Electronics > Projects, Designs, and Technical Stuff
fillament power supply for dht tube
scsi:
Hey all! So I want to create simple, clean, regulated power supply for dht tube to implement fillament bias.
Idea is verry simple: to use a 6.3V rms 3A transformer winding rectify it, than clean it with capacitance multiplier and fed it to tl431 current shunt regulator to get a stabilised 4.2V 650mA output. Could this work?
Zero999:
The circuit you posted won't work, because R5 will drop too much voltage, if any appreciable current is drawn.
Why not use the LM317? It's cheap and easy to use.
james_s:
Or at least a classic voltage regulator circuit with a pass transistor, that circuit is bizarre, I'm not quite sure what the designer was trying to do.
TimFox:
The 1k value must be a typo: at 650 mA, it would drop 650 V! Perhaps 1 ohm was intended?
The above suggestion of an LM317 is reasonable, and there are app notes that show how to include current limiting to three-terminal regulators to give a softer start to the filament heating.
David Hess:
The dropout voltage of a 317 might make operation marginal without a lot of input capacitance however there are several low dropout equivalents to the 317 which would work fine in this application, or a discrete low dropout regulator could be implemented in several different ways.
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