🛠️ 【硬體】設計細節 🛠️
設計大電流降壓板思路
1. 基本需求
- 源電壓為 18V 工具機電池。
- 降壓至 12V、5V。
- 支援 PD 快充協議。
- 電源防反接、LED 指示燈。
- 預留 UPS、電壓偵測引腳。
2. 詳細參數估算
我是以剛好滿足各器件的官方參數最高值去做設計。
綜上所述,源電壓最高會承受 33.55 安培。
3. 線寬初步計算
閱讀 PCB走線線寬與電流的關係。附上 PCB 走線寬度計算器。
根據 IPC-2221 規範,厚度 2 oz 銅箔、溫升 10°C 下的最小走線寬度:
- 母線電壓(18V, 33.55A):內層 52 mm、外層 20 mm。
- 12V 電位(16.78A):內層 19.1 mm、外層 7.3 mm。
- 5V 電位(12.77A):內層 13.1 mm、外層 5.0 mm。
- PD 電位(5A):內層 3.6 mm、外層 1.4 mm。
實際上大電流走線會用大面積鋪銅,並非如訊號線一條條地拉。另外做好散熱設計,如散熱孔、開窗鋪錫或外接風扇等也可以適當縮減線寬。參考下圖實際範例。
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所以此寬度算是個在沒作額外處理下,一個保險的設計參考值。
除了 PCB 線寬,還須注意「端子座」及「實體電線」。
端子座依型號查詢額定電流。電線參考 電線AWG尺寸電流對照表。
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4. 選擇晶片
這裡我會簡述晶片選擇的依據,實際拓樸結構與佈局會於其他章節說明。
5. 繪製原理圖
盡量先多參考手冊 application 電路,或其他網路範例。
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重要參數會列 Excel 計算。
Excel 參數計算範例

6. 佈局
佈局觀念和細節多,會在其他章節詳述。