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電路能力測試-2：直流電源穩壓電路
Circuit Knowledge Test-2: DC-DC LDO Regulator
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- What will be the supply current for DV 5V regulated output on this drawing?
- If 78M05 with DPAK package dissipation 60°C/W, then what surface temperature will be for IC 78M05 at 25°C room temperature?
- Same condition as the Question-3: If DC 5V output will supply 150 mA for all circuits, what surface temperature will be for IC 78M05 at 25°C room temperature?
- What minimum input voltage will be allowed for 5V stabilized output if the minimum dropout voltage for LM78M05 is 1.5 Volt?
- What will be the suitable resistance value and power rating of RP92 & RP93 for lowest LM78M05 surface temperature theoretically at 100 mA supply current and 10 volt low line input?
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試題解答
Circuit Knowledge Test-2: DC-DC LDO Regulator
ANS-1:
Vin = 12 – 34 * 0.084 = 12 – 2.86 = 9.14 Volt.
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ANS-2:
Same as the input current 84 mA.
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ANS-3:
Power loss = (9.14 – 5.0) * 0.084 = 0.35 W. then Tht = 0.35 * 60 = 21 °C
Final junction temperature Tj = 25 + 21 = 46 °C
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ANS-4:
Vin = 12 – 34 * 0.15 = 6.9 Volt.
Power loss = (6.9 – 5.0) * 0.15 = 0.285 W. then Tht = 0.285 * 60 = 17 °C
Final junction temperature Tj = 25 + 17 = 42 °C
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ANS-5:
Vmin = 34 * 0.084 + 1.5 + 5.0 = 9.36 Volt.
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ANS-6:
Vdrop = 10 – 5.0 – 1.5 = 3.5 then R = 3.5/0.1 = 35 Ohm.
RP92 = RP93 = 68 Ohm.
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