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Mosfet switching DC motor

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Makaram

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Hey guys, trying to design a circuit that uses 555IC to time a DC motor.
the motor is drawing about 3A at 9.6V.
Initially was using darlington transistors but that failed miserably and it was suggested i try using Mosfet
With a little investigation i've read that mosfets require about 10x the gate voltage compared to the source/drain? is this true? If so how would i possibly run my motor on the 9.6V battery alone??? would i not need approx 96 volts through the gate in that case?!?!
if im completely wrong and you know of any mosfets that would suit my problem i'd very much appreciate a suggestion.
thanks for any assistance you can provide
 
Don't know where you got that bit of misinformation. The highest gate voltage most MOSFETs need to fully turn on is 10V.

To insure good turn on you can use a logic-level type MOSFET. They turn on well with 5V or less gate-source voltage.
 
With a little investigation i've read that mosfets require about 10x the gate voltage compared to the source/drain? is this true? If so how would i possibly run my motor on the 9.6V battery alone??? would i not need approx 96 volts through the gate in that case?!?!
Can you provide a link for this? It's wrong of course.

A lot of mosfets will be able to operate with 9.6V on the gate (VGS=9.6V). What mosfets are available in your location?
 
sorry cant find it again, i was thinking maybe a TO-220. i have a jaycar just around the street so supply should be quite easy. Any suggestions would be most appreciated
 
Just had a quick look at jaycar (australia), not sure of your location - they have a BUZ71 for $4.95 which will work. Seems a little expensive (and it's not a great fet, it does have a large RDSon), if you purchase from Farnell / Element14 you can get suitable FETs for probably 50c (but $10 min order).

Did you ever mention what frequency the 555 is operating at?
 
You look at the datasheet, in particular the output characteristics graph in handy. Figure for the BUZ71 is attached.
 

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No worries. I hope the graph made sense; if you need any help, just ask.

What frequency is the 555 operating at? If it's too high, the mosfet will have trouble responding fast enough...
 
using the 555 as a timer rather than oscillator. Basically using the circuit to control a lead screw extension, e.g. 2sec ---> actuator extends, with an H bridge do the process can be reversed. Just been teaching myself the basics of electronics for projects/ interest so forgive my ignorance
 
Oh, OK. I just assumed there may be some PWM or something for speed control; there's no problem with switching frequency then... It should all be fine.
 
You will need both P and N Channel Mos Fets to make an H-bridge or else a driver between the 555 and the FETs.
 
Here's a couple of bridges you may like or try
 

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I just entered a long Quick Reply.
But it is gone because I forgot that this website has a wrong error that says
the reply needs more characters.

WHY ISN'T IT FIXED YET?
 
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