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7-14. Power supply STR-S5707

1 . V in te rm in a l, sta rt-u p c ircu it

A start-up circuit is to start and stop a operation of a control IC by detecting a voltage appearing at a Vin terminal (pin 9).

A t s ta rt u p o f a p o w e r s u p p ly, w h e n a v olta g e a t th e V in te rm in a l re a ch e s to 8 V (typ ic a l) b y ch a rg in g u p C 8 1 7
b y th e fu n c tio n o f a s ta rt-up re s isto r, R 8 0 4 , a co n tro l c ircu it sta rts o p eratin g b y th e fu n ctio n o f the s ta rt-u p circu it.

A fte r th e co n tro l circ u it s ta rts its o p e ratio n , p o w er so u rce is o b ta ine d b y sm o o th in g vo lta g e a p p e a ring a t
w in d in g of p in 6 ,7 o f T 8 0 1 .

2 . O s cilla to r,F /B te rm in a l vo lta g e (p in 7 )
A o s cilla to r g e n e ra te s p u ls e s ig n a ls w h ic h tu rn s a po w e r tra n s is to r o n a n d o ff b y m a k in g u s e o f ch a rg e a n d

d is c ha rg e o f C 1 an d C 2 in c o rp o ra te d in th e H yb rid IC .
C o n sta n t vo lta g e c o n tro l o f a sw itch -m o d e p ow e r s u p p ly is p e rfo rm e d b y ch a n g in g bo th o n -tim e a n d

o ff-tim e e x c e p t w h e n th e lo a d is lig h t (e x. re m o te c o n tro l s ta n d -b y m o d e o f T V s ).
T h e o n -tim e is c o ntro lle d b y c h a n g in g a c u rre n t c h a rge d b y C 1 , w h ic h is as th e re s u lt o f th a t th e d ete ctio n

w in d in g o f p in 5 -7 o f T 80 1 , w h ic h d e te cts a c h a n g e o f v o lta g e in a s e co n d a ry side , c o n n e cte d to th e s e n sin g
te rm in a l (p in 7). h a s th e c urre n t in a c co rd a n c e w ith a n o u tp u t s ig n a l fro m a n o u tp u t vo lta g e d e te ctio n c ircu it

(a n e rro r a m p lifie r) b u ilt in .
A s a n A C in p u t vo lta g e to the p o w er su p p ly g a ts th e hig h er a nd a lo a d cu rre n t th e s m a ller,

th e c u rre n t flo w in g to th e S E N S term in a l g e ts th e la rg e r, an d th e o n-tim e ge ts th e sh o rte r.

3 . F u n c tio n o f IN H te rm in a l (p in 6 ), co n tro l o f o ff-tim e

S ig n a l to th e IN H te rm in a l is u se d a s in p u ts to C O M P.1 a n d C O M P.2 in s id e o f th e co n trol IC .

A th re s h o ld v o lta ge o f C O M P.1 ,V T H 1 is s e t a t 0 .7 5 V (Ta = 2 5

) a n d a n in p u t s ig n al to a driv e c irc uit b ec o m e s

a lm o st 0 V (th e p ow e r tran s is to r is in O F F m od e ) w h e n a v olta g e a t th e IN H te rm in a l re a c h e s th e V T H 1 .

A th re s h o ld v o lta g e o f C O M P.2, V T H 2 , is s e t a t 1 .5 V (Ta = 2 5

W h e n th e IN H te rm in a l v o ltag e re a c h e s V T H 2 , a n o u tp u t fro m C O M P.2 re v e rse s (th e p o w e r T R is in o n m o d e ).

Quasi-resonant operation

B y in p u ttin g th e v o lta g e o f w in d in g o f p in 6 -7 o f T 8 0 1 w h ic h is s y n ch ro n iz ed w ith th e e n e rg y d is ch a rg e tim e
o f a s ec o n d a ry w ind in g to the IN H te rm in a l th ro u gh D 8 1 0 a n d R 8 0 8 , q u a si-re s o n an t o p e ra tion c a n b e a c h ieve d .

W h e n th e p o w e r tra n s isto r turn s o ff a n d a v o lta g e h ig h e r th a n V T H 2 is a p p lie d to th e IN H te rm in a l,
C 3 im m e d ia te ly d is ch a rg e s a n d th e n sta rts c h a rg in g a g ain .

E ve n a fter th e d isc h a rg e o f e ne rg y o f a s e c o nd a ry w in d in g is co m p le te d , V IN H d o e s n o t im m e d ia te ly
in c re a se s . w h e n it g e ts lo w e r th a n V T H 1 , th e tra n s is to r tu rn s o n .

4 . D rive circ u it

T h e S T R -S 5 7 0 7 a p plie s th e p ro p o rtio n a l d rive sy s te m in o rd e r to m in im iz e tu rn -o n a n d s a tu ra tio n lo s s,
a n d s to ra g e tim e .

5 . O C P fu n c tio n

O ver-cu rre n t p ro tectio n is p e rfo rm e d p u lse b y p u ls e b y dire c tly d e tectin g c o lle c to r c u rre n t o f th e p o w e r tra n sistor.

d e tec tin g v o lta g e is se t to -1 V b e lo w a re fe re n c e p o in t o f G N D (g ro u n d ).

6 . L a tc h c ircu it w h ic h s u sta in s a n o u tp u t fro m th e o s cilla to r lo w a n d s to p s o p e ratio n o f th e p o w e r su p p ly w h e n

o v e r-v o lta g e p ro te ctio n (O V P ) c ircu it a n d th e rm a l sh u tdo w n (T S D ) c irc u it a re in o p e ra tio n .

A s th e su s ta in in g cu rre n t o f th e la tch circ u it is 5 0 0

m a x im u m w h e n V in te rm in a l v o lta ge is 4 V,