equipment/power

view history talk

Lab power supply
Bench power supply
The Earth binding posts is not "common"

Lab power supply

Bench power supply

What do you think about using an ATX PC power supply as a bench unit?

ATX power supplies are relatively cheap and easy to come by, so why not use one as a project power supply?

Pros:

Low cost.
You possibly already have a spare one lying around.
High current output.
Versatile 5V and 12V rails, with -5V and (perhaps) -12V (low current) too.

Cons:

Ability to deliver very high currents under fault conditions - high risk of your project failing in a spectacular way and/or catching fire.
No adjustable current limiting. Current limiting is is extremely useful, and recommended when testing new circuits (to limit fault current) and also for charging some cells/batteries.
No adjustable voltage, also doesn't have higher voltage for popular OpAmp voltage rails such as 30V and +/- 15V.
Some units need a load (resistor) to draw a standing current on one or more supply lines (3.3V and/or 5V), to make the PSU regulate correctly - this wastes power.
+12V rail is often not very accurate or stable when there is only a small, or little, load on the 5V output.
Outputs are electrically noisy so may not be suitable for sensitive analogue designs without additional filtering.

Some redditors recommend using old ATX PSUs as cheap bench supplies, though in reality they are better suited as a "Bulk DC Power" source for the input of a second power supply that provides variable voltage / variable current / short protection / noise filtering.

If you plan to do a serious amount of hobby work with microelectronics and analogue circuits, you should get yourself a cheap linear 0V to 30V at 1/3/5Amp bench supply with adjustable current limiting. At a minimum, some thing like this is better than nothing http://www.ebay.com/itm/232058112709 (see notes and modifications/improvements here: http://www.paulvdiyblogs.net/2015/05/tuning-030v-dc-with-03a-psu-diy-kit.html), though a power supply with a voltage and current display is the preferred recommendation. If you need to work with op-amps and such with split rails you need to build a rail splitter circuit. There is a pretty decent one in here which can be used for free and was designed by one of the askelectronics mods http://imgur.com/a/mO02X#fVOWsua

Can you recommend a good, cheap bench PSU?

Recommendations are always very subjective, so you should do your own research, but the following makes/models often get a mention in discussions:

Buy a used HP/Agilent E3610 (but older models sometimes need their electrolytic capacitors replaced for stability)
Korad KA3005D
Tenma 72-10480
MB102 Breadboard Module with 3.3V and 5V (powered by USB or a 7-12V DC power adapter) (note: you may need to replace the voltage regulators with a better chip)
GOPHERT CPS-3205 0-32V 0-5A Portable Adjustable DC Power Supply

Make Your Own

Here's some ideas for DIY builds. As ever, do be careful around mains electricity.

Minghe makes a range of cheap and mostly half-decent buck/boost converters. See this review: https://www.falatic.com/index.php/161/minghe-buckboost-converters-handy-if-youre-careful
There's a range of front panel boards, generically known as 'DPS5005' types. These boards have a display and voltage and current controls, plus feature support for comms such as Bluetooth and USB. There's plenty of searchable info on these. See: https://johan.kanflo.com/dps5005-now-with-comms/
To supplement the above, see the OpenDPS project
See also the more sophisticated Riden RD6006 units

Here's an excellent post on the subject of bench supplies from /u/enlightenment777:

The problem with bench supplies is not all of them are created the same. There are some crappy china designs out there! Some bench power supplies don't even have good current limiting capabilities, then might have short-circuit detection but not limiting to a specific maximum current. Download PDF manuals, investigate before buying!!!

If you want an incremental improvement compared to a cheap voltage regulator, then choose a BETTER voltage regulator that will automatically shut itself down on shorted output, protects against reverse currents, protects against over-current, protects against over-temperature, protect against over-voltage, .... Automotive voltage regulators are typically more robust and designed to handle unexpected extremes.

If you can't afford a bench power supply, then build a 1-Amp variable-voltage variable-current power supply (see below), such as one of the following then add a cheap digital voltmeter display module from China.

If you want to build your own variable-voltage variable-current-limit power supply, see FIGURE 21 in ON Semiconductor LM350 datasheet. The LM350 is a higher current version of the well known LM317, so you can substitute the LM317 in place of LM350 in this figure. The problem with LM317/LM350 is they can't create an output voltage below 1.25V, unless you use a negative voltage trick to do it, like figure 21.

http://www.onsemi.com/pub/Collateral/LM350-D.PDF

If you don't mind spending more money for voltage regulator parts, the Linear Technology LT3080 is easier to create a similar variable power supply, because it uses an internal current reference instead of a voltage reference, thus it can output voltages down to zero volts without adding a bunch of extra parts like the LM350 example above. See at bottom of page 18 of LINEAR LT3080 datasheet.

http://www.analog.com/media/en/technical-documentation/data-sheets/3080fc.pdf

The Earth binding posts is not "common"

If a power supply has 3 binding posts (red, green and black) it won't power a circuit that requires a dual supply.

The green post is connected to earth ground, in is not a "common". There is no voltage between the green terminal and the red (positive) terminal. There is no voltage between the green terminal and the black (negative) terminal. That green posts is only good for "grounding" yourself, such as for Electrostatic Discharge (ESD). This is what a single supply with Earth post looks like:

.-----o V+ (red)
|
|
0 V
|
|
'-----o V- (black)

E-----0 E (green)

A circuit that requires a dual supply (positive, ground, and negative) needs two power supplies connected in series (or, equivalently, a dual power supply). Your single power supply with an earth ground posts is not a dual power supply. This is what a dual supply looks like:

.-----o V+ (red)
|
|
0 V
|
|
+-----o Common (black)
|
|
0 V
|
|
'-----o V- (blue)

If you can't get a second power supply, there is a nifty circuit called a "virtual ground" that creates a voltage midway between the positive and negative posts of a single power supply.

## Lab power supply
## Bench power supply
### What do you think about using an ATX PC power supply as a bench unit?

ATX power supplies are relatively cheap and easy to come by, so why not use one as a project power supply?

Pros:

* Low cost.
* You possibly already have a spare one lying around.
* High current output.
* Versatile 5V and 12V rails, with -5V and (perhaps) -12V (low current) too.

Cons:

* Ability to deliver very high currents under fault conditions - high risk of your project failing in a spectacular way and/or catching fire. 
* No adjustable current limiting. Current limiting is is extremely useful, and recommended when testing new circuits (to limit fault current) and also for charging some cells/batteries.
* No adjustable voltage, also doesn't have higher voltage for popular OpAmp voltage rails such as 30V and +/- 15V.
* Some units need a load (resistor) to draw a standing current on one or more supply lines (3.3V and/or 5V), to make the PSU regulate correctly - this wastes power.
* +12V rail is often not very accurate or stable when there is only a small, or little, load on the 5V output.
* Outputs are electrically noisy so may not be suitable for sensitive analogue designs without additional filtering.

Some redditors recommend using old ATX PSUs as cheap bench supplies, though in reality they are better suited as a "Bulk DC Power" source for the input of a second power supply that provides variable voltage / variable current / short protection / noise filtering.

If you plan to do a serious amount of hobby work with microelectronics and analogue circuits, you should get yourself a cheap linear 0V to 30V at 1/3/5Amp bench supply with adjustable current limiting. At a minimum, some thing like this is better than nothing  http://www.ebay.com/itm/232058112709 (see notes and modifications/improvements here: http://www.paulvdiyblogs.net/2015/05/tuning-030v-dc-with-03a-psu-diy-kit.html), though a power supply with a voltage and current display is the preferred recommendation.  If you need to work with op-amps and such with split rails you need to build a rail splitter circuit.  There is a pretty decent one in here which can be used for free and was designed by one of the askelectronics mods http://imgur.com/a/mO02X#fVOWsua

### Can you recommend a good, cheap bench PSU?
Recommendations are always very subjective, so you should do your own research, but the following makes/models often get a mention in discussions:

* Buy a used HP/Agilent E3610 (but older models sometimes need their electrolytic capacitors replaced for stability)
* Korad KA3005D
* Tenma 72-10480 
* MB102 Breadboard Module with 3.3V and 5V (powered by USB or a 7-12V DC power adapter) (note: you may need to replace the voltage regulators with a better chip)
* [GOPHERT CPS-3205 0-32V 0-5A Portable Adjustable DC Power Supply](https://www.banggood.com/GOPHERT-CPS-3205-0-32V-0-5A-Portable-Adjustable-DC-Power-Supply-110V220V-p-934530.html)

### Make Your Own

Here's some ideas for DIY builds. As ever, do be careful around mains electricity.

* Minghe makes a range of cheap and mostly half-decent buck/boost converters. See this review: https://www.falatic.com/index.php/161/minghe-buckboost-converters-handy-if-youre-careful
* There's a range of front panel boards, generically known as 'DPS5005' types. These boards have a display and voltage and current controls, plus feature support for comms such as Bluetooth and USB. There's plenty of searchable info on these. See: https://johan.kanflo.com/dps5005-now-with-comms/
* To supplement the above, see the [OpenDPS project](https://github.com/kanflo/opendps) 
* See also the more sophisticated [Riden RD6006 units](https://doug-gilbert.github.io/rd60xx-unisoft/rd60xx-unisoft.html)

**Here's an excellent post on the subject of bench supplies from /u/enlightenment777:**

>
> The problem with bench supplies is not all of them are created the same. There are some crappy china designs out there! Some bench power supplies don't even have good current limiting capabilities, then might have short-circuit detection but not limiting to a specific maximum current. Download PDF manuals, investigate before buying!!!
>
> If you want an incremental improvement compared to a cheap voltage regulator, then choose a BETTER voltage regulator that will automatically shut itself down on shorted output, protects against reverse currents, protects against over-current, protects against over-temperature, protect against over-voltage, ....  Automotive voltage regulators are typically more robust and designed to handle unexpected extremes.
>
> If you can't afford a bench power supply, then build a 1-Amp variable-voltage variable-current power supply (see below), such as one of the following then add a cheap digital voltmeter display module from China.
>
> If you want to build your own variable-voltage variable-current-limit power supply, see FIGURE 21 in **ON Semiconductor LM350** datasheet. The LM350 is a higher current version of the well known LM317, so you can substitute the LM317 in place of LM350 in this figure. The problem with LM317/LM350 is they can't create an output voltage below 1.25V, unless you use a negative voltage trick to do it, like figure 21.
>
> [http://www.onsemi.com/pub/Collateral/LM350-D.PDF](http://www.onsemi.com/pub/Collateral/LM350-D.PDF)
>
> If you don't mind spending more money for voltage regulator parts, the **Linear Technology LT3080** is easier to create a similar variable power supply, because it uses an internal current reference instead of a voltage reference, thus it can output voltages down to zero volts without adding a bunch of extra parts like the LM350 example above. See at bottom of page 18 of LINEAR LT3080 datasheet.
>
> http://www.analog.com/media/en/technical-documentation/data-sheets/3080fc.pdf 
>

# The Earth binding posts is not "common"

If a power supply has 3 binding posts (red, green and black) it won't power a circuit that requires a dual supply.

The green post is connected to earth ground, in is not a "common". There is no voltage between the green terminal and the red (positive) terminal. There is no voltage between the green terminal and the black (negative) terminal. That green posts is only good for "grounding" yourself, such as for Electrostatic Discharge (ESD). This is what a single supply with Earth post looks like:

    .-----o V+ (red)
    |
    |
    0 V
    |
    |
    '-----o V- (black)

    E-----0 E (green)



A circuit that requires a dual supply (positive, ground, and negative) needs **two** power supplies connected in series (or, equivalently, a dual power supply). Your single power supply with an earth ground posts is not a dual power supply. This is what a dual supply looks like:


    .-----o V+ (red)
    |
    |
    0 V
    |
    |
    +-----o Common (black)
    |
    |
    0 V
    |
    |
    '-----o V- (blue)


If you can't get a second power supply, there is a nifty circuit called a "[virtual ground](https://en.wikipedia.org/wiki/Virtual_ground)" that creates a voltage midway between the positive and negative posts of a single power supply.

revision by 1Davide— 2 years agoview source

π Rendered by PID 26514 on reddit-service-r2-loggedout-64d45c4758-hclv6 at 2024-08-20 01:15:17.274276+00:00 running 9f3e233 country code: US.

AskElectronics

Click for the wiki/FAQ

Click for the rules

Click for related subs

WIKI TOOLS

MODERATORS