I'm working on a personal project for college right now. I'm working on a circuit that can change the direction of current flow going through a solenoid, depending on an input signal. I'm using an ELVIS Prototyping board to output the 5 V signal through a Virtual Writer on NI LabVIEW, if that matters.
Right now, I'm doing this with an electromechanical relay, and my 5 V output decides if it is open or closed. The COM is connected to the solenoid and into the ground, the NC to a 10 V and the NO to a -10 V. Because of the way it is set up, switching the relay's state changes the direction of current flow depending on the 5 V I/O, hence changing the solenoid's polarity.
Now, I have read on many websites that relays usually take a lot of time to change state, in comparison to transistors. Also, the relay produces a lot of noise when switching, as my montage is switching between the two states a couple of times every seconds (which I read is not that good to do with relays).
I would like to know if there is a way I could do the same type of thing, but using transistors. If not, is there a type of relay that would be best suitable for frequencies of around 5-20 Hz, current of around 1.25 A and voltage of 20-50 V?
Best Answer
For 20Hz you should definitely use solid state switching. A typical 50-100K operations relay life will be expended in a day or so otherwise. Even if you derate substantially, it will be difficult to get more than a week or two life.
You can use a MOSFET H-bridge to do this, however you will need to level shift your control signal to control the high side MOSFETs and you should prevent shoot-through caused by high and low MOSFETs being on at the same time. One chip that might prove useful is the LMD18201. It's designed as a motor driver, but it should work fine driving a solenoid provided the current is within the <3A capability. It includes anti-shoot through circuitry and thermal protection.
This particular part includes a charge pump for the high-side MOSFETs so it should work down to DC, unlike many of the common half-bridge drivers that depend on continuous switching to charge the boostrap capacitor supply.