2 Aug
2014
2 Aug
'14
12:44 p.m.
Older ?linear? regulator supplies, or unregulated
ones, don?t need a
minimum load, they are ok with no load at all. High voltage supplies
I've come across linear PSUs [1] which have a reasistor in parallel with
the pass transistor. Under the correct load conditions, this resistor
would not pass enough current to give the required output votlages, but
along wit hthe pass transistor it will
The problem is that with too little load (or no load at all), the pass
trnasistor can be fully cut fof and the output votlage will stil lrise
too hig hdue to this reissotr.
One to watch for!
[1] The HP59500 HPIB interface fr the Multiprogrammer is one such...
are typically unregulated, at least in the kind of
equipment discussed
here. (You?d find regulated high voltage upplies in other disciplines;
for example, traveling wave tubes require kilovolt or above voltages
regulated to 1% or so.)
Thge HV power supplies in mpst monitorsm, certainyl those usign a true
flyback transofrmer, _are_ swithcing supplies, techncially. It is also
not at all uncommon to have the rgulated, particualrly in colour
mnoitors, where changes in the EHT will affect convergence and purity
[2]. But given that a totally black screen is essentiually no beam
current and thus no load on the supply it is common for such suppleis not
to min no load.
[2] Sometime I will tell you about the PD500 'shunt stabiliser triode'
and the Bang and Olufsen TV with 2 output stages and thus 5 valves in the
EHT cage so as to avoid the PD500 and its attendant Xrays.
-tony