Try KiCAD. Now it even does SPICE simulations, ngspice
specifically, and it handles pretty much everything else. Other than that, if you wish, KiCAD has also the tools to design printed circuit boards, and even has a 3D viewer and exporter for the boards!
KiCAD runs on Windows, Linux and Apple OS X.
There is also a project called ESIM that bundles KiCAD with a SPICE simulator and differential equation solver.
There are a number of uncertainties in what you say you are doing. You need to stabilize the patient and understand what is really going on in order to make progress. At present there are several things wrong which are obscuring each other. Being able to deal with each ne in isolation makes life much easier.
(1) Your sentence below does not make sense. Can you please explain more clearly what you mean. "The MOSFETS are connected" and "drain and source ... connected" can both mean the same thing. If they DON'T mean the same you need to explain what you mean. You said:
- " My main concern is that in the datasheet schematic, The mosfets are connected. Whereas in my circuit (and others that I've seen over the web), the drain and source are connected together."
(2) This would be fatal:
- My Vdd is the same as Vss, and so I'm using the same cap. for both of them - assuming thats ok.
As Oli says, presumably you mean Vdd = Vcc. You need to read what you write before sending. We all need to and we all get it wrong sometimes BUT when you are asking the questions and want help then confusing the assembled masses with typos is a very bad idea.
(3) This probably means that your IC is dead or walking wounded OR you have a disconnected line - possibly ground. When things go this wrong you need to carefully measure everything - voltages when on and ohmic connections when off. look for shorts AND opens.
- ... the SD pin is supposed to low in order to enable the chip - yet, having it high makes no difference to the output. I am still able to switch the Low-Side MOSFET. Furthermore, it seems that somehow the Lin and Hin pins are switched. If I connect the Lin pin to High, it doesn't switch on/off the Low-Side. Infact, if I take the Hin pin and take it High, it causes Lo output to turn on the Low-Side.
(4) If you were using "real" voltages your IC and random other things would now be dead. Shorting the capacitor connects the isolated high voltage "island" in thje IC to the drain of the lower FET which gets connected to ground when the lower FET is turned on. Shorting this cap could be an extremely exciting and non productive thing to do in many situations. Hopefully you determined before you did this what you expected to happen and didn't just do it to see what happened. When you are dealing with power rather than signal the magic smoke is never too far away. You may have had some already without being aware of it.
- That didn't cause any change in the circuit. However, if I short out the capacitor the High-Side does turn on. The gate voltage is around 11V. If I don't short out the capacitor, the gate voltage is around 5.5V.
(5) Making the capacitor 100 times larger than you calculate in a circuit that may be switching at 10's to 100's of kHz is highly likely to produce interesting results. These could include an interesting emulation of lot's wife. But may not. The capacitor has to charge in the time that the low side FET is on. It discharges when the high side FET turns on. There will be charge & discharge time constants controlled by the resistance in the IC power paths. This may still work OK OR the voltages may only rise to a fraction of what is intended in the time available. Which may be consistent with what you are seeing.
I could add a bit more but that should do to start :-). Sometimes we all have a bad day - you need to try and not let too many things at once get out of control as then you can't asily analyse what is going wrong.
As others (and I) have suggested, measure everything you can and see if it makes sense. If you have an oscilloscope see what it can tell you. If you don't have a'scope, start putting lunch money aside for one. Even a relatively cheap scope can be a mightily powerful tool. An oscilloscope is possibly the most effective and powerful debugging and fault finding aid you will ever have for analog circuits.
- In my initial calculation, the bootstrap capacitor's value came out to be 1uF or so. Initially, since the circuit didn't work, I decided to change the capacitor to a higher value (100uF).
Practical aspects:
If hand driving at low speed, connect Hin and Lin and SD low with pull down resistors. Then, if you hand switch them and they "bounce" they will bounce from low to applied signal level and not to some unknown state.
BUT the bootstrap powering circuit for the upper gate completely relies on there being an AC signal at VS to supply AC at Vb which draws power from Vcc and delivers it to Vb. If there is no AC your =upper gate signal will decay "rapidly". How long it takes depends on upper driver power consumption and was part of your capacitor calculations (from memory). This is an example of where an oscilloscope will help you see what is happening. The 100 uF you are using is a large value and decay time may be long enough to see what is happening "by eye", but maybe not.
If you want to drive with a microcontroller you could reduce Vcc to Vdd rather than raising Vcc - as long as IC minimum voltage spec is still met.
Re-etch of PCB MAY be a good idea BUT you should be able to carefully go over circuit and check that what you have is what you intend. Do it pin by pin.Talking to yourself about it as you go can help :-) (really). Describe what you expect to see and what you really see and why they are or aren't compatible. [Watch for men in white coats observing you suspiciously when you are talking to yourself - or do it in your head or, works well, get a knowledgeable friend and explain it to them. The very act of explaining often works wonders.]
Best Answer
Historical Context
I was trained at Tektronix to be an electronics draftsman.
Tektronix provided classes for anyone interested. It's quite similar to drafting for construction. You had the usual pencils, sharpeners, specialized erasers and paper, a tilted table, T-square, triangle, etc. The same basic tools of the trade for any draftsman. There were some additional tools added, such as some nice stencils for electronics components and descriptive picture items (like an oscilloscope tube -- see here for some idea of those.) But that's about all we had to work with, then.
I'd been an electronics hobbyist of some kind since about age 10, or so. Like most, I struggled to understand circuits I saw in Popular Electronics and Radio Electronics magazines. They were actually pretty hard to understand, at least as presented, because they were made for people who wanted to wire them up. Not so much for people who wanted to learn more and to understand them better. These wiring schematics would bus around all the power wiring details, most of which (I found over time) doesn't really help in understanding how a circuit works. So, as a hobbyist, I gradually tumbled to the idea of redrawing schematics so that I could better understand them. I'd literally tear down a circuit layout to its bare parts (almost) and then rebuild them back up, after I'd arranged the parts better (in my mind.)
I joined Tektronix as a software developer in 1979. I'd been working on operating systems -- such as the Unix v6 kernel in 1978 -- and software generally for large computing systems since 1972, and MCUs since 1975. But I also had a personal interest in understanding and using the products that Tektronix made, too. And when I joined Tektronix, I already had good experiences in redrawing schematics for my own understanding.
I used the word joining, above. I meant that. Joining is exactly how it felt to be a Tektronix employee back then. Your boss encouraged your personal interests, if there was any way it could be of mutual rewards. They would pay you to continue your education at universities in the area, for example. And they offered high quality classes, themselves, too. You are provided with profit share. And if your position was no longer required, they'd encourage you to go around to various departments and see if there was another job elsewhere. They'd pay you your salary while you met people and sought some other position. (I was told there was almost no limit to this, though I'm sure someone would intervene if you took too long to find work elsewhere.)
Employees paid that back after a fashion. If I decided to go to the office and work on a Sunday, for example, I'd often find many other employees also in the building and working diligently on some project needing extra effort to meet a schedule. Rarely did I walk into a building on Sunday and have it feel empty. There was almost always something going on and plenty of employees willing to provide their weekend or night time to Tektronix when needed.
Since I'd been a hobbyist for some time before joining Tektronix, I was of course also actively encouraged by my boss to take these classes when they became available.
Learning to Draw Schematics
In my first class, the instructor pointed out two simple organizing concepts. So simple, in fact, that I was immediately able to recognize their value despite the fact that I'd never been exposed to them beforehand.
Just these two:
With these, one could take any random schematic they saw, tear it completely down to the ground, and re-draw it from scratch so that it obeyed these rules. The result was something almost magical. A schematic which communicated concepts quickly to other electronics engineers (and us hobbyists, too!)
The instructor also pointed out something I'd already learned on my own:
That's important for understanding. No signal flows on those wires. So drawing wires all around a schematic, wires without any signal on them, just gets in the way and distracts you from actually understanding what you are looking at. It's lots better to get rid of those wires and just annotate the voltage, instead.
The part of all this that takes a little patience (and it really is a continuing thing for one's entire life to be honest) is learning to recognize sections that are common to many schematics. Such things as: current mirrors, voltage references, analog amplifier stages, etc. This is something you cannot just be told about. Instead, we must see them, learn about them, grow to understand more of them, and then finally acquire them. And this just takes time. There's no magic bullet or pill to take here.
How did people calculate sine and cosine or logarithms or even multiply big numbers before there were calculators? They used books with tables inside, along with the training to use those tables properly. Or they used slide rules.
Life gets done. The tools change. But life still gets done.
Rules for Re-Drawing Schematics
Not Entirely Improbable Example
Here's an example of a less readable CE amplifier stage. It's a little more of a wiring diagram than a schematic. See if you can manage to recognize that this is a relatively standard, bootstrapped single BJT stage, CE amplifier:
simulate this circuit – Schematic created using CircuitLab
Here's a more readable example of the same circuit. Here, despite being a bootstrapped design (which is seen a little less often), you can recognize the basic CE topology and begin to pick out the similarities and differences better:
simulate this circuit
Note that I've rid it of the power supply and ground bus wires. Instead, I've simply noted that certain end-points are attached to one or the other of the power suppy (+) rail or ground. For someone wiring this up, it isn't as helpful because they might miss a connection they need. But for someone trying to understand the circuit, those connection-details just get in the way.
Also note that I've carefully arranged the new circuit so that conventional current flows from the top of the schematic downwards towards the bottom of it. The general idea is to imagine this as a kind of "curtain" of electron flow (bottom to top) or positive charges from top to bottom (conventional.) Either way, it's like a force of gravity that causes the curtain to hang from top to bottom.
Flowing through this curtain of top to bottom currents, the signal passes from left to right. This is also very helpful for others trying to understand a circuit.
Combined, these details help orient a reader.
Also, if you imagine that \$C_1\$ and \$C_2\$ are absent from the schematic (left open) and that \$R_6\$ is bypassed (shorted), then this is a very familiar single BJT CE stage found almost everywhere. So this provides some additional guidance or orientation for understanding the circuit. It allows you now to realize that \$C_1\$ acts as an AC-bypass across \$R_4\$ so that the AC gain can be independently set, separately from the DC operating point of the amplifier stage. The only remaining details are to work out what \$C_2\$ and \$R_6\$ are achieving (bootstrapping.)
The original layout above (the confusing one) would greatly hinder the ability to zero in on the bootstrapping aspect (which may, or may not already be familiar.) But at least this means there is very much less to focus on and try and understand, if unfamiliar. (The first schematic would make all of this almost entirely hopeless from the start.)
This may not be the best example, but at least it shows some of why it helps to avoid wires that simply bus power around and why it's important to arrange the schematic with a specific flow of conventional current from top to bottom and for signal to flow from left to right.
More Likely Example Case
A better example (not provided yet) would include a more complex circuit (which as the one for the LM380.) This would help illustrate the knots of circuit groups that can be organized into separate sections (more tightly interwoven within themselves, but communicating to other sections via a sparser set of wires communicating signals.) So I'll end this by including a nicely divided LM380 schematic to illustrate that point:
simulate this circuit
Note that there are individual sections, now isolated as identifiable groups such as current mirrors, long-tailed differential amplifier (here, really, more of a \$\pi\$ type arrangement), and an output stage.
It's also annotated, as well.
Try and imagine what this would have been like to read through had the power supply and ground rails been all connected up with additional wiring and/or with no particular arrangement of current flow on the page.