Can I use a 4n25 opto

mnemonics

Hello Gentlemen ! Can I use the 4n24 Optocoupler to drive mosfet drivers without adding anything else?. Also what pins on the quick start board do I use to power up the prop from a 12v power supply? The Prop quick start board is USB powered but I need to power it from a 12 volt battery for my project. I only see a 3.3 volt regulator will I damage it if I send 12 volt to VIN pins. Thanks

kwinn

mnemonics wrote: »

Hello Gentlemen ! Can I use the 4n24 Optocoupler to drive mosfet drivers without adding anything else?.

Yes, you can as long as you add a pullup resistor to +12V, however the 4N24 switches on/off fairly slowly which will increase power consumption in the drivers and output transistors. OK for turning power to something on/off, not so good for PWM.

Also what pins on the quick start board do I use to power up the prop from a 12v power supply? The Prop quick start board is USB powered but I need to power it from a 12 volt battery for my project. I only see a 3.3 volt regulator will I damage it if I send 12 volt to VIN pins. Thanks

Not a good idea to to put 12V in to the QS board. Some of the chips on the board are powered from the USB +5V and would be destroyed. Simpler to add a small external +12V to +5V power supply using a 3 terminal regulator IC and input that to the QS.

mnemonics

Thanks kwinn . What I meant was can the prop drive the 4n25 directly from the pins. The project i am doing does not require any kind of high speed switching. I just wanted to see if the 3.3 volt pin output will turn on the 4n24 so i don't have to go to a 5 volt circuit. Thanks again

kwinn

Yes. The IR diode has a forward voltage of about 1.3V so a 180 ohm resistor between the uC pin and the 4N24 would provide about 11mA of current from a 3.3V output.

BTW same is true of the 4N25 except the forward voltage is about 1.15 at room temp so a 200 ohm resistor will provide about 10.75mA from a 3.3V output.

jmg

mnemonics wrote: »

Hello Gentlemen ! Can I use the 4n24 Optocoupler to drive mosfet drivers without adding anything else?.

Are you driving a mosfet gate, or into a mosfet gate-driver ?

4N2x optocouplers are open collector, and not fast, so take a look at the H11N1, an opto with a schmitt output stage.
Same LED driving rules (needs > 1.6mA IIRC), but much faster rise/fall/tpd figures.

mnemonics

JMG
I am using the 4N25 to drive a mosfet driver. I have that part of the circuit working perfectly. The mosfet driver however is using a 12 volt power supply to drive the mosfet. I was going to use the Prop Quick start board which is USB powered but I decided to use the Propeller Project Board since it has everything I need on it and the supply voltage is from 5 to 16 VDC. Thanks for the reply guys and info I appreciate all of the members on this forum.