Hello out there.
I plan to buy two Ucd180 modules. I have a powersupply which delivers +-60V DC / 5A unregulated with 2x10mF on each rail which I plan to use.
My plan is to build two simple linear regulators using a power transistor, zener diode, resistor and a capacitor to lower the voltage to around +-48V before supplying the Ucd180. The circuit will be very simple and intended only for protection of the module.
Could this cause any problems? Any special things to consider when building this? Should this circuit be placed before, in between or after the capacitors?
Grateful for any feedback.
--- Mikael Rosbacke
I plan to buy two Ucd180 modules. I have a powersupply which delivers +-60V DC / 5A unregulated with 2x10mF on each rail which I plan to use.
My plan is to build two simple linear regulators using a power transistor, zener diode, resistor and a capacitor to lower the voltage to around +-48V before supplying the Ucd180. The circuit will be very simple and intended only for protection of the module.
Could this cause any problems? Any special things to consider when building this? Should this circuit be placed before, in between or after the capacitors?
Grateful for any feedback.
--- Mikael Rosbacke
Hi,
A problem I see is the loss of efficiency you'll have by using a linear regulator in a class d circuit.
Are you doing this to make use of the transformer you already have, or to run the modulator up to it's limite safely?
I doubt it would be necessary for protection purposes if you left a bit of headroom on the rails as previously mentioned.
A problem I see is the loss of efficiency you'll have by using a linear regulator in a class d circuit.
Are you doing this to make use of the transformer you already have, or to run the modulator up to it's limite safely?
I doubt it would be necessary for protection purposes if you left a bit of headroom on the rails as previously mentioned.
classd4sure, thanks for the answer.
The reason is that I have an unused power supply already assembled and want to avoid buying a new one. I'd figured I will still get around 240W of power to the two modules. It should still be plenty for my flat to turn into a disco...
I know I will lose energy in the linear regulators but I can live with that. But I'm uncertain if the regulator will have some degrading effect on the sound or if the module draw power in such a way that my regulators can affect their performance. Hence the question.
--- Mikael R
The reason is that I have an unused power supply already assembled and want to avoid buying a new one. I'd figured I will still get around 240W of power to the two modules. It should still be plenty for my flat to turn into a disco...
I know I will lose energy in the linear regulators but I can live with that. But I'm uncertain if the regulator will have some degrading effect on the sound or if the module draw power in such a way that my regulators can affect their performance. Hence the question.
--- Mikael R
I'd definitely wait for the UcD400 which runs at 60 V and abandon the PSU idea. Cost is +EUR 40 each meaning +EUR 80 in total. Power is higher and less work and simpler to get running alright.
Hi,
I like your approach to the situation, making what you have work.
Soundwise my guess is if your regulator is a winner there's a good chance it sounds even better due to the decreased ripple >psrr
Make sure your regulator is a winner.
You mentioned using one resistor and one cap, is that to bias and filter the zener current? I think that's two resistors and you need another power resistor to limite the current through your pass transistor.
You could look into using an active current source to feed the zener with, won't need to filter it then.
I'm certain you can find all kinds of variations on the circuit to look at here that could give you some ideas.
You shouldn't have to make anything too extravagant but with the few parts you mentioned I feel it's a bit too simple, at least add the power resistor.
You might want higher current capability in the end but it will get you started.
I like your approach to the situation, making what you have work.
Soundwise my guess is if your regulator is a winner there's a good chance it sounds even better due to the decreased ripple >psrr
Make sure your regulator is a winner.
You mentioned using one resistor and one cap, is that to bias and filter the zener current? I think that's two resistors and you need another power resistor to limite the current through your pass transistor.
You could look into using an active current source to feed the zener with, won't need to filter it then.
I'm certain you can find all kinds of variations on the circuit to look at here that could give you some ideas.
You shouldn't have to make anything too extravagant but with the few parts you mentioned I feel it's a bit too simple, at least add the power resistor.
You might want higher current capability in the end but it will get you started.
UrSv said:
That's an option too but .... I wonder what kind of power his speakers can handle. That would be a small supply for it, you don't want to skimp on the current capability, it's a small supply for a 180watt system. No point paying for the extra power if you can't put it to use, that's just throwing money at it for nothing, and a regulated supply could improve things if it's done right, less than 1/4 the cost of two 400's.
In the end I think his money would best be spent on a proper transformer of the correct voltage rating and muuuuuuch higher current capability. People seem to like the 1000VA ones for instance, but trying it with linear regulators first would be alot cheaper than that and once he gets to hear it he'll be more apt to want to fork over more money for a decent transformer.
I don't think 5amps will cut it at all. These modules should be worth building a good supply for, but if ya can't swing it right now go for the regulator to make the lights glow and I hope you get to hear something from it too, I think it will work, but it won't come to life until you get a real supply for it.
Thanks for the replies.
UrSv, It is a tempting idea. But i don't think it will solve my problem. The absolute maximum supply rating of the 400 module is +-60V, i.e. there is no margin at all. Even I would like maybe 5% safety margin.
But my main problem is that two 400W modules could potentially draw 800W of power. This could really take my 2x160VA transformers over the top.
classd4sure, A good transformer is the right solution in the long run. But currently there are other parts of my system in need of an upgrade before I can really appreciate the full potential of this module.
The speakers are fairly OK (Two way using Vifa PL18 and DX25 drivers) but I don't think they can handle more than 100-150W of power. The source is my main problem and the next DIY project. It will be some kind of DAC so I have a good signal to start with.
I havn't done the details yet of the regulators. I made a point of keeping them simple but given the voltage 48V and currents of 5A I will probably need to use some additional small signal transistors and capacitors unless the zener is going to handle a lot of power.
Anyway, I'll have to view the regulators as a temporary solution until I can justify a new transformer.
--- Mikael R
UrSv, It is a tempting idea. But i don't think it will solve my problem. The absolute maximum supply rating of the 400 module is +-60V, i.e. there is no margin at all. Even I would like maybe 5% safety margin.
But my main problem is that two 400W modules could potentially draw 800W of power. This could really take my 2x160VA transformers over the top.
classd4sure, A good transformer is the right solution in the long run. But currently there are other parts of my system in need of an upgrade before I can really appreciate the full potential of this module.
The speakers are fairly OK (Two way using Vifa PL18 and DX25 drivers) but I don't think they can handle more than 100-150W of power. The source is my main problem and the next DIY project. It will be some kind of DAC so I have a good signal to start with.
I havn't done the details yet of the regulators. I made a point of keeping them simple but given the voltage 48V and currents of 5A I will probably need to use some additional small signal transistors and capacitors unless the zener is going to handle a lot of power.
Anyway, I'll have to view the regulators as a temporary solution until I can justify a new transformer.
--- Mikael R
I think it would solve your problem completely. ..
Sure your modules could potentially draw even more than 800 W but that's when YOU draw that from them. With music and keeping reasonably well away from frying your speakers you will get nowhere near. Besides, if I'm not mistaking the recommendation is 60 V but they will take 63 V easily.
I know it's controversial and there are many views and beliefs on the subject of transformers for Class D amps but IMHO I think it's clear that if you don't play them flat out then a proportionally smaller transformer will *suffice*. Lars at LC Audio (ZAPpulse et al) tested to run their module with something like 55 VA for a 200 W module with very good results if my memory serves me correctly. Sure it was an analog PWM supply but still. I'm sure that will mean some will tell you he hasn't got a clue but after all he makes a living doing these things. Also, the fact that a transformer is rated at 320 VA only means that's the power when internal temp rise is according to spec. It will probably happily let you have 800 VA when asked for shorter peaks.
Just my two öre.
Sure your modules could potentially draw even more than 800 W but that's when YOU draw that from them. With music and keeping reasonably well away from frying your speakers you will get nowhere near. Besides, if I'm not mistaking the recommendation is 60 V but they will take 63 V easily.
I know it's controversial and there are many views and beliefs on the subject of transformers for Class D amps but IMHO I think it's clear that if you don't play them flat out then a proportionally smaller transformer will *suffice*. Lars at LC Audio (ZAPpulse et al) tested to run their module with something like 55 VA for a 200 W module with very good results if my memory serves me correctly. Sure it was an analog PWM supply but still. I'm sure that will mean some will tell you he hasn't got a clue but after all he makes a living doing these things. Also, the fact that a transformer is rated at 320 VA only means that's the power when internal temp rise is according to spec. It will probably happily let you have 800 VA when asked for shorter peaks.
Just my two öre.
Hi,
Sounds like a working plan you have there to me.
Regarding your source, I really like new audigy's... it isn't very diy though but ... hard to beat the quality and options for the price of them, thx certified aside they sound great. It's enough to overlook the low quality outputs used on them. I wonder how others feel about that. Kind of off topic though. Sorry
Sounds like a working plan you have there to me.
Regarding your source, I really like new audigy's... it isn't very diy though but ... hard to beat the quality and options for the price of them, thx certified aside they sound great. It's enough to overlook the low quality outputs used on them. I wonder how others feel about that. Kind of off topic though. Sorry
JohnW said:
This is indeed the case if the spike is delivered by a low-impedance source, like a test generator. If this source is capable of delivering large currents, the avalanche mechanism is indeed destructive.
This is not the case with ordinary overshoot/ringing. The energy "stuck" in the ringing corresponds to what can be stored in the stray inductances (pins, bond wires) at the current that's flowing (0.5*L*I^2). When this energy is released across an open FET it'll go in avalanche, absorb the impulse like a zener and come out of avalanche when the stored energy has petered out and the voltage is returned to below-breakdown. The single-pulse maximum one can dump into a FET is actually given in the data sheet.
This is not to be taken for granted btw, MOSFET designers take special care to allow absorption of impulse energies without turning on the parasitic bjt. This is what they call "ruggedness". Current day mosfets are orders of magnitude more "rugged" than what is required to absorb the kind of spikes found in a class D amp.
If a MOSFET breaks down gate oxide before going into avalanche this is called a case of bad fet design... 🙂
If you have experienced sudden breakdowns near maximum operating voltage (and current) this was more likely caused by parasitic bjt turn-on due to excessive diode recovery currents. Ringing on the actual power rail (which encompasses electrolytic's parasitic inductance and the local ceramic cap) is another thing the FET may not be too happy about.
Cheers,
Bruno
UrSv said:
In consumer electronics the general rule of thumb is to use a transformer with a VA rating half of the amplifier rating. Fully-loaded output voltage will be roughly 80% of unloaded voltage, so if a supply is designed to have an unloaded output voltage of 90%*Vmax (to allow for Vmax at 10% mains over-voltage), fully loaded with nominal mains lands somewhere at 70% of Vmax.
The worst test normally applied to an amplifier is first to let it run at 33% of rated output for an hour, then to have it deliver full rated power for another 5 minutes. After this test, a transformer rated as per the above will be hot (70-80 ºC), but well below its rated maximum temperature
Now you know this, you share the full extent of power amplifier expertise most CE manufacturer's "power amp gurus" have. They guard this knowledge closely.
Hi Bruno,
From your explanation, I’m I to understand that the Rise-Edge ringing seen on the output of an HBridge is not seen by the MOSFET Die itself? Surly the “off FET” in the bridge must see the full voltage (including the ringing) as measured between HBridge PSU rail and the output? The “Die” after all is tied between two inductance paths – S & D.
I’ve seen 60V MOSFET’s blow with as little as 10V across them, due ringing spike – I always put this failure down to the ringing spikes exceeding the rated D/S voltage – not my design I would like to add 🙂 but a great fly-back converter!
I could be wrong?
John
From your explanation, I’m I to understand that the Rise-Edge ringing seen on the output of an HBridge is not seen by the MOSFET Die itself? Surly the “off FET” in the bridge must see the full voltage (including the ringing) as measured between HBridge PSU rail and the output? The “Die” after all is tied between two inductance paths – S & D.
I’ve seen 60V MOSFET’s blow with as little as 10V across them, due ringing spike – I always put this failure down to the ringing spikes exceeding the rated D/S voltage – not my design I would like to add 🙂 but a great fly-back converter!
I could be wrong?
John
The die sees most of that voltage. However, if the energy stored in the parasitics is low, it can be safely absorbed in avalanche mode (think of the FET as acting like a zener). I've seen that very graphically in a 500W/2ohm FB device I made years ago using 55V fets. As power was increased, the overshoots increased too, but they were neatly stopped at 60V. Power could be increased way beyond that without problems.
I presume that the extreme case you were confronted with had a lot of inductance sitting there. Could you elaborate?
Cheers,
Bruno
I presume that the extreme case you were confronted with had a lot of inductance sitting there. Could you elaborate?
Cheers,
Bruno
The designer – or rather the PCB layout engineer made the classic mistake of insuring the HF decoupling cap was near to the Positive connection of the HBridge – but with about 1 Inch of poor (thin) PCB track, and then though a couple of vias to add - return to the lower FET ground pin! This when combined with 5nS Gate drive edges and wide open deadtime – meant the poor guy could not increase the PSU rails beyond say 10V before the “60V” Fets blow!!!
Get that Dead-time and decoupling right!
Yes – I’ve also seen the “Ringing” – “clamped” (you know with a bad design as the modulation index increases) - but is this safe and advisable to operate continuously like this?
For me avalanche, means driving a high power fast Laser with say 100 – 200 pulses (if you where lucky) before the pulser died!
John
Get that Dead-time and decoupling right!
Yes – I’ve also seen the “Ringing” – “clamped” (you know with a bad design as the modulation index increases) - but is this safe and advisable to operate continuously like this?
For me avalanche, means driving a high power fast Laser with say 100 – 200 pulses (if you where lucky) before the pulser died!
John
power supply
> In consumer electronics the general rule of thumb
> is to use a transformer with a VA rating half of the
> amplifier rating.
which rating? the UcD180 is rated at 180W into 4ohms, but only 105W into 8ohms.
does this mean that 2 modules driving 8ohms, would only require a smaller transformer (say, 150VA) than 2 modules driving 4ohms (which would presumably require 200VA)
>The maximum power supply voltage for the UCD180
>is specified at + and - 50V. So a transformer that gives
> 35-0-35 would be close to the edge, giving about 48V
> DC after rectification. I personally would take a bit
> more margin and go for say a 30-0-30 transformer,
> that would give about 41V power supply.
Would the modules' performance vary with a smaller supply voltage? (eg 41V vs 48V)
also, is it possible to use two smaller transformers of the same type instead of one larger one? eg. 2x300VA instead of 1x600VA? if so, how would you connect them? in parallel? before or after rectification?
i have a pair of 330VA 45-0-45 toroids, and would rather use them than buy something new, if i can. one alternative is to get UcD400's instead of 180's. Gertjan suggested these would deliver about 62V after rectification. would that be too much for the UcD400's?
cheers for all your help!
ben
> In consumer electronics the general rule of thumb
> is to use a transformer with a VA rating half of the
> amplifier rating.
which rating? the UcD180 is rated at 180W into 4ohms, but only 105W into 8ohms.
does this mean that 2 modules driving 8ohms, would only require a smaller transformer (say, 150VA) than 2 modules driving 4ohms (which would presumably require 200VA)
>The maximum power supply voltage for the UCD180
>is specified at + and - 50V. So a transformer that gives
> 35-0-35 would be close to the edge, giving about 48V
> DC after rectification. I personally would take a bit
> more margin and go for say a 30-0-30 transformer,
> that would give about 41V power supply.
Would the modules' performance vary with a smaller supply voltage? (eg 41V vs 48V)
also, is it possible to use two smaller transformers of the same type instead of one larger one? eg. 2x300VA instead of 1x600VA? if so, how would you connect them? in parallel? before or after rectification?
i have a pair of 330VA 45-0-45 toroids, and would rather use them than buy something new, if i can. one alternative is to get UcD400's instead of 180's. Gertjan suggested these would deliver about 62V after rectification. would that be too much for the UcD400's?
cheers for all your help!
ben
Usually it would be into an 8 ohm load, that's why should you attempt to bridge them, or halve the load, you might get only 1/4 the power increase you expected to.
You can tell this by looking at the amp ratings for both an 8ohm and 4ohm load.
I would think it can also contribute to the nasty clipping issues all CE amps seem to have.. you can't turn them up the power just isn't there.
I remember with my pioneer amp, if a series of fast bass hits were to occur at its higher power level, the first one would be far louder then all those which followed, reproducible with any song.
That's when you start looking into making your own amplifiers so you can make the decisions not to cut such corners in order to save a dime, which is why manufacturers under rate their power supplies in the first place.
You can tell this by looking at the amp ratings for both an 8ohm and 4ohm load.
I would think it can also contribute to the nasty clipping issues all CE amps seem to have.. you can't turn them up the power just isn't there.
I remember with my pioneer amp, if a series of fast bass hits were to occur at its higher power level, the first one would be far louder then all those which followed, reproducible with any song.
That's when you start looking into making your own amplifiers so you can make the decisions not to cut such corners in order to save a dime, which is why manufacturers under rate their power supplies in the first place.
Bruno Putzeys said:
I'm aware of this and my remark was actually in relation/reference to the opinions normally expressed here which usually are quite different than the rule of thumb you posted. I think rosbacke would be quite happy with the UcD400s running off of his existing supply which was the point I was trying to make. The commercial rule of thumb has been discussed before but most people here like something not quite so commercial as you might have noticed...
Thanks for your great input in this thread and others.
I have purchased two 500 VA transformers with 2x32 Volts for supplying 3 UcDs each. From the average power requirements this would not have been necessary. But I did so because of the better "load regulation". The UcD only has a PSRR of about 36 dB, so I think my active crossover solution will profit from this.
Apart from that, amps with generously dimensioned PSUs usually have a little more authority.
OTOH switching amps usually excel in this respect from the beginning .....
Regards
Charles
Not only bad designs have overshoot... Good designs delivering 30A also produce overshoot. Think of it: 10...20nH circuit inductance, 30A current... No way you can stop that from overshooting, apart from using these fancy top-cooled SMD fets (e.g. IR DirectFET). Ringing is a different affair. If you have it (ie when using through-hole packages) snubbers do magic.JohnW said:
I've been talking to MOSFET designers about operating FETs in avalanche like this. Having properly analysed the whole thing we agreed there's nothing to worry about.
Cheers,
Bruno
Hi Bruno,
Thanks for the info. This then leads to the next question - do the FET’s have to be "Avalanche rated" – or will "normal" FET’s be OK? The reason I ask is I get conflicting advise from the MOSFET designer guys – they seem to be concerned about the edge termination on the Die…
30A…. thankfully I design only for consumer applications – leadless SMD fine…
Cheers,
John
Thanks for the info. This then leads to the next question - do the FET’s have to be "Avalanche rated" – or will "normal" FET’s be OK? The reason I ask is I get conflicting advise from the MOSFET designer guys – they seem to be concerned about the edge termination on the Die…
30A…. thankfully I design only for consumer applications – leadless SMD fine…
Cheers,
John