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Registered Member #2303
Joined: Mon Aug 17 2009, 05:51AM
Location:
Posts: 3
I am attempting to build the circuit here:
Am I wrong with thinking that pins 9 and 10 on the TL494 should NOT be both connected together like that as from what I got out of the datasheet for the IC is that they are inverted outputs from each other?
Also, when I hook up my 30v supply to the 30V point on the circuit, I get CC (constant current.) I'm not sure what else could be wrong, maybe the schematic was designed poorly? Any areas I should check first?
The 12V supply says it is drawing about 0.36A, does this seem normal?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I think that schematic is missing a pull-down resistor on the pins 9/10 (which should be connected together, it's not a mistake) Search the forum/archives, it's been discussed before IIRC.
I designed the original circuit, but the TL494 part was tacked on by someone else who's no longer a member.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Yes, if anybody ought to be shot for bad choice of pin names, it's the guy who named FET terminals (actually a BJT's pins are named similarly, but at least they're more unusual and don't evoke a water analogy so readily).
I always remember which way round an N channel FET goes by thinking it's *NOT* what it sounds like, source is not at the top, and drain is not in the ground.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Dr. Slack wrote ...
Yes, if anybody ought to be shot for bad choice of pin names, it's the guy who named FET terminals (actually a BJT's pins are named similarly, but at least they're more unusual and don't evoke a water analogy so readily).
The charge carriers in the semiconductor move from Source to Drain (or Emitter to Collector in BJTs). They just happen to be negative in N-channel FETs, so their motion is opposite to the direction of conventional current. And that's because electrical polarity conventions (and units of measurement) were well established in the century before last, long before the discovery of electrons.
Advice to noobs who want to be EE's: get used to thinking in terms of conventional current, and don't fret about which way the electrons go. It rarely matters unless you are working with vacuum tubes/valves or electrochemistry.
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Help with circuit
