Choosing a Mosfet to switch an Electric Match

[xenobie]

Hi Guys,

I have a couple of questions but I know you might be busy, I would appreciate ANY answer even for 1 question.  :-*

I have a situation where I would like to switch an electric match. The typical trigger power for such a device is 12v 800mA - 1A. I have three questions for this.

1. I was told that Mosfets are better than Transistors for this situation. Why? Is this true?
2. I need to choose a Mosfet which is fast and reliable. I need it to turn on fast but its only going to turn on once in an hour's time, and its only going to be used for a few mS until the match is lit.
3. Lets say I connect 12V DIRECTLY to Drain/Collector, and Ground DIRECTLY to Source/Emitter and when I switch the Gate/Base an 'infinite' amount of current passes to the match however it takes mS to burn and once it burns the current flow is not possible anymore. Would you recommend such a design? I calculated that to put a resistor to limit the current to 1A, it needs to be at least 12W which is huge and expensive. I need to switch around 300 of these... imagine having 300 resistors of 12W each ...  :-\ Any other Ideas?

Info on Electric Matches for your information only:
http://en.wikipedia.org/wiki/Electric_match

 

[Hero999]

Hi Guys,

I have a couple of questions but I know you might be busy, I would appreciate ANY answer even for 1 question.  :-*

I have a situation where I would like to switch an electric match. The typical trigger power for such a device is 12v 800mA - 1A. I have three questions for this.

1. I was told that Mosfets are better than Transistors for this situation. Why? Is this true?

http://www.google.co.uk/search?client=opera&rls=en-GB&q=MOSFET+BJT+advantages+disadvantages&sourceid=opera&ie=utf-8&oe=utf-8&channel=suggest

2. I need to choose a Mosfet which is fast and reliable. I need it to turn on fast but its only going to turn on once in an hour's time, and its only going to be used for a few mS until the match is lit.

Going from your previous posts, you need a logic level MOSFET.

3. Lets say I connect 12V DIRECTLY to Drain/Collector, and Ground DIRECTLY to Source/Emitter and when I switch the Gate/Base an 'infinite' amount of current passes to the match however it takes mS to burn and once it burns the current flow is not possible anymore. Would you recommend such a design? I calculated that to put a resistor to limit the current to 1A, it needs to be at least 12W which is huge and expensive. I need to switch around 300 of these... imagine having 300 resistors of 12W each ...  :-\ Any other Ideas?

You don't need a 12W resistor, as the power dissipation will only 12W for a few ms, a lower power resistor (try 1W or 2W) will be fine as the power won't be applied for long enough to overheat the resistor.

With no resistor to limit the current, all of the power will be dissipated in the transistor which will have a lower resistance than 12R so will dissipate much more power, possibly enough to overheat it.

 

[xenobie]

Thanks Hero for your reply.

I will read about these level logic mosfets later on but I have a feeling they switch on / off rather than turn on slowly etc...

Regarding the 12W resistor, you are right. 1W should be enough because I'm only going to pulse 1A for 100 - 200mS

Thanks

 

[Hero999]

I will read about these level logic mosfets later on but I have a feeling they switch on / off rather than turn on slowly etc...

It's nothing to do with switching speed, a logic level MOSFET has a low threshold voltage so can be switched from 5V or less, a normal MOSFET usually needs 10V.