Address quoted in this article: https://www.eepw.com.cn/article/201706/346888.htm.
one, overview
The power consumption of power supply is various, including switching loss, input/output capacitance loss, static power consumption of controller and. This paper mainly introduces the simple calculation. Including two aspects: one is the loss related to the magnetic core, that is, the traditional iron loss; The second is the loss associated with the inductor winding, which is commonly called copper loss.
Total Power Dissipation（W）= CopperLoss + CoreLoss
CopperLoss = IRMS2*RDC(mΩ )/1000
CoreLossGenerally, it is obtained by checking the manufacturer’s form.
Photos of switching power supply on a motherboard
2, calculation method
Take Pulse’s PA1513NL series inductor as an example, and adopt PA1513NL.321NLT. The datasheet downloaded from official website is as follows. The basic parameters are: the inductance is 320nH, and the DC resistance is 0.53 11.3%.
In the design, we use this resistor in the switching frequency of 600kHz and the load current I.LOADIn the BUCK circuit of 30A, where iripple = 30% * i.LOAD.
According to the above formula, it can be easily calculated that the maximum copper loss is:
CopperLoss = IRMS2* RDC(mΩ )/1000 =（30A）2 *(0.53*111.3% mΩ ）/1000 = 0.531W
Regarding the maximum iron loss, we must first calculate △B: (because the inductance error is a curve, we use the normal value to calculate it).
△B = .23* L(nH)* △I = 0.23 * 320（nH）* 30% * ILOAD = 662.4
Since the switching power supply works at a frequency below 600KHz, the iron loss can be found to be about 0.18W by looking up the table.
Then the total loss is as follows:
Total Power Dissipation（W）= CopperLoss + CoreLoss = 0.711W
By looking up the table, we can get that the temperature rise of the inductor is about 45 degrees Celsius under normal working conditions.
The main functions of evaluating the loss of inductance are: first, to see whether the loss of inductance will cause the overheating of inductance, which will lead to the decrease or even damage of inductance value; The second function is to adjust the parameters of inductance and improve the efficiency of the whole power conversion system.
threeAbout CoreLoss
In fact, the calculation method and curve of CoreLoss are not given on the datasheet of many inductance companies. If so, it is almost impossible to calculate the iron loss. In this case, there are two suggestions.
If this inductor is used in high-current and critical equipment, then please choose a supplier that provides iron loss, such as Pulse, Wurth, JW Miller, etc.
If the current is relatively small or the switching frequency is relatively low, the general iron loss is not the key factor. Then first evaluate whether the copper loss is OK, and leave a certain margin. If the inductance is overheated in the subsequent test, try to reduce the switching frequency of the power supply, or adopt an inductance with a smaller DCR.
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