Help Learning Power Electronics - Page 1
Forum section: electronics / beginners

author: braddrew0
author_rank: Regular Contributor
timestamp: June 09, 2019, 11:30:07 pm
content: Hi Guys,I'm predominately self-taught and I'm trying to get better at power electronics. I've been watching some interesting videos lately on YouTube on designs which use power electronics (eg CD spot welders, DIY soldering stations, basic SMPS, etc) and while I understand the rough concepts, being able to design something like that is well outside my league.I'm a practical learner, and I learn best by making things. I was wondering if it would be possible for someone to propose a bunch of 'challenges' or problems, in increasing order of difficulty, that I could work my way through in order to learn practical power electronics design? Alternatively, if there's a good resource that offers practical challenges, I'd love to hear about it.Thanks!

author: Psi
author_rank: Super Contributor
timestamp: June 10, 2019, 12:52:50 am
content: You will be better off choosing your own challenges.Something that, if you get it to work, is actually useful to you and that you will enjoy learning.The main issue is getting the motivation to continue going through the periods when stuff doesn't work or keeps blowing up.To keep going when it all seems hopeless and you just want to give up.The best thing to help with that is working on something you actually want to work on. Not something someone else recommended.

author: braddrew0
author_rank: Regular Contributor
timestamp: June 10, 2019, 02:10:18 am
content: That's really good advice but I think that's also my problem - I pick a project that seems simple and that I'm interested in, but then when it gets to be more than I can handle I lose motivation. I don't really have the experience to figure out what an 'easy' project is rather than something 'complex'.... maybe a better way to phrase my question is what are some easy power electronics projects and what are some more complex ones?

author: tpowell1830
author_rank: Frequent Contributor
timestamp: June 10, 2019, 02:39:11 am
content: Quote from: braddrew0 on June 10, 2019, 02:10:18 amTransformer with ferrous laminations with primary at mains voltage, secondary at a lower RMS voltage than desired DC voltage (use square root of 2 to multiply RMS voltage to get desired DC voltage), bridge rectifier, capacitor(s). Choose your desired power output - efficiency of transformer.Very simple, yet a bit complex for beginners. Read up on this type of power supply. Determine desired ripple voltage and do your calcs to achieve, measure ripple to see if you achieve.Hope this helps...EDIT: To stave off all of the folks who are afraid to let beginners use mains voltage, make sure you are very careful and safety oriented around mains voltage because it can harm or kill you!

author: xavier60
author_rank: Super Contributor
timestamp: June 10, 2019, 03:03:23 am
content: A bench power supply is a good project although I hesitate making the suggestion because of the risk of electric shock.I have a suggestion that should minimize the risk.Choose a transformer that has fly leads for the mains input and make fully insulated connections to the mains cord using two layers of heatshrink tubing. The idea is to have no exposed mains connections at least during the development stages.An oscilloscope will eventually be needed for more advanced projects.

author: braddrew0
author_rank: Regular Contributor
timestamp: June 10, 2019, 03:54:20 am
content: Great ideas, thanks!

author: MosherIV
author_rank: Super Contributor
timestamp: June 10, 2019, 06:51:07 am
content: Building on what Xavier60 suggested, build your own voltage regulation out of op-amps and transistors. Do not try current limit on your first design.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 10, 2019, 11:46:02 pm
content: You can never have enough power supplies!A fun project is to start with a L200 voltage regulator.It's a bit like the standard voltage regulators (Like 7805, LM317, etc), but it has a few extra pins for current sensing.With a single resistor you can set a maximum output current.Then you can extend this project in a few ways.One way is to add an opamp to amplify the voltage over the current shunt resistor, and feed the amplified voltage back to the regulator.This wil result (with a potmeter) in a power supply with an adjustable current limit.Another way to extend this power supply is to add a charge pump to generate a small negative voltage, and use that to power the "GND" pin of the L200. Then you can regulate the output voltage all the way to 0.But even with circuits as simple as this, you should have an oscilloscope to check for oscillations and other anomalities.---------Another (famous) and fun circuit to build is a reference voltage with an opamp, a zener diode and 3 resistors.LM358 is a cheap opamp that can be used from a single supply voltage (input and output work to close to 0V).The circuit should work as follows:The voltage over a zener diode usually is not very stable. It depends on the current through the zener.However, if you have a stable voltage, with a series connection of a zener and a resistor, then the zener current will be constant, and thererefore also the voltage over the zener.The opamp is then used to amplify the zener voltage (1.5 to 4 or so times), to a higher DC voltage, and the zener + series resistor are powered from the stable output voltage of the opamp.If you do not have a zener diode, you can also use a LED, The voltage over a LED depends on the color of the LED. Most are between 1.5V and 2.1V. White Leds (which are almost always blue leds, coated with fosfor to make the other colors) can go upto around 3V.You can use it as a puzzle, and design the circuit from my description, or you can find it on the 'net.-------------------------------Opamps are used for almost any analog circuit.Get yourself a copy of "opamps for everyone" aka slod006bA very simple and still educational is to use an opamp with FET inputs, such as the TL072 (also very cheap, buy a bag full)With opamps, traditionally a distinction is made between "single power supply" opamps, and "dual power supply" opamps.But this is mostly bollocks. There simply is no way in which an opamp can magically sense where "GND" is."GND" is usually some arbitrarily chosen reference.Opamps which are considered "dual power supply" usually do not work when the inputs or output are close to either voltage rail. They often need 1 to 2V headroom.One of the simplest circuits with an opamp is a buffer.Use a somewhat higher power supply voltage ( between 15V and 32V) for the TL072.Then connect the output to the inverting input.Connect the non-inverting input to a capacitor, and the other side of the capacitor to your "GND" reference (usually the lowest voltage rail).put a bit of charge on the capacitor, by touching the positive voltage rail with one hand, and the connection between the capactior and opamp with your other hand.Measure the output voltage of the opamp.If you stop touching the capacitor, the output voltage should be fairly stable. It can take hours to discharge a capacitor through a high impedance input of an opamp.Experiment with different capacitors.Some have internal leakage, others don't.From the rate the output voltage of the opamp changes, you can calculate the current through the capacitor.Do that, and compare it with the datasheet of your opamp.

author: braddrew0
author_rank: Regular Contributor
timestamp: June 11, 2019, 08:25:31 am
content: Wow, this is awesome, thanks!