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APPLICATION NOTE
TV AND MONITORS :
CHOICE OF DIODE FOR A HORIZONTAL DEFLECTION
B. Rivet
I - INTRODUCTION
The purpose of this note is to review the operation
of the basic horizontal deflection circuit, to do an
analysis of the different losses in the damper
diode, and to suggest criteria for choosing
between the DTV32-1500A and DTV32-1500B for
a given application.
II - BEHAVIOUR OF THE BASIC HORIZONTAL
DEFLECTION CIRCUIT
The basic horizontal deflection circuit is shown in
Fig.1
Fig.2 : Wavesform in the basic horizontal deflection circuit
IT
IP
t
IC
IP
tD
t1
t2
t D +T
t
IP
Fig.1 : Basic horizontal deflection circuit
ID
IP
POFF
Va
t
IL
IP
t
L IL
IP
T
D
C
VT
VO
VT
IT
ID
IC
VP
P ON
VF
V CEsat
t
VFP
The current and voltage waveforms in the circuit
are shown in Fig.2
At t = to the transistor starts to turn ON. The current
in the line yoke and in the transistor is given by
Vo.t
I T (t) = I L (t) =
L
The voltage VT across the diode is equal to the
VCEsat of the transistor. The damper diode is
blocked.
At t = t1 the transistor starts to turn OFF, the circuit
becomes resonant (VO . L . C). The current in the
line decreases from Ip to -Ip and an overvoltage
(VFP) appears across the diode.
AN600/1092
At t = t2 the voltage VT across the diode becomes
negative and the damper diode conducts. The
current in the diode and in the line Yoke is then :
I D (t) = − I L (t) = IP −
Vo.t
L
At t = to + T a new cycle starts
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APPLICATION NOTE
III - ANALYSIS OF THE POWER LOSSES IN THE
DAMPER DIODE
a) Conduction losses : PCOND
The current in the damper diode is triangular Fig.3
Fig.3 : Current in the damper diode
Fig.4 : Current and voltage in the damper diode at
switch ON
10V/div
1A/div
50ns/div
IF
VFP
ID
IP
VF
0V
0A
t
T
PON is calculated with the oscillogram of Fig.4 and
the following formula :
T
tfr
∫
1
PON=
VF . IF dt
T 0
The conduction losses are given by :
PCOND = VTO . IF(AV) + rd IF2(RMS)
with
IF(AV)=
tfr is the time during which the voltage accross the
diode increases from OV to VFP and then
decreases from VFP to VFR = 2V
Example : With a DTV32-1500B
and
Tj = 100°C
dIF/dt = 80A/µs
VFP = 42V
f = 32kHz
IP = 6A
IP δ
2
and
2
I F(RMS)=
I2 δ
P
3
Example : With a DTV32-1500 A
VTO = 1 V
rd = 25 mΩ
and
IP = 6 A
δ = 0.45
We find : PON
We find PCOND = 1.5 W
b) Switch ON losses : PON
When the diode switches ON (t=t2 Fig.2), the
current in it increases from 0 to Ip with an high
dIF/dt ( 80A/µs). This current variation results in an
overvoltage across the diode (VFP) and switch ON
losses.
Fig.4 shows the oscillogram of the current and the
voltage across the damper diode when it is
switched ON.
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=1W
c)Switch OFF losses : POFF
When the switching frequency of the horizontal
deflection circuit is low ( 40 kHz), POFF is negligible.
The diode disposes of all its stored charge with a
low voltage across it (VCEsat). At high frequencies
there is insufficient time to complete this discharge
during the conduction time of the transistor. In this
case, when the transistor switches off, a current
appears in the diode (at t=t1 Fig.2) and the voltage
reaches a high value (600V) resulting in
switch-OFF losses (Fig.5)
APPLICATION NOTE
Fig.5 : Current and voltage in the damper diode at
switch OFF (f = 70kHz)
Figs:7 - 9 show the total loss (PT = PCOND + PON +
POFF) in the damper diodes A and B versus
frequency, for different currents IP and different
junction temperatures.
These curves have the same forms for the different
junction temperatures (80°C - 100°C - 120°C)
For the lower frequencies ( & lt; 55 kHz) total losses
are greater in the DTV32-1500B. In this area
conduction and switch ON losses are
predominant. For the high frequencies ( & gt; 65 kHz)
total losses become greater in the DTV32-1500A
(switch OFF losses are more significant in this
diode). This difference in high- frequency losses
between the two devices also increases with
temperature.
Example : With a DTV32-1500A
and P = 6A
f = 70 kHz
Tj = 80°C
trr = 210 ns
(Tj = 25C IF = 1A VR = 30V dIF/dt = -50A/s)
POFF is estimated at POFF = 0.9 W
This estimate has been made by measurements
on the board whose circuit diagram is given in appendix A.
IV - CHOICE BETWEEN THE DTV32-1500A AND
THE
DTV32-1500B
FOR
A
GIVEN
APPLICATION
SGS THOMSON offers two high voltage damper
diodes : the DTV32- 1500A and the DTV32-1500B.
The principal characteristics of these two diodes
are given in the following table :
Fig.3 : Principal characteristics of the DTVV321500A and the DTV32-1500B
Parameters
VTO
rd
VFP
typ
tfr
trr
max
max
80 A/µs
VFR = 2 V
typ
25°C
IF = 1A
VR = 30 V
-50 A/µs
typ
DTV32-1500A DTV32-1500B
1V
25 mΩ
30 V
1.2 V
34 mΩ
39 V
500 ns
250 ns
600 ns
130 ns
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APPLICATION NOTE
Fig.6 : Comparison type " A " and type " B " at Tj = 80°C
Total power dissipation versus operationg frequency for different peak currents
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APPLICATION NOTE
Fig.7 : Comparison type " A " and type " B " at Tj = 100°C
Total power dissipation versus operationg frequency for different peak currents
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APPLICATION NOTE
Fig.8 : Comparison type " A " and type " B " at Tj = 120°C
Total power dissipation versus operationg frequency for different peak currents
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APPLICATION NOTE
V - CONCLUSION
APPENDIX A
SGS-THOMSON offers two Damper diodes to
cover the need in horizontal deflection circuit for
televisions and monitors. The operating frequency
determines the choice of damper diode. For
frequencies below 55 kHz the DTV32-1500A is
preferable while above 65 kHz the DTV32-1500B
is the better choice.
+V
150V
DTV32-1500
150 H
BD435
BUH517
4.7nH
10 F
BD436
-V
Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsability for the
consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No
license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifications mentioned
in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied.
SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems without express
written approval of SGS-THOMSON Microelectronics.
© 1995 SGS-THOMSON Microelectronics - Printed in Italy - All rights reserved.
SGS-THOMSON Microelectronics GROUP OF COMPANIES
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