Design Considerations The LM79XX fixed voltage regulator series has thermal Where TJ Junction Temperatur for reducing the output current as the voltage across the PD Power Dissipation ss transistor is increased BJa Junction-to-Ambient Thermal Resistance ough the internal power eJc Junction-to-Case Thermal Resistance BCA Case-to-Ambient Thermal itions. To calculate the maximum junction ecs Case-to-Heat Sink Thermal Resistance at sink required, the following thermal resistance values esa Heat Sink-to-Ambient Thermal Resistance should be used. Typical Applications(Continued) Bypass capacitors ssary for stable operation of the Package LM79XX series of regulators over the input voltage and out- ecw|"cwlc/w°c/W actors will he transient response by the regulator To-220 J Max IA eca =ecs+ esa (without heat sink) pass capacitors should be mounted with the shortest Solving for TJ leads, and if possible, directly across the regulator termi- TJ= TA Pp(OJC t OcA) TA+ PoOja(without heat sink High Stability 1 Amp Regulator R2 LM308 LM7905 o our(-) TLH/7340·6 gulation< 0.01% temperature stability s 0.2% "Select resistors to set output voltage. 2 ppm/C tracking suggestedDesign Considerations The LM79XX fixed voltage regulator series has thermal overload protection from excessive power dissipation, inter￾nal short circuit protection which limits the circuit’s maxi￾mum current, and output transistor safe-area compensation for reducing the output current as the voltage across the pass transistor is increased. Although the internal power dissipation is limited, the junc￾tion temperature must be kept below the maximum speci￾fied temperature (125§C) in order to meet data sheet specifi￾cations. To calculate the maximum junction temperature or heat sink required, the following thermal resistance values should be used: Typ Max Typ Max Package iJC iJC iJA iJA §C/W §C/W §C/W §C/W TO-220 3.0 5.0 60 40 PD MAX e TJ Max b TA iJC a iCA or TJ Max TA iJA iCA e iCS a iSA (without heat sink) Solving for TJ: TJ e TA a PD (iJC a iCA) or e TA a PDiJA (without heat sink) Where: TJ e Junction Temperature TA e Ambient Temperature PD e Power Dissipation iJA e Junction-to-Ambient Thermal Resistance iJC e Junction-to-Case Thermal Resistance iCA e Case-to-Ambient Thermal Resistance iCS e Case-to-Heat Sink Thermal Resistance iSA e Heat Sink-to-Ambient Thermal Resistance Typical Applications (Continued) Bypass capacitors are necessary for stable operation of the LM79XX series of regulators over the input voltage and out￾put current ranges. Output bypass capacitors will improve the transient response by the regulator. The bypass capacitors, (2.2 mF on the input, 1.0 mF on the output) should be ceramic or solid tantalum which have good high frequency characteristics. If aluminum electrolyt￾ics are used, their values should be 10 mF or larger. The bypass capacitors should be mounted with the shortest leads, and if possible, directly across the regulator termi￾nals. High Stability 1 Amp Regulator TL/H/7340 –5 Load and line regulation k 0.01% temperature stability s 0.2% ²Determine Zener current ² ²Solid tantalum *Select resistors to set output voltage. 2 ppm/§C tracking suggested 4