Why many DIYers want a 30 Volt bench PSU ? - Page 1
Forum section: electronics / general

author: BravoV
author_rank: Super Contributor
timestamp: January 09, 2019, 09:14:55 am
content: DIY crowd just love to build bench adjustable PSU up to 30 Volt, is there any reason or maybe history related ?

author: capt bullshot
author_rank: Super Contributor
timestamp: January 09, 2019, 09:45:06 am
content: Depends on your circuits.No one needs a 30V supply for arduino or similar stuff, but when you go analog or power, a wide range of supplies is useful.Having standard voltages as +5V, +12V and +24V available from a single lab supply is useful, and you always need some headroom, so just go for 30V.Prototyping analog transistor circuits may be easier with higher supply voltages, imagine "long tailed pairs" in differential amplifier stages.

author: leeatljs
author_rank: Contributor
timestamp: January 09, 2019, 09:55:55 am
content: I sometimes have to series two 35V supplies to get even more volts. Sometimes some projects and experiments just require that bit more.

author: Rerouter
author_rank: Super Contributor
timestamp: January 09, 2019, 10:04:07 am
content: I feel a fair bit of it revolves around the LM317 and its negative counterpart, they where good to about 33V, So as it was so easy to build your first DIY power supply with that IC, and a potentiometer, A large amount of hobbiests ended up with a lot of 30V power supplies, and I assume the trend worked forward even when the technology improved, most things can be tested with a 30V or +-30V variable PSU, So people continued building them,Personally I like higher voltage ranges, most of my own DIY supplies where 50V, but they came after I already had made 2 different variable current limit LM317 supplies.

author: Gyro
author_rank: Super Contributor
timestamp: January 09, 2019, 10:11:01 am
content: Iirc, 30V bench PSUs have been around a lot longer than LM317s and almost none of them use them anyway. I wouldn't be surprised if it had more to do with maximum supply voltage of uA723s and decent overhead (and SOA) of 2N3055s or similar.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 09, 2019, 10:11:16 am
content: 24V is very common, and you need headroom.

author: dmills
author_rank: Super Contributor
timestamp: January 09, 2019, 10:25:18 am
content: The 2N3055 SOA and 723 argument may well have merit.30V is about the top end of what a jellybean opamp can take, and back in the day the entry point to the game was often audio projects of some kind which were usually either +-15V, +12V or +24V give or take, so it also fitted well with what people actually needed.Reality is that almost everyone ends up with multiple power supplies in the lab, there is no one size fits all.I have a couple of TTi/Farnell jobs that do the usual 30V at an amp or so, a couple of big switchers for more serious power, two HP programmable units, and a biscuit tin with two stacks of D cells and some BNC connectors for testing very low noise, high impedance things (And I am not shy about throwing an extra supply together if I have a particular need).These days I do not consider a power supply to be a particularly good early project, you can find a second hand TTi or such for not much money, and a general purpose lab supply is actually quite tricky to do well, at least until you have some control theory and some experience of the practical stuff under your belt.Regards, Dan.

author: JohnPen
author_rank: Regular Contributor
timestamp: January 09, 2019, 10:44:26 am
content: Quite a lot of years ago I built a low voltage PSU to power a home computer I was building. That required +/- 12v and+ 5v. I used a 100 VA Mains TFR in which the original secondary centre tapped winding could be easily separated. I also added a few isolated turns to provide sufficient voltage for a regulated 5v rail. The final independent outputs were 2 adjustable 0-22v at 2Amp and a 5v at 1 Amp. Both the 22v rails had adjustable current limiting and the 5v rail just using an 7805 regulator. This arrangement covered all my low voltage needs, + and - rails plus a 5v logic rail, and as already mentioned in a previous post I could get up to to 44v by a series connection if really needed. For other projects needing higher power or voltage generally were covered by separate dedicated supplies. That said I recently checked out a suspect +/- 40v audio amp in an effectively safe mode using my old +/- 22v current limited supply rather than risking the full voltage dedicated supply and possible transistor 'blowing' or some other unanticipated failure. It was only a simple voltage /current check not a quality of output and definitely gave me confidence that all was OK .

author: daqq
author_rank: Super Contributor
timestamp: January 09, 2019, 10:50:26 am
content: Enables 24V (and 28V), while still allowing for fine enough adjustment on the lower voltages.

author: BravoV
author_rank: Super Contributor
timestamp: January 09, 2019, 12:15:58 pm
content: I'm probably not old enough to aware of the trend back then, how about the common +15 and -15 Volt rails PSU that used to power op-amp or maybe audio ?As this perfectly fits at +30 Volt ? Hence where this number originating from ? CMIIWFor 12 volt (or 13.8V) is obvious as lead acid battery, or even 24 Volt as its twice.Just curious where the 30 Volt trend originated or started from, and apparently its still stuck until today for DIYers.

author: David Hess
author_rank: Super Contributor
timestamp: January 09, 2019, 12:28:48 pm
content: Old analog processes had absolute maximum voltage ratings of 36, 40, and 44 volts with 36 being the most common for commercial parts. Personally I prefer +/-20 volt tracking supplies which can produce up to 40 volts with a 20 volt regulator design and +/-15 through +/-20 volts for these parts.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 09, 2019, 12:43:38 pm
content: I must not fit the Many category. Top end of my first power supply is 25V that I built in the early 80s. The transformer comes from a UNIVAC terminal! Keypad was from an old girlfriends dead phone. Plastic was from a friend of mine who worked at a plastic molding company. I used a toroid that I had cut a slit into and mounted a hall sensor in for a current sense to minimize the losses. It never worked very well.The 8-bit 2K micro has an external ADC, DAC, RS232 transceiver and some Sprague HV drivers for the VFD. I wrote all the code is in assembler. I made a PCB for the analog section but the digital is all WW.I also had a small box with a breadboard attached. Inside the box I had a +/- something and a fixed 5V. Also a speaker and amp, TTL - RS232 and a 0-5V 0-?? Hz squarewave generator. It ran from the AC line. I gave it away to a friend who was starting to learn electronics.

author: KerryW
author_rank: Regular Contributor
timestamp: January 09, 2019, 08:19:57 pm
content: Well, if you take a 24V transformer and full wave rectify it, you get about 34V DC, minus a couple of volts for the diode drops and a couple of volts for regulator headroom and you end up with ~30V max.

author: janoc
author_rank: Super Contributor
timestamp: January 09, 2019, 08:38:10 pm
content: Quote from: BravoV on January 09, 2019, 09:14:55 amI think among the beginners it is because they see these being sold online for about $100 or so and think they can build one with the same specs cheaper, not because they explicitly need it.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 09, 2019, 08:43:30 pm
content: Quote from: KerryW on January 09, 2019, 08:19:57 pmThis is about the wishful thinking to start with. However in real life one should consider a line voltage up to 10% low and some 10% ripple at the filter capacitor. So one kind of ends up at some 24 V max. under load and maybe 27 V with no load.

author: In Vacuo Veritas
author_rank: Frequent Contributor
timestamp: January 09, 2019, 09:06:11 pm
content: Don't know. I rarely need more than 12V at 1 A. I suspect it's a holdover from a bygone era. It's probably a virtual manhood substitute. Mine's bigger than yours!!

author: Berni
author_rank: Super Contributor
timestamp: January 09, 2019, 09:23:55 pm
content: Yeah most of it is tradition. And that likley came from the sort of voltages parts would run at, its useful to be able to get 24V and some headroom. And its about the highest voltage PSU you could build from jelly bean parts, also later the integrated regulators commonly worked up to those sort of voltages.That being said i have plenty of lab PSUs that don't go to 30V for example:15V 2A25V 1A50V 0.8A20V 5A60V 50A7V 300A10kV 7mAActually i have only one PSU that is the classic 30V 3A. Its a Rigol DP832

author: MarkF
author_rank: Super Contributor
timestamp: January 09, 2019, 09:59:57 pm
content: Back in the day, we used lots of relays with 28VDC coils and 28V light bulbs.

author: james_s
author_rank: Super Contributor
timestamp: January 09, 2019, 10:15:45 pm
content: I use 24V pretty frequently, and 30V is a nice round number, gotta pick something as a reasonable output goal.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 09, 2019, 10:39:12 pm
content: I have 75 and 80 volts psus, i have 60 volts battery packs i charge once in a while and 48vdc rf systems, 30 vdc is not enough, had a 30vdc psu once, changed it quickly.Really depends of your actual needs and some anticipation / futur needs ?

author: steve30
author_rank: Frequent Contributor
timestamp: January 09, 2019, 11:08:59 pm
content: I'd say its a useful range, especially when dealing with battery packs, LEDs, lamps etc.

author: Inverted18650
author_rank: Frequent Contributor
timestamp: January 10, 2019, 12:44:02 am
content: I feel like due to the simplicity of design and easy availability of the BOM, PLUS its what is everywhere on eBay, its an easy first build. If you go looking for an adjustable PSU on eBay, they all are 30V-5A....so new guys and gals (thats right #feminish #girlsbuildPSUtoo) think it is what they are supposed to have.

author: PTR_1275
author_rank: Frequent Contributor
timestamp: January 10, 2019, 01:10:00 am
content: Most of the work I do is 12 or 24v automotive equipment, so the 32v maximum gives me a good range for 99% of what I do.If I want more power I have a few chunky HP power supplies that will get me to 60v or 50a to a max of 1kw, or one that is 20v or 120a upto 1kw. (Models 6011a, 6012a and 6032a if anyone is curious)For higher voltage still I have a PLH-120v tti power supply, but that doesn’t get used much at high voltage. Most of the time it is locked out to anything over 30v, but the low current range is really REALLY helpfulUntil recently I didn’t do much work in the mA range of things but that changed with a change of jobs.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 10, 2019, 04:47:00 am
content: Jellybean universal transistors have a VCEO, and jellybean opamps are rated for a VCC- VEEaround 30V. So that voltage is good enough for most small projects. At least, that has been my experience as a DIYer.

author: capt bullshot
author_rank: Super Contributor
timestamp: January 10, 2019, 06:58:26 am
content: Quote from: Berni on January 09, 2019, 09:23:55 pmAs far as I can tell without looking them all up, none of the supplied in my environment has a 30V rating. There's +/-20V, 6V / dual 20/40V (selectable range), single 50V, 6V / dual 25V, single 600V, high power 45V, 32V, dual 40V, dual 32V.So I see the triple ones (like 6V / 5A + dual 25V / 1A) often, but in most cases I consider the 6V channel not as useful as the higher voltages. So I'd prefer dual and tracking dual supplies.I believe there's also some history in the 5V / +/- 20V combination (for combined logic / analog circuitry), but I've rarely used that combination as todays logic / uC circuitry usually has local regulation.

author: JoeN
author_rank: Frequent Contributor
timestamp: January 10, 2019, 07:08:28 am
content: I have a pair of E3612A Agilent 120V/0.25A DC power supplies, you can run them in serial for 240V. Good for nixies and higher voltage stuff.