Gel Electrophoresis Power supply Design - Page 1
Forum section: electronics / projects

author: hrshovon
author_rank: Newbie
timestamp: March 21, 2018, 10:14:38 pm
content: Hello all,Hopefully this is the right topic for asking this question. I am designing a gel electrophoresis power supply for a friend. I saw Dave's teardown video. His lab has got a similar supply which I took apart to see whats inside. Looked pretty much the same. Now I am making one for him. Specs are as follows:Voltage: 0 to 150VCurrent: max 500mA(adjustable)Voltage and current both adjustable via keypad. There is a single LCD for showing information.I have completed the digital electronics interface part but need to make a decision about the analog part.My questions are as follows:Is it necessary for this kind of supplies to be noise free? I mean Do I really need to design a Linear Supply? Using a BJT to swing between such a huge voltage range seems like a pain. Didnt want to use relay board for tap switching as that would take up both space and add cost. I am using a triac based setup for now for input voltage adjustment. But if I can get away with using an SMPS switching solution, I would like to do that. When it comes to power electronics design, I am a sort of total noob so may be asking silly questions.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 22, 2018, 02:57:25 am
content: When we did it in high school science, there was only a knob and a meter and some terminals. I think it was low voltage only though.

author: hrshovon
author_rank: Newbie
timestamp: March 22, 2018, 11:51:31 pm
content: Thanks for replying. So what topology is suited for such power conversion? Linear?SMPS?

author: Teledog
author_rank: Regular Contributor
timestamp: March 23, 2018, 02:21:34 am
content: I've made something very similar to this years ago; {KISS method}https://www.eleccircuit.com/the-variable-high-voltage-power-supply-0-300v/I don't believe you need 500mA for electrophoresis..unless you're running Kg size gelsUsed a 120/220 ~200mA Xformer (100mA SB fuse on the output)Seemed to work well..(but got bored..cain't git me no ethidium bromide!)edit: actually had an old analog/meter electrophoresis PSU given to me some time ago (and stupidly got rid of it)

author: CNe7532294
author_rank: Regular Contributor
timestamp: March 23, 2018, 03:54:23 am
content: Quote from: hrshovon on March 22, 2018, 11:51:31 pmIt can be any. SMPS is better though. Noise does not matter. The specs are about right. High voltage is more of a concern than current. The goal is to use an electric field to move, I assume DNA since Teledog made mention of Ethidium Bromide.(can be done with proteins as well but with a different gel type and dye). Remember that DNA is a negatively charged molecule courtesy of the phosphate backbone so please do remember to orient the leads with (-) as the starting point and (+) as the end if you are in charge of doing so. As for variance of Volt or Amps, its not really necessary. That more along the lines of varying the chemical make up of the gel itself. (ie. 0.5%, 1.5%, or 3% Agarose). If fact your friend has to get the chemistry right. Too much Agarose and the DNA won't even bother moving. Even if your PSU managed to output 1kV. Not recommended using anything over 150V by the way. Besides the safety hazard of electrocution and hydrogen explosion, higher voltage will outright melt the gel.

author: Gyro
author_rank: Super Contributor
timestamp: March 23, 2018, 10:12:29 am
content: SMPS is certainly used in some professional Electrophoresis power supplies, eg. Amersham EPS-301. Manual and range catalogue [EDIT: Which includes voltage and current useage for different Electrophoresis types] also attached in case they are useful.

author: hrshovon
author_rank: Newbie
timestamp: March 24, 2018, 05:34:22 pm
content: Thanks a ton to everyoneI was considering making a linear power supply at first. Since I have most of the parts, I shall try that. My strategy is to adjust the input voltage according to set output voltage by using a triac at the primary of my transformer which converts 220V AC to some 120V AC. Then I shall use my transistor based regulator to set my desired output voltage otherwise if I am setting 10V at the output and my input is 160V DC I guess the transistor would die due to excess heat.I would really like ur suggestion on that.If this doesnt work, I shall try smps. My plan is to use uc3843 as either a buck or a boost converter(boost looks easier since its just low side switching, buck looks more eficient but high side switching)

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 24, 2018, 06:04:29 pm
content: I would suggest a SCR preregulator on the secondary side.

author: hrshovon
author_rank: Newbie
timestamp: March 30, 2018, 09:13:04 am
content: Quote from: NiHaoMike on March 24, 2018, 06:04:29 pmCan u provide me with a schematic? I have no experience with SCRs

author: ch_scr
author_rank: Frequent Contributor
timestamp: March 30, 2018, 03:15:25 pm
content: Try AN32 from Linear on Page 3. Also the Philips PE1540 linear power supplies with SCR Prereg are of a nice old school design, schematic is in the operating manual.

author: ArthurDent
author_rank: Super Contributor
timestamp: March 31, 2018, 01:24:17 am
content: I assume that this supply is to be used in a commercial lab and not for a hobby use so you may want features such as open circuit sensing, timer, watts used, etc.. If you are designing a supply from scratch it will be difficult to foresee all possible problems a one-off supply could have or to incorporate all the safety features a commercially made supply would have.If possible I would try to buy a used supply identical to the supply your friend is currently using so if there are some differences in results you can rule out the differences in supplies. At least in the United States on Ebay there are over 900 used supplies of all descriptions, a lot in the $100US range. I’m not sure what the used market where you are is like or if this is an option worth checking. I bought a Bio Rad PowerPac 1000 that looks and works like new on Ebay to use as a high voltage bench supply and got a great deal on it because no one else bid.

author: hrshovon
author_rank: Newbie
timestamp: April 02, 2018, 08:09:35 pm
content: Quote from: ArthurDent on March 31, 2018, 01:24:17 amWell, if I could it would have been better but getting one of these in my country would cost as much as buying a new one, considering tax and all.The user interface design is complete and it works as expected. Used an Atmel micro, a 20x4 LCD and a keypad for that. My main concern was the analog frontend .btw I did take one apart and the schematics matched what Dave showed a few years back.

author: hrshovon
author_rank: Newbie
timestamp: April 03, 2018, 10:10:34 pm
content: After some googling and utilizing knowledge from Dave's video on linear regulators and his famous power supply series, I came up with the attached schematic. I have tried this much on breadboard and it seems to work(Not yet tested for anything higher than 10mA though as I dont want to make this circuit on veroboard and flimsy jumper wires cause too much voltage drop). I havent done anything anout current sensing as I am yet to choose a suitable amplifier. My choices are limited on that one. I am using a pot where I will be putting the DAC.Now this circuit does its job pretty well above 2-3 V but doesnt go below 1.6V or so. May be some breadboard thingy happening or some transistor issues. I hope someone will clear me on that one.Now here are my questions:1. I havent shown capacitors for the op amp power lines etc. but will put them. Do I need to add capacitors in the feedback line and such for noise removal etc. ?2. Do I need to do something at the inverting and non inverting inputs of the op amp? Like putting diodes and such for offset or other issues?3. I am looking for a current sense amp suitable for my purpose which would be single supply and rail to rail. I dont trust simulation results but LM324 showed good performance with a constant offset voltage. The higher end options available in my country are INA122P, AD620 and LT1167.Should I go for those for 1mA resolution? I want to sense 0-500mA.May be I am asking stupid questions but please help me with these.Note: I havent included the transformer tap switching relay circuit or SCR based solution as I am still studying those.Any suggestions are welcome.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: April 03, 2018, 11:16:30 pm
content: https://topac.com/ep_ps_E800.htmlhttps://www.cleaverscientific.com/wp-content/uploads/2015/06/Power-Supply-selection-specification-chart-Page-1.pdfit seems needs:constant voltage and constant current, or gradual increase the voltage or current.depend on work, it can be max 70V and 3000V .... 30ma up to 500ma

author: hrshovon
author_rank: Newbie
timestamp: April 04, 2018, 06:08:28 am
content: I suppose the ramp thing can be programmed since this power supply is digitally controlled