Teach you step by step to design high frequency transformers for switching power supplies

- May 09, 2019-

High-frequency transformers are small in size and can work in power supply circuits with high switching frequency. They are important carriers of energy transfer.However, in the design of switching power supply, many parameters of transformer need to be set and calculated, which is very tedious. This paper summarizes the design steps of high-frequency transformer in the design of switching power supply step by step, and gives the significance and calculation method of each parameter.

Determine the basic parameters of the switching power supply

Ac input voltage minimum umin
(2) ac input voltage maximum umax
The grid frequency Fl switching frequency f
(4) output voltage VO (V) : known
(5) output power PO (W) : known
6. Power efficiency: normally take 80%

7 loss allocation coefficient Z: Z represents the ratio of secondary loss and total loss, Z=0 represents the total loss occurred in the primary, Z=1 represents the secondary loss. Generally take Z = 0.5

Step 2
According to the output requirements, select the type of feedback circuit and feedback voltage VFB
Step 3
According to u and PO values, the input filter capacitor CIN and dc input voltage minimum value VImin are determined
(1) make the response time of the rectifier bridge tc=3ms
According to u, find the CIN value
(3) get Vimin


Step 4
Based on u, VOR and VB were determined
VOR and VB values were detected from the table according to u

(2) select TVS by VB value

Select the magnetic core and skeleton used by the transformer and find out the following parameters:

(1) magnetic core effective cross-sectional area Sj (cm2), that is, effective magnetic flux area.
(2) the effective magnetic circuit length of the core l (cm)
(3) the core in no gap with the number of turns related to the equivalent inductance AL(H/ turn 2)

(4) skeleton broadband b (mm)