1N5817, 1N5818, 1N5819
125
NOTE 3. — DETERMINING MAXIMUM RATINGS
40 30 23
Reverse power dissipation and the possibility of thermal
runaway must be considered when operating this rectifier at
115
105
95
°
reverse voltages above 0.1 V
. Proper derating may be
RWM
accomplished by use of equation (1).
(1)
T
=
=
=
T
− R
P
− R
P
A(max)
q
q
JA R(AV)
J(max)
JA F(AV)
where T
Maximum allowable ambient temperature
Maximum allowable junction temperature
(125°C or the temperature at which thermal
runaway occurs, whichever is lowest)
A(max)
R
(°C/W) = 110
q
JA
T
J(max)
80
60
P
= Average forward power dissipation
F(AV)
85
P
=
=
Average reverse power dissipation
Junction−to−ambient thermal resistance
R(AV)
R
q
JA
Figures 1, 2, and 3 permit easier use of equation (1) by
taking reverse power dissipation and thermal runaway into
consideration. The figures solve for a reference temperature
as determined by equation (2).
75
3.0
4.0 5.0
7.0
10
15
20
2.0
V , DC REVERSE VOLTAGE (VOLTS)
R
Figure 1. Maximum Reference Temperature
1N5817
T
= T
− R P
q
JA R(AV)
(2)
R
J(max)
125
115
Substituting equation (2) into equation (1) yields:
40
23
30
T
= T − R P
q
JA F(AV)
(3)
A(max)
R
°
Inspection of equations (2) and (3) reveals that T is the
R
ambient temperature at which thermal runaway occurs or
105
95
where T = 125°C, when forward power is zero. The
J
R
(°C/W) = 110
q
JA
transition from one boundary condition to the other is
evident on the curves of Figures 1, 2, and 3 as a difference
in the rate of change of the slope in the vicinity of 115°C. The
data of Figures 1, 2, and 3 is based upon dc conditions. For
use in common rectifier circuits, Table 1 indicates suggested
factors for an equivalent dc voltage to use for conservative
design, that is:
80
60
85
75
3.0
4.0
5.0
7.0
10
15
20
30
(4)
V
= V
x F
R(equiv)
in(PK)
V , DC REVERSE VOLTAGE (VOLTS)
R
The factor F is derived by considering the properties of the
various rectifier circuits and the reverse characteristics of
Schottky diodes.
Figure 2. Maximum Reference Temperature
1N5818
125
115
40
EXAMPLE: Find T
for 1N5818 operated in a
A(max)
30
23
12−volt dc supply using a bridge circuit with capacitive filter
°
such that I = 0.4 A (I
= 0.5 A), I /I = 10, Input
DC
F(AV)
(FM) (AV)
Voltage = 10 V , R
(rms) qJA
= 80°C/W.
105
95
Step 1. Find V
Step 1. Find ∴ V
. Read F = 0.65 from Table 1,
= (1.41)(10)(0.65) = 9.2 V.
R
(°C/W) = 110
R(equiv)
q
JA
R(equiv)
80
60
Step 2. Find T from Figure 2. Read T = 109°C
R
R
Step 1. Find @ V = 9.2 V and R
= 80°C/W.
q
R
JA
Step 3. Find P
from Figure 4. **Read P
= 0.5 W
F(AV)
(FM)
F(AV)
I
85
@
= 10 and IF(AV) = 0.5 A.
I
(AV)
Step 4. Find T
Step 4. Find T
from equation (3).
= 109 − (80) (0.5) = 69°C.
A(max)
A(max)
75
4.0 5.0
7.0
10
15
20
V , DC REVERSE VOLTAGE (VOLTS)
30
40
R
**Values given are for the 1N5818. Power is slightly lower for the
1N5817 because of its lower forward voltage, and higher for the
1N5819.
Figure 3. Maximum Reference Temperature
1N5819
Table 1. Values for Factor F
Full Wave, Bridge
Half Wave
Circuit
Load
Full Wave, Center Tapped*†
Resistive
Capacitive*
Resistive
0.5
Capacitive
Resistive
1.0
Capacitive
Sine Wave
0.5
1.3
1.5
0.65
0.75
1.3
1.5
Square Wave
**Note that V
0.75
0.75
1.5
†Use line to center tap voltage for V .
≈ 2.0 V
.
in
R(PK)
in(PK)
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