Sony DTV-01, Manual

Page: 90 / 132

93
P M 3 3 9 4 , F L U K E & P H I L I P S
c h 3
c h 2
c h 1
c h 1 : f r e q = 3 1 . 6 k H z
C H 1 1 0 . 0 V =
C H 2 1 0 . 0 V =
C H 3 0 . 5 V = C H P M T B 1 0 . 0 u s c h 1 -
1
2
3
T
Horizontal Driver
This horizontal driver stage consists of:
1. The horizontal driver MOSFET
2. The Driver PWM stage that makes B+ for the driver
Horizontal Driver MOSFET
A MOSFET horizontal driver is used to boost the horizontal drive level
before applying the signal to the H Output stage. The horizontal drive
signal from Q1703 is input to the gate and the amplified signal leaves
Q4011’s drain. The signal is coupled through T4001 to the Horizontal Output
Transistor Q4018/base (not shown).
The horizontal drive signal can be seen in this scope shot showing the
horizontal drive signal (ch 1) compared to the FBT pulse (channel 3).
W a v e f o r m H D 2 2 A – H o r iz o n t a l D r iv e S ig n a ls
N a m e L o c a t io n V o lt a g e / d iv
C h a n n e l 1 H . D r iv e s ig n a l C N 4 0 0 9 / p in 1 0 1 2 V p - p
C h a n n e l 2 H . O u t p u t / b a s e Q 4 0 1 8 / b a s e 2 V p - p w it h o u t
s p ik e s
C h a n n e l 3 F B T p u ls e s F B T N / A
T im e b a s e 1 0 u s e c / d iv
MOSFET/Transistor Characteristic Comparison
A power MOSFET device in an N channel format is most similar to a NPN
transistor in overall operation, just as a P channel device is similar to a
PNP.
M O S F E T – T r a n s is t o r O p e r a t io n C o m p a r is o n
D if f e r e n c e s S im ila r it ie s
M a x im u m g a t e v o lt a g e c a n g o t o
a b o u t + 2 0 V o lt s w it h r e f e r e n c e t o
t h e s o u r c e le a d .
T h e g a t e is r e f e r e n c e d t o t h e
s o u r c e , lik e t h e b a s e is t o t h e
e m it t e r .
T u r n O N g a t e t h r e s h o ld v o lt a g e is
1 - 2 V ( lo w p o w e r ) o r 2 - 4 V ( h ig h
p o w e r T O - 2 2 0 c a s e o r la r g e r ) . A g a t e v o lt a g e t h a t is b r o u g h t
t o w a r d t h e d r a in v o lta g e tu r n s it
O N , ju s t lik e a b a s e v o lt a g e b e in g
b r o u g h t t o w a r d t h e c o lle c t o r
p o t e n t ia l t u r n s a t r a n s is t o r O N .
O n a n d O F F t im e s a r e a f fe c t e d
b y in t e r n a l g a t e c a p a c it a n c e s o
g a t e c u r r e n t d e t e r m in e s O N t im e . N P N a n d N c h a n n e l a r e s im ila r in
c ir c u it c o n f ig u r a t io n . S u m m a r ily ,
s o a r e P N P & P c h a n n e l
M O S F E T s .
T h e O F F t im e is d e la y e d b y lo a d
c a p a c it a n c e t h a t in c r e a s e s t h e
g a t e c a p a c it a n c e ( C g d ) .
I n H V a p p lic a t io n s , a s a t u r a t e d
M O S F E T ( d r a in t o s o u r c e is
a p p r o x . 2 V . T h is is g r e a t e r t h a n a
t r a n s is t o r ’s V c e s a t v o lt a g e .
M O S F E T s d o n o t h a v e t h e r m a l
r u n a w a y a n d c a n t h e r e f o r e
w it h s t a n d s im u lt a n e o u s h ig h
c u r r e n t a n d v o lt a g e , b u t f a ils
in s t a n t ly w h e n s p e c s a r e
e x c e e d e d .
M O S F E T s h a v e lo w e r h ig h
f r e q u e n c y s w it c h in g lo s s e s
Testing a MOSFET
Testing a MOSFET device is easy. The leads show infinite resistance to
any other lead except for some power MOSFETs that have an internal
protective zener connected between the drain and source.
To prove the device is functional:
1. Connect the negative lead of the ohmmeter to the SOURCE lead.
2. Touch the ohmmeter positive lead to the gate, to pre-charge it.