Hello,

I wonder what is the best way to step down voltage to positive and negative voltage. Lets say I have 15 V input and i need to step down it to +- 5V at 100 mA each. I think it is best to use Buck converter to step down 15 V to 5 V and then use charge pump to invert that 5 V. I thought about using buck-boost (sepic) with dual output, but they have relatively big output current or very small output current (which makes me loose efficiency). So for this application its best to use charge pump if i want to achieve >90% effinciency, am i right?

Please correct me if im wrong

 

Why not voltage regulator IC's?

 

Why not voltage regulator IC's?

What do you mean by IC's? I was talking about swiching voltage regulator IC's

 

'best' is an ambiguous term, and depends on the application. Switch mode supplies have less energy loss than linear, but greater noise introduced. A buck converter followed by a linear regulator tries to get the advantages of both.

What is 'best' for your application? That is, what are the requirements?

 

There should be some dual output switchers available, BUT not shown on the cartoon channel or the ripoff channel. You may also find them with 12 volt inputs delivering +/-5 volts, intended for automotive applications. And possibly an actual low power inverter that delivers both. Check the T.I. website, they do quite well with switcher supplies.

 

There should be some dual output switchers available, BUT not shown on the cartoon channel or the ripoff channel. You may also find them with 12 volt inputs delivering +/-5 volts, intended for automotive applications. And possibly an actual low power inverter that delivers both. Check the T.I. website, they do quite well with switcher supplies.

I have found some switcher’s, but they have for example 3A output, which is overkill for my 100mA each channel. Efficiency is pretty bad when using those switchers. Thats why I want to use low power buck to step down to 5V and then inverting pump to invert those 5V. I could achieve good efficiency using this setup (I think)

 

'best' is an ambiguous term, and depends on the application. Switch mode supplies have less energy loss than linear, but greater noise introduced. A buck converter followed by a linear regulator tries to get the advantages of both.

What is 'best' for your application? That is, what are the requirements?

100mA each output (+- 5V) from 15 volts and efficiency greater than 90%

 

It seems like a lot of current to ask a charge pump to deliver. If noise isn't an issue then I'd use switching for both sides.

 

I have found some switcher’s, but they have for example 3A output, which is overkill for my 100mA each channel. Efficiency is pretty bad when using those switchers. Thats why I want to use low power buck to step down to 5V and then inverting pump to invert those 5V. I could achieve good efficiency using this setup (I think)

What is your evidence for poor efficiency from an SMPS (Switch Mode Power Supply) IC. I find this claim of your to be dubious.

 

What do you mean by IC's? I was talking about swiching voltage regulator IC's

78L05/7805 etc ?

 

What is your evidence for poor efficiency from an SMPS (Switch Mode Power Supply) IC. I find this claim of your to be dubious.

Switcher efficiency fall rapidly at very low loads, and TS supplying 0.1A with a 3A switcher is running at only 3% loading.

For example, LM3150:

 

There do exist lower power switching regulator supplies, but it seems that not all distributors carry those products.

 

OK, but the efficiency is just reduced and it still beats the efficiency of a linear regulator. I do agree that when selecting a unit for purchase it pays to match the unit to your requirements.

 

So what is wrong with 78lxx ?
Always worked for me!
https://www.digikey.ca/en/products/detail/texas-instruments/LM78L05ACZ-NOPB/6333

 

Hello,

I wonder what is the best way to step down voltage to positive and negative voltage. Lets say I have 15 V input and i need to step down it to +- 5V at 100 mA each. I think it is best to use Buck converter to step down 15 V to 5 V and then use charge pump to invert that 5 V. I thought about using buck-boost (sepic) with dual output, but they have relatively big output current or very small output current (which makes me loose efficiency). So for this application its best to use charge pump if i want to achieve >90% effinciency, am i right?

Please correct me if im wrong

Use a standard buck regulator circuit, set to output 5V but use an inductor with two windings (you can get surface mount coupled inductors).
You can then produce -5V from the second winding. It's called a "flybuck" circuit.

https://www.ti.com/lit/an/snva790a/...25080&ref_url=https%3A%2F%2Fwww.google.com%2F

 

Use a standard buck regulator circuit, set to output 5V but use an inductor with two windings (you can get surface mount coupled inductors).
You can then produce -5V from the second winding. It's called a "flybuck" circuit.

https://www.ti.com/lit/an/snva790a/snva790a.pdf?ts=1728329925080&ref_url=https%3A%2F%2Fwww.google.com%2F

THAT is a CREATIVE solution!!!! Not very common, though.

 

Here's the inductor for it.
https://www.mouser.co.uk/ProductDetail/Bourns/SRF1260A-101M?qs=jtImr9hqsuE7MGP%2B4fGbJw==

 

OK, so there is the correct transformer available! I know that I have seen quite a few switcher supplies with multiple secondary windings. So that is what they are all for.