what does the term "pass transistor" mean?? ive seen the datasheets of regulators and about all of them show one or two diagrams showing pass transistors connected to increase the current. okay thats good but what does this term mean.

my second question is that what does "electrical isolation". a transformer provides electrical isolation from the main line voltage. what does that mean. transformerless power supplies are dangerous to use because they dont provide electrical isolation. what does this mean. i read somewhere that if u use a transformerless power supply, the circuit is actually at a higher level than ground and thats why it shouldnt be connected to other circuits. what does this mean

thanx alot

 

samcheetah,

Pass transistor means a transistor that bypass the majority of the current thus relieve the regulator of the load.

Ante :roll:

 

to separate a direct electrical connection, one voltage source from another, ie mains voltage from low voltage, using a transformer. The secondary side of the transformer is electrically coupled to the primary, but without a wire joining the two.

In the case of mains operated supplies, no transformer means that either side of the line is at mains voltage, relative to ground. One danger is that you cannot connect test equipment that has one terminal grounded, or you will short the mains voltage to ground, not good.