DPS3003 Power Supply - AC/DC Converter + Output Filter - Page 1
Forum section: electronics / beginners

author: MAntunes
author_rank: Regular Contributor
timestamp: December 28, 2018, 11:07:34 pm
content: Hi guys,I'm designing a small bench power supply using the DPS3003 module.I have a 24VAC transformer and some big capacitors and I want to use them so I'm designing an AC to DC converter using a LM317.I'm regulating the output to 32V so I can use the full DPS3003 module's voltage range.I don't think I'll be using currents higher than 1A but do you think I should add series pass transistors to handle higher currents, just to be safe? The datasheet recommends a 2N2905 and a TIP73, but are there any alternatives? My local electronics store does not have these.The current schematic is in attachment.Also, I'd like to design an output filter to remove the higher frequencies of the switching converter, but I don't know where to start. A LC filter would be enough? Or would an active filter be better?I'll be posting the updates in this thread so everyone can check on this project's progress.Thank you,Miguel

author: StillTrying
author_rank: Super Contributor
timestamp: December 28, 2018, 11:30:57 pm
content: "I have a 24VAC transformer and some big capacitors and I want to use them so I'm designing an AC to DC converter using a LM317.I'm regulating the output to 32V so I can use the full DPS3003 module's voltage range."The first 3 sites I looked at all say the DPS3003 can have up 40VDC input, so I don't see how the LM317 is needed, just the bridge and caps ?

author: thedoc298
author_rank: Contributor
timestamp: December 29, 2018, 05:59:58 am
content: Skip all that and just connect the bridge>cap to the dps3003 input and let it do the rest. As StillTrying also mentioned.

author: spec
author_rank: Frequent Contributor
timestamp: December 29, 2018, 10:46:40 am
content: Hi MAntunes: interesting PSU project.Quote from: MAntunes on December 28, 2018, 11:07:34 pmWhat is the secondary current rating of your transformer?Quote from: MAntunes on December 28, 2018, 11:07:34 pmAs the other members say, an LM317 stage is not required. In fact it would limit your output voltage range considerably and would add heat and unnecessary complication. I like your nice neat schematic though.Quote from: MAntunes on December 28, 2018, 11:07:34 pmAfraid you will not be able to get an output of 32V with a 24V AC transformer. If you let us know the secondary current rating of your transformer and the maximum PSU output current that you want, I will work out what your maximum output voltage can be.Quote from: MAntunes on December 28, 2018, 11:07:34 pmCan we take it that the maximum current you want is 1A?Quote from: MAntunes on December 28, 2018, 11:07:34 pmThere are standard techniques to reduce switching noise. I would not think that an active filter would be necessary or desirable.The 1N400x type rectifier diodes in your schematic are not the best for this application. I can recommend a better type if you like.

author: nsrmagazin
author_rank: Regular Contributor
timestamp: December 29, 2018, 02:26:04 pm
content: I don't mean to offend you, some consider this description right, but its very wrong to me.Please don't do this: "I have 24VAC and 32VDC". The right way would be: I have "230VAC RMS" lowered by a transformer to "24VAC RMS", from where I get "24*1.4 = 32VDC". When I remove the voltage drop over the diodes and other components I get.......Also please provide a circuit, so we can tell you more. The voltage regulator is useful, but you may need to make LM317 as a current and voltage regulator setup. Sometimes the load can drain a large current and burn your circuits. You will certainly need a heatsink for the LM317 for this current. You have "3V over the LM317 * 1ADC == 3W".EDIT:The transistors that you are looking for are 2n3055(NPN) and 2n2955(PNP). You should calculate will they need a heatsink.

author: MAntunes
author_rank: Regular Contributor
timestamp: January 03, 2019, 05:46:43 pm
content: Quote from: StillTrying on December 28, 2018, 11:30:57 pmQuote from: thedoc298 on December 29, 2018, 05:59:58 amThank you, I thought having a more stable input would contribute to a more stable output.Quote from: spec on December 29, 2018, 10:46:40 amI'm not sure about the current rating. I'll check the transformer later.If the LM317 is not really needed the better for me: less components = less money.I don't really need the the full 32V of the DPS3003 module, I'm happy with 30V. I'm not even sure I'll need that much.Yes, 30VDC@1A is what I'm aiming for.Could you tell me these techniques to reduce switching noise? What you be better? LC filter, Pi network? What should be the cut-off frequency?About the diodes, I'm always ready to learn so yes, I'd like it if you could recommend better components. I know I have a diode bridge at home somewhere, but I can't find it at the momentQuote from: nsrmagazin on December 29, 2018, 02:26:04 pmI know, I should have explained myself better. I pretend to build a AC-DC converter to power a DPS3003 module (https://goo.gl/hii2nP) which is a buck converter. I have a 230VAC RMS to 24VAC RMS (~34V peak) transformer so in the output, taking into account the voltage drop of the diodes, I will have around 32V.I also want to design an output filter to remove the high frequency components of the switching converter.Thank you all.

author: nsrmagazin
author_rank: Regular Contributor
timestamp: January 04, 2019, 09:06:11 am
content: If you give the circuit it will be better.Can I ask why did you choose this buck converter?

author: MAntunes
author_rank: Regular Contributor
timestamp: January 04, 2019, 05:07:29 pm
content: Quote from: nsrmagazin on January 04, 2019, 09:06:11 amWhat circuit are you looking for, the DPS3003? This is a pre-made module.I choose the DPS3003 module because I want to build a simple power supply and I saw Dave's review video (). There are several modules in this "family" but this one was the cheapest that met my requirements.