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What is AN1048D?

This electronic component, produced by the manufacturer "ON Semiconductor", performs the same function as "RC Snubber Networks".


AN1048D Datasheet PDF - ON Semiconductor

Part Number AN1048D
Description RC Snubber Networks
Manufacturers ON Semiconductor 
Logo ON Semiconductor Logo 


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AN1048/D
RC Snubber Networks
For Thyristor
Power Control and
Transient Suppression
By George Templeton
Thyristor Applications Engineer
http://onsemi.com
APPLICATION NOTE
INTRODUCTION
Edited and Updated
RC networks are used to control voltage transients that
could falsely turn-on a thyristor. These networks are called
snubbers.
The simple snubber consists of a series resistor and
capacitor placed around the thyristor. These components
along with the load inductance form a series CRL circuit.
Snubber theory follows from the solution of the circuit’s
differential equation.
Many RC combinations are capable of providing accept-
able performance. However, improperly used snubbers can
cause unreliable circuit operation and damage to the semi-
conductor device.
Both turn-on and turn-off protection may be necessary
for reliability. Sometimes the thyristor must function with a
range of load values. The type of thyristors used, circuit
configuration, and load characteristics are influential.
Snubber design involves compromises. They include
cost, voltage rate, peak voltage, and turn-on stress. Practi-
cal solutions depend on device and circuit physics.
STATIC
dV
dt
WHAT
IS
STATIC
dV
dt
?
Static
dV
dt
is
a
measure
of
the
ability
of
a
thyristor
to
retain a blocking state under the influence of a voltage
transient.
ǒ ǓdV
dt
DEVICE PHYSICS
s
Static
dV
dt
turn-on
is
a
consequence
of
the
Miller
effect
and regeneration (Figure 1). A change in voltage across the
junction capacitance induces a current through it. This cur-
ǒ Ǔrent is proportional to the rate of voltage change
dV
dt
. It
triggers the device on when it becomes large enough to
raise the sum of the NPN and PNP transistor alphas to unity.
A
I1 CJP
CJN
ICN IJ
NPN
IBP IA
PNP
IJ ICP
V
I2
G
dv CJ
dt G
t
IBN
IK
K
IA
+
1
*
CJ
dV
dt
(aN )
ap)
TWO TRANSISTOR MODEL
OF
SCR
CEFF + 1*(aCNJ)ap)
A
PE
NB
C
PB
NE
K
INTEGRATED
STRUCTURE
ǒ ǓFigure 6.1.
dV
dt
Model
s
© Semiconductor Components Industries, LLC, 2008
June, 2008 Rev. 3
1
Publication Order Number:
AN1048/D
Free Datasheet http://www.datasheet-pdf.com/

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AN1048D equivalent
AN1048/D
ǒ Ǔdi
dt c
0
ǒ ǓdV
dt c
TIME
VMT2‐1
VOLUME
STORAGE
CHARGE
IRRM
CHARGE
DUE TO
dV/dt
Figure 6.10. TRIAC Current and Voltage
at Commutation
E
V
E
ǒ ǓCONDITIONS INFLUENCING
dV
dt c
Commutating
dV
dt
depends
on
charge
storage
and
recov-
ery dynamics in addition to the variables influencing static
ddVt . High temperatures increase minority carrier life-time
and the size of recovery currents, making turn-off more dif-
ficult. Loads that slow the rate of current zero-crossing aid
turn-off. Those with harmonic content hinder turn-off.
Circuit Examples
Figure 13 shows a TRIAC controlling an inductive load
in a bridge. The inductive load has a time constant longer
than the line period. This causes the load current to remain
constant and the TRIAC current to switch rapidly as the line
voltage reverses. This application is notorious for causing
ǒ ǓTRIAC turn-off difficulty because of high
dI
dt
.
c
RS C
LS
60 Hz i
i
ǒ ǓdI
dt c
-
t
DC MOTOR
RL
+
ǒ ǓL
R
u 8.3
ms
VT
0
td
TIME
Figure 6.11. Snubber Delay Time
0.5
0.2
0.2 0.1
0.1 0.05
0.05
0.03
RL = 0
M=1
0.02 IRRM = 0
0.02
0.01
VT
E
0.005
0.001 0.002 0.005 0.01 0.02 0.05 0.1 0.2 0.3 0.5
DAMPING FACTOR
Figure 6.12. Delay Time To Normalized Voltage
1
Figure 6.13. Phase Controlling a Motor in a Bridge
High currents lead to high junction temperatures and
rates of current crossing. Motors can have 5 to 6 times the
normal current amplitude at start-up. This increases both
junction temperature and the rate of current crossing, lead-
ing to turn-off problems.
The line frequency causes high rates of current crossing
in 400 Hz applications. Resonant transformer circuits are
doubly periodic and have current harmonics at both the pri-
mary and secondary resonance. Non-sinusoidal currents
can lead to turn-off difficulty even if the current amplitude
is low before zero-crossing.
ǒ ǓdV
dt
FAILURE MODE
c
ǒ ǓdV
dt
c
failure
causes a
loss
of phase
control. Temporary
turn-on or total turn-off failure is possible. This can be
destructive if the TRIAC conducts asymmetrically causing a
dc current component and magnetic saturation. The winding
resistance limits the current. Failure results because of
excessive surge current and junction temperature.
http://onsemi.com
5
Free Datasheet http://www.datasheet-pdf.com/


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Featured Datasheets

Part NumberDescriptionMFRS
AN1048The function is RC Snubber Networks. ON SemiconductorON Semiconductor
AN1048DThe function is RC Snubber Networks. ON SemiconductorON Semiconductor

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