Cool Cap Engineer

Engineering by an anime nerd


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Mini Projects: Boost Converter Experimentation

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.

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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.

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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.

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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.

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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!


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Rants: Second Room, New Lab

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Back in March, I moved from Kingston NY to Lawrence/Andover MA to work as a design engineer for a power electronics company. Due to the fact I needed to find an apartment within a 3 week time frame, I had no other choice but to rent a two bedroom apartment, even though I will be the only one living in the apartment. So, what did I do with the extra room? I turned it into a lab! Although I still need to get a bench multimeter, hot air soldering iron, etc, I think it’s a good starting point. Anyway, here’s a small tour of my lab.

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So right now my inventory is pretty sparse. The cabinet on the bottom I had before I moved to MA and contains spare items.Some of the items include diodes, op amps, atmel and PIC18F  microcontrollers, PIC programmers, and AVR programmers. However, one of my co-workers gave me his old electronics cabinet. This one contained a diverse amount of through-hole discrete parts such as resistors, capacitors, even some inductors. Either way, I will not run out of discrete components anytime soon.

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So I obtained another goodie from my co-worker- a power supply (15V/1A). Although I do not use it often since I have a higher wattage power supply (32V/5A),  I’ll find a use for it soon. For the first time in my engineering career, I finally invested in a….meh function generator. I never heard of Victor before obtaining the function generator, but it does a decent job. My chief complaint is the minimum and maximum duty cycles for square waves. This function generator can only be set to have a 20%-80% duty cycle for square waves. As a person who likes to switching things at a fast pace, this continues to annoy me.

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One of my electrical engineering colleague told me that a good electrical engineer typically has an analog and digital oscilloscope. I took that advice to heart and obtained an old school analog oscilloscope from – you guess it – my current co-worker. I’m not going to lie, I’m still tying to figure out how to use this scope. I tried looking for the instruction manual online and even asked my co-worker who lend me the oscilloscope, and I still cannot figure out how to use it.

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So this is one of the supplies I brought while I was living in Kingston. As embarrassing as it sounds, I lost the caps to the power supply’s output during the move to MA. For now, I have alligator clips attached to the power supply’s output. Although the current capability of the cables is a little less that the maximum current the power supply can deliver, my current projects are not really current demanding, so I can get away with it. Of course, I cannot forget my multimeter from Radioshack, Although I was groomed to love Fluke multimeters, I cannot complain about it as it gets the job done. I will get a bench and Fluke multimeter sometime in the future.

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So here’s my current oscilloscope. Originally I wanted to get a small cheap Techtronix oscilloscope but apparently the cheapest Techtronix oscilloscope I could find at the time was $1000. So…I brought a Hantek oscilloscope from Ebay. Although I find the screen to be a little hard on the eyes and the speed isn’t something to brag about,I can save pictures using USB! I cannot tell how many oscilloscopes I used in the past could only save waveforms using a floppy drive. I know it’s petty, but after using oscilloscopes for two years  now, it’s kind of a big deal.

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So the last item I got for my lab is my new soldering iron. My previous soldering iron I obtained from Radioshack started to affect my soldering. Instead of getting another cheap crappy soldering iron, I decided to invest in a Hakko 936 soldering iron. Not only did I get a new soldering iron, but I got two chisel tips with them. What’s great about these chisel tips is that the heat is spread out a little more, making through hole soldering a little easier.

So that’s it for my little post for today. Again, I apologize for the delay, but assimilating to life in MA was….more time consuming that I thought. Anyway, thanks for reading this post and if you have any suggestions on any lab equipment I should get, then please comment below! I will see you guys next week and have a wonderful day!