Since building switchers for the military is my profession these days i would like to think i have some authority on the subject. Failures can occur almost anywhere in a switcher and the most typical type depends on the topology of the supply. Typically there is a pass transistor on the input that will turn off power to the whole supply (at least in my designs) if anything goes "out of spec" however i would bet in cheap commercial supplies this is not always the case. My most common failure in lab tests for me is the primary side transistor, what happens depends on whether the transistor fails short or open. If it fails open you typically have no voltage on the output (again this is dependent on topology) but if it fails closed, you can get runaway on the output in certain topologies. I would like to think any 'smart' design has a pass transistor and enough bit and supervision circuitry as to shut the supply down if something goes wrong, Component failure in the feedback loop is going to be rare, as these are typically passive components, either a resistive divider, a sense winding on the transformer, these parts typically don't fail, and if they do, they fail in spectacular fashion which usually gives you a clue something is going wrong.
Matt KD8DAO _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
