Introduction: In the Search of Efficiency.
BUCK Converter on "DPAK" Size.
Usually, the beginners designer electronic or a hobbyist we need a voltage regulator in circuit board printed or a breadboard.
Unfortunately by simplicity, we use a linear voltage regulator but there aren't totally bad because ever is depending on the applications is important.
For example in precision analog devices (like measurement equipment) ever better uses a linear voltage regulator (to minimize noise problems). But in power electronics devices like a lamp LED, or a pre-regulator for linear regulators stage (to improve efficiency) is better to use a DC/DC BUCK converter voltage regulator as the main supply because these devices are better efficiency that a linear regulator in high current outputs or load hard.
Another option that is not so elegant but is fast, is to use DC / DC converters in prefabricated modules and just add them on top of our printed circuit but this makes the circuit board much bigger.
The solution that I propose to the hobbyist or the electronics beginner uses a module DC/DC BUCK converter that a module that is surface mount but, saving space.
- 1 Buck switching converter 3A --- RT6214.
- 1 Inductor 4.7uH/2.9A --- ECS-MPI4040R4-4R7-R
- 4 Capacitor 0805 22uF/25V --- GRM21BR61E226ME44L
- 2 Capacitor 0402 100nF/50V --- GRM155R71H104ME14D
- 1 Capacitor 0402 68pF/50V --- GRM1555C1H680JA01D
- 1 Resistor 0402 7.32k --- CRCW04027K32FKED
- 3 Resistor 0402 10k --- RC0402JR-0710KL
Step 1: Selecting the Best Ridder.
Selecting the DC/DC BUCK Converter.
The first step to designing a DC/DC Buck converter is to find the best solution for our application. The solution more fast is to use a switching regulator instead of using a switching controller.
The difference between these two options is shown below.
- Switching regulator.
Many times they are monolithic.
The efficiency is better.
They don't support very high output currents.
They are easier to stabilize (Only require a circuit RC).
The user hasn't needed a lot of knowledge about the DC/DC converter to make the circuit design.
Are preconfigured to works only in a specific topology.
- The final price is lower.
Show below an example reduced by a Switching Regulator [The first image on this step].
- Switching controller.
- Require a lot of external components such as MOSFETs and Diodes.
- They are more complex and the user needs more knowledge about DC/DC converter to make the circuit design.
- They can use more topologies.
- Support a very high output current.
- The final price is higher.
Show below a typical application circuit of a Switching Controller [The second image on this step]
- Considering the following points.
- Space [The power output is dependent on this].
- Power output.
In this case, I use a Richtek RT6214 [A for continuous mode is better for the hard load, and the option B that it works in the discontinuous mode which is better for light load and improve efficiency at low output currents] that is a DC/DC Buck Converter monolithic [and thus we don't need any external components such as Power MOSFETs and diodes Schottky because the converter has integrated MOSFET switches and other MOSFET that works such as Diode].
Step 2: The Inductor Is Your Best Ally in the DC/DC Converter.
Understanding the inductor [Analysis of datasheet].
Considering the space on my circuit, I use an ECS-MPI4040R4-4R7-R with has a 4.7uH, nominal current of 2.9A, and a saturation current of 3.9A and DC resistance 67m ohms.
- Nominal current.
The nominal current is the current value where the inductor doesn't lose the properties such as inductance and doesn't significative increment the ambient temperature.
- Saturation current.
The saturation current in the inductor is the current value where the inductor loses its properties and doesn't work to store energy in a magnetic field.
- Size vs Resistance.
Its normal behavior that space and resistance are dependent on each other because if need saves space we need to save space reducing the AWG value in the magnet wire and if I want to lose resistance I should increment the AWG value in the magnet wire.
- Self-resonance frequency
The self-resonance frequency is achieved when the switching frequency canceled the inductance and only now exists the parasitic capacitance. Many manufacturers recommended maintaining switching frequency an inductor for at least a decade below of self-resonance frequency. For example
Self-resonance frequency = 10MHz.
f-switching = 1MHz.
Decade = log[base 10](Self - Resonance frequency / f - switching)
Decade = log[base 10](10MHz / 1MHz)
Decade = 1
Step 3: The Inductor Is the Heart.
Selection the Ideal Inductor
The inductor is the heart of DC / DC converters, therefore it is extremely important to keep the following points in mind in order to achieve good voltage regulator performance.
The output current of regulator voltage, nominal current, saturation current, and ripple current.
In this case, the manufacturer provides equations to calculate the ideal inductor according to the ripple current, voltage output, voltage input, switching frequency. The equation is shown below.
L = Vout (Vin-Vout) / Vin x f-switching x ripple current.
Ripple current = Vout (Vin-Vout) / Vin x f-switching x L.
IL(peak) = Iout(Max) + ripple current / 2.
Applying the equation of ripple current on my inductor [The values are in the previous Step] the results be shown below.
Vin = 9V.
Vout = 5V.
f-Switching = 500kHz.
L = 4.7uH.
Iout = 1.5A.
Ideal ripple current = 1.5A * 50%
Ideal ripple current = 0.750A
Ripple current = 5V (9V - 5V) / 9V x 500kHz x 4.7uH
Ripple current = 0.95A*
IL(peak) = 1.5A + 0.95A / 2
IL(peak) = 1.975A**
*Is recommended use the ripple current near to 20% - 50% of the output current. But this isn't a general rule because it depends on the response time of the switching regulator. When we need a fast time response we should use a low inductance because the charge time on inductor is short and when we need a slow time response we should use a high inductance because the charge time is long and with this, we reducing the EMI.
**The manufacturer recommended doesn't exceed the maximum valley current that supports the device to maintain a secure range. In this case, the maximum valley current is 4.5A.
Step 4: The Future Is Now.
Use REDEXPERT to select the best inductor for your buck converter.
REDEXPERT is a great tool when you need to know what is the best inductor for your buck converter, boost converter, sepic converter, etc. This tool supports multiple topologies to simulate your inductor behavior, but this tool only supports part numbers from Würth Electronik. In this tool, we can view in graphs the temperature increment vs current and the losses of inductance vs current in the inductor. It only needs simple input parameters such as shown below.
- Input voltage
- output voltage
- current output
- switching frequency
- ripple current
The link is the next: REDEXPERT Simulator
Step 5: Our Need Is Important
Calculating the output values.
It is very simple to calculate the output voltage, we just need to define a voltage divider defined by the following equation. Only we need a R1 and define a voltage output.
Vref = 0.8 [RT6214A/BHGJ6F].
Vref = 0.765 [RT6214A/BHRGJ6/8F].
R1= R2 (Vout - Vref) / Vref
Shown below an example using a RT6214AHGJ6F.
R2 = 10k.
Vout = 5.
Vref = 0.8.
R1 = 10k (5 - 0.8) / 0.8.
R1 = 52.5k
Step 6: Great Tool for a Great Electronics Designer.
Use the tools of the manufacturer.
I used the simulation tools provided by Richtek. In this environment, you can view the behavior of the DC/DC converter in steady-state analysis, transient analysis, startup analysis.
And the results can be consulted in the images, documents, and video simulation.
Step 7: Two Are Better Than One.
PCB Design in Eagle and Fusion 360
The PCB design is make on Eagle 9.5.6 in collaboration with Fusion 360 I synchronize the 3D design with the PCB design to obtain a real view the circuit design.
Shown below the important points to create a PCB in Eagle CAD.
- Library create.
- Schematic design.
- PCB design or Layout design
- Generate Real 2D view.
- Add 3D model to device in layout design.
- Synchronize the Eagle PCB to Fusion 360.
Note: All the important point are illustrated by images that you find in beginning of this step.
You can download this circuit on GitLab repository: https://gitlab.com/zzabrahamzz/d2pak-buck-converter.git
Step 8: One Problem, One Solution
Ever try to consider all the variables.
The simplest isn't ever better... I said that to myself this when my project heating for up to 80ºC. Yes, if you need a relatively high output current, don't use linear regulators because they dissipate a lot of power.
My problem... the output current. The solution... uses a DC/DC converter to replace a linear voltage regulator in a DPAK package.
Because this I called the Buck DPAK project
Step 9: Conclusion.
DC / DC converters are very efficient systems for regulating voltage at very high currents, however at low currents they are generally less efficient but not less efficient than a linear regulator.
Nowadays it is very easy to be able to design a DC / DC converter thanks to the fact that the manufacturers have facilitated the way in which they are controlled and used.
Participated in the
PCB Design Challenge