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Project Introduction
This module is a simple switching power supply module. Through the XL6019 switch chip (switching frequency is about 220kHz) BOOST boost circuit to boost the 20V output by the PD charger, and output
28V2A to power high-power LEDs. (In fact, the constant current drive circuit should be used for current regulation, but this project is mainly to test the performance of the domestic XL6019, so the voltage regulation output is used)
The design is derived from the project "XL6019 Verification Board"
V2.0 update content
■ Changed the output capacitor and optimized the output ripple (naturally it became more expensive)
If you want to use the original version, you can open the project> right-click version management and manually switch to the original version (V1.0)
Project content
Schematic diagram
The whole circuit consists of a power boost circuit and an output voltage feedback circuit. Under normal conditions, it works in a constant voltage output mode.
By changing the resistance of the voltage divider resistor (sliding resistor R3) connected to V_out in the feedback circuit, the V_out voltage can be adjusted
Design ideas (general for BOOST design)
If you want to use the Texas Instruments family bucket to design a power supply, you can visit this website https://webench.ti.com/power-designer/ to determine the design plan
Figure 1, Texas Instruments WBENCH page, the left side is a DC-DC power supply, the right side is an AC-DC power supply, and the DC boost and buck selects the left side.
Then copy the datasheet crazily, and it is full of various magical materials, which can meet most of your needs.
However, due to funding issues, I chose a cheap (relative to the same level of Texas Instruments power IC) but the manual is relatively simple (very simple, I dare not use it, After all, the power supply is stable rather than new) XL6019 is used as the boost IC.
The characteristics of XL chip are simple peripheral circuits and easy design. The switching frequency of XL6019 is 220kHz, which is a relatively high switching frequency choice among high current (>=4A) ICs in the XL family bucket, and it has a good adaptability to this application.
1. Determine the switching frequency of
XL6019 to be a fixed frequency of 220kHz (this frequency, there are really few power chips in this package), which will affect the overall layout, especially the selection of inductors and capacitors.
2. To select the inductor, you
can use this website https://product.tdk.com/en/search/lc_select_tool
to match the inductance value according to your needs, but the website has very limited support for Chinese, and using this tool requires a little English. The following is a screenshot of
Figure 2, BUCK (classic buck switching power supply topology) circuit design, where Vf is the diode in the buck circuit.
Click the drop-down menu on the right side of this page and replace step-down with BOOST. For XL6019, the chip itself is equivalent to Vsw, The diode is equivalent to Vf.
The circuit requires you to select the type of original parts. Generally, there is no need to select Automotive components. Commercial components are of sufficient quality
(except for those who are not good at it. Are there really inductor enthusiasts?).
After filling in the relevant parameters, click Search to get the inductors that can be selected
. For my application, the model recommended by TDK is SPM10054T-330M-HZR (unfortunately, only automotive-grade inductors are available here).
Next, search the mall, and you can generally see the corresponding model. Then use the inductor. This method can solve most inductor selection problems.
In the actual picture, in order to "give full play" to the output capacity of XL6019, I chose an inductor with a larger rated current (7A rated current), which is actually not necessary. In the application of driving LEDs, this is a waste of resources.
One disadvantage of TDK's inductors is that they are expensive. If you plan to choose an inductor to solve the problem yourself, please consider carefully: the selection of the inductor is related to the overall efficiency, performance and stability of the circuit. Many designers in this community and many designers who sell and make "standardized" modules ignore this point.
Guide to choosing power inductors
1. Determine the type of magnetic core according to the frequency.
The power inductors on the market can be divided into 4 categories: iron powder core, iron silicon aluminum alloy core, iron silicon chromium alloy core & iron-based material and carbonyl material core. The principle of specific materials is very complicated, and a complete explanation requires electrodynamics. A major breakthrough in the field of magnetization can definitely win the Nobel Prize.
The attached passive device introduction pdf (copyright@taiyouyouden) introduces some characteristics and value meanings of passive devices.
Iron powder core is suitable for switching frequencies below 50kHz,
iron silicon aluminum alloy core is suitable for switching frequencies below 100kHz, and
iron silicon chromium alloy core is suitable for higher switching frequencies.
2. Determine the internal resistance and current parameters of the inductor.
For the needs of this project, the average current of the inductor is about 3.5A (considering the overall efficiency is about 90%). Considering that the board has good heat dissipation, the internal resistance is more suitable within 80mOhm.
For the design of this power supply (220kHz), Iron-silicon-chromium alloy is selected as the core material. After consultation,
the PDMTAT series produced by PROD is made of iron-silicon-aluminum and cannot be used in power circuits above 100kHz (it cannot be used, but it is a pity at this price~).
The SMMS1360-330M produced by SXN can be used as a substitute. The price is similar, the internal resistance is smaller and it is integrally formed.
2. Select the rectifier
diode. Some solutions at this power level use synchronous rectification. The characteristic advantage of synchronous rectification is that semiconductor switching elements are used instead of diodes as the Vf switch in Figure 2. Since the diode conduction current must overcome the built-in electric field of its PN junction (Schottky diode is a metal-semiconductor dielectric junction) to do work, and switching elements such as MOSFET do not have the above problems. Therefore, the efficiency of synchronous rectification is higher when the current is larger (>=4A).
The rectifier diode usually uses a suitable Schottky diode. When selecting a suitable Schottky diode, the parameters to pay attention to are:
1. Reverse withstand voltage, the rated current
reverse withstand voltage is more than 1.5 times the designed output voltage, and the rated current is greater than the maximum switching current of the switch chip.
This design selects a diode with a reverse withstand voltage of 100V and a rated current of 10A, which can meet the requirements
2. The conduction voltage drop and the maximum dissipation allowed under the diode package (very important for circuit stability, many circuit makers will ignore it)
Since the diode heating caused by the charging and discharging of the junction capacitance can be ignored at this operating frequency, only the heat
generation caused by the voltage drop is discussed:
1. Calculate the duty cycle D of the IC switch at full load (duty cycle: circuit on time/(circuit off time + circuit on time))
D = (Vout - Vin)/Vout ~= 0.50
2. Estimate the maximum heat generation power, where Ilim is the maximum current of the switching IC, and ΔV is the conduction voltage drop of the diode (substitute the model I chose below to verify)
P >= (1-D) * Ilim * ΔV = (1-0.5) * 5 * 1 = 2.5W
The heat dissipation of this package can meet the requirements.
--To be continued--
Appendix 1:
Comparison between XL6019 and TI series competitive products
The first difference is the data sheet: As a hardware engineer, the understanding of IC comes largely from the data sheet, which is difficult for most domestic manufacturers to reach the level of international manufacturers. The left picture below is a screenshot of the LM2577 data sheet, and the right picture is a screenshot of the XL6019 data sheet (right picture)
Figure 1 Left: Partial screenshot of the LM2577 data sheet Right: Partial screenshot of the XL6019 data sheet
Although both pictures contain information on the design maximum value, there is at least one difference that has a great impact on my power supply design:
Parameters under extreme working conditions: In many cases, in order to save costs, the chip will work under critical conditions. At this time, the parameters are crucial to the stability of the power supply system. Even if the heat dissipation of this solution is good, the temperature rise cannot be completely ignored. Generally, the design should be based on the worst case (such as working under the maximum temperature rise), and if these parameters are not given, it may cause many problems and unnecessary design redundancy in future designs.
Of course, there are other problems in the specification such as
1. Lack of circuit design suggestions, especially passive device (capacitor and inductor) selection guide, which is particularly important for novice designers
2. Lack of circuit waveform and protection mechanism, which increases the difficulty of later debugging
and also affects the design.
The second is the problem of pin definition:
Figure 2: Left: LM2577 specification screenshot (pin definition part) Right: XL6019 specification screenshot (pin definition part)
Although the two IC packages are the same, the pins corresponding to the large area metal sheet are different. In practical applications, for better heat dissipation and working performance, the area of the GND network is required to be as large as possible, and in order to reduce switching losses (especially at high frequencies), the parasitic capacitance of the switch network in the PCB relative to other circuits should be reduced as much as possible, which requires the total area of the SW network to be as small as possible, and the design of the SW network corresponding to the XL6019 Metal Tab is not conducive to large-area GND copper heat dissipation on the PCB, nor is it conducive to reducing switching losses.
Putting aside the specifications and pins, let's look at the actual situation.
1. LM2577, LM2587 (classic low-power non-isolated integrated power supply chips, many domestic manufacturers have copied them, and the current mall prices are relatively high)
First, let's talk about the conclusion: In practical applications, they can mostly replace LM2577.
The reason is: the switching frequency of LM2577 is 53kHz, and the frequency of this IC is above 150kHz. In practical applications, the circuit output can usually be maintained while the inductor volume remains unchanged or even reduced. It should be noted that the specifications of passive components, especially inductors, must be re-selected, which is a large amount of work.
2. LM2589
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