Recent content by anvoice

Thanks for the suggestion, I'll look into it. It's probably a long shot, as I would need to match the diode geometry, cone angle, and account for the slight difference in refractive index. I was actually hoping to use a full spectrum camera (which I don't have, so was looking at modifying an...

Wish I always had this much detail to work with! Thanks a bunch, this really helps. In this case, a circular spot is not nearly as important as keeping costs down initially (what I have in mind doesn't need a circle, and if it doesn't work I'll have a collection of unusable optics)...

That applies if I use a biconvex lens, but also means I would have a short length to the spot image. Could that be remedied by using 2 plano convex lenses with varying focal lengths, one short to capture and collimate light, and one longer to project the image to a longer distance?

Thanks! I'm guessing the 1/u + 1/v = 1/f formula applies to a pair plano convex lenses facing each other (not just one hemisphere), with v = 4.2mm being the distance from the flat portion of the second lens? Also, I found some lenses with varying focal points (25-100mm) and a 12.7mm diameter...

Hello, I'm trying to focus a 275nm (with proper safety precautions) LED that looks to be a few mm in length and width (the light-emitting portion) to a smaller dot size. The LED should probably be fairly close to the surface of the lens to collect more of the light. The dot size would hopefully...

Ah, I see. I'll need to keep reading to understand that formula properly. Thanks a bunch!

Ok, I think it's clearing up. I was looking at the subcircuit without considering it as a complete device and that might have confused me. So our input resistance is literally just the resistance it takes to get to (and through, assuming a nonzero base resistance) the base of the transistor...

Thanks Tom, I'm counting on it! Let's hope the resistance on that is not too high. :biggrin: That's what's confusing me in the example then. As the current iB from the + input splits, depending on which way you turn to get to ground, the current becomes either -iC or iE. So why are we justified...

Thank you to everyone who tried to help. I understand that the diagram might not detail a typically used circuit, its virtue is simplicity so I was hoping to at least understand that. I will definitely try to understand the common emitter fully, along with the approximations made, when I come to...

Thanks, I'll be reading through that. Big thanks, I will take a look at those. I see one definition of "input resistance" as the resistance seen by the current source or voltage source which drives the circuit. Unfortunately I don't see a good definition of "seen" here, nor do I understand why...

The diagram of the BJT amplifier small signal model is below. This is not really a homework question as I am self-learning electronics, but I was advised it may be better placed here than in the technical portion of the forum. Thus I do not have an "attempt" at a solution (which is given as RI...

I think I figured it out. Looking at just this subcircuit, I forgot to shut down the signal vc (common-mode input) to the MOSFETs. If vc is off, naturally the dependent current source becomes an open circuit and the resistance is indeed RL. It is also a warning sign in this case that if you...

I am currently reading about small signal analysis of a MOSFET differential amplifier. The text I am using has the below two figures for a common-mode equivalent circuit for the amplifier. The first makes sense to me except where it calls it a "Norton equivalent circuit", whereas I thought a...

The problem applies to a thin liquid film, so technically it would be a line. Naturally, it's also not a point: what drains concentration is a growing crystal. However I am trying to first solve the simpler problem so as to get a better idea of how the system evolves over time. So the one I was...

Thanks, good to be here. Also thank you for the good reference. You're right, diffusion and heat transfer are analogous. I did look through that book, but the closest thing I could find there was the time-dependent equation for an instantaneous or continuous point source in 3d space. The...