Set R2 = 2k2 gives ~10 mA drive.Īlso, add a 15V zener across R3, cathode to FET gate, Anode o ground, This provides. R2 sets the FET gate capacitor charge current. BUT here I will use 24 Vdc and use R2 + R3 to divided the supply voltage by 2 to limit Vgate to a safe value for the FET. Taking it to +12 Vdc would be good and +5Vdc would be OK if the logic gate FETs mentioned are used. R2 is shown gointo +24 Vdc but this is too high for the FET maximum gate rating. So, make R3 the same value as R2 - see next paragraph. BUT we wil use it here to make a voltage divider to reduce FET gate voltage when on. That's \$ \frac = 360 \Omega\$ - say 330Rīy itself 1K to 10k would be OK - Value affects turn off time but not too important for static drive. Voltage drop will be \$V = I \times R = 6V \times 0.18 \Omega =~ 1.1V\$. That is easily handled in a TO220 package with an adequate heatsink (somewhat better than a flag type preferably) but this much dissipation is totally unnecessary as much lower Rdson FETs are available. Power dissipation = \$ I^2 \times R\$ so at 6A the power loss will be \$(6A)^2 \times 0.18 \Omega =~ 6.5W\$. The latter is not too significant but is unnecessary.Ĭonsider - the data sheet says that the on resistance (Rdson - specified at top right on page 1) = \$0.18 \Omega\$. The main issues are that the FET has a very bad (= high) on resistance, which leads to high power dissipation and a reduced level of drive to the motor. It could be made to work if it was all you had but there are much much much more suitable FETs available, probably at little or no extra cost. Principally, that FET is only very very marginally suited to the task. There is a severe risk that the result will be a smoking ruin :-(. Keep in mind for as long as the RaspberryPI keeps it's GPIO pin high that the button will be held, so you may need to work on getting the timing right for this device.The suggested MOSFET is not well suited to this application. When your RaspberryPI fires up the transmitter by enabling/turning on the GPIO pin which it is attached to, that will in turn "press" the button on the receiving side of the OptoIsolator. How can I use it?Įssentially you connect the transmitter end to your RaspberryPI, and the receiver end to your remote (you will need to desolder a button and wire up the OptoIsolator's receiver in it's place). The devices are great for isolating electronics from one another to avoid damage and work ideal in low power environments where a relay maybe overkill. When the infrared is powered, it shines light on the photoresistor which then allows voltage to pass through the two wires on the receiving end. Instead it often relies on infrared light transmitter (sends light) and a photoresistor (to detect light) on opposite ends of each other. So an OptoIsolator is kind of like a relay except it doesn't rely on electromagnets. These components are used in a wide variety of communications, control and monitoring systems that use light to prevent electrical high voltage from affecting a lower power system receiving a signal. What is an OptoIsolator?Īn optoisolator (also known as optical coupler, optocoupler and opto-isolator) is a semiconductor device that uses a short optical transmission path to transfer an electrical signal between circuits or elements of a circuit, while keeping them electrically isolated from each other. First, let's talk about what an OptoIsolator is.
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