar (buck erive) converer Biirecional core exciaion Puh-pull, half-brige an full-brige converer L 1, L u be a all a poible for power lo conieraion of he wiche. L u be a large a poible fro energy orage conieraion. Lecure 15 Flyback converer 3 F. ahan

Operaion wih flux ree increae he range of variaion of he flux in he core hereby increaing he uiliaion of he ranforer (or reucing i ize).

4 ELEC440/940 Flyback Converer (erive fro he Buck-Boo Converer) o 1 C Buck-Boo i 1 L i v C o o 1 : i 1 L i v C o o 1 : Circui uring on ; i 1 L i v C o o 1 : Circui uring off ; i i Figure 15.3 Lecure 15 Flyback converer 4 F. ahan

5 ELEC440/940 Analyi of he Flyback converer φ o o φ, T T (1-)T i φ v or v Figure 15.4 φ (15.1) uring 0 < < on, for he priary ie, φ φ (15.) φ( on ) φ φ φ (15.3) 0 on 0 T ax 1 1 uring on < < T for he econary ie, φ (15.4) o o o φax ( on ) (15.5) 1 on φ(t ) φ ( T ) φ T ( T ) (15.6) o o ax on o on 1 f he core flux i copleely ree in each cycle, i.e., φ(0) φ(t ) 0 o 1 1 (15.7) Lecure 15 Flyback converer 5 F. ahan

3) 0 on 0 T ax 1 1 uring on < < T for he econary ie, φ (15.4) o o o φax ( on ) (15.

6 ELEC440/940 Fro power balance, (15.8) Analyi for coninuou conucion Fro v i L uring 0 < < on, i 0, i (15.9) L i i i on T in 0 L L i i T (15.10) ax in on L uring on < < T, i T 0 an v 1 1 o ( / ) i () i ( ) (15.10) 1 o ax on L ( / ) i () i i ( ) o ax on L oe ha i or becoe iniu when T. Thu, ( / ) 1 1 o in i ax ( 1 ) T L 1 Alo, ax i ax (15.11) ow, i i (1 )T o T ax in 1 i i ( 1 ) T o 1 ax T ax o 1 1 L (15.1) Lecure 15 Flyback converer 6 F. ahan

10) 1 o ax on L ( / ) i () i i ( ) 1 1 1 o ax on L oe ha i or becoe iniu when T.

7 ELEC440/940 Operaion a he coninuou-iconinuou bounary,ax T 1 o on off Figure 15.5 P P o T o (15.13) (15.14) T where i he average agneiing curren rawn fro he C ource. o o ha o (15.15) An 0 0 (1 ) 1 (1 ) 1 (15.16) i T,ax (1 ) 1 L i T,in (1 ) 1 L i (1 ) 1 L f in (15.17) (15.18) (15.19) o enure iconinuou conucion. The ae reul i alo obaine fro (15.1). Lecure 15 Flyback converer 7 F. ahan

15) An 0 0 (1 ) 1 (1 ) 1 (15.16) i T,ax (1 ) 1 L i T,in (1 ) 1 L i (1 ) 1 L f in (15.17) (15.

8 ELEC440/940 Flyback converer uner iconinuou conucion,ax T T Figure 15.6 i ax T L 0 (15.0) 1 T (15.1) T / T L T L (15.) T 0 L (15.3) o T L (15.4) f L Lecure 15 Flyback converer 8 F. ahan

9 ELEC440/940 Swich volage, v T, uring on < < T v 1 T o (15.5) oe: Operaion in iconinuou oe uilie he ranforer beer. Snubber requireen i alo he lowe. Oupu volage ripple 0 a for a buck-boo converer. (15.6) Cf 0 auing coninuou conucion. For iconinuo conucion, o will be wore han hi becaue he ou capacior will loe charge for longer han T on. Two-wich flyback converer T 1 1 C T Figure 15.7 Tranior T1 an T are urne on an off iulaneouly. Energy rappe in he leakage inucance now ha a regeneraive pah o flow hrough. Trappe energie in hee inucance reurn o he C ource. Snubber requireen i hu even aller. n fac, iipaive nubber ay no be neee a all. The wo ranior have half he volage raing of he ingle-ranior flyback converer. Lecure 15 Flyback converer 9 F. ahan

Two-wich flyback converer T 1 1 C T Figure 15.7 Tranior T1 an T are urne on an off iulaneouly. Energy rappe in he leakage inucance now ha a regeneraive pah o flow hrough.

Tripping Current and Short Circuit Current of High Voltage Tester

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