The main goal is to document the modules used in my UPS project and also promote the use of switch mode power supplies as efficient and/or more flexible substitutions. Most users simply pick the 7805 because they don't know the more efficient alternatives. They just copy/paste what they see on youtube or other sites.
Some of these modules have no simple linear alternatives e.g. Boost, isolated or Buck-Boost converters. One would otherwise require the use of multiple transformers windings or operate multiple supplies from a much higher input voltage.
I used what I had lying around, so they might not make sense anymore. I use parts from Aliexpress these days - a 2A module at $0.40 in my Audio switch project and a $0.10 boost converter chip: MT3608(.pdf) in my new LED flashlight project.
Buck Mode Power Supply
The traditional 78xx linear regulator are simple and convenient to use, but they are highly inefficient especially if you are powering it from a high voltage.
This power supply is pretty much straight from TI/National's LM3485 datasheet with what I have in my parts bin. Just a plug-in regulator module for one of my old projects. Just need to add a bulk electrolytic/tantalum etc. cap for the power input. You should already have that one in your project.
This was developed to be used 24/7 in my DC UPS since 2008 and has proven itself to be reliable.
From the datasheet - Typical Performance Characteristic (i.e. your mileage may vary)
There are all kinds of designs out there. I happen to have samples for this part. This is designed as pluggable modules e.g. 5V or 12V module for my UPS project.
A number of power supply chips have an upper limit on the duty cycles at 90-95%. This basically means that your output voltage is at most 90-95% of the input. They are sort of like the older generation of linear regulator with a higher drop out. For battery operations, such as running a 5V module from 4 AA batteries, don't leave you with a lot of head room before the 5V output is outside of the +/- 10% range needed.
When the input voltage is below the set point for the output, the MOSFET in this design is allowed to run at 100% duty cycle. It connects the input to the output and acts like a straight pass through. This drop out mode makes this design behave like a LDO. My routers runs off a 12V module and when running off the backup battery, the drop out mode allows my router to run all the way down to the low battery cut off voltage of 9.5V.
Buck Module - KIS-3R33S
These are pulled modules that was popular from Chinese site a few years ago. There was some minimal efforts in reverse engineering without understanding the design. Most of them require modifications inside the module to use them other than 3.3V modules. I did my homework and show you how to use these without modifications the way the original designer intended. Why else would they put a voltage adjustment pin?
I measured some of the internal component values. The current rating is not even close to 2A probably due to the inductor and the cooling problem in the case.
Coincidentally the 2A modules I mentioned above seem to be using the same chip, a better inductor, smaller footprint and some come with a trimpot for adjusting the output voltage.
By connecting an external resistor to the ADJ pin (7) to ground, you can increase the output voltage. By connecting an external resistor between the output and ADJ pin, you can decrease the output voltage. You do not need to modify them if you want to use them as a fixed output supply unless you want to get higher than 10V output. You also need to use a higher input voltage than 12V as the duty cycle is limited.
JP1 selects 5V/3.3V outputs. JP2 and JP3 are lined up with supply rails on the breadboard. When S1 is closed, the output is turned off.
Boost Module
These are modules that has a higher output than the input voltage. This was designed for my old ST516V6 ADSL modem to be used on my UPS. That modem comes with a huge transformer with a non-standard plug. It uses a high voltage, so I have to make a 26V boost module.
Design is also pretty much text book from the LM3478 documentation. Due to the high voltage, I use an Al electrolytic cap for the output bulk cap. R5 sets the switching frequency. The output voltage can be tweaked by playing with R6 and R7. R8 controls the inductor current. The chip doesn't have a whole lot of gate drive currents, so I would recommend a MOSFET with small gate capacitance (435pF). You can probably find a smaller MOSFET that does the job.
This board was designed to be etched at home. All the vias are large and outside of the components footprints and a piece of component lead was used to connect to the other side of the PCB.
Here is what I actually built:. I have to make do with the parts I have.
I ended up using a Sanyo 100uF/35V cap because the SMT part was too tall. A 10uH inductor was re-wounded for the right values.
I didn't have 22nF, so I had two 10nF at C2 and C6. I used two 0.15 ohms in parallel for the 0.075 ohms resistor. That used up the space for the 2 ceramic output cap, but the circuit works fine.
Isolated Module
Both my VoIP (ATA) and cordless phone decided to cut cost and eliminated their isolation circuits as they assume that the other device would have it. The end result is that these devices cannot coexist from power supplies that shared a common ground. This isolated supply module allow these two devices to work together in my UPS.
This is based on a boost converter in a flyback configuration. D1 and D3 are the zener clamp to keep the back EMF to protect Q1. L1B provides a feedback for the output voltage. The isolated output at winding L1C is poorly regulated as it is regulated by proxy via transformer ratio. That's all I need for the phone as it has its own regulator.
To make the transformer, I counted the number of turns on a 10uH inductor as I unwind it. To reduce the leak inductance, I rewound it with 3 thinner strands of wires at the same time (aka trifilar winding). L1B is for feedback and requires very little current, so you can get by with very thin wires. Keep the same number of turns as before and you'll have the same inductance.
The output as on the two solder pads - 0V on top and +6V on bottom.
SEPIC Converter
It is basically a buck-boost converter that can regulate an input that is lower or higher than its output. It sounds too good to be true. There are some draw back as it has a lower efficiency - power going through a few more parts means more losses. When your input voltage can be higher or lower, then this is an interesting and useful building block. This is taken from my Dual charger design which has such a requirement. You are otherwise better off from an efficiency point of view to use either a buck or a boost converter.
I have a working prototype of a 5V/100mA SEPIC converter. It is designed to work from 3V to 15V. I did some quick test here.
You can turn a boost converter into a buck-boost by adding a cap (C11) and an inductor (L2). The output is taken from L2 with rectifier diode (D4) and output cap (C14). The cap C11 serves as energy transfer between the two inductors. This particular version is built with 2 separate inductors. There are also version of the design that have L1 and L2 as a pair of coupled inductors. I use a couple of those in my charger project.
Reference:
This is the current layout I have for it. The switching frequency is 1.5MHz and it deserves a bit of care. It is mostly a single layer design with a full ground plane on the secondary side optimized for home made PCB. I have minimize the high frequency/high current loop area. Use shielded inductors if you want to minimize EMC issues.
I have ordered the cheapest inductors from China, so it might take a few week to arrive. This is what it would look like.
I notice that AP3019AKTR-G1 (boost converter for LED) are being sold on Aliexpress at $3.09 for 10 pieces. It is probably a variant of the Diodes Inc AP3012. The feedback voltage is lower, but it is a matter of changing the voltage divider ratios. Maybe I should use the SOT23-6 package so that it would take either chips.
Here is the home made PCB.
Negative rail Analog supply:
Switched cap inverter/boost:
Licenses:
Schematic: Creative Commons 4.0 Attribution-ShareAlike 4.0 International
PCB & Layout: Creative Commons 4.0 Attribution-NonCommercial
3D modelling: Creative Commons 4.0 Attribution-ShareAlike 4.0 International
Creative Commons 4.0 Attribution-NonCommercial:
Creative Commons 4.0 Attribution-ShareAlike 4.0 International
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