Datasheet 1N5817, 1N5818, 1N5819 (ON Semiconductor) - 3

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