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How to increase amperage in SMPS circuit?
How to increase amperage in SMPS circuit?
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Old 1st October 2019, 06:58 PM   #51
FauxFrench is online now FauxFrench  France
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Hi Formas,

I get the impression that the flow of suggestions how to modify the old SMPS has reduced heavily.
You still wish to modify the ďoldĒ SMPS?

As already suggested by Osvaldo, the TOPxxx from Power Integrations are interesting candidates. A single IC, looking like an LM1875 (TO-220) but with 6 pins that can deliver well above 100W at the output of a transformer. The TOP260 can deliver more than 100W with the right transformer.

TI shows in 1st page of their TNY268 datasheet ( https://www.power.com/sites/default/...tny263_268.pdf ) the power levels this IC can deliver. 10-20W with the right transfomer. The old SMPS transformer is not optimized for the TNY268 and it would never be possible to get the 75W you need.

The max. output power depends on the max. current the power switch can handle and the switching frequency. The TOP260 exists in versions that should allow both 66KHz or 132KHz switching. The old SMPS probably ran closer to 66KHz than 132KHz. You say you have one that still functions and delivers +/-13.6V. Could you please measure the switching frequency on that one?

If you decide to try with the TOP260, you still need to draw-up the circuit of the old SMPS so we know what we are modifying. The second primary winding you mention could be an auxiliary winding for supplying the IC after start-up.
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Old 1st October 2019, 07:12 PM   #52
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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Quote:
Originally Posted by FauxFrench View Post
The max. output power depends on the max. current the power switch can handle and the switching frequency.
It also depends in the transformer design (In fact, coupled inductors in Fly Back and Quasi Resonant topologies), because the core area and wire section defines the temperature rise, and the gap, the max voltages and DC through the windings,
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Last edited by Osvaldo de Banfield; 1st October 2019 at 07:13 PM. Reason: Typos
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Old 1st October 2019, 07:52 PM   #53
Formas is offline Formas  Jamaica
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Iím converting to linear, smps didnít turn out well on the forum.
Iím at 12v center tap transformer with 3amp, Iíve wired up it plays loud, but itís swinging from between 11ish and 13ish on idle itís at 15ish, my question are as follows:
Why is it still cutting out when driven volume hard, Iím still losing amperage. **(itís way better than previous with the smps tho)
Should I just add the secondary transformer wires where the smps secondary was removed?
Should I remove the two diodes and add an full bridge rectifier?
Should I upgrade 25/1000uf to 25/2200uf?
Should I use a 12v (pos) regulator for the usb/card reader circuit.
What can be done to make it stablish?
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Old 2nd October 2019, 07:15 AM   #54
FauxFrench is online now FauxFrench  France
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Hi Formas,

With an ordinary transformer and full-rectification using a bridge-rectifier, the power line decoupling capacitors are recharged by the transformer every 10ms. In-between the recharging, the current for the amplifier is taken from the decoupling capacitors.
A 10000uF capacitor will in 10ms loose 1V of its voltage when loaded with 1A.
With 60Hz net frequency, it is slightly better but not much.

In your case when you turn up the volume, let's assume you pull a current of 1A. With only 1000uF, the capacitor will lose 10V in 10ms. If the capacitor was recharged to 16V for a start, it will fall well below 10V toward the end of the 10ms period. You have an enormous voltage ripple when you turn up the volume. That shows when you measure an "11ish" voltage with your voltmeter (slow).
Further, it seems you are using only two diodes thus single rectification. Then, the period in-between recharge becomes 20ms and the voltage drop the double!

You need to use the 12V center tap trafo with a bridge rectifier and at least 10000uF for each voltage rail before it will start function well.
You can leave the 1000uF that are already there. If you have decided for a traditional transformer supply, you better remove the two diodes such that the old SMPS power supply circuit is disconnected from the amplifier. The outputs from the new 10000uF (or more) capacitors are connected directly to the 1000uF capacitors. Be careful using the correct polarity.

Last edited by FauxFrench; 2nd October 2019 at 07:43 AM.
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Old 2nd October 2019, 08:32 AM   #55
jan.didden is online now jan.didden  Europe
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+1
How refreshing - a guy who knows what he is talking about ;-)
(and others too of course)

Jan
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Old 2nd October 2019, 10:43 AM   #56
chermann is offline chermann  Austria
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Quote:
Originally Posted by FauxFrench View Post
Hi Formas,

With an ordinary transformer and full-rectification using a bridge-rectifier, the power line decoupling capacitors are recharged by the transformer every 10ms. In-between the recharging, the current for the amplifier is taken from the decoupling capacitors.
A 10000uF capacitor will in 10ms loose 1V of its voltage when loaded with 1A.
With 60Hz net frequency, it is slightly better but not much.

In your case when you turn up the volume, let's assume you pull a current of 1A. With only 1000uF, the capacitor will lose 10V in 10ms. If the capacitor was recharged to 16V for a start, it will fall well below 10V toward the end of the 10ms period. You have an enormous voltage ripple when you turn up the volume. That shows when you measure an "11ish" voltage with your voltmeter (slow).
Further, it seems you are using only two diodes thus single rectification. Then, the period in-between recharge becomes 20ms and the voltage drop the double!

You need to use the 12V center tap trafo with a bridge rectifier and at least 10000uF for each voltage rail before it will start function well.
You can leave the 1000uF that are already there. If you have decided for a traditional transformer supply, you better remove the two diodes such that the old SMPS power supply circuit is disconnected from the amplifier. The outputs from the new 10000uF (or more) capacitors are connected directly to the 1000uF capacitors. Be careful using the correct polarity.
FF

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Old 4th October 2019, 06:31 AM   #57
Rick PA Stadel is offline Rick PA Stadel  United States
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Good, solid advice and decision .. and bets are that your customers will be the happier for it.

Sure is an interesting problem, though -- how many of these naughty little guys are you stuck with, anyway?

And I should confess, I'm more than a little OCD -- now that I've worked most of the way through the TNY268 data sheet, a decent bit of the LTV-8x7 sheets, and every last post in this thread (aagh!), and hacked through the small storm of misunderstandings and unintended insults, I feel ready to tackle what I THINK was your original request -- 'what parts [that are available this side of the Pacific Ocean] could replace the smoked originals, giving the same performance and (hopefully) better reliability?'

I can tell you with certainty that the TNY263-268 series parts won't do it. You'll need a controller IC and separate MOSFET. But the pinout of the original IC is unfamiliar to me -- 7/8 pin options are common enough, but the ones I've encountered don't employ a separate output device. The pinout of the MOSFET is common enough, and with some time we may be able to find a pin-compatible replacement for the controller IC, but you'd probably need more than 10 or 15 of these failed bad boys to warrant the effort. We'll need full specs or an examplar of the transformer to start with -- and that's the point at which we start duplicating the work the original designer did (or should have).

Couple things to note about the TNY263/68 series parts: Their data sheet says they top-out at 23 Watts (output). And, just about any 7/8-pin IC that handles line juice - and has multiple pins devoted to 'Hot negative'(usually MOSFET Source), will need ALL OF THEM connected to a large copper plane for heat sinking. The 'Dead Bug' style shown in one of your pictures won't work; connect ALL of the Source pins to a decent copper plane for heat sinking. If you don't, chances are that the IC will impose thermal [current] limiting well before you reach the desired output power.

I may be too slow to help you with this situation, but I am willing ...

On the other hand, if you (and your customers) are completely happy with the linear replacement PSU, I'm OK with that, too.

-Rick

Last edited by Rick PA Stadel; 4th October 2019 at 06:38 AM.
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Old 9th October 2019, 12:42 PM   #58
schiirrn is offline schiirrn  Germany
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Quote:
Originally Posted by wiseoldtech View Post
Seems like Jan is steadfast in his beliefs and opinions of SMPS supplies, and nobody is going to tell him differently.
But to conclude that some others are "nostalgic DIY'ers" because of different beliefs is going a bit far out.

There is nothing to tell differently. Jan knows switch mode supplies, you don't.
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Old 9th October 2019, 01:36 PM   #59
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by wiseoldtech View Post
Seems like Jan is steadfast in his beliefs and opinions of SMPS supplies, and nobody is going to tell him differently.
May I say you sound the exact same, without being impolite?
Can we mention the pot calling the kettle black?
Quote:
But to conclude that some others are "nostalgic DIY'ers" because of different beliefs is going a bit far out.
Maybe your user name choice slightly hints at that, WISEOLD Tech?

Seriously:
1) SMPS have come a long way.

2) **ALL** supplies eventually fail.

Of course we see here the bad ones so failures are over represented.

Only difference is that being way more complex and still not standardized by any means (meaning they are not mature technology by any means, they change all the time) people find them harder to repair, while, well, a transformer, 4 diodes and 2 capacitors are simpler and faster to troubleshoot.

That said, we still get cries for help on these every day.
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Old 9th October 2019, 01:48 PM   #60
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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In my opinion, SMPS are by far much better than standard linear ones. Think for example, what a power supply will needed for a standard PC if they must be done with common materials, say, BJT's as series regulators, 50Hz trafos, big can caps, etc.

SMPS's generally destroys itself preventing damages to their loads, and from this inherent safety they have price.

I designed and repaired several of them including DC/DC converters, and are a largely interesting item.
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