{"id":3473,"date":"2026-10-23T12:11:56","date_gmt":"2026-10-23T04:11:56","guid":{"rendered":"http:\/\/www.pojokrakyat.com\/blog\/?p=3473"},"modified":"2026-10-23T12:11:56","modified_gmt":"2026-10-23T04:11:56","slug":"how-to-calculate-the-power-loss-in-a-flyback-transformer-4e71-c534cc","status":"publish","type":"post","link":"http:\/\/www.pojokrakyat.com\/blog\/2026\/10\/23\/how-to-calculate-the-power-loss-in-a-flyback-transformer-4e71-c534cc\/","title":{"rendered":"How to calculate the power loss in a Flyback Transformer?"},"content":{"rendered":"

Hey folks, let\u2019s cut to the chase if you\u2019re working with flyback transformers\u2014whether you\u2019re a design engineer, a product manager, or even someone just testing power supply prototypes\u2014power loss is the silent killer that screws up efficiency, generates unnecessary heat, and can even make your whole design fail way before it\u2019s supposed to. As a flyback transformer supplier who\u2019s talked to dozens of customers who\u2019ve pulled their hair out over this, I\u2019ve seen way too many people guess at losses instead of calculating them right. Today, I\u2019m breaking this down like we\u2019re chatting over coffee, no fancy jargon that makes you Google every other word. First, let\u2019s get one thing straight: flyback transformers don\u2019t just have one loss\u2014they have a few different types, and if you skip any of \u2019em, your number\u2019s gonna be off. Flyback Transformer<\/a><\/p>\n

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First, let\u2019s start with the basics: what\u2019s a flyback transformer\u2019s deal anyway? It stores energy in its core when the primary side is on, then dumps that energy to the secondary when the primary turns off. That switching on and off is where a ton of losses happen, trust me. Now, let\u2019s list the losses we actually care about, because that\u2019s where most people mess up. There are two main buckets: core losses (those from the transformer\u2019s magnetic core) and copper losses (from the wires, duh). Wait, don\u2019t sleep on other small ones like leakage losses or winding capacitance, but let\u2019s keep this practical\u2014stuff that actually matters for your daily design.<\/p>\n

Let\u2019s kick off with copper losses, because that\u2019s the one people usually get right, but sometimes mess up when they\u2019re picking wire gauge. Copper loss is just I\u00b2R loss, right? But let\u2019s make that specific to flyback. The primary winding carries current every time the switch is on, and the secondary winding carries current every time the switch is off. So first, get your RMS current for each winding\u2014because it\u2019s not just the peak current you see on the scope. For a typical DCM (discontinuous conduction mode) flyback, the primary current ramps up from 0 to I_peak during the on-time T_on, so the RMS current for primary is I_p_rms = I_peak * sqrt(D\/3), where D is the duty cycle (T_on over switching period T_s). For CCM (continuous conduction mode), it\u2019s a bit different\u2014primary current doesn\u2019t drop to 0, so I_p_rms is sqrt(I_p_avg\u00b2 + (I_peak\/\u221a12)\u00b2). The secondary side? Its RMS current is I_s_rms = I_s_peak * sqrt(1-D)\/3, same as primary but for the off-time. Then multiply each by its own winding resistance (R_p for primary, R_s for secondary), add \u2019em up: P_copper = (I_p_rms)\u00b2 * R_p + (I_s_rms)\u00b2 * R_s. Wait, but how do you get R_p and R_s? Simple\u2014look up the wire\u2019s AWG (American Wire Gauge) resistance per meter, multiply by the length of each winding. Pro tip: if you\u2019re ordering transformers from us, we already calculate R_p and R_s into the part spec, so you don\u2019t have to guess, but it\u2019s good to know where that number comes from. A lot of folks pick too thin wire to save space, and that makes R way higher\u2014copper losses blow up, the transformer gets hot, and you have to derate the whole supply. I\u2019ve had customers come back saying their efficiency dropped 5% just because they went with a smaller wire than recommended, and that\u2019s 100% copper loss.<\/p>\n

Next up, core losses\u2014this is the one that trips even experienced engineers, because it\u2019s not just a simple formula. Core loss happens because the magnetic domain walls in the core material flip back and forth every switching cycle. That flipping creates hysteresis loss, and also eddy current loss from the current induced in the core itself. The standard formula for core loss is P_core = k * f^\u03b1 * B_peak^\u03b2 * V_core, where k, \u03b1, \u03b2 are constants you get from the core material\u2019s data sheet, f is switching frequency, B_peak is the peak magnetic flux density, and V_core is the volume of the core\u2019s magnetic path. Wait, let\u2019s make that less scary. First, B_peak is easy to calculate for flyback: B_peak = (V_p * T_on) \/ (N_p * A_c), where V_p is the primary input voltage, T_on is on-time, N_p is primary turns, A_c is the core\u2019s cross-sectional area. Most core manufacturers (we use top-grade ones here, so their data sheets have the k, \u03b1, \u03b2 numbers) will give you core loss per unit volume at a certain f and B. For example, if a core has a core loss of 100 mW\/cm\u00b3 at 100 kHz, 0.2 T, and your B_peak is 0.15 T, you scale that: P_core = core_loss_per_cm\u00b3 * (B_peak \/ rated_B)^\u03b2 * total_core_volume. That\u2019s way easier than messing with the exponents if you use the data sheet\u2019s reference point. Common mistake here: switching frequency is going up these days to make transformers smaller, but core loss goes up with f^\u03b1\u2014\u03b1 is usually between 1.5 and 2, so if you double frequency, core loss goes 2.8x to 4x. I see people cranking f to 500 kHz to shrink the transformer, then wondering why it\u2019s burning up\u2014core loss is the reason. That\u2019s why we spec core materials with low core loss at high frequencies for our high-freq flybacks, saves our customers so much headache.<\/p>\n

Now, the other small losses\u2014let\u2019s not gloss over these, because they add up if you\u2019re working with high-power designs. Leakage inductance loss: when the magnetic flux from the primary doesn\u2019t link all the way to the secondary, that\u2019s leakage, and when that energy gets dissipated every switch cycle, that\u2019s loss. For small power supplies, it\u2019s usually less than 10% of total loss, but for 100W+ supplies, it can be 5-15% if the transformer isn\u2019t wound right. Winding capacitance loss: at high frequencies, the capacitance between windings creates current that doesn\u2019t do any useful work, just dissipates as heat. Again, smaller at low freq, bigger above 200 kHz. Most of our transformers have minimal leakage and capacitance because we use interleaved winding designs\u2014we alternate primary and secondary layers to cut down leakage, and that knocks those extra losses way down.<\/p>\n

Wait, let\u2019s test this with a real example, not just numbers. Let\u2019s say a customer has a 24W flyback charger for a phone, switching at 65 kHz. Primary is AWG 30, secondary is AWG 36. They calculated: I_p_rms = 0.5 A, R_p = 0.5 \u03a9, I_s_rms = 2.5 A, R_s = 0.02 \u03a9. Copper loss is (0.5\u00b2 * 0.5) + (2.5\u00b2 * 0.02) = 0.125 + 0.125 = 0.25 W. Core loss: they\u2019re using a standard EE13 core, 0.5 cm\u00b3 volume, data sheet says core loss is 80 mW\/cm\u00b3 at 65 kHz, 0.1 T, their B_peak is 0.08 T, \u03b2=1.6. So P_core = 80 * (0.08\/0.1)^1.6 * 0.5 = 80 * 0.86 * 0.5 = ~34 mW. Total loss is 0.25 + 0.034 = ~0.284 W. That means efficiency is (24 \/ (24 + 0.284)) * 100 = ~99.88%? Wait, no, wait\u2014this is a tiny 24W charger, so those numbers are right, but if it\u2019s a 200W supply, copper loss might be 5W, core loss 1W, total 6W, efficiency 200\/206 = ~97%. That checks out with real-world numbers.<\/p>\n

Now, let\u2019s talk about common mistakes people make when calculating losses, because even if you do the math right, messing up inputs gives you wrong numbers. First, using peak current instead of RMS current for copper loss\u2014huge one. Peak current is what you use for wire insulation, but copper loss uses RMS, because it\u2019s based on heat from average power. Second, guessing B_peak instead of calculating it properly\u2014too high B_peak makes core loss skyrocket, too low and you\u2019re using a bigger core than needed, which costs more and adds weight. Third, using the wrong core material constants\u2014some materials are for low freq, some for high, if you grab k from a ferrite for 10 kHz and use it at 100 kHz, your core loss will be way off. Fourth, forgetting temperature\u2014both copper resistance goes up with temp (about 0.4% per \u00b0C) and core loss too, because ferrite\u2019s loss changes at higher temps. So if your transformer runs hot, R goes up, so copper loss goes up even more. That\u2019s why when we make transformers for industrial apps, we test them at 100\u00b0C, not room temp, so our customers don\u2019t get surprised when their unit gets hot and efficiency drops.<\/p>\n

Another thing: if you\u2019re testing a real transformer, not just calculating, how do you verify these numbers? We use a power analyzer to measure total input and output power, subtract to get total loss, then break it down with a thermal test. You can also measure R_p and R_s with an ohmmeter, use a fluxmeter to measure B_peak, so your calculation matches real life. I\u2019ve had customers send us their calculation and say \u201cwhy is your transformer\u2019s loss lower than mine?\u201d and it\u2019s usually because they guessed R_p or used generic core loss numbers, while we use actual measured values from our production line.<\/p>\n

Now, why does this matter for you? If you\u2019re designing a power supply that needs to be efficient (like EV chargers, telecom gear, or even small consumer electronics), power loss directly impacts your product\u2019s battery life, thermal management, and compliance. If your transformer\u2019s loss is higher than expected, you need a bigger heat sink, which adds cost and size, or your product might run too hot and trigger safety shutdowns. As a flyback transformer supplier, we don\u2019t just sell parts\u2014we help you get these numbers right. We provide data sheets with accurate R_p, R_s, core loss curves, and even can work with you on custom designs if your specs are tight. Whether you\u2019re a startup with a new product or an OEM upgrading an existing line, we can tailor transformers to minimize your power loss without forcing you to overspend.<\/p>\n

Wait, let\u2019s wrap this up with a quick recap, so you\u2019ve got a cheat sheet: 1. Separate losses into copper (I\u00b2R) and core (kf^\u03b1<\/em>B^\u03b2*V), add the small leakage\/capacitance losses if needed. 2. Use RMS current for copper, not peak. 3. Pull core material constants from your actual core\u2019s data sheet, not generic ones. 4. Account for temperature when calculating, since R and core loss change with heat. 5. Test with a power analyzer to confirm your numbers, because real life is never perfect.<\/p>\n

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At the end of the day, calculating flyback transformer power loss doesn\u2019t have to be rocket science. It\u2019s just breaking down the losses into their two main types, using the right variables, and avoiding the common mistakes that trip so many engineers. If you\u2019re working on a design and want to double-check your numbers, or need a custom transformer optimized for low power loss, hit us up. We\u2019ve got years of experience building flybacks for all kinds of applications, and we\u2019ll walk you through every step so you don\u2019t have to guess. No jargon, no hoops\u2014just straight answers to get your design right the first time.<\/p>\n

High-voltage Transformer<\/a> References:<\/p>\n

    \n
  1. Mohan, N., Undeland, T. M., & Robbins, W. P. (2003). Power Electronics: Converters, Applications, and Design (3rd ed.). John Wiley & Sons.<\/li>\n
  2. Ferrite Core Material Data Sheets, TDK Corporation.<\/li>\n
  3. "Flyback Transformer Design Guide", Texas Instruments Application Report SLUA657.<\/li>\n
  4. Sullivan, C. R. (2010). "Optimal Core Loss Models for High-Frequency Power Magnetics". IEEE Transactions on Power Electronics, vol. 25, no. 10, pp. 2508-2516.<\/li>\n<\/ol>\n
    \n

    Dongguan Hensiron Electric Co., Ltd.<\/a>
    As one of the most professional flyback transformer suppliers in China, we have world-leading production equipment and strong manufacturing capabilities. Please feel free to buy high quality flyback transformer made in China here from our factory. Customized orders are welcome.
    Address: Building 4, Xinxing Industrial Zone, Wangao Road, Wanjiang Street, Dongguan City, China
    E-mail: jessica@dghensiron.com
    WebSite:     https:\/\/www.dghensiron.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

    Hey folks, let\u2019s cut to the chase if you\u2019re working with flyback transformers\u2014whether you\u2019re a design … How to calculate the power loss in a Flyback Transformer?<\/span>Read more<\/a><\/p>\n","protected":false},"author":948,"featured_media":3473,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3436],"class_list":["post-3473","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-flyback-transformer-4512-c60b65"],"_links":{"self":[{"href":"http:\/\/www.pojokrakyat.com\/blog\/wp-json\/wp\/v2\/posts\/3473","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.pojokrakyat.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.pojokrakyat.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.pojokrakyat.com\/blog\/wp-json\/wp\/v2\/users\/948"}],"replies":[{"embeddable":true,"href":"http:\/\/www.pojokrakyat.com\/blog\/wp-json\/wp\/v2\/comments?post=3473"}],"version-history":[{"count":0,"href":"http:\/\/www.pojokrakyat.com\/blog\/wp-json\/wp\/v2\/posts\/3473\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.pojokrakyat.com\/blog\/wp-json\/wp\/v2\/posts\/3473"}],"wp:attachment":[{"href":"http:\/\/www.pojokrakyat.com\/blog\/wp-json\/wp\/v2\/media?parent=3473"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.pojokrakyat.com\/blog\/wp-json\/wp\/v2\/categories?post=3473"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.pojokrakyat.com\/blog\/wp-json\/wp\/v2\/tags?post=3473"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}