Hi I have designed a mosfet h bridge for a bot i am currently working on from parts i have in my parts bin and was wondering if it would work as i haven't really used fets before and if anyone had any suggestions on how to keep the magic smoke in. I know i probably need some resistors in there but where and what values?
Thanks in advance
Damian
Hi I have designed a mosfet h bridge for a bot i am currently working on from parts i have in my parts bin and was wondering if it would work as i haven't really used fets before and if anyone had any suggestions on how to keep the magic smoke in. I know i probably need some resistors in there but where and what values?
Thanks in advance
Damian
It depends on the switching speed, if it's just DC, i.e. you just want to reverse the motor, it's not important, just add a 10k pull-down to each MOSFET gate.
Look at the datasheet to find out what gate voltage is required to pass the current required by the motor.
My guess is that you'll need to increase the voltage ot Q5 and Q6 to 12V and you'll need some additional level shifting to enable the PIC to control them.
looking at the datasheet it seems to me that it has a required gate voltage of 2-4v but im not exactly sure. is it the gate to source threshold voltage im looking at?
You need to look in the notes for the Rds(on) parameter and see what voltage they used to determine it. In your case it's 10V (which is typical of most MOSFETS) above the source pin. You will need a bootstrap supply to drive the high side FETs, or they will not turn on properly. It would be easier to get some actual MOSFET drivers at this point, as it will make the entire h-bridge much more functional and stable.
looking at the datasheet it seems to me that it has a required gate voltage of 2-4v but im not exactly sure. is it the gate to source threshold voltage im looking at?
Why are you using a 500V MOSFET to drive a 3V motor?
There's nothing wrong with overrating components but higher voltage MOSFETs have a much higher drain resistance than lower voltage MOSFETs. Use a lower voltage MOSFET such as the IRL540.
You still haven't said what current the motor requires?
If it's <1.5A you'll be fine with a gate voltage of just 5V (see figure 6 on the datasheet) but that still means the gate voltage on the high side needs to be at least 8V, relative to 0V, because the motor is 3V.
The motor will turn slowly with those transistors because they have a high saturation voltage.
The transistor does not need to be able to pass 2A continuously, as long as it can withstand it for half a second or so.
The current will be higher than 0.2A with a load connected to the motor. How much current does the motor draw when the load you want to drive is connected?
OK I'm going to Jaycar tomorrow. Can some one provide me a schematic using only parts from Jacar that can drive a motor (3v 0.5A max load normal conditions) from 5v logic.