Design Rait to Rail power supply with no isolated dcdc converters

[flote21]

Hello guys!

I am wondering about how to design a symetric (or Rail to Rail) power supply with the next feautures:

- Input Voltage: 24Vdc
- Output Voltage: +-15Vdc
- Output current: +-2A.

The target is to supplu 38 current sensors (HTA-300-S) and other analog and digital ICs (like OpAmps and uC). This sensor must be supplied with a rail to rail +-15Vdc and I have been thinkinto to use some kind of commercial SW regultor with a rail to rail output. However I would like to hear some tips to address the desing the power supply tree.

Thanks in advance.

 

[barry]

This is a pretty simple requirement. If you're only designing one system, then it would probably make more sense to just buy an off-the-shelf unit. If you're going to be selling thousands of these, then maybe you should look into designing your own supply.

(And, by the way, there's no such thing as a "rail to rail power supply". The power supply IS the rail. Opamps are rail-to-rail.)

 

[d123]

Hi,

Is SW regulator a switching regulator? An IC that does combined boost + buck/boost, lots to choose from.

Alternatively, a parametric search of voltage supervisor/power path management/etc. ICs and similar should/could come up with loads that turn a +Vin to a +-Vout.

 

[treez]

try off the shelf products from recom, TDK, etc etc.

Otherwise do a flyback with split output coil. you could interleave the primary between the two secondaries to get good equal coupling.

 

[schmitt trigger]

Fortunately the required voltages are very common requirements. Plenty of of-the-shelf modules.

Otherwise as trees mentions, a split output flyback would be the way to go. Again a common topology with common voltages, and there must be already some off-the-shelf components from the major suppliers which would meet the criteria,

 

[FvM]

If you want to avoid custom magnetics, separate +24 -> +15 buck and +24 -> -15 inverting switcher might be the best solution.

 

[flote21]

Hello guys!

Thanks for the tips. I need a cheap solution because it must be a low cost design. FvM solution looks pretty interesting but I am wondering where can I find a commercial inverter power part with Iout=2A...

Greetings

 

[schmitt trigger]

Do a search in Digikey, Farnell or Mouser. There are plenty of modules available. As mentioned earlier, these are very ubiquitous voltage and current requirements.

 

[flote21]

Well it is not easy to find a commercial inverter with Vin=24Vdc and vout/iout=-15V/2A.
However I have been doing an internet research and according to the next maxim paper, it is possible to use a buck regulator like an inverter:

Making a Voltage Inverter from a Buck (St | Maxim Integrated

Any step-down DC-DC converter can be used as an inverter with no changes to the operating schematic. The only differences between the normal step-down application and inverting operation are the labels of the connection points. The step-down VOUT is

www.maximintegrated.com

Traco Power has a part: TSR2-2415 which fits the requirements described previously. Do you think, it is possible to generate -15Vdc from TSR2-2415 following the maxim paper tips?

Thanks in advance

 

[BradtheRad]

I need a cheap solution because it must be a low cost design.

Here is simple and low-cost. A half-bridge alternately switches a 2-capacitor stack. A single-ended supply is split into two power supplies, totaling more than the original voltage.

The capacitors power the split supplies as their own supply rails, distinct from the power source.

 

[FvM]

Do you think, it is possible to generate -15Vdc from TSR2-2415 following the maxim paper tips?

No, because 24 + 15 = 39V exceeds the maximum converter rating of 36V.

 

[flote21]

Ahh ok then I need to search a switching regulator solution. I thinking to use this part from TI: LM5085, doing the next design to get -15Vdc/2A. To reach this target I have used the WEBENCH desgin tool from TI website.

However with the WEBENCH tool you can only calculate component values for positive voltages:

In order to get the negative output, I need to do the next output polaritation, right?

**broken link removed**

Thanks in advance.

Greetings

 

[FvM]

Most buck converters can be used in an inverting configuration, probably also LM5085. Some may have stability or start-up problems. For some converters, TI is describing circuit details to overcome these problems in an application note.

 

[flote21]

Hi!

Finally I think I am going to use the TI part TPS54260 configured as inverter: There is an application note speak about this here:

https://www.ti.com/lit/an/slva540/slva540.pdf?ts=1592671859196&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS54260

however I am afraid about the heating dissipation. Could it be that I am gonna have an overheating issue when the sw regulator delivering and Iout=2A?

Greetings

 

[d123]

Hi,

What PD max does the datasheet say and have you done any calculations yourself about the IC overheating?

There are loads of app notes and online resources to calculate PD and junction temperature rise in ICs and MOSFETs and every other component... I reckon TI should have a handy app note or ten thousand on that topic.

 

[d123]

Page 36: 8.2.1.2.13 Power Dissipation Estimate
(IC power dissipation and junction temperature rise formulas)
Page 28: 8 Application and Implementation
"8.1 Application Information The TPS54260 is a 60-V, 2.5-A, step-down regulator with an integrated high-side MOSFET. This device is typically used to convert a higher DC voltage to a lower DC voltage with a maximum available output current of 2.5 A. Example applications are 12-V, 24-V and 48-V Industrial, Automotive and Commercial power systems. Use the following design procedure to select component values for the TPS54260. This procedure illustrates the design of a high-frequency switching regulator. The Excel® spreadsheet (SLVC432) located on the product page can help on all calculations. Alternatively, use the WEBENCH software to generate a complete design. The WEBENCH software uses an iterative design procedure and accesses a comprehensive database of components when generating a design."

Page 30: 8.2.1.2 Detailed Design Procedure "8.2.1.2.1 Custom Design With WEBENCH® Tools Click here to create a custom design using the TPS54260 device with the WEBENCH® Power Designer."

This, and so much more, is all in the TPS54260 datasheet. I'll say no more.