Fpga Programmer - Quest For Fuse

[Altera_Forum]

Hello, 

  i'm in between a project and stuck with the design of safety of the system. I'm in need of the following fuses,   :confused: 

• 15 mA, 3.3V 
• 75 micro-ampere, 3.3V 
• 15 mA, 12V 
• 15 mA, 5V 
• 75 micro-ampere, 12V

were could i get these. I have goggled and got details of 200mA, 150 mA, 25mA.........etc. But couldn't find the correct one.  Any one knowing the solution kindly post your comments..... It will be very thankful and grateful.   thanks & regards  varun v g

[Altera_Forum]

Typically fuses have a maximum voltage rating but they are not designed for a specific voltage. So you're going to use the same 15mA fuse for the 3.3V,5V, and 12V application. Likewise you will use the same 75uA fuse (assuming it exists) for the 3.3V and 12V application. So really you are looking for two fuses. 

 Try digikey. I've never put a fuse on anything as low as 75uA so can't help you there.  http://www.digikey.com  Jake

[Altera_Forum]

What do you exactly mean with safety? If you intend to protect a connected device against damage by overcurrent, any melting fuse is possibly to slow to provide effective protection slow. Fuses down to a mA range are available, but rather expensive. uA fuses don't exist, I think. 

 Actually, an electronic current limiting would be an appropriate means, but it has to be designed to the circuit, it doesn't work as a simple passive add-on.

[Altera_Forum]

thank you for your valuble data... 

 i searched in http://www.digikey.com for 15mA fuses and found similar fuse, but the problem is it's has a voltage rating of 125v. :confused: Could i use this fuse in 3.3v circuitry ?   thanks & regards  varun v g

[Altera_Forum]

thank you for your valuble data... 

 with safety i meant that protecting my FPGA and other components, which works on 3.3v http://www.alteraforum.com/images/smilies/confused.gif  isn't it possible to find the fuses of my specified requirement.   thanks & regards  varun v g

[Altera_Forum]

Normally a good way to clamp voltage is with diodes. 

 And I dont know why you'd want a fuse to protect an FPGA. are you powering it from an unreliable source. I wouldnt recommend it!

[Altera_Forum]

Hi, 

The selection of fuses is quite complex and you also need to cosider the amount of energy that is avallable to melt the fuse wire. At the currents you are mentioning you are not going to get a standard fuse. What you could use for the uA currents is a fusable resistor so long as you mount it correctly. For protection of the 3.3v supply and similar you can consider a hotswap controler such as http://www.linear.com/pc/productdetail.jsp?navid=h0,c1,c1003,c1006,c1163,p85534  If this is a product that is being sold then you need to protect to IEC 60950 or similar.