Talk:Circuit Idea/How do We Compensate the Diode Forward Voltage Drop?

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I would like to start the discussion about the passive diode compensation with a record from the lab about diode circuits that I conducted with my students on March 26, 2009. Please, join the discussion. Circuit-fantasist (talk) 18:45, 7 April 2009 (UTC)

Fig. 1: The input and the output voltage on the same coordinate system.

What do we have to make? We have to make a diode limiter. How do we make it? What is the idea? Your colleague will present it. Maybe you are supposed that I have not only the goal to present circuit ideas. I would like also to form your way of thinking; to learn you how to think creatively. I prefer to build circuits instead to use ready-made circuits. Instead to say you "See in the laboratory manual and make this circuit" I will say "Let's pose the problem and to solve it by ourselves".

Well, let's pose the problem. First, we need to apply an input voltage. What kind of input voltage? Of course, a bipolar one. We will generate it by a computer and a digital-to-analog converter (analog output 1 of Microlab system). Remember when you press CTRL X a linearly changing voltage from -10V to +10V appears at analog output 1. Let's draw it in red color. Then, what have to be the output voltage? What kind of limiter do we make? For instance, lets it limits the positive part of the input voltage. Let's draw the outpu voltage in blue color on Fig. 1. Well, how to make this circuit? How do we make a limiter that limits or clips off the positive part of the input voltage?

If you like sinusoidal waveforms, draw the input voltage as a sinusoid. In this case, the limiter will clips off the positive half-wave. We can name such a limiter rectifier. Well, draw a circuit that will operate in this way. We may say this circuit converts a linear signal to non-linear one. What non-linear elements do you know? Obviosly, the diode is the most suitable non-linear element. But from where do we get to know how a diode behaves? Where do we get a notion about the diode's behavior?

Fig. 2: The diode IV curve.

The diode is a two-terminal element that is described by its IV curve. As we know, the curve bends at voltage drop VF (0.6 - 0.7 V for a silicon diode). But in this case we need a diode with zero voltage drop VF.


Fig. 3: Series diode limiter.
Fig. 4: Parallel diode limiter.


Fig. 5a: Investigating a parallel diode limiter by Microlab.
Fig. 5b: Investigating a parallel diode limiter.
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