{"id":84,"date":"2025-10-28T15:41:11","date_gmt":"2025-10-28T08:41:11","guid":{"rendered":"https:\/\/phamquangvuong.com\/?p=84"},"modified":"2025-10-28T15:41:11","modified_gmt":"2025-10-28T08:41:11","slug":"hieu-ve-cong-suat-va-hieu-suat-mach-dien","status":"publish","type":"post","link":"https:\/\/phamquangvuong.com\/en\/understanding-electrical-power-and-circuit-efficiency\/","title":{"rendered":"Understanding Electrical Power and Circuit Efficiency"},"content":{"rendered":"

<\/p>\n

1. Introduction<\/h2>\n

Electrical power and efficiency are two key parameters that determine how effectively a circuit converts and uses energy. In real circuits, not all supplied energy reaches the load \u2014 part of it is inevitably lost as heat or electromagnetic interference (EMI).<\/p>\n

2. Electrical Power<\/h2>\n

Symbol:<\/strong> P \u00a0\u00a0 Unit:<\/strong> Watt (W)<\/p>\n

Power represents the rate at which electrical energy is consumed or converted. The basic formula is:<\/p>\n

P = V \u00d7 I<\/code><\/pre>\n
Other useful forms (when resistance is known):<\/p>\n
P = I\u00b2 \u00d7 R\r\nP = V\u00b2 \/ R<\/code><\/pre>\n
\"Power<\/a>
Graph:<\/em> Relationship between power and current for a fixed resistance (P = I\u00b2R).<\/figcaption><\/figure>\n
3. Example Calculations<\/h2>\n
Example 1:<\/strong> A 10\u03a9 resistor carries 2A of current. Calculate its power dissipation.<\/p>\n
P = I\u00b2 \u00d7 R = 2\u00b2 \u00d7 10 = 40 W<\/code><\/pre>\n
Example 2:<\/strong> A 12V\u20136W lamp. Find the current:<\/p>\n
I = P \/ V = 6 \/ 12 = 0.5 A<\/code><\/pre>\n
4. Circuit Efficiency<\/h2>\n
Symbol:<\/strong> \u03b7 (eta) \u00a0\u00a0 Unit:<\/strong> %<\/p>\n
Efficiency measures the ratio of useful output power to total input power:<\/p>\n
\u03b7 = (P_out \/ P_in) \u00d7 100%<\/code><\/pre>\n
Example:<\/strong> A linear regulator with 12V input, 1A load, and 5V output:<\/p>\n
P_in = 12 \u00d7 1 = 12W\r\nP_out = 5 \u00d7 1 = 5W\r\n\u03b7 = (5 \/ 12) \u00d7 100% \u2248 41.7%<\/code><\/pre>\n
Over 7W are lost as heat \u2014 which is why linear regulators need large heatsinks.<\/p>\n
5. Linear vs Switching Power Supplies<\/h2>\n\n\n\n\n\n\n\n\n
Criteria<\/th>\nLinear Supply<\/th>\nSwitching Supply (SMPS)<\/th>\n<\/tr>\n<\/thead>\n
Efficiency<\/td>\n40\u201360%<\/td>\n80\u201395%<\/td>\n<\/tr>\n
Size<\/td>\nBulky<\/td>\nCompact, lightweight<\/td>\n<\/tr>\n
Noise<\/td>\nLow<\/td>\nHigh (EMI)<\/td>\n<\/tr>\n
Applications<\/td>\nAudio, measurement devices<\/td>\nComputers, chargers, industrial systems<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
6. Factors Affecting Power and Efficiency<\/h2>\n
    \n
  • Conductor resistance:<\/strong> Power loss increases with I\u00b2R.<\/li>\n
  • Temperature:<\/strong> High heat raises resistance, lowering efficiency.<\/li>\n
  • Design quality:<\/strong> Poor layout or cooling reduces performance.<\/li>\n<\/ul>\n
    7. Practical Design Tips<\/h2>\n
      \n
    • Choose components rated at least 2\u00d7 the expected power dissipation.<\/li>\n
    • Ensure proper airflow and spacing between heat-generating components.<\/li>\n
    • Use MOSFETs or high-efficiency ICs (low Rds-on, synchronous buck converters) to minimize losses.<\/li>\n<\/ul>\n
      8. Exercises<\/h2>\n
      Exercise 1:<\/strong> A 24V source powers a 120\u03a9 resistor. Calculate the current and power.<\/p>\n
      I = 24 \/ 120 = 0.2A\r\nP = 24 \u00d7 0.2 = 4.8W<\/code><\/pre>\n
      Exercise 2:<\/strong> A power supply input: 9V\u20132A; output: 5V\u20133A. Find its efficiency.<\/p>\n
      P_in = 9 \u00d7 2 = 18W\r\nP_out = 5 \u00d7 3 = 15W\r\n\u03b7 = (15 \/ 18) \u00d7 100% = 83.3%<\/code><\/pre>\n
      9. Conclusion<\/h2>\n
      Understanding power and efficiency allows engineers to design safe, reliable, and energy-efficient circuits. Applying P = V\u00d7I and \u03b7 = P_out\/P_in helps optimize power consumption, reduce thermal losses, and improve circuit longevity.<\/p>\n
      References<\/h3>\n
        \n
      • Thomas L. Floyd, Electronics Fundamentals: Circuits, Devices, and Applications<\/em>, Pearson, 2014.<\/li>\n
      • Paul Horowitz & Winfield Hill, The Art of Electronics<\/em>, Cambridge University Press, 2015.<\/li>\n<\/ul>\n
        Keywords:<\/strong> electrical power, efficiency, P=VI, power dissipation, SMPS, linear supply, circuit design, basic electronics<\/p>","protected":false},"excerpt":{"rendered":"
        1. Introduction Electrical power and efficiency are two key parameters that determine how effectively a circuit converts and uses energy. In real circuits, not all supplied energy reaches the load \u2014 part of it is inevitably lost as heat or electromagnetic interference (EMI). 2. Electrical Power Symbol: P \u00a0\u00a0 Unit: Watt (W) Power represents the […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[14],"tags":[],"class_list":["post-84","post","type-post","status-publish","format-standard","hentry","category-dien-tu-co-ban"],"_links":{"self":[{"href":"https:\/\/phamquangvuong.com\/en\/wp-json\/wp\/v2\/posts\/84","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/phamquangvuong.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/phamquangvuong.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/phamquangvuong.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/phamquangvuong.com\/en\/wp-json\/wp\/v2\/comments?post=84"}],"version-history":[{"count":1,"href":"https:\/\/phamquangvuong.com\/en\/wp-json\/wp\/v2\/posts\/84\/revisions"}],"predecessor-version":[{"id":86,"href":"https:\/\/phamquangvuong.com\/en\/wp-json\/wp\/v2\/posts\/84\/revisions\/86"}],"wp:attachment":[{"href":"https:\/\/phamquangvuong.com\/en\/wp-json\/wp\/v2\/media?parent=84"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/phamquangvuong.com\/en\/wp-json\/wp\/v2\/categories?post=84"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/phamquangvuong.com\/en\/wp-json\/wp\/v2\/tags?post=84"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}