1N5818 查看數據表（PDF） - Motorola => Freescale
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1N5818 Datasheet PDF : 6 Pages
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1N5817 1N5818 1N5819
NOTE 1 — DETERMINING MAXIMUM RATINGS
Reverse power dissipation and the possibility of thermal runaway
must be considered when operating this rectifier at reverse voltages
above 0.1 VRWM. Proper derating may be accomplished by use of
equation (1).
TA(max) = TJ(max) – RθJAPF(AV) – RθJAPR(AV)
(1)
where TA(max) = Maximum allowable ambient temperature
TJ(max) = Maximum allowable junction temperature
(125°C or the temperature at which thermal
runaway occurs, whichever is lowest)
PF(AV) = Average forward power dissipation
PR(AV) = Average reverse power dissipation
RθJA = Junction–to–ambient thermal resistance
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).
TR = TJ(max) – RθJAPR(AV)
(2)
Substituting equation (2) into equation (1) yields:
TA(max) = TR – RθJAPF(AV)
(3)
Inspection of equations (2) and (3) reveals that TR is the ambient
temperature at which thermal runaway occurs or where TJ = 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
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 com-
mon rectifier circuits, Table 1 indicates suggested factors for an equiv-
alent dc voltage to use for conservative design, that is:
VR(equiv) = Vin(PK) x F
(4)
The factor F is derived by considering the properties of the various rec-
tifier circuits and the reverse characteristics of Schottky diodes.
EXAMPLE: Find TA(max) for 1N5818 operated in a 12–volt dc supply
using a bridge circuit with capacitive filter such that IDC = 0.4 A (IF(AV) =
0.5 A), I(FM)/I(AV) = 10, Input Voltage = 10 V(rms), RθJA = 80°C/W.
Step 1. Find VR(equiv). Read F = 0.65 from Table 1,
Step 1. Find ∴ VR(equiv) = (1.41)(10)(0.65) = 9.2 V.
Step 2. Find TR from Figure 2. Read TR = 109°C
Step 1. Find @ VR = 9.2 V and RθJA = 80°C/W.
Step 3. Find PF(AV) from Figure 4. **Read PF(AV) = 0.5 W
@
I(FM)
I(AV)
= 10 and IF(AV) = 0.5 A.
Step 4. Find TA(max) from equation (3).
Step 4. Find TA(max) = 109 – (80) (0.5) = 69°C.
**Values given are for the 1N5818. Power is slightly lower for the
1N5817 because of its lower forward voltage, and higher for the
1N5819.
125
° 115
105
95
85
40 30 23
RθJA (°C/W) = 110
80
60
75
2.0
3.0 4.0 5.0
7.0
10
15 20
VR, DC REVERSE VOLTAGE (VOLTS)
Figure 1. Maximum Reference Temperature
1N5817
125
° 115
40 30 23
105
RθJA (°C/W) = 110
80
95
60
85
75
3.0 4.0 5.0
7.0
10
15
20
30
VR, DC REVERSE VOLTAGE (VOLTS)
Figure 2. Maximum Reference Temperature
1N5818
125
40
30
° 115
23
105 RθJA (°C/W) = 110
80
95
60
85
754.0 5.0
7.0
10
15
20
30 40
VR, DC REVERSE VOLTAGE (VOLTS)
Figure 3. Maximum Reference Temperature
1N5819
Table 1. Values for Factor F
Circuit
Half Wave
Full Wave, Bridge
Full Wave, Center Tapped* †
Load
Resistive
Capacitive*
Resistive
Capacitive
Resistive
Capacitive
Sine Wave
0.5
1.3
0.5
Square Wave
0.75
1.5
0.75
*Note that VR(PK) ≈ 2.0 Vin(PK).
† Use line to center tap voltage for Vin.
0.65
0.75
1.0
1.3
1.5
1.5
2
Rectifier Device Data
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