Cool Cap Engineer

Engineering by an anime nerd

Mini Projects: Boost Converter Experimentation

Leave a comment

Since I started working in the power electronics industry, I figured I should spend a little more time building power electronic circuits. I remembered that I understood how non-isolated boost converters worked during my school work and decided to build one for myself.  For those who do not know, a boost converter is a power electronic circuit that converts incoming voltage to a higher voltage. I decided for starting purposes, I would build a 12V to 24V boost converter. Although I plan to write a tutorial which shows how boost converters work,  this post is to talk about what I did in my free time.

boost_converter_schematic

12V TO 24V Boost Converter Schematic

After a week relearning important boost converter design parameters, I managed to draw out the basic schematic. Although there are 3 components missing from my schematic, those parts functioned as a way to implement a controller for the boost converter. There are alot of major improvements that could be made, such as protecting Q2 from high voltages, solving the logic inversion caused by Q1, and prevent L1 from causing my power supply to current limit. However, I just want to see the boost converter work.

wpid-20140603_201022.jpg

Boost converter circuit soldered onto a perfboard

After buying my parts from Digi-key, I soldered my parts to a perfboard. Why not assemble the circuit on a breadboard? In order for this  boost converter to properly work, I needed to switch the main transistor (Q2 in the schematic) at a high frequency (I based my calculations around a 62.5KHZ switching frequency). Since I’m switching at a high frequency, building the circuit on a breadboard will screw up the signal due to the breadboard’s nature of acting as a capacitor at high switching frequencies.

wpid-20140529_214732.jpg

The boost converter load

Finally, to make sure the boost converter functions correctly, I needed to connect a load. I decided to go with a 25 ohm/50W resistor. If the boost converter was not connected to a load, then there’s a high chance the boost converter will go unstable. A high value resistor can be connected at the output to function as a dummy load to prevent the boost converter from going unstable. Also, I was dissipating a lot of heat through this resistor. The resistor got so hot that it melted one of my oscilloscope clips.

boost_converter_waveform

Blue waveform is the output at the load, while yellow is the square pulse going into the the Q1.

 

So I was ready to power up my converter. Since I was using my multimeter as a current meter, I had to setup my crappy Hantek oscilloscope to measure the voltage by measuring the DC level. One thing that surprised me was the actual duty cycle needed to set the voltage to 24V. To get 24V, instead of setting my frequency generator to 62.5KHZ with a 50% duty cycle, I got a 24V output  using the same frequency, but a 25% duty cycle. This usually happens when your boost converter is incredibly inefficient. Brother, my boost converter was the definition of it. According to my calculations, my boost converter efficiency was around 70%.Well…it was a good attempt, but converter needs a lot more work. I will need to investigate the causes of the low efficiency, and rectify it. My first suspicion involves the big bulky inductor. The bigger the inductor, the higher the parasitic resistance.

Thank you guys for reading this post, and if you have any suggestions on how I can improve the efficiency, then leave a comment below!

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s