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Realise though that it is an inverting circuit. The following circuit is the result of my research and testing in Livewire. Post was not sent – check your email addresses! In order to use a N-channel FET here, you need to be able to pull its gate above its source, which your 4N35’s transistor output has no ability to do. Thank you, Leo, for your time and your help. I seem to have missed your reply at first since I did not subscribe to your posts fast enough apparently: This should be correct, isn’t it?

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IRFZ44, and you want to switch somewhat higher voltages i. But if it is working for you, that is good.

It would be easy to test. I presume modfet are aware of the designcriteria of an H-bridge and the chances of shorting your PSU if you dont do the switching correctly. I am not sure if there is an easier way to do it.

What you need instead omsfet the 4N35 is a device called a photovoltaic isolator that replaces the transistor output with a tiny solar 4n53 that can actually generate the voltage needed when the LED shines on it.

Good luck, but dont hesitate to ask again shld you need further advice. Thanks Adriaan, Though technically it is a voltage divider, that is not really the function of it.


Since I want to learn, I tried to redesign it again by adding another resistor for the voltage divider.

Dinah, that your lights do not light up immediately seems kinda odd, but could be a habit of the lamp you are using. Moreover, in the datasheet, I don’t find any information about pin6 of the optoisolator: How can I find the current in the LED? Hook up the circuit without the FET or the peltier.

So, make R3 43n5 same value as R2 – see next paragraph.

Using MOSFETS with TTL levels (5 Volt and 3.3 Volt)

The circuit should be robust enough to support the load during a few minutes. Q2 is just for speeding up, isn’t it; is there any other reason for adding up Q2 to the schematic?

Using the transistor to drive the gate with higher voltage solved the problem. ThreePhaseEel 6, 4 14 The two P-channel mosfet will be driven by transistors. The IRF can obviously take 4 amps, but sadly it expects a higher voltage on its gate than the most microcontrollers can deliver i presume you will use a microcontroller. I am an engineer but not an EE so I could use some guidance on circuit setup.

If it does open at 3 volt and your PIC supplies that, adding a transistor is not really necesary and if you do it doesnt need to be the BC, can be a regular signal transistor too, like the Twisted wire is good.


R1 limits the current into the optoisolater. It shows the same behaviour when I use 3.

Thank you a lot for all your precious support, Leo! Do you have any idea why is the mosfet not working properly and letting the 12v works on the led strip?

Using MOSFETS with TTL levels (5 Volt and Volt) – Arduino, ESP & Raspberry Pi stuff

Sorry no T2 and R1. What type of step up converter are you using?

Is this what you mosfer That means you have to have a 12 Volt driver as in this circuit: I noticed that the range is very low. It will feel warm to the touch when run mosfst a heatsink. Can i use this circuit with Arduino to drive 2 x 20W 1. However, it doesn’t indicate that the light bulb at CN3 lights up. Also, from the graphs, Ids changes with Vds, is it because of the channel shortening effect?

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