Datasheet 1N5820, 1N5821, 1N5822 (ON Semiconductor) - 4

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1N5820, 1N5821, 1N5822 NOTE 3 — DETERMINING MAXIMUM RATINGS
Reverse power dissipation and the possibility of thermal use in common rectifier circuits, Table 1 indicates suggested runaway must be considered when operating this rectifier at factors for an equivalent dc voltage to use for conservative reverse voltages above 0.1 VRWM. Proper derating may be design, that is: accomplished by use of equation (1). VR(equiv) = V(FM) F (4) TA(max) = TJ(max) RqJAPF(AV) RqJAPR(AV)(1) The factor F is derived by considering the properties of the where TA(max) = Maximum allowable ambient temperature various rectifier circuits and the reverse characteristics of TJ(max) = Maximum allowable junction temperature Schottky diodes. (125°C or the temperature at which thermal EXAMPLE: Find TA(max) for 1N5821 operated in a runaway occurs, whichever is lowest) 12-volt dc supply using a bridge circuit with capacitive filter PF(AV) = Average forward power dissipation such that IDC = 2.0 A (IF(AV) = 1.0 A), I(FM)/I(AV) = 10, Input PR(AV) = Average reverse power dissipation Voltage = 10 V(rms), RqJA = 40°C/W. RqJA = Junction-to-ambient thermal resistance Step 1. Find VR(equiv). Read F = 0.65 from Table 1, Figures 1, 2, and 3 permit easier use of equation (1) by V taking reverse power dissipation and thermal runaway into R(equiv) = (1.41) (10) (0.65) = 9.2 V. consideration. The figures solve for a reference temperature Step 2. Find TR from Figure 2. Read TR = 108°C as determined by equation (2). @ VR = 9.2 V and RqJA = 40°C/W. TR = TJ(max) RqJAPR(AV) (2) Step 3. Find PF(AV) from Figure 6. **Read PF(AV) = 0.85 W Substituting equation (2) into equation (1) yields: I(FM) @ 10 and I I F(AV) 1.0A. (AV) TA(max) = TR RqJAPF(AV) (3) Step 4. Find TA(max) from equation (3). Inspection of equations (2) and (3) reveals that TR is the TA(max) = 108 (0.85) (40) = 74°C. ambient temperature at which thermal runaway occurs or **Values given are for the 1N5821. Power is slightly lower where TJ = 125°C, when forward power is zero. The for the 1N5820 because of its lower forward voltage, and transition from one boundary condition to the other is higher for the 1N5822. Variations will be similar for the evident on the curves of Figures 1, 2, and 3 as a difference MBR-prefix devices, using P in the rate of change of the slope in the vicinity of 115°C. The F(AV) from Figure 6. data of Figures 1, 2, and 3 is based upon dc conditions. For
Table 1. Values for Factor F Full Wave, Circuit Half Wave Full Wave, Bridge 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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