I am a novice in the field of electronics, and I would like to get the community's recommendation for what I am trying to achieve.
My current setup, I am using an Arduino Nano to control a solid state relay (please find specs below). However, I am planning to swap the Nano for a Nano RP2040 Connect. Since the latter is based on 3.3Vdc, I would not be able to have a direct connection between the Nano RP2040 and the solid state relay (min. control circuit voltage: 3.5Vdc).
Hence, I am looking for a component to "bridge" the Nano RP2040 and the solid state relay. I have read about FETs and BJTs; the parameters to consider are a bit overwhelming. I had a look at 2N2222, BC548 & 2N2007, but I am not quite sure which one would be suitable.
Additionally, I would prefer a part number that is commonly available and an all-rounder that can be used for other projects with higher current requirement ~200mA.
Specification of solid state relay: Make/Model: Schneider SSP1D425BD Control circuit voltage: 3.5-32 Vdc Input current: 10-15 mA
For the relay, just about any NPN transistor will work. For other projects, look at the transistor data sheets. Any introductory textbook or decent tutorial on transistor circuits will explain the notation.
The most important parameters are the absolute maximum ratings for collector current (Ic) and power dissipation. For a switch, you must ensure saturation (base current between Ic/20 and Ic/10) and stay well below the maximum collector current.
2N2222 and BC548 are pretty much equivalent. The main difference is that you will find the first readily in the US, and the second in Europe. I don't know which one is more common in Asia.
Either is fine, good to have a handful of those on hand.
2N2007 is a MOSFET, the other two are BJT types.
For power MOSFET the IRLZ44N is a popular general purpose one for use with Arduinos. It can handle currents up to 20A or even more, subject to heat sinking.
@flashko thank you for that part number. But I forgot to mention in my post, I am looking for something that is easy to solder similar to TO-92 package. I am considering 2N7000 which seems sufficient.
Agreed with the first statement, but the "output characteristics" curve of the TN0604 tells a very different story. That doesn't look like a suitable part for OP, unless they switch less than about 200 mA in which case a BJT may be the better solution. Also its on resistance of 0.5-1 Ohm is quite high by current standards.
What you will find in TO92 package are old and very old designs. No modern designs are put in that package it seems, it's all TO-220 (very easy to hand solder) and SMD packages like the easy to hand solder SOT89 and SOT223, and the smaller SOT-23. The latter is also not too hard to hand solder with proper tools - they also fit beautifully in between three holes of a piece of 2.54mm pitch perfboard.
Thank you for pointing out these details. To be honest my soldering skill is not that great, hence why I prefer a package type that can be easily hand soldered on a perfboard. I feel comfortable with TO-220/TO-92, I am not ready to handle SMD packages yet.
Regarding the component selection, do you reckon I should opt for a BJT over a FET? I won't be switching more than 200mA. I am just looking for an all-rounder that I can throw in arduino/raspberry pi projects keeping in mind not to exceed a continuous drain current of 200mA .
If you decide to use bipolar transistors, it might be worth looking into digital bipolar transistors. These types of transistors work like electronic switches and have built-in resistors. If you need to use more transistors, look at transistor array chips - the ULN2803 is such an array with 8 transistors, but it's for 5 volt logic. Maybe the ULN2801 is suitable for 3.3 volt logic, but I'm not sure. Let the more knowledgeable have their say.
That are darlington transistors. Those are much better replaced by a power MOSFET.
Likewise, the ULN2803 can be replaced by a TPIC6B595
Main difference: when on, a MOSFET has an on resistance, in modern MOSFETs that can be as low as 10 mΩ (see datasheet). That means little heat. Even at a current of 5A you probably don't need to worry about heat.
In contrast, a darlington has a voltage drop of 1-1.2V. Even at a modest current of 1-2A you need a heat sink for that.
Just compare the "output characteristics" charts of the 2SK2851 and the TN0604. You see how at 3.5V you're fully on - the graph goes up and up. So it's good for a 5V circuit, not very suited for a 3.3V circuit.
On resistance <100 mΩ, maximum dissipation 900 mW, this means that you can switch up to 3A without heat sinking (but make sure there is good ventilation, and heat sinking is becoming a very good idea at this point).
Unfortunately, I was not able to source any of the equivalent from the list in my previous post.
Looking at the datasheet for 2N7000, I think I should be able to use it for the scenario described in the my first post. Assuming VGS would be less than 3V, 2N7000 should be able to handle 10-15mA required for the solid state relay.
Please do correct me if I am wrong.
And if I have a higher current requirement, I will stick to the beefier IRLZ44N.
