直流电源交换电路
电路能力测试-1：直流电源交换电路
circuit knowledge test-1: dc-dc switching regulator
if mp1580 switching frequency set at 400 khz, and dc regulator output 5v, then please plot the switching wave-shape at ic pin-3 with line input 12v and 16v.假设mp1580工作在400 khz,且稳压输出为5v,画出输入电压分别为12v 及 16v时，ic pin-3的正确波形。
now the dc regulated output is 5v. if we want to change the dc regulated output to 9v, what value of rp86 and rp89 are suitable for this change.目前的直流稳压输出为5v，如果希望提升为9v输出，如何修改rp86 及 rp89的数值。
explain the charge and discharge functions of ma701, lp15, cp61 components in details. 说明ma701, lp15, cp61元件的冲放电功能。
according to mp1580 switching efficiency chart data: dc 12v input and dc 5v 240ma output will display 85% efficiency. what input current rating will be for 12v supply? 根据mp1580的规格书，当直流12v输入，输出为5v 240ma时，转换效率为85%，计算输入电流值。
same condition as the question-4: if mp1580 ic with sop-8 package dissipation 160°c/w, then what surface temperature will be for mp1580 at 25°c room temperature?同上第四题，mp1580采用sop-8包装的传热系数为160°c/w，计算其室温25°c时的ic表面温度。
what is the maximum allowable ripple voltage at 5v dc regulated output to assure 40 db s/n if this 5v will supply for a video function ic? 当直流稳压输出5v，用来供应影像电路时，为了确保达到40 db s/n，求其最大容许连波电压数值。
explain the function of cp59, lp17, lp16 components? 说明cp59, lp17, lp16元件的功能。
试题解答
circuit knowledge test-1: dc-dc switching regulator
ans-1:
ans-2:
rp86=62k, rp89=1k8.
(r86+r89+r87)/r87 = 5.0/vref then vref=5.0/4.12=1.22
rn86+rn89 = (9.0/vref * r87) –r87 = 63.8k (62k + 1k8)
rp86=62k, rp89=1k8.
ans-3:
switching pulse comes from icp9 pin-3 and charge through lp15 to cp61 during switching-on duty-cycle. the inductive voltage across lp15 will then charge through dp8 to cp61 during switching-off duty-cycle. (note that inductive current will produce reverse voltage across coil lp15)
ans-4:
120 ma
dc input power = 5 * 0.24 / 0.85 = 1.41 w then dc input current = 1.41/12 = 120 ma.
ans-5:
58.6 °c
power loss = 1.41-1.2 = 0.21 w then thermal heat rise tht = 160 * 0.21 = 33.6 °c
final junction temperature tj = 25 + 33.6 = 58.6 °c
ans-6:
50 mvpp.
because 40 db means 1% level, then 5 volt d-c only allows for 50 mvpp ripple noise.
ans-7:
cp59: boot-straping capacitor for driving output power fet.
lp17: filter choke for filtering switching pulse generated from icp9.
lp16: filter choke for filtering switching noise to reach 40 db noise limit.
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circuit knowledge test-1: dc-dc switching regulator
if mp1580 switching frequency set at 400 khz, and dc regulator output 5v, then please plot the switching wave-shape at ic pin-3 with line input 12v and 16v.假设mp1580工作在400 khz,且稳压输出为5v,画出输入电压分别为12v 及 16v时，ic pin-3的正确波形。
now the dc regulated output is 5v. if we want to change the dc regulated output to 9v, what value of rp86 and rp89 are suitable for this change.目前的直流稳压输出为5v，如果希望提升为9v输出，如何修改rp86 及 rp89的数值。
explain the charge and discharge functions of ma701, lp15, cp61 components in details. 说明ma701, lp15, cp61元件的冲放电功能。
according to mp1580 switching efficiency chart data: dc 12v input and dc 5v 240ma output will display 85% efficiency. what input current rating will be for 12v supply? 根据mp1580的规格书，当直流12v输入，输出为5v 240ma时，转换效率为85%，计算输入电流值。
same condition as the question-4: if mp1580 ic with sop-8 package dissipation 160°c/w, then what surface temperature will be for mp1580 at 25°c room temperature?同上第四题，mp1580采用sop-8包装的传热系数为160°c/w，计算其室温25°c时的ic表面温度。
what is the maximum allowable ripple voltage at 5v dc regulated output to assure 40 db s/n if this 5v will supply for a video function ic? 当直流稳压输出5v，用来供应影像电路时，为了确保达到40 db s/n，求其最大容许连波电压数值。
explain the function of cp59, lp17, lp16 components? 说明cp59, lp17, lp16元件的功能。
试题解答
circuit knowledge test-1: dc-dc switching regulator
ans-1:
ans-2:
rp86=62k, rp89=1k8.
(r86+r89+r87)/r87 = 5.0/vref then vref=5.0/4.12=1.22
rn86+rn89 = (9.0/vref * r87) –r87 = 63.8k (62k + 1k8)
rp86=62k, rp89=1k8.
ans-3:
switching pulse comes from icp9 pin-3 and charge through lp15 to cp61 during switching-on duty-cycle. the inductive voltage across lp15 will then charge through dp8 to cp61 during switching-off duty-cycle. (note that inductive current will produce reverse voltage across coil lp15)
ans-4:
120 ma
dc input power = 5 * 0.24 / 0.85 = 1.41 w then dc input current = 1.41/12 = 120 ma.
ans-5:
58.6 °c
power loss = 1.41-1.2 = 0.21 w then thermal heat rise tht = 160 * 0.21 = 33.6 °c
final junction temperature tj = 25 + 33.6 = 58.6 °c
ans-6:
50 mvpp.
because 40 db means 1% level, then 5 volt d-c only allows for 50 mvpp ripple noise.
ans-7:
cp59: boot-straping capacitor for driving output power fet.
lp17: filter choke for filtering switching pulse generated from icp9.
lp16: filter choke for filtering switching noise to reach 40 db noise limit.
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