Boost Converter
A boost converter using the MT3608 module.
This project is mostly designing and printing the case - there is no
custom circuitry involved, other than connectors for the module. However
there are a few twists to the project.
The boost converter is a widely-available module that takes an input of
2v - 24v and produces an output of 5v - 28v at about 2A. It features a
multi-turn potentiometer for adjustment of the output voltage, but in this
application it is used as a fixed-voltage boost converter for a number of
9v devices so they can be powered off a USB connector. To enable
this it has been matched with a USB micro connector as the input. A
screw connector is mounted for the output.
Parts
MT3608 DC-DC Step Up Converter Module
MICRO USB to DIP Adapter 5-pin female connector B type
2-Way PCB-Mount Screw Terminal
Warning!
Many of the
MT3608 modules have a fault that means that can easily be damaged when used
as supplied. The fault is that one end of the variable resistor used
for adjusting the output voltage is left open, when it should be connected
to the wiper. The image shows the link that needs to be added to the
underside of the PCB for these versions in order to make the connection and
ensure that the proper voltage is supplied to the feedback input of the
chip. There are a number of videos on the 'net that explain the
problem and show the fix.
Note that although the module is typically quoted as capable of supplying
2A, it will get very hot and possibly burn out if run continuously at that
current without a heatsink. A sensible limit is about 1A. The
devices used for this implementation are a digital ammeter, a transistor
tester, and a timer for time-lapse photography: each one consumes much
less than 1A. A suitable heatsink that will allow operation at more
than about 1A is the type supplied with the A4988/DRV8825 style of stepper
motor driver modules.
The case
The case is a
simple base with lid, however the mounting for the USB connector is
important, as it takes a lot of strain when the cable is plugged and
unplugged. In this design the support for the connector comes
from several places: Firstly, it is wired to the boost module using
heavy tinned copy wire. Secondly it straddles a beam molded in the
bottom of the base and positioned so that the back of the connector is
pushed up against the edge of the beam. And thirdly, it is screwed
down to two holes in the beam. The screw holes in the connector PCB
are very large, so a plastic strap was used across the connector PCB.
The module itself is simply a press fit onto side rails in the bottom of
the base. Note that no provision has been made for access to the voltage
adjustment screw. For this application the voltage was going to be
fixed. If the voltage needs to be adjustable then a hole in
the side of the case must be added.
The surround for the USB connection has been attached to the lid.
This makes it simpler to change, if needed, for a different style plug, in
case the existing cutout is not large enough. It also simplifies printing
the base because there is no overhang.
The Layout
The screw
terminal is soldered across the output pads. Note that the pads are
more than 5mm apart, so the thru-holes must be widened slightly on their
inner sides to fit the pin spacing of the terminal. The holes will then
extend almost to edge of the solder pads. The remainder of the pad
is large enough to provide a secure solder joint. The terminal fits
snugly against the side of the potentiometer.
The USB
connector is wired to the input pads using heavy tinned copper wire, as
mentioned above. The best way to do this is to solder the wires into
the module, insert the module in the base, position the connector on the
beam with the wires poking through, and solder in place. There is
enough angle in the lead from the module to the connector to enable the
connector to be positioned precisely. Note that the USB connector is upside
down with respect to the module - this puts the + and - solder pads on the
correct sides, and enables the beam to keep the connector from being pushed
back as the lead is inserted.
Usage
Plug a
USB cable in at one end and connect a multimeter to the other end.
Wind the potentiometer in (clockwise) until it starts to click, then wind
back until the desired voltage is shown. Rotate the potentiometer
back and forth a little to find the middle of the sweet spot - there is
quite a large amount of backlash.
Install the module, screw the USB connector down to the bridge, and connect
the device to be powered.
