LT1241 - examples?

[Grabhanem]

Does anyone have any good example schematics for an LT1241 buck regulator? I'm looking to set up a basic power supply for a Raspberry Pi and a few drives, and I found this part in a scrap pile of components. All of the example circuits I'm seeing are for complex AC converters, and the simple ones don't list any component values.

 

edit-- had the wrong number

[Hackentosher]

I’m not familiar with that chip, but 90% of component data sheets I come across have example circuits you can follow. If not, order an ldo or buck off digikey that suits your needs. 

[Grabhanem]

Just now, Hackentosher said:

I’m not familiar with that chip, but 90% of component data sheets I come across have example circuits you can follow. If not, order an ldo or buck off digikey that suits your needs. 

The datasheet does have some examples, but they seem to be mostly for high voltage AC applications and I can't 100% wrap my head around what components are necessary for DC-DC.

[Hackentosher]

45 minutes ago, Grabhanem said:

The datasheet does have some examples, but they seem to be mostly for high voltage AC applications and I can't 100% wrap my head around what components are necessary for DC-DC.

Oh dang so it looks like the LT1241 is a driver for switch mode power supplies. I would have a look at the LM317, they're cheap and super easy to implement.

https://www.digikey.com/products/en/integrated-circuits-ics/pmic-voltage-regulators-linear/699?k=lm317&k=&pkeyword=lm317&sv=0&pv69=411897&sf=0&FV=-8|699&quantity=&ColumnSort=0&page=1&pageSize=500

 

http://www.ti.com/general/docs/suppproductinfo.tsp?distId=10&gotoUrl=http%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Flm117

[Grabhanem]

Just now, Hackentosher said:

Oh dang so it looks like the LT1241 is a driver for switch mode power supplies. I would have a look at the LM317, they're cheap and super easy to implement.

https://www.digikey.com/products/en/integrated-circuits-ics/pmic-voltage-regulators-linear/699?k=lm317&k=&pkeyword=lm317&sv=0&pv69=411897&sf=0&FV=-8|699&quantity=&ColumnSort=0&page=1&pageSize=500

 

http://www.ti.com/general/docs/suppproductinfo.tsp?distId=10&gotoUrl=http%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Flm117

I have regulators like that-- they're linear, and I'm going to be drawing 3A+ at 5V coming from a 12V line, so that would be around 21W of heat dissipation from that component alone. That's why I wanted a buck regulator-- for the efficiency.

[Hackentosher]

20 hours ago, Grabhanem said:

I have regulators like that-- they're linear, and I'm going to be drawing 3A+ at 5V coming from a 12V line, so that would be around 21W of heat dissipation from that component alone. That's why I wanted a buck regulator-- for the efficiency.

Wait how do you figure? 5*3A = 15W of delivered power. 21W/15W = 140% dissipated power? 
 

anyway, the ncp1117 is only good for an amp, but I’m sure you could find a linear regulator that would work here. I like linear regulators because they are idiot proof to implement, but if you really need/want a buck I’d suggest finding one on digikey. That or buying one of those $2 buck modules on eBay. 

[Grabhanem]

20 minutes ago, Hackentosher said:

Wait how do you figure? 5*3A = 15W of delivered power. 21W/15W = 140% dissipated power? 
 

anyway, the ncp1117 is only good for an amp, but I’m sure you could find a linear regulator that would work here. I like linear regulators because they are idiot proof to implement, but if you really need/want a buck I’d suggest finding one on digikey. That or buying one of those $2 buck modules on eBay. 

A linear regulator keeps current constant on both sides, and dissipates the difference in power as heat. 12*3A = 36W in, 5*3A = 15W out.

 

Those are certainly an option, but I figured I'd at least try to use this chip as it seems nicer than a lot of alternatives and was free.

[Hackentosher]

13 minutes ago, Grabhanem said:

A linear regulator keeps current constant on both sides, and dissipates the difference in power as heat. 12*3A = 36W in, 5*3A = 15W out.

 

Those are certainly an option, but I figured I'd at least try to use this chip as it seems nicer than a lot of alternatives and was free.

Whoops, today I learn

 

In the quick bit of digging I did on Digikey, I couldn't find a through hole (I'm assuming you don't want to spin up your own board for this project) buck chip that quite fit your application. I don't think it would be worth it anyway with the likes of this on the market https://www.ebay.com/itm/XL4015-36V-5A-DC-Buck-Step-Down-Voltage-Converter-Constant-Current-Power-Module/123928792557?hash=item1cdabb4ded:g:cPoAAOSwPGBdyOzV

[Grabhanem]

1 hour ago, Hackentosher said:

Whoops, today I learn

 

In the quick bit of digging I did on Digikey, I couldn't find a through hole (I'm assuming you don't want to spin up your own board for this project) buck chip that quite fit your application. I don't think it would be worth it anyway with the likes of this on the market https://www.ebay.com/itm/XL4015-36V-5A-DC-Buck-Step-Down-Voltage-Converter-Constant-Current-Power-Module/123928792557?hash=item1cdabb4ded:g:cPoAAOSwPGBdyOzV

I've found plenty of buck converter chips that fit my application online. I wouldn't be asking here if I wanted to buy something new, I'd buy something that has an example circuit that makes sense to me.

[mariushm]

This LT1241 is not a good chip to make a simple switching power supply as it requires custom transformers with feedback windings and a lot of parts.

 

It's overkill for a 3a-5a power supply.

IF you really want to push on with this chip just because you have it, the datasheet has an example circuit on page : https://www.analog.com/media/en/technical-documentation/data-sheets/lt1241.pdf

 

Look into more basic chips that only require an inductor and maybe a few diodes and ceramic capacitors and resistors, which can be easily installed in a circuit .... for example, go on digikey at switching regulators, set the input voltage to 14v or more, set the output current range you're interested in and go on from there... 

Here's a starting point, with some filters pre-applied : https://www.digikey.com/short/zh48w2

 

For example, look at that first result AOZ6663, which can take in up to 18v and output up to 3A of current at up to 95% efficiency.

The datasheet - http://www.aosmd.com/res/data_sheets/AOZ6663DI-01.pdf - shows a typical circuit on the first page, and the following pages explain what each component does and what technical properties those components need when you configure for a specific output voltage. The datasheet even shows you how to place the components on a circuit board 

 

If you're worried about the weird footprint of that chip there's others like AOZ6606 in standard soic package which can do up to 6A of current : https://www.digikey.com/product-detail/en/alpha-omega-semiconductor-inc/AOZ6606PI/785-1854-1-ND/10258151

Here's datasheet : http://www.aosmd.com/res/data_sheets/AOZ6606PI.pdf  - again, you have example circuit on the first page.

 

There's other brands, I typicaly avoid TPSxxxx chips as suggestions but they're ok.

You have Diodes Inc, Richtek, Monolitic Power, On Semi, even Microchip wih good switching regulaors which are also cheap.

 

For example see Richtek RT7263, another 3A chip (max 15v input) .. https://www.richtek.com/assets/product_file/RT7263A/DS7263A-01.pdf - examples on page  7, example pcb layout on page 15, lots of explanations for parts choice...

 

There's even through hole regulators, but they're usually more expensive and through hole parts usually run at lower switching frequencies which means bigger inductors and capacitors, more expensive parts around the chip.

But there are... some examples

Sanken ND111D : https://www.digikey.com/product-detail/en/sanken/NR111D/NR111D-ND/4289389

Datasheet with example circuit, pcb layout, parts explanation etc : https://www.semicon.sanken-ele.co.jp/sk_content/nr111d_ds_en.pdf

 

Rohm BD9702 : https://www.digikey.com/product-detail/en/rohm-semiconductor/BD9702T-V5/BD9702T-V5CT-ND/5720090

Example circuit on first page: http://rohmfs.rohm.com/en/products/databook/datasheet/ic/power/switching_regulator/bd9702xx-e.pdf

 

 

AP1501 from Diodes Inc : https://www.digikey.com/product-detail/en/diodes-incorporated/AP1501-T5G-U/AP1501-T5G-UDI-ND/5267937

 

Datasheet: https://www.diodes.com/assets/Datasheets/AP1501.pdf

 

 

 

[Grabhanem]

1 hour ago, mariushm said:

This LT1241 is not a good chip to make a simple switching power supply as it requires custom transformers with feedback windings and a lot of parts.

 

It's overkill for a 3a-5a power supply.

IF you really want to push on with this chip just because you have it, the datasheet has an example circuit on page : https://www.analog.com/media/en/technical-documentation/data-sheets/lt1241.pdf

 

Look into more basic chips that only require an inductor and maybe a few diodes and ceramic capacitors and resistors, which can be easily installed in a circuit .... for example, go on digikey at switching regulators, set the input voltage to 14v or more, set the output current range you're interested in and go on from there... 

Here's a starting point, with some filters pre-applied : https://www.digikey.com/short/zh48w2

 

For example, look at that first result AOZ6663, which can take in up to 18v and output up to 3A of current at up to 95% efficiency.

The datasheet - http://www.aosmd.com/res/data_sheets/AOZ6663DI-01.pdf - shows a typical circuit on the first page, and the following pages explain what each component does and what technical properties those components need when you configure for a specific output voltage. The datasheet even shows you how to place the components on a circuit board 

 

If you're worried about the weird footprint of that chip there's others like AOZ6606 in standard soic package which can do up to 6A of current : https://www.digikey.com/product-detail/en/alpha-omega-semiconductor-inc/AOZ6606PI/785-1854-1-ND/10258151

Here's datasheet : http://www.aosmd.com/res/data_sheets/AOZ6606PI.pdf  - again, you have example circuit on the first page.

 

There's other brands, I typicaly avoid TPSxxxx chips as suggestions but they're ok.

You have Diodes Inc, Richtek, Monolitic Power, On Semi, even Microchip wih good switching regulaors which are also cheap.

 

For example see Richtek RT7263, another 3A chip (max 15v input) .. https://www.richtek.com/assets/product_file/RT7263A/DS7263A-01.pdf - examples on page  7, example pcb layout on page 15, lots of explanations for parts choice...

 

There's even through hole regulators, but they're usually more expensive and through hole parts usually run at lower switching frequencies which means bigger inductors and capacitors, more expensive parts around the chip.

But there are... some examples

Sanken ND111D : https://www.digikey.com/product-detail/en/sanken/NR111D/NR111D-ND/4289389

Datasheet with example circuit, pcb layout, parts explanation etc : https://www.semicon.sanken-ele.co.jp/sk_content/nr111d_ds_en.pdf

 

Rohm BD9702 : https://www.digikey.com/product-detail/en/rohm-semiconductor/BD9702T-V5/BD9702T-V5CT-ND/5720090

Example circuit on first page: http://rohmfs.rohm.com/en/products/databook/datasheet/ic/power/switching_regulator/bd9702xx-e.pdf

 

 

AP1501 from Diodes Inc : https://www.digikey.com/product-detail/en/diodes-incorporated/AP1501-T5G-U/AP1501-T5G-UDI-ND/5267937

 

Datasheet: https://www.diodes.com/assets/Datasheets/AP1501.pdf

 

 

 

It seems like it's possible to make simpler circuits with this chip-- take this for example, from the datasheet:

I've also seen a couple of other circuits that look a lot like this, but none seem to show any values. Are they simplifying the actual setup, then?

 

My main source of confusion is that the project this was pulled from was built by a group of college students and seems to be much simpler than anything I've seen online. I guess it's possible their circuit just didn't work, but I'd expect them to at least have found some sort of reference for it.

[mariushm]

17 minutes ago, Grabhanem said:

It seems like it's possible to make simpler circuits with this chip-- take this for example, from the datasheet:

I've also seen a couple of other circuits that look a lot like this, but none seem to show any values. Are they simplifying the actual setup, then?

 

My main source of confusion is that the project this was pulled from was built by a group of college students and seems to be much simpler than anything I've seen online. I guess it's possible their circuit just didn't work, but I'd expect them to at least have found some sort of reference for it.

That's not a standard regulator circuit, it's a CLAMP as the title shows , and as the formulas show.

The current is clamped to some value (which will depend on Rs as Rs is used for current feedback) and the voltage will be limited based on resistor choices. You also have a soft star "side effect", something you don't want when powering things because in rare cases they can latch into weird states ... you either want no output, or the desired output voltage... no voltage raising slowly to desired levels.

 

You still need an external mosfet (the component after the output pin) AND the inductor

Use switching regulator ICs like the ones I showed you, which have mosfets or pass transitors built in and have plent of explanations in the datasheets and leave this chip be, it's not optimal for what you want.

[Grabhanem]

11 minutes ago, mariushm said:

That's not a standard regulator circuit, it's a CLAMP as the title shows , and as the formulas show.

The current is clamped to some value (which will depend on Rs as Rs is used for current feedback) and the voltage will be limited based on resistor choices. You also have a soft star "side effect", something you don't want when powering things because in rare cases they can latch into weird states ... you either want no output, or the desired output voltage... no voltage raising slowly to desired levels.

 

You still need an external mosfet (the component after the output pin) AND the inductor

Use switching regulator ICs like the ones I showed you, which have mosfets or pass transitors built in and have plent of explanations in the datasheets and leave this chip be, it's not optimal for what you want.

I'm not worried about needing external MOSFETs, I have lots of those to spare. I was just using this circuit as an example of what's possible, even if it's not exactly what I need.

 

I'm seeing lots of examples of boost converters using this chip as well that don't require the multi-coil transformers.

[Unimportant]

On 6/15/2020 at 10:10 PM, Grabhanem said:

I'm not worried about needing external MOSFETs, I have lots of those to spare. I was just using this circuit as an example of what's possible, even if it's not exactly what I need.

 

I'm seeing lots of examples of boost converters using this chip as well that don't require the multi-coil transformers.

It looks like this might be possible with the LT1241, but if you have to ask I'd advice against it.

You'd have manually add frequency compensation in the feedback loop to make sure you have enough phase/gain margin for it to be stable. If you don't understand what that means I'd advise you go for a fully integrated buck converter IC that handles all this for you. (And don't stray too far from the manufacturer's recommended PCB layout, PCB layout is critical for buck converters, or the thing will ring like a bell.)