直流電源交換電路

電路能力測試-1：直流電源交換電路

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.假設MP1580工作在400 KHz,且穩壓輸出為5V,畫出輸入電壓分別為12V 及 16V時，IC pin-3的正確波形。

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.目前的直流穩壓輸出為5V，如果希望提升為9V輸出，如何修改RP86 及 RP89的數值。

3. Explain the charge and discharge functions of MA701, LP15, CP61 components in details. 說明MA701, LP15, CP61元件的沖放電功能。

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? 根據MP1580的規格書，當直流12V輸入，輸出為5V 240mA時，轉換效率為85%，計算輸入電流值。

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?同上第四題，MP1580采用SOP-8包裝的傳熱系數為160°C/W，計算其室溫25°C時的IC表面溫度。

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? 當直流穩壓輸出5V，用來供應影像電路時，為了確保達到40 db S/N，求其最大容許連波電壓數值。

7. Explain the function of CP59, LP17, LP16 components? 說明CP59, LP17, LP16元件的功能。

試題解答

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.