1N5820(2006) Просмотр технического описания (PDF) - ON Semiconductor
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1N5820 Datasheet PDF : 8 Pages
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1N5820, 1N5821, 1N5822
NOTE 3 — 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) * RqJAPF(AV) * RqJAPR(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
RqJA = Junction−to−ambient thermal resistance
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).
TR = TJ(max) * RqJAPR(AV)
(2)
Substituting equation (2) into equation (1) yields:
TA(max) = TR * RqJAPF(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 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:
VR(equiv) = V(FM) F
(4)
The factor F is derived by considering the properties of the
various rectifier circuits and the reverse characteristics of
Schottky diodes.
EXAMPLE: Find TA(max) for 1N5821 operated in a
12−volt dc supply using a bridge circuit with capacitive filter
such that IDC = 2.0 A (IF(AV) = 1.0 A), I(FM)/I(AV) = 10, Input
Voltage = 10 V(rms), RqJA = 40°C/W.
Step 1. Find VR(equiv). Read F = 0.65 from Table 1,
NVR(equiv) = (1.41) (10) (0.65) = 9.2 V.
Step 2. Find TR from Figure 2. Read TR = 108°C
@ VR = 9.2 V and RqJA = 40°C/W.
Step 3. Find PF(AV) from Figure 6. **Read PF(AV) = 0.85 W
@
I(FM)
I(AV)
+
10 and
IF(AV)
+
1.0
A.
Step 4. Find TA(max) from equation (3).
TA(max) = 108 * (0.85) (40) = 74°C.
**Values given are for the 1N5821. Power is slightly lower
for the 1N5820 because of its lower forward voltage, and
higher for the 1N5822. Variations will be similar for the
MBR−prefix devices, using PF(AV) from Figure 6.
Table 1. Values for Factor F
Circuit
Half Wave
Load
Sine Wave
Resistive
0.5
Capacitive*
1.3
Square Wave
0.75
1.5
*Note that VR(PK) [ 2.0 Vin(PK).
†Use line to center tap voltage for Vin.
Full Wave, Bridge
Resistive
0.5
Capacitive
0.65
0.75
0.75
Full Wave,
Center Tapped*†
Resistive
1.0
Capacitive
1.3
1.5
1.5
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