Half-bridge DC/DC power supply based on LM5036

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Half-bridge DC/DC power supply based on LM5036 [Copy link]

The LM5036 is a highly integrated half-bridge PWM controller with integrated auxiliary bias power supply, providing a high power density solution for telecommunications, data communications, and industrial power converters. The LM5036 contains all the functions required to implement a half-bridge topology power converter using voltage mode control. The device is suitable for the primary side of isolated DC-DC converters with an input voltage of up to 100V. Compared with traditional half-bridge and full-bridge controllers, the LM5036 has its own irreplaceable advantages:
(1) Integrated auxiliary bias power supply to power the LM5036 and primary and secondary side components, without the need for external auxiliary power supply, reducing circuit board size and cost, and helping to achieve high power density and good thermal reliability.
(2) Enhanced pre-bias startup performance can achieve monotonic increase of output voltage and avoid reverse current when the load is started with voltage.
(3) Improved cycle-by-cycle current limit through pulse matching, resulting in a uniform output current limit level within the input voltage range, and also preventing transformer saturation.

Integrated auxiliary source:
For half-bridge drivers, when there is no external auxiliary power supply, the system requires a separate bias power supply and more components. The secondary bias voltage cannot be easily adjusted to control the system soft start process. Therefore, a separate external power supply and more components are required, which will eventually occupy a large amount of board area.

The LM5036 integrates a Fly-buck controller with COT control mode to generate power for the LM5036 and the devices on the primary and secondary sides. Moreover, the length of the ON time in the COT control mode here can be set by the Ron of Pin-6. The voltage values of VAUX1 and VAUX2 can be set by connecting RFB1 and RFB2 externally. Only a small auxiliary source transformer is needed to realize the power supply of the LM5036 primary side VCC, the secondary side isolation drive power supply, the isolation optocoupler op amp, etc. (as shown in the power supply of each part in the figure above). Vaux2 also participates in the pre-bias startup process as an enable signal for communicating between the primary and secondary sides, and realizes the timing control of pre-bias startup by cooperating with the discharge reset circuit. It can be seen that Vaux2 completes the communication between the primary and secondary sides here, avoiding the use of additional isolation signal circuits. Indirectly reduce the number of BOMs and increase power density. In addition, for the design of the auxiliary transformer, a simple tool design calculation table can be used to realize the design of the transformer and related devices. The application is simple, which greatly saves board area and comprehensive cost. As shown in the figure below, these functions can be easily realized by adding a small auxiliary transformer (yellow part), greatly improving the system power density.

As shown in the figure above, SW_AUX is the output terminal of Fly-buck, L3 is the output side inductor of the buck circuit, C36 is the output side capacitor, R22 and R23 are feedback voltage divider resistors, and R24, C34 and C35 form a Type-3 ripple injection circuit. When using the calculation tool, first enter some basic information of the auxiliary power supply, frequency, load current value, and inductance value. The corresponding capacitor selection can be calculated.
For the FB resistor, the corresponding FB resistor can be calculated based on the voltage of the front and rear stages of Flybuck. As shown in the Auxiliary Feedback Circuit table.

As for the parameter selection of the RCC ripple injection circuit, there are three different circuit options in the calculation table. After selecting TYPE-3, you can enter the target ripple voltage value and ripple current value to calculate the corresponding RCC resistance and capacitance values. Here, the values of Cac and Rr are generally fixed, and the corresponding selection of Cr can be made according to the calculated value.

As shown in the figure above, the evaluation board based on LM5036 is shown in the figure. Referring to the layout rules of the evaluation board, the upper part is the input filter circuit, half-bridge circuit, output side synchronous rectification and output filter circuit. The lower part is the key components around LM5036, auxiliary power supply circuit and feedback loop regulation circuit. The auxiliary power supply uses a very small board area to achieve multiple goals at one stroke. The common 200W brick power supply in the industry usually uses a 1/8 brick layout. Due to the high integration of LM5036, a 200W power supply can now be realized on a 1/16 brick module, and the same power can be achieved on a smaller layout area.

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lm5036具有集成辅助偏置电源的LM5036半桥PWM控制器.pdf (3.5 MB, downloads: 8)

2020-7-20 21:03 上传

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led2015

The information is very detailed. I will look for the experiment.

okhxyyo

Thanks for sharing, good information