[SOLVED] Connecting power mosfet with digital input module.

[electronic_satya]

Hi,

I have this clarification
I have a power mosfet ic interfaced to the io port of a microcontroller. The purpose of the power mosfet ic is to switch on lamp (of different wattages ex 25W, 75W etc) which will switch ON if a 24v is coming out of the IC. Before actually connecting the lamp i want to test my software for that iam planning to buy a digital input module which can withstand 24V and connecting the output of the power mosfet ic to the digital input module. My main doubt and worry is how to check the current requirements? whether i need to worry at all about the current ratings? will the power mosfet is going to damage my digital input module?

Somebody please clarify this doubt,

Thanks in advance,

regards,
satya

 

[alexan_e]

I don't know the level of the voltage in the output of the mosfet (I assume it is low and from the same source as the mcu) but if you take the output and use a voltage divider which can provide a proper level to the mcu (like 3v3 or 5v) then there is no problem.
The pins are usually internally clamped to the power supplies so as long as you have a resistance that can limit the current there is no problem but you can also use an additional zener or Schottky diode externally.
If you want to isolate the mosfet output from the mcu you can use an optocoupler.

Alex

 

[electronic_satya]

i think i have not explained my question properly i assume this because i have not understood ur reply properly. i have represented pictorially and put it as attachment.

thanks in advance,
regards,
satya

 

[alexan_e]

Oh.. I thought that you wanted to connect the mosfet output to an mcu but your second post shows that you want to connect it to a PC.
The current is not a problem , it depends on the load connected, in this case there is a lamp that will use a higher current and the output will also go to a high impedance input (the card) which will translate and transfer the signal to the PC.

Alex

 

[electronic_satya]

hi alex,

Thanks for the reply. but when i read the specifications of the digital card then i see the following things
OFF state
Input current <= 150uA

ON state
Input Current >= 330uA. how should I ensure that these things happen when i connect the system. is there a method to measure the input currents?

thanks in advance,
regards,
satya

 

[alexan_e]

This is mentioned to give you the specification of the current that the card will absorb (as a load) and as you can see it is a high impedance input.
There should be a max input voltage specification, this is the important one, you shouldn't go above that voltage, don't worry about the current.

Alex

 

[electronic_satya]

Thank you very much for your replies.

Regards,
Satya