125
115
NOTE 1 — DETERMINING MAXIMUM RATINGS
40 30 23
Reverse power dissipation and the possibility of thermal runaway
must be considered when operating this rectifier at reverse voltages
°
above 0.1 V
equation (1).
. Proper derating may be accomplished by use of
RWM
105
95
T
=
=
=
(1)
T
– R
P
– R P
θJA R(AV)
A(max)
J(max)
θJA F(AV)
where T
A(max)
Maximum allowable ambient temperature
Maximum allowable junction temperature
(125°C or the temperature at which thermal
runaway occurs, whichever is lowest)
Average forward power dissipation
R
(°C/W) = 110
JA
θ
T
J(max)
80
60
P
P
=
=
=
F(AV)
85
75
Average reverse power dissipation
Junction–to–ambient thermal resistance
R(AV)
R
θJA
Figures 1, 2, and 3 permit easier use of equation (1) by taking re-
verse power dissipation and thermal runaway into consideration. The
figures solve for a reference temperature as determined by equation
(2).
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
R
= T
– R P
J(max)
Substituting equation (2) into equation (1) yields:
= T – R P
θJA F(AV)
Inspection of equations (2) and (3) reveals that T is the ambient
temperature at which thermal runaway occurs or where T = 125°C,
when forward power is zero. The transition from one boundary condi-
tion to the other is evident on the curves of Figures 1, 2, and 3 as a
differenceintherateofchangeoftheslopeinthevicinityof115°C. The
dataofFigures1, 2, and3isbasedupondcconditions. Foruseincom-
mon rectifier circuits, Table 1 indicates suggested factors for an equiv-
alent dc voltage to use for conservative design, that is:
θJA R(AV)
(2)
125
115
T
A(max)
R
(3)
R
40
23
30
J
°
105
95
R
(°
C/W) = 110
80
θ
JA
60
(4)
V
= V x F
in(PK)
R(equiv)
ThefactorFisderivedbyconsideringthepropertiesofthevariousrec-
tifier circuits and the reverse characteristics of Schottky diodes.
85
EXAMPLE:FindT
A(max)
for1N5818operatedina12–voltdcsupply
usingabridgecircuitwithcapacitivefiltersuchthatI
=0.4A(I
=
75
DC
F(AV)
= 80°C/W.
3.0
4.0
5.0
7.0
10
15
20
30
0.5 A), I
/I
= 10, Input Voltage = 10 V
, R
(FM) (AV)
(rms) θJA
V
, DC REVERSE VOLTAGE (VOLTS)
R
Step 1. Find V
Step 1. Find
. Read F = 0.65 from Table 1,
R(equiv)
Figure 2. Maximum Reference Temperature
1N5818
V
= (1.41)(10)(0.65) = 9.2 V.
R(equiv)
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.
R
F(AV)
θJA
from Figure 4. **Read P
Step 3. Find P
= 0.5 W
F(AV)
125
115
40
I
(FM)
30
23
@
= 10 and I
= 0.5 A.
F(AV)
I
°
(AV)
Step 4. Find T
Step 4. Find T
from equation (3).
= 109 – (80) (0.5) = 69°C.
A(max)
A(max)
105
95
R
(°C/W) = 110
θ
JA
**Values given are for the 1N5818. Power is slightly lower for the
1N5817 because of its lower forward voltage, and higher for the
1N5819.
80
60
85
75
4.0
5.0
7.0
10
15
20
30
40
V
, DC REVERSE VOLTAGE (VOLTS)
R
Figure 3. Maximum Reference Temperature
1N5819
Table 1. Values for Factor F
Full Wave, Bridge
Half Wave
Circuit
Full Wave, Center Tapped*†
Load
Resistive
Capacitive*
Resistive
Capacitive
Resistive
1.0
Capacitive
Sine Wave
Square Wave
0.5
1.3
0.5
0.65
0.75
1.3
1.5
0.75
1.5
0.75
1.5
*Note that V
≈ 2.0 V .
in(PK)
†Use line to center tap voltage for V
.
R(PK)
in
2
Rectifier Device Data
MOTOROLA [ MOTOROLA ]
