ruffrecords
Well-known member
Excellent. I may try a couple.Matador said:Indeed it is. There are a plethora of inexpensive 12V high current wall adapters on the market because of the popularity of LED strips. I purchased mine on Amazon for about $15, and it even came with European plugs.
I suspect our requirements may differ in some respects. I am mostly interested in powering tube mixers, or at the very least a 3U rack containing a number of tube modules. The heater current of the 3U rack is about 2A at 12V and for the mixer is can be several times this (typically 10A). Both Holger Classen and I have tried AC/DC SMPS for heaters at these sort of currents and have only been able to get them to fire up the heaters if the SMPS is heavily over rated. Simple ones I used years ago which go into SC current limit when presented with tube heaters can never input enough current to get the heaters warm enough to exit current limit even if well over rated. Only recently did I look at this again and came across hiccup mode which can cope with large capacitive loads which require similarly large inrush currents to tubes. I have had success with versions of these from Mean Well. At present I have a 100W unit that will successfully light up 4A of heaters at 12V. I am not yet convinced a 50W unit would do so but I would be very pleased if it could be so.This isn't so much an issue with PWM buck topologies, because the FET and inductor are both in series with the load. Essentially the controller turns on the FET until the output voltage rises to the set point at which point it starts to PWM average the output. I could see what you describe happening with a boost module, since it relies on charging the output cap through a diode after the FET switches off. However I've never had any problems with using the raw LED supply for the heaters on any of the tubes I've tested so far.
I've probably logged 200+ hours on the scope with my design and would be happy to help if you need it. I've tested half a dozen FET's, and since the current requirements for tube gain stages are modest, you don't need to use the $15 ones either.
Thank you for the kind offer to help out with the design. I will certainly take you up on that.
Cheers
Ian