First (Linear) Power Supply Seen Under $100 with Output On/Off Switch? - Page 1
Forum section: electronics / testgear

author: Electro Fan
author_rank: Super Contributor
timestamp: July 16, 2015, 01:31:16 am
content: http://www.amazon.com/Tekpower-TP3005DC-Controlled-Protection-Precision/dp/B010MRG0WW/ref=sr_1_cc_2?s=aps&ie=UTF8&qid=1437010094&sr=1-2-catcorr&keywords=Tekpower+TP3005DKind of different numeric key pad layout but it seems to be a contender for the lowest priced Power Supply that has a DC output on/off switch. (I'm not saying this is a good or bad power supply, just that it's nice to see manufacturers adding the DC on/off switch.)

author: dadler
author_rank: Unknown
timestamp: July 16, 2015, 01:40:38 am
content: I am going to guess, and it's only a guess, that the device does not actually meet these specs:Stable Voltage:- The output voltage is between 0 and nominal value continuously adjustable- Voltage Stability: ?0.005% +1mV- Load Stability: ? 0.005% +1mV- Recovery Time: ?100µS- Ripple Noise: ?1 MVRMS(RMS)- Temperature Coefficient: ? 200PPM/°CStable Current:- Power Stability: 0.1% + 1mA- Load Stability: 0.2% + 2mA- Ripple Noise : ?1mArms(RMS)

author: Electro Fan
author_rank: Super Contributor
timestamp: July 16, 2015, 01:48:28 am
content: Quote from: dadler on July 16, 2015, 01:40:38 amyeah, maybe not, but it has a DC on/off button

author: dadler
author_rank: Unknown
timestamp: July 16, 2015, 01:51:00 am
content: I do like the button and interface.

author: Fungus
author_rank: Super Contributor
timestamp: July 16, 2015, 08:24:42 am
content: Quote from: Electro Fan on July 16, 2015, 01:31:16 amHuh? Are you the seller or something?These have DC on/off switches and have been around for ages:http://www.ebay.com/sch/i.html?_nkw=CPS-3205They're also $20 cheaper than that one... and they're smaller, and they're silent.Wait, this guy is selling them for $60 with shipping:http://www.ebay.com/itm/391161762889

author: Electro Fan
author_rank: Super Contributor
timestamp: July 17, 2015, 02:31:59 am
content: Quote from: Fungus on July 16, 2015, 08:24:42 amUh, some points of clarification.First, no, I'm not the seller "or something" - I'm not selling this power supply or anything related.Second, (I might be wrong about this one) I have a hunch the power supplies in your links are perhaps Switching Power Supplies; I didn't explicitly mention that my comments were directed at Linear Power Supplies, but that was my intention.So, as far as I have seen, the unit I referenced might be the low price leader so far for a new (not used) Linear Power Supply that has a DC output on off switch.If I'm wrong about any of these notions please feel free to correct me. My only interest in all this is to encourage users and sellers to consider the value of incorporating DC output on off controls on Linear Power Supplies, ideally that are well designed and that can minimize or substantially eliminate spikes when powering up or powering down DC circuits, and that can add convenience (as opposed to having to switch off and on the AC input to a Linear Power Supply).If the unit in your links is a Linear Power Supply that would indeed be a lower cost device and I'm happy that you pointed it out as an example of a Linear Power Supply with a DC on off switch.---PostScript: looks like some EEVers have previously found and commented on the Gopher PS; it does appear to be a Switching Power Supply but it got a pretty good review here:https://youtu.be/t49P2nh9_t0https://www.eevblog.com/forum/testgear/switching-power-supply-gopher-cps-3010-30v-10a/msg539867/#msg539867- might just come down to whether 30mV ripple is ok for an intended use

author: mtdoc
author_rank: Super Contributor
timestamp: July 17, 2015, 03:20:52 am
content: Quote from: Fungus on July 16, 2015, 08:24:42 amI see an on/off switch on the front of that but isn't that just to turn the power supply on and off and not an output on/off? If not then how do you turn the power supply on and off?EDIT: ok never mind - just watched the video - it looks like you can use that button for both functions - but seems a bit confusing - definitely not as convenient as a dedicated output switch.

author: Electro Fan
author_rank: Super Contributor
timestamp: July 17, 2015, 04:45:10 am
content: I think the Gopher uses a button on the front to do on/off for the DC output; on the back is an on/off switch for the AC input. Again, good to see a DC output control on this Switching Power Supply but it would be nice to see the DC output control on more lower end Linear Power Supplies.

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 17, 2015, 06:52:17 am
content: I think you may be reading more into the description than is accurate.I further think half of what they say is of questionable accuracy.Please remind us what you think is the perceived benefit of an output on/off switch?And then you might explain why you think it is that the overwhelming range of bench supply products from low-end to super-premium don't include this particular feature?The need for an output on/off switch would appear to indicate a flaw in the test procedure. At least IME.

author: Fungus
author_rank: Super Contributor
timestamp: July 17, 2015, 10:02:32 am
content: Quote from: Electro Fan on July 17, 2015, 02:31:59 amOK, I guess that changes things. It just smelt funny that you'd post a link to a page where there's only 9 available (ie. it's not really a power supply at that price, it's a one-off lot of them at half price)Quote from: Electro Fan on July 17, 2015, 02:31:59 amI don't see it as a big deal, because:a) It's easy to add a switch to your output cables if you really want oneb) So long as there's no power-on-overshoot then there's no real difference.Quote from: Electro Fan on July 17, 2015, 02:31:59 amNo, but this one is a linear supply:http://www.ebay.com/itm/291504031170I'm guessing it's cheap because it's not the 'industry standard' 150 Watt, 30V, 5A.

author: Fungus
author_rank: Super Contributor
timestamp: July 17, 2015, 10:04:32 am
content: Quote from: mtdoc on July 17, 2015, 03:20:52 amNo, the button on the front is output on/off. There's a proper mains switch 'round the back.

author: Electro Fan
author_rank: Super Contributor
timestamp: July 17, 2015, 05:24:06 pm
content: Quote from: Richard Crowley on July 17, 2015, 06:52:17 amIt might just be me, but when I'm powering DC circuits on and off I think it's handy to be able to do so without having to turn on and off the AC to the Power Supply itself. Maybe you prefer to turn the AC input on and off each time you power up and down the DC to the DUT circuit - that's your choice. In my mind, done well, a PS can be turned on with AC to the PS and then the DC output switch can be toggled on and off without adding spikes to the DUT. Obviously, just because a PS has a DC output switch doesn't mean the output switch was well implemented (it could still produce spikes to the DUT when turned on and off) but the preferred design in my mind would have two separate switches (or buttons or controls of some sort) for AC input and DC output with a goal of providing clean signals (with no overshoot) to the DUT. Again, if you want to do it all through the AC input switch for some reason, that's your choice.To clarify, I didn't mean to imply (and didn't say) that "the overwhelming range of bench supply products from low-end to super-premium don't include this particular feature". What I intended to convey is that mostlow endLinear Power Supplies (those that sell new for roughly $100 and less) have not had a DC output switch. I think the farther downstream in the market a DC output switch can be included (assuming it performs well) the better - but again it's just my preference, YMMV.

author: Macbeth
author_rank: Super Contributor
timestamp: July 17, 2015, 05:37:16 pm
content: Quote from: Richard Crowley on July 17, 2015, 06:52:17 amWTF? I guess I have to junk my HP 6632B and DP832 as they are clearly for bellends who can't perform test procedures.Are there any high end supplies without an Output On/Off switch? (and that means I don't want them getting away with having a fancy shmancy SCPI programmable :OUTPUT:ON/OFF command either - just what are they thinking?).Back to the auto transformer mains dropper wirewound and ammeter setup for me.

author: Electro Fan
author_rank: Super Contributor
timestamp: July 17, 2015, 05:45:22 pm
content: Quote from: Fungus on July 17, 2015, 10:02:32 amhttp://www.ebay.com/itm/291504031170Yes, this is a linear power supply - they can be readily found for $50 new and even less. What the model in the link doesn't have is a DC output switch.Certainly, an output switch could be added by a user. My point in the original post is that it would be nice to see more low end (roughly $100 and less) Linear Power Supplies manufactured with a DC output switch included.My thought is that a Linear Power Supply that comes standard with a well implemented DC Output switch would enjoy more sales than a comparable Linear Power Supply without a DC output switch. (Most mid level to high end Power Supplies do include a DC output switch, so there must be some affinity for the feature by buyers in the mid-range and high end PS market segments.)If I was Tekpower for example and had several models of Linear Power Supplies selling for less than $100 I would introduce models that included a DC power output switch.To be clear, this idea/suggestion/preference isn't intended to be a thought so profound as to compete with Ohm's Law for significance, it's just an impression regarding a feature that might possibly be considered useful for some sellers and preferable for some users.PS, I edited the original post Subject line to include "(Linear)" to clarify that the discussion topic was/is intended to focus on Linear Power Supplies

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 17, 2015, 08:16:39 pm
content: Quote from: Electro Fan on July 17, 2015, 05:24:06 pmPerhaps we are not on the same page here. Certainly any proper bench supply can have its output value set for ZERO volts. But my perception is that you want some sort of "shorting switch" on the output, not simply a way to turn "off" the output power. Output overshoot or ramp glitching or other anomalies are a different matter and seem unrelated to the presence or absence of an output switch, which, as you say, a switch wouldn't remedy anyway.

author: Matje
author_rank: Regular Contributor
timestamp: July 17, 2015, 10:37:40 pm
content: Quote from: Electro Fan on July 16, 2015, 01:31:16 amWell, without actually knowing how it behaves that doesn't buy you much.I have seen at least two (linear) el cheapo chinese power supplies with an on/off switch where one can safely switch the outputs on, but switching them off may well destroy whatever is connected. Probably used the same b0rken basic design.Switching the output off would create a voltage jump of 2-3 volts for 100 or more msecs, even if the load was pulling multiple amps. Imagine the expensive, rather delicate digital thingy connected, expecting 3.3 (or 1.8 ;-) volts +- 5%...

author: Electro Fan
author_rank: Super Contributor
timestamp: July 18, 2015, 12:02:44 am
content: Quote from: Richard Crowley on July 17, 2015, 08:16:39 pmApparently we are not on the same page. I'm thinking a DC output switch on a Linear Power Supply should turn the electricity to a DUT circuit on and off without any impact on the signal other than turning it on and off.

author: Electro Fan
author_rank: Super Contributor
timestamp: July 18, 2015, 12:59:38 am
content: Quote from: AcHmed99 on July 18, 2015, 12:15:54 amSo you are saying this is the case for all Linear Power Supplies with DC output switches?

author: Matje
author_rank: Regular Contributor
timestamp: July 18, 2015, 10:39:03 pm
content: Quote from: AcHmed99 on July 18, 2015, 12:15:54 amThe actual (push button) switch clearly doesn't switch the output, there is some electronics in between. Anyway, I don't think some parasitics could explain the nasty behaviour.

author: jimdeane
author_rank: Regular Contributor
timestamp: September 26, 2015, 06:59:51 pm
content: Has anyone done a review of this supply? It is currently $79 on Amazon, $50 less than the Korad programmable. The only outward thing I don't like as much is the lack of a dial input.