直流电源交换电路 - 模拟电源 -

电路能力测试-1：直流电源交换电路

Circuit Knowledge Test-1: DC-DC Switching Regulator

1. 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。

2. 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。

3. 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。

4. 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。

5. 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。

6. 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。

7. 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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