power How can I switch a high current with a low-rated switch

Posted on Feb 5, 2014

Designing and building a breadboard power supply for myself, which draws power from an ATX-like SMPS (Mains in, single Molex plug out) via a 4-pin Molex connector. The design includes a switch to select either 12V or 5V output, but the only appropriate switch I can source is rated for a paltry 30mA! Obviously I can`t switch up to 2A with a 30mA-rated switch, but what can I do (that`s cheaper than the ~$5-10 local vendors

power How can I switch a high current with a low-rated switch
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want for 2A-rated switches) I thought of using an NPN transistor (see diagram, below), but in simulations that resulted in an unwanted voltage drop, and having the load connected to both emitters seemed to do weird things to the voltage. I realise the obvious answer here is "use a 2A-rated switch", DigiKey have plenty. The trouble is, DigiKey have considerably high shipping charges; I really have to make do with what`s available where I live. Calrion Mar 5 `13 at 9:00 Gah! How did I not see this question when I searched Still, this seems slightly different in that I`m wanting to switch between two (different voltage) supplies. Calrion Mar 5 `13 at 9:05 You are selecting between 5V and 12V. For the 5V a simple diode will do, because it will block when you apply the 12V. For the 12V (and for the diode) you will have to use something that is rated for the current you want to draw, no alternative for that! Wouter van Ooijen Mar 5 `13 at 11:46 No matter what voltage you supply (which transistor conducts), the current source will only take 2A. The rest of the voltage will be dissipated by the transistor. Did you really mean to draw a current source there jippie Mar 5 `13 at 18:38

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