555 smps inductor?

[Marcos - Munky]

I'm building this 555 SMPS to power a submini amp (Superfly):


Question: I know I have to use one of those radial black inductors, but how much current the inductor needs to handle?

[bluebunny]

This is the part that Rick originally specified (on the schematic above) - 0.66A.

[GibsonGM]

Does anyone know of a US supplier of an inductor for this of the same specs?   I lucked out using a junkbox find, but would like to have a couple of them around for tube projects.  Shipping from the UK might be expensive...

[duck_arse]

transmogrifox has posted a few times on the calculation of inductor size and current for smps, well worth a search.

[Marcos - Munky]

Thanks, Marc! I got to find 2 sellers here in Brazil, just waiting to get the shipping price from one of them to buy it (the other asks about $5 for a $0.77 inductor ).

Mike, I found this and this one on mouser, and this one on digikey.

[Marcos - Munky]

transmogrifox has posted a few times on the calculation of inductor size and current for smps, well worth a search.

https://www.diystompboxes.com/smfforum/index.php?topic=112122.msg1033723#msg1033723
He posted some great info on inductors!

[vigilante397]

I use the ones from Mouser, but Tayda (semi-)recently started stocking a 100uH inductor that works as well. I've used them in a couple builds and they work fine, and are reasonably priced, but they're HUGE

[GibsonGM]

Thanks, Marc! I got to find 2 sellers here in Brazil, just waiting to get the shipping price from one of them to buy it (the other asks about $5 for a $0.77 inductor ).

Mike, I found this and this one on mouser, and this one on digikey.

Thanks, Marcos!  Gee, last time I looked at Mouser, they didn't seem to have any. Maybe I was not in the right place on their site???  Very helpful!

[J0K3RX]

I use the ones from Mouser, but Tayda (semi-)recently started stocking a 100uH inductor that works as well. I've used them in a couple builds and they work fine, and are reasonably priced, but they're HUGE

Originally I used some that were rated 670 mA or a little more and they seemed to work fine, no failures but, they would get screamin hot! I use ones that are rated at or above 2A now and they seem to handle the heat better.

[Marcos - Munky]

Ended up buying 10 3A inductors from the other seller I found. The smps is just missing the inductor, so I'll test it as soon as the inductor arrives. The amp board is done too, waiting the output transformer to be made and shipped.

[pinkjimiphoton]

Does anyone know of a US supplier of an inductor for this of the same specs?   I lucked out using a junkbox find, but would like to have a couple of them around for tube projects.  Shipping from the UK might be expensive...

hey parks, maybe this? .45 cents a piece,  100uH and good for 2.5 amps

https://www.futurlec.com/Components_Others/PIND100pr.shtml

[Transmogrifox]

With the 555 smps the general rule is you can use >=100uH inductor without changing anything.  If you want to go to a smaller inductor (higher current usually with smaller physical size) you need to increase the switching frequency.

In comes the "beefier" 555 timer....or just get an IC made for this purpose.  These are an old classic that remains cheap:
https://www.digikey.com/product-detail/en/on-semiconductor/UC2842BNG/UC2842BNGOS-ND/1485404
http://www.onsemi.com/pub/Collateral/UC3842B-D.PDF

Duck Arse said he liked the discrete converter I posted a while back because it uses common parts most DIY stompboxers have in their bin of spare parts.

If there's any interest I can work up an application for a boost converter based on one of these PWM converters.  These simplify stuff quite a bit, but perhaps not really straightforward to apply if you don't have a guide like what is available for the 555 SMPS.

Because the UC28xx chips have a precision voltage reference you don't need the trimpot because you can set the output level you want within about 2% accuracy, or maybe a little worse if using 5% resistors (most of the time 5% resistors won't be as bad as 5%).

Anyway, give a +1 or something if you want to see a design based on this.

The chips are cheap and really reliable....but you have to be able to get them.  The nice thing about the 555 is you can usually get them anywhere.

[duck_arse]

I like the discrete converter Transmogrifox posted a while back because it uses common parts most DIY stompboxers have in their parts bin. it's quite exciting, and it runs fast.

Transm - I've been meaning to send you some more "findings" on that basic circuit, but haven't done the CRO time yet.

[Marcos - Munky]

Which circuit is this one? The one at the link I posted?

Transmogrifox, how many mA those UC2842 can supply?

[Transmogrifox]

Transmogrifox, how many mA those UC2842 can supply?

The power (current) isn't constrained by the UC2842 so a circuit can be designed for any amount of power you need.

This depends on the external capacitors, FET, inductor and diode you use.  With the right selection of external components these could be at the heart of a 2 kW converter (think PS for a rack-mount mains power amp).  This could be used to generate a supply for  a tube power amp with 4x6L6's or similar.

In other words, with the right components, you could supply several amps at 250V if you wanted to do this and the UC2842 doesn't know any different..

For stompbox tube preamp purposes components would be chosen for smaller space and a lower-power target -- whatever you need.

Here's one of the variants of this circuit that Duck Arse is talking about.  Note the MOSFET and BJT's used are not special selections.  You can probably get it to work with any >250V MOSFET and any general purpose transistors. The only little irritation with this circuit is it needs to have the power switched on fast in order for it to start up. 

You could always replace the discrete gate driver with an IC like this one to make the startup reliable:
http://www.ti.com/lit/ds/symlink/ucc27511.pdf
...but then if using a special IC why not use a purpose-built SMPS IC?  As duck_arse points out, the attractive feature is that it can be built with stuff you can pull out of your scrap bin and/or cannibalize from other electronics junk.

[Marcos - Munky]

Got it. Thanks for all the info. A 4x6L6 SMPS power supply sounds interesting but probably it's easier to go with a transformer, correct? Thinking "smaller", I think something that can supply like 60-70mA can be very useful. There's a lot of bedroom tube amps that works with this current.

If there's any interest I can work up an application for a boost converter based on one of these PWM converters.  These simplify stuff quite a bit, but perhaps not really straightforward to apply if you don't have a guide like what is available for the 555 SMPS.

The chips are cheap and really reliable....but you have to be able to get them.  The nice thing about the 555 is you can usually get them anywhere.

Thanks for the offer. If it doesn't take up too much of your time, I'm interested to see an application. Got to find the ICs for cheap on Aliexpress, so if I get them from China it'll take something like 3 months to be delivered at my place (brazilian customs s*cks). Still didn't searched for them here in Brazil.

On the inductors, found a seller that asks $.64 for a 100uH 3A piece, with a $6.4 shipping fee. Bought a bag of 10 pieces, and the seller told me he added 4 extra pieces with no charge, so I eded up paying $.46 a piece plus shipping . They'll probably be delivered next week.

[Transmogrifox]

Got it. Thanks for all the info. A 4x6L6 SMPS power supply sounds interesting but probably it's easier to go with a transformer, correct?

In general I think this is a correct statement.  An SMPS will put it all into a smaller space, but if you aren't an experienced SMPS designer it's far easier to understand and troubleshoot a plain 50/60Hz transformer and rectifier.

The point in my mentioning this is to demonstrate that the PWM controller chip is not the limitation, but the external components.  The same is true for the 555 SMPS.  The main caveat is because the 555 circuit does not include soft-start, then higher power applications could stress your external components enough to blow the lead-frame connections off the silicon on startup.

The main advantage of the SMPS is small space, which isn't always a really big deal for tube power amp desings.  Another advantage is good SMPS design is usually more efficient so there is less heat wasted in power conversion.  For tube amp designs, I would doubt power supply heating is really the problem people are trying to solve since the tubes are able to operate at really high temperatures and heat radiating from power supply losses is pretty small compared to heat dissipated in the tubes themselves.  A more efficient power supply design probably doesn't significantly reduce the space required for a tube head (although it does reduce the weight a good deal since you get rid of one of the heavy transformers).

I'll post here if I find some time to draw up a simulation based on one of the PWM controllers.

[Marcos - Munky]

True, small space and heat dissipation usually aren't big deals when building tube amps.

I'm interested in the UC2842 smps, especially if the external circuit can supply about 60-70mA. Getting rid of the power transformer would make possible build some amps in enclosures like 1590B and even 1590B (using an ECL82 for example) if the circuit is small enough.

I'll get them from China. Hope brazilian customs plays nice and doesn't hold the package for 5-6 months like it happened a few times .