Dear all, looking for a bit of helps here.
i have tried 2 different versions of a heater supply from the 'valve amplifiers' book but cannot get the output to go above 5.4V.
The supply uses a single phase rectifier rated at 4A 50v, a 10,000uf cap into a 1085 low drop regultater through a variable resitor (4.7k) and a 270ohm resistor adjust to output then thorugh another 10,000 uf cap.
this only supplies two preamp valves which together only draw 0.6 amps, the transformer i am using has a 6.3v ac tap rated at 3 amps.
ive built two versions now, both in the book, withoiut the valves attached i can adjust the output from about 7 .5 vots down to 6.3v but when i have connected the valves i cant get it above 5.4 v. what's going wrong - i cant have built two duff PSU's or could I ?
i have tried 2 different versions of a heater supply from the 'valve amplifiers' book but cannot get the output to go above 5.4V.
The supply uses a single phase rectifier rated at 4A 50v, a 10,000uf cap into a 1085 low drop regultater through a variable resitor (4.7k) and a 270ohm resistor adjust to output then thorugh another 10,000 uf cap.
this only supplies two preamp valves which together only draw 0.6 amps, the transformer i am using has a 6.3v ac tap rated at 3 amps.
ive built two versions now, both in the book, withoiut the valves attached i can adjust the output from about 7 .5 vots down to 6.3v but when i have connected the valves i cant get it above 5.4 v. what's going wrong - i cant have built two duff PSU's or could I ?
With a load attached you will get extra voltage drop in the transformer secondary and rectifiers. As the current here will be charging pulses the voltage drop will be much greater than you may expect - a factor of 5 would not be surprising. I would ditch the regulator as you don't have enough headroom for that. Just use an 'adjust on test' power resistor between the two caps to drop the voltage to the required level on load. Alternatively, unless it is an MC input, just use correctly-wired AC heaters.
To get enough voltage you have to use Shottky diodes with low forwardvoltage drop.
There´s also 1085s with maximum output voltage limitation if you got one of those it will never regulate much over 5v with load.
I salvaged some 1084´s from a computermainboard and it took a few rewirings untill i found out about the regs
There´s also 1085s with maximum output voltage limitation if you got one of those it will never regulate much over 5v with load.
I salvaged some 1084´s from a computermainboard and it took a few rewirings untill i found out about the regs
It will be difficult, even with schottky's. A synchronous rectifier perhaps?
http://www.diyaudio.com/forums/power-supplies/177458-6-3-filament-5vac-winding-2.html#post2435043
http://www.diyaudio.com/forums/power-supplies/177458-6-3-filament-5vac-winding-2.html#post2435043
Taking in account that he wants 0.6A out of a 3A heater winding things should work.
There´s some good schottkys not to pricey available.
@Elvee thats a nice solution have to look more at it.
If possible to get away with a 1085 partscount is a bit lower
Just read first post again and you don´t want a big 10000uF cap after the reg a 100Uf is fine.
There´s some good schottkys not to pricey available.
@Elvee thats a nice solution have to look more at it.
If possible to get away with a 1085 partscount is a bit lower
Just read first post again and you don´t want a big 10000uF cap after the reg a 100Uf is fine.
Problem with single phase rectification, it puts a huge stress on the transformer.
Sorry but now i´m totally confused instead of singlephase what are you suggesting ?
Not this exact version, but I'll give it a try tomorrow, it's something you can breadboard in 5 minutes....
I do it with Schottky rectifiers, lots of smoothing, and a very low dropout regulator. I've been able to keep in regulation with the mains 10% below expected as well.
You just need to check the specs of the diodes and the regulator carefully and find the lowest possible Vf and dropout voltage for the load current you are expecting.
You just need to check the specs of the diodes and the regulator carefully and find the lowest possible Vf and dropout voltage for the load current you are expecting.
Tested!
Works exactly as expected, which comes as no surprise given the reliability of LTspice.
For practical use, I would recommend some standard protection measures: a B-E diode for the transistor, a G-S zener for the MOS, plus a gate stopper if there is a substantial length of track.
I might find a use for that circuit in + and - versions if there were a circuit board available. Currently using half-wave rectification from a wall wart to get +/-18V in a LF equalizer unit and I can't seem to get that last little bit of ripple out, even with a CRC stage followed by a Belleson super regulator. Not a whole lot of room in the box.
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