![]() ![]() That ripple seems to be at the low frequency (200Hz) at which the mc34063 is controlling the switching signal. Is it because it generates noise as the switching signal turns on and off? I have added a capacitance multiplier to filter out most of the ripple and it seems to work great in the sim, with only 15mV peak-to-peak ripple at 300V. I guess it works at a fixed frequency and it switches the pulsing signal on and off, and that makes it a worse option than a proper PWM chip, but I don't understand why that may be a problem. ![]() I've read that the MC34063 is old and doesn't support PWM. I will know for sure once I build it, but I thought I would ask in case some of the local experts can help me understand all this stuff. According to my research, the MC34063 would exceed it's 1.5A peak current limit at some 50mA in the output at 300V, so 200mA seems way above spec. It also seems to make R7 unnecessary, I guess because the mosfet's gate current is negligible so it's not loading pin 2 of the IC, but is this a result that makes sense? Does the mosfet do a better job at staying away from the linear zone hence dissipating less power? Or is this simply an artifact of the simulation? Perhaps even more impressive, or at least it was surprising to me, is that the simulation is perfectly fine outputing 200mA at 300V for 60W at 85% efficiency. (See attachment 1 for schematic) The guy on the above link who built those boards to power nixie tubes got pretty terrible efficiency figures at 30-40% with this circuit, and the simulation agrees, but then I swapped the switching transistor (FJN13009) for a mosfet (IRF740) and the efficiency (again, in LTSpice) skyrocketed to a 85%. I've already done some research and found a few chips that might do the trick, like the MT3608, the LM3478 or the MAX1771, but because I already have some MC34063 lying around, I decided to try this ratio extender circuit: So far I have only simulated the circuit, and to my surprise, the simulation throws very promising results. ![]() This would be used for the plate and screen voltages, I would deal with the heaters separately. I reckon it should be easy to build one capable of powering a two 12AX7 preamp, but I wonder if I can build something with enough juice for an EL84 single ended amp, or even a push pull with two EL84's. I've been mulling over the idea of building a dc-dc boost converter that outputs some 300V to power tube amps. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |