It's the bottom resistor, over the two resistors added together. Which as, we see up here, is the ratio of the bottom If that current is really small, you can use this voltageĭivider expression. And if you remember at the beginning, if you remember at the beginning, we made an assumption that this current going out here, was appr- about zero. And if I do my calculations right, 'V out' is 4.5 volts.
MACSPICE VOLTAGE DIVIDER CODE PLUS
And that equals six times, six over, two plus six is eight. And notice this always happens, the 'k's' all cancel out. 'R2' is '6k' ohms, divided by '2k' ohms, plus '6k' ohms. So let's solve this using the voltage divider expression. And we'll hook it up to an input source that looks like, let's say it's 6 volts. Then real quick, I'm gonna build a voltageĭivider that we can practice on. We'll put that up in theĬorner so we can see it. And it's adjustable, by adjusting the resistor values. Which means that 'V out' is always somewhat less than 'V in'. And so this fraction is always less than one. It gives us an expression for 'V out', in terms of 'V in', and the ratio of resistors. And this is called, this is called the voltageĭivider expression. Sorry, 'V in' times 'R2' over 'R1' plus 'R2'. So now I'm gonna take 'R2' and move it over to the 'i' is 'V zero' over 'R2', equals 'V1' over 'R1' plus 'R2'. So, let's set those equal to each other and see what we get. Of zero current going out, those two 'i's' are the same. Equals 'V zero' over 'R2' And now we have two expressions for 'i' in our circuit, because we made this assumption And I'll solve this equationįor 'i' the same way. So we can write 'V out' equals 'i' times 'R2'. Alright, next step is gonna be, let's solve for- let's write an expression 'i' equals 'V in' divided by 'R1' plus 'R2'.
MACSPICE VOLTAGE DIVIDER CODE SERIES
And the series combination is the sum: 'R1' plus 'R2'. In a specific case here, 'V in' equals 'i' times what? Times the series combination First thing we're gonna write is, we know that, using Ohm's law, we can write an expression for these series resistors on this side here. And now we want to develop an expression that tells us what 'V out' is, in terms of these two resistors and the input voltage.
And that means, of course, that this current here is also 'i'. There's no current going out of our little circuit here. We'll make an assumption that this current here, is zero.
So, let's first put a current through here. And we're gonna developĪn expression for this. So now we're gonna developĪn expression for this. With the series resistor, driven by some voltage from So, we basically just have a pattern here And then, the midpoint of the two resistors, and typically the bottom, that's called the 'out'. We hook up a voltage over here like this. And we assume that there'sĪ voltage over here. The pattern is, we have two resistors in series. And it's a nickname, in the sense of, it's just a pattern that we see when we look at circuits. Give to a simple circuit of two series resistors. Now I'm gonna show you what a circuit, that'sĬalled a voltage divider. Find Vfingertip in terms of Vin, R1, and R2. You can figure out any voltage from the physical length of resistance above and below your fingertip.Ĭan you come up with a formula to give the answer? Hint: Break the resistor into two parts: R1 is the portion above your fingertip, and R2 is the portion below your fingertip. What are the voltages? Ans: (work out the proportions).
What is the voltage of your fingertip? Ans: what does your intuition say? Touch your finger right in the middle of the resistor. What is the voltage of your fingertip? Ans: 0. Touch your finger to the bottom of the resistor. What is the voltage of your fingertip? Ans: Vin. Touch your finger to the resistor at the top. The value of the long tall resistor is R. Connect the top of the resistor to voltage Vin. Draw a picture of one long resistor 10 cm tall on the page.
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