1N5820 データシートの表示（PDF） - ON Semiconductor

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1N5820

SCHOTTKY BARRIER RECTIFIERS 3.0 AMPERES 20, 30, 40 VOLTS

ON Semiconductor 

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

andĂ

IF(AV)

+

1.0ĂA.

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

Resistive Capacitive*

Sine Wave

0.5

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 Capacitive

0.5

0.65

0.75

0.75

Full Wave,

Center Tapped*†

Resistive Capacitive

1.0

1.3

1.5

1.5

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