Skip to main content

Lessons Learned - High Side Optocouplers

Optocouplers can be used on the high side without issue.

Optocouplers let us isolate two separate power systems.  In the case of my pinball project, I am using a computer PSU to power the logic, lights, and lower voltage items like motors etc; and I am using a somewhat suspect 48V power supply for the solenoids.  To keep these systems separated, I used optocouplers on my mosfet driver board.

When designing the board, I was concerned that my transistor like optocouplers would not perform on the high side of the mosfet gate.  You cannot easily use a NPN transitor on the high side (Emitter Load).  You would normally use a PNP transistor.  The test circuit in the data sheet also showed the optocoupler in a low-side (Collector Load) configuration. 

Why did I not use a high-side configuration?  Well, say if something went wrong with my optocoupler, I want my mosfets to default to the off position, ie. ground the gate.  With a high-side configuration they would default on due to the pull up resistor.

As it turns out, unlike a normal transistor, the base current is independent and where the optocoupler is placed in the circuit has no effect on its operation. 

Optocoupler Switch Configurations via Renesas.com

Labels:

Comments

  1. ubrigynsyaccarino4 March 2022 at 10:36

    Caesars to hold first-ever tribal casino event in - JTM Hub
    Caesars Entertainment Inc. (CZR) 안성 출장마사지 will 춘천 출장샵 hold its first tribal 경기도 출장마사지 gaming event in In 삼척 출장마사지 addition to live sports, Foxwoods 제주도 출장안마 Resort Casino

    ReplyDelete

Post a Comment

Popular posts from this blog

ATX Breakout Board

Last November, I fried my 'lab power supply' that I made from a computer PSU.  I was testing my solenoids and the stress was just too much for the PSU.  The mistake I made was rapidly turning on and off my solenoid which likely resulted in voltage transients (spikes).  Since the PSU does have a current limiter, it was likely the constant voltage spikes that caused the damage.  There are various methods to suppress voltage transients such as by-pass capacitors and zener diodes.  In particular solenoids and other inductive loads experience these voltage spikes, hence my no longer functioning bench power supply. ATX Breakout Board I could have just rebuilt the same power supply by adding binding posts etc to the PSU housing but after searching the internet an ATX power supply breakout board seemed a popular option.  The main advantage compared to my old power supply was the addition of fuses on the outputs.  The extra safety this provides is perf...
Post a Comment
Read more

Microcontrollers

My initial plan to control the pinball machine was so have a computer communicate through a USB link to control all my electronics.  Apparently, that's pretty difficult.  Thankfully, microcontrollers exist.  Microcontrollers are, in essence, programmable chips.  Kind of like a mini-computer that controls the voltages to a number of pins or reads the voltages off those pins.  Start varying voltages and you've got signals. I borrowed a Arduino microcontroller from a friend of mine who happens to be an electronics wizz.  I did a couple basic things with it.  I started with the all important turning on a LED (with a resistor this time!).  Then I used the transistors from my now disassembled electronics kit, to power the LEDs from a power source other than the microcontroller itself as it can only supply so much power.  The Arduino's software is C based which is really close to Java which is the only programming language I learned in class....
Post a Comment
Read more

Pinball Cabinet Beginnings

I was getting to the point where I really needed to build on something. I have numerous pinball parts but have nothing to attach them to. I managed to find some pinball plans for a Williams Widebody pinball machine. All the measurements are in mm sadly even though all pinball cabinets are in inches. I converted and change it all to the nearest quarter inch. Well sort of. The guy who measured this was intending on using 45 deg cuts in the corners. My skill saw is too cheap for that so I changed the measurements for butted joints. The interior is set for a 23.5" wide playfield. The length of the cabinet is 51.5" in total. I used 3/4 inch plywood so the bottom would be 50" long for example. You can pretty much dimension the rest from there.  I did get a little chipping of the plywood but I went out and bought a blade with more teeth for finer cuts. It's a 60 tooth saw blade and my skill saw doesn't really have enough power for it so I have...
Post a Comment
Read more