Hi all,
As the title says, I have some class-d amps powered by a pair of smps . I would like to use a soft start with the power resistors bypassed with straight wire so I can still use the remote on function, momentary switch option and led driver on the SS module.
Does anyone see a problem with doing that?
Thank you in advance,
Troy
As the title says, I have some class-d amps powered by a pair of smps . I would like to use a soft start with the power resistors bypassed with straight wire so I can still use the remote on function, momentary switch option and led driver on the SS module.
Does anyone see a problem with doing that?
Thank you in advance,
Troy
SMPS usually have a soft start anyway.
On the last one I designed I lower the switching frequency slowly until the output caps get charged then I run as normal.
On the last one I designed I lower the switching frequency slowly until the output caps get charged then I run as normal.
If the two SMPS modules cause dimming of lights at power on (shorted softstart resistor) consider leaving a lower value resistance for softstart, rather than a short.
Normal softstart modules (for toroids) used for SMPS, combined with own intermal SMPS softstart (for primary side capacitance), can only be a problem if the SMPS tries to start charging lots of output capacitance (secondary side) before primary side softstart has finished. That could lead to a failed start attempt.
Normal softstart modules (for toroids) used for SMPS, combined with own intermal SMPS softstart (for primary side capacitance), can only be a problem if the SMPS tries to start charging lots of output capacitance (secondary side) before primary side softstart has finished. That could lead to a failed start attempt.
Thank you very much.
Rather light secondary side capacitance so I don't think that would be an issue.
Definitely no dimming of lights..
Two smps500rxe supplies powering four crossed over UcD180's.
I just want to add a 12 volt trigger so the wife will get off my ____ about all the switches.
I am facing this same problem, so I am reviving this thread.
I want to use a moderate power (350W) smps with a class-D power amp. The SMPS does not incorporate a soft start. The datasheet states inrush can be up to 60A (!) so inrush limiting seems like a good idea.
Can inrush limiting be done as simply as it is for e.g. a toroidal transformer, by putting resistance (e.g. 10 to 20 Ohms for 120VAC mains) in series with the unit and then switching it out after 100msec or so?
I want to use a moderate power (350W) smps with a class-D power amp. The SMPS does not incorporate a soft start. The datasheet states inrush can be up to 60A (!) so inrush limiting seems like a good idea.
Can inrush limiting be done as simply as it is for e.g. a toroidal transformer, by putting resistance (e.g. 10 to 20 Ohms for 120VAC mains) in series with the unit and then switching it out after 100msec or so?
Well I shorted out the power resistors and it has been working perfectly ever since.
Can you just use a CL-60?
Can you just use a CL-60?
Whatever I use, I will bypass it after a short while, e.g. 100 msec. The element could be power resistors, or a NTC thermistor like CL-60 or similar.
My question is more about whether this is the right way (or at least a valid way) to implement a soft start with an SMPS. I have DIYed my own transformerless supply and time-delay relay PCBs and have all the parts on hand. Just want to get some feedback, etc. on this approach.
Do your amplifiers have a standby or reset function?
If so it might make more sense to use this, get the inrush over on first startup and just leave everything powered on with the amp in standby.
They learned this lesson the hard way with PC power supplies. People were shutting off the babysitter switch on the back, with the BIOS set to power on after power loss ... and after a while they ended up killing the power supply since the rectifier diodes couldn't take the repeated surges of current.
The simple answer was to leave them turned on and use the front panel "power" button to start and stop the electronics.
If so it might make more sense to use this, get the inrush over on first startup and just leave everything powered on with the amp in standby.
They learned this lesson the hard way with PC power supplies. People were shutting off the babysitter switch on the back, with the BIOS set to power on after power loss ... and after a while they ended up killing the power supply since the rectifier diodes couldn't take the repeated surges of current.
The simple answer was to leave them turned on and use the front panel "power" button to start and stop the electronics.
Interesting point, although I am not convinced that what happened sometime in the (distant?) past with PC power supplies applies here...
So, yes, the amp has shutdown/standby capability, so I could do as you say and just leave the PS powered up all the time and bring the amp in and out of standby when needed. That still wouldn't solve the inrush problem it just makes it happen less often.
I changed one last week for this reason. It's not ancient history.
AND... it was only one example of many. Laptop chargers exhibit the same problem and we use them for mini-amps all the time.
Unless you are in the habit of unplugging stuff and moving it around the inrush would happen once. None the less, that has been the solution in most non-commercial power supplies.
Most modern gear has "soft off" they leave the supply on all the time, leave the bulk capacitors charged up and put the electronics into standby mode. Think about it... if your TV was actually off, how does it see the remote?
My PC works like that. PC is off but USB is still powered.
My PICKIT3 lights stay on when PC is shutdown.
I still think if the SMPS does NOT have a soft start function ( behaves like a transformer) then a simple CL-60 would function the same and be a simple solution.
So do most consumer grade things ... it lets the manufacturer use parts more reasonably rated for continual use, without having to worry about 30 and 40 amp surges blowing up the rectifiers.
Unless you have a class-A amp, you should NOT permanently install a thermistor in series with your power supply mains connection.
The problem with doing this is that, except for Class-A, the current flow into most amps is anything but steady and is modulated along with the music signal. This means that the thermistor's impedance will go up and down along with the average power demand, and it's in series with the PS. With a class-A amp there is quite a lot of constant current relative to the music-modulated current, so the thermistor stays hot and its impedance low. This is why NP just throws one in series on his projects. But in general for other amp classes it's not a good solution IMHO.
It's always best to short across the current limiting element (thermistor, resistor, or whatever) after the initial inrush is over using a relay. I designed a transformerless power supply and relay boards for this purpose a couple of years ago.