Short cirucit protection

[Johnjacob]

I have built an AC/AC cuk converter for an assignment I am doing. It works as such, I provide 50V AC in and I get an adjustable voltage out from 0V to 50V AC, depending on the duty cycle of the PWM that I gate to the MOSFETs. It is designed to supply a max of 1.5A rms to the load. I have included a schematic below, drive circuit as not been shown.

It works extacly as I have explained. However, I would like to incorporate some sort of rudementry simple short circuit protection.

Any ideas would help, thanks.

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I know a fuse may be the simplest option, but my main goal is protecting the components-in a recoverable manual sense (like press a button or turning it off/on.. to reset it)

 

[kam1787]

I'd suggest using a triac whose gate voltage is normally on, but is turned off in the event of a short.

 

[Anna Conda]

@ kam1787, if a triac is already on, and then there is a large current flowing through it, surely it will stay on rather than turning off? especially if the gate drive is always there? surely the gate drive would have to be removed and you would have to wait for a zero crossing for the triac to turn off? by then it will be too late....?

 

[andre_luis]

I know a fuse may be the simplest option, but my main goal is protecting the components-in a recoverable manual sense (like press a button or turning it off/on.. to reset it)

There are some small break switches, but this would be not a cheap solution.

 

[FvM]

A problem of the shown converter topology seems to be that it has no safe off-state. Requiring it asks for a different topology, I guess.

It's not obvious, by the way, if the claimed 0 to 100 % conversion factor can be achieved for any output load, respectively what the constraints are. It would be also interesting to see the related switching patterns.

 

[Johnjacob]

There are some small break switches, but this would be not a cheap solution.

Hi, thanks for the advice..it shouldn't have more then 2 amps of flow through it, would you suggest something like this to be a suitable solution

http://uk.farnell.com/multicomp/an-161-fc67203/circuit-breaker-1-6a/dp/698246

 

[Johnjacob]

A problem of the shown converter topology seems to be that it has no safe off-state. Requiring it asks for a different topology, I guess.

It's not obvious, by the way, if the claimed 0 to 100 % conversion factor can be achieved for any output load, respectively what the constraints are. It would be also interesting to see the related switching patterns.

That is true, it is for a project I am doing in school..so I have no choice but to use it...since it is a cuk topology- it goes beyond the input voltage, and the conversion factor can be achieved for both inductive and resistive loads.

 

[asdf44]

There are lots of ways to design descrete over-current protection including many integrated solutions, though the choices will drop off at 50V.

Look for high side load switches and controllers and you'll find chips with current sensing amplifiers and NFET drivers. Or use your own pass fet and some current sensing method (high side current sensing chips for example) to detect the overcurrent and open the fet and/or shut down the supply.

There are also devices like PTC though they have very poor properties and will be surprisingly large for true 1.5A/50V.

A problem of the shown converter topology seems to be that it has no safe off-state. Requiring it asks for a different topology, I guess.

Why? Primary fets OFF, secondary fets ON or OFF looks safe.

 

[andre_luis]

Hi, thanks for the advice..it shouldn't have more then 2 amps of flow through it, would you suggest something like this to be a suitable solution

http://uk.farnell.com/multicomp/an-161-fc67203/circuit-breaker-1-6a/dp/698246

I was not exactly referring to a component do be soldered at PCB board, but an external intelligent device, having a faster and more sensitive feature. The one that you found above is a thermal protection, which do not retrieve to the original condition manually as you expect.