How Can I Convert a Bench PSU to Dual +/- Voltages for My Project?

  • Thread starter Thread starter msymms
  • Start date Start date
  • Tags Tags
    Power
Click For Summary

Discussion Overview

The discussion revolves around converting a bench power supply (PSU) providing +13.8V into dual +/- voltages for a project. Participants explore various methods for achieving this conversion, including the use of DC-DC converters and linear voltage regulators. The context includes both theoretical and practical aspects of power supply design, with considerations for voltage stability and current requirements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests using an inverting topology DC-DC converter to create the negative voltage rail, followed by a linear voltage regulator to smooth the output.
  • Another participant mentions that if the +13.8V supply is mains powered, it could be converted to +/- 7V, but notes potential compatibility issues with the zero reference.
  • Some participants propose using a second power supply instead of an inverter for simplicity and cost-effectiveness.
  • Linear Technologies is mentioned as a source for inverting switching regulators that may meet the project’s requirements.
  • One participant expresses a desire to create a portable, variable power supply with independently adjustable outputs, emphasizing the project’s personal significance over cost.
  • Concerns are raised about the inefficiencies of the system, with estimates of power draw around 25 watts for each rail.
  • Participants discuss the need for a lower voltage inverter to work with linear regulators like the LM317 and LM337, as higher voltage inverters may not be compatible.
  • Clarification is made regarding the type of inverter needed, distinguishing between DC-DC converters and those that convert DC to AC mains voltage.
  • One participant notes that DC-DC static inverters capable of supplying higher currents can be costly and may offer limited voltage flexibility.

Areas of Agreement / Disagreement

Participants express a range of opinions on the best approach to achieve the desired voltage conversion. There is no consensus on a single method, as some advocate for inverters while others suggest alternative solutions. The discussion remains unresolved regarding the optimal design choice.

Contextual Notes

Participants have not specified the exact voltage range required for the negative output, which may influence the choice of components. Additionally, there are mentions of potential inefficiencies and limitations of the proposed solutions, but these remain unaddressed in terms of specific designs.

Who May Find This Useful

Individuals interested in power supply design, hobby electronics, and those looking to create custom power solutions for projects may find this discussion relevant.

msymms
Messages
2
Reaction score
0
Hi All,
New to the forum. I am a Ham operator and attorney by trade, not an EE, hence my question. I have a bench PSU for my radios +13.8V 15-20A. I want to use this as my source for a project that has been mulling around in my head. But first I need to convert/invert my power source into +/- voltages with 1-1.5A per side (more Amperage would be nice but not necessary). I have looked at the 34063 but the power constraints are too low.

What are my options?


Would like to clean the power up as much as possible, but this is not for RF or audio. Also, each rail will be channeled through a voltage regulator circuit (e.g. LM317 or similar). Will this clean it up?

-mark
 
Engineering news on Phys.org
msymms said:
Hi All,
New to the forum. I am a Ham operator and attorney by trade, not an EE, hence my question. I have a bench PSU for my radios +13.8V 15-20A. I want to use this as my source for a project that has been mulling around in my head. But first I need to convert/invert my power source into +/- voltages with 1-1.5A per side (more Amperage would be nice but not necessary). I have looked at the 34063 but the power constraints are too low.

What are my options?


Would like to clean the power up as much as possible, but this is not for RF or audio. Also, each rail will be channeled through a voltage regulator circuit (e.g. LM317 or similar). Will this clean it up?

-mark

Welcome to the PF!

You can invert the voltage using an inverting topology DC-DC converter, and then do as you say to use a linear voltage regulator to smooth out the final negative rail.

National Semiconductor makes the Simple Switcher series of DC-DC converter controller ICs. They should have something that can provide the current that you need. Have a look at their website -- let us know if you aren't seeing what you need.

73
 
If your +13.8 volt supply is already mains powered you can readily change this to +/- 7volts max. This can even be variable.

However the zero will not be compatible (at the same zero as your original supply)

If the supply is mains powered is there any point using an inverter, compared to a second supply? The latter option would be far cheaper and less complicated.
 
Thanks for the quick replies. My project, whether more complicated or expensive than it should be, is this: to make a portable/detachable variable power supply, with independently variable +/- outputs; using my existing bench psu or even a automobile power socket as the source. It can be expanded upon but that is the gist of it.
The point here is no so much economics but seeing the idea come to life. Very similar to hobby furniture makers with shops in the garage. The homemade furniture is unique, but always more expensive than something ready made that merely offers the same functionality. Of course, that ideal does have limits.
 
Last edited:
msymms said:
Thanks for the quick replies. My project, whether more complicated or expensive than it should be, is this: to make a portable/detachable variable power supply, with independently variable +/- outputs; using my existing bench psu or even a automobile power socket as the source. It can be expanded upon but that is the gist of it.
The point here is no so much economics but seeing the idea come to life. Very similar to hobby furniture makers with shops in the garage. The homemade furniture is unique, but always more expensive than something ready made that merely offers the same functionality. Of course, that ideal does have limits.

Okay, then you do need an inverter unit to give you the negative rail. Then follow the positive and negative rails with variable linear regulators for simplicity and low output noise. You can look at the LM317 for the positive adjustable regulator (in a big package with heat sink), and the LM337 for the negative adjustable linear regulator.
 
So allowing for inefficiencies you will be drawing around 25 watts for each of the + and - supplies.

This is certainly achievable with portable inverters.
You can easily get 12 volt DC to 120 or 240 v AC invertors at 50 watts.

Since you haven't yet specified, your next decision is the voltage range required, since you have specified variable supplies.

To use a 317/337 you will have to step such an invertor down as 120 volts+ is too high for them. Lower voltage inverters are less common.

You should also realize that the 317 / 337 will not adjust all the way to zero without extra circuitry.
 
Sorry, by Inverting DC-DC, I meant just invert the + voltage into a - voltage rail:

http://www.national.com/cat/index.cgi?i=i//310

Not the type of inverter that takes DC and makes mains-level AC.
 
Last edited by a moderator:
Yes I am aware that you can also get DC - DC static inverters.
It's just that such devices to supply 4 amps+ can be quite costly and offer less flexible voltage options.

Despite the 'Mr Chequebook' approach from the OP I am still considering cost.

Added to which such design considerations are part of the fun of the project aren't they?
 

Similar threads

How do I properly connect a bench power supply to a pulse generator for testing?
  • · Replies 19 ·
Replies
19
Views
3K
How to power up a DIY LED panel with a PC PSU?
  • · Replies 27 ·
Replies
27
Views
6K
How can I safely energize a suspect alternator
  • · Replies 16 ·
Replies
16
Views
3K
How many Peltier elements can I use in my power outlet?
  • · Replies 33 ·
2
Replies
33
Views
5K
How Do I Design an EMI Filter for a Converter with Only Voltage and Power Specs?
  • · Replies 8 ·
Replies
8
Views
2K
How can I modify a LM337 circuit to increase current output?
  • · Replies 3 ·
Replies
3
Views
4K
Can I Safely Connect a 12V LED Strip to a 300W PSU with 2A Draw?
  • · Replies 16 ·
Replies
16
Views
3K
What's the deal with the power section in my Adcom amp?
  • · Replies 3 ·
Replies
3
Views
2K
How Can I Efficiently Source Bitter Plates for an Electromagnet Project?
  • · Replies 3 ·
Replies
3
Views
3K
Can I Convert My 9vdc Sprinkler Actuators to Run on Low Voltage AC?
  • · Replies 6 ·
Replies
6
Views
3K