Problems with executing clampers with DC bias

[swastik]

I have been trying to execute clampers practically but cudnt do so especially the ones with the DC bias. They seem to b ineffective once we connect the DC bias.Any suggestions?

 

[Euler's Identity]

clippers and clamper wave form

First, are we talking about a clipper or a clamper?

A clipper uses a diode to remove part of the signal. Whereas a clamper shifts the signal up or down.

I've often heard clippers called "clamping to a supply," which is why I ask.

If you're talking about a clamper, a shifter (also called a "dc restore"), it is important that the capacitor (clippers don't use capacitors) be able to charge to the peak and hold it, as that's where the shift is coming from. It's making things look like you have a battery in series with the signal. If the battery isn't charged, then you get nada for a shift, and the diode kills your signal. But if you get the cap charged, all you get is a signal shifted by the dc bias you mentioned.

Here's a trick to "getting" the clamper. The arrow of the diode shows you which way the signal will be pushed, while the dc bias shows you how far the push. ...assuming the capacitor gets charged and stays.

Also, a rule of thumb is 10x. Make sure the cap discharges (there is always a load, remember) slower than your signal's period (1/f) by 10x.

However, bear in mind that the above is just off the top of my head. Clampers were confusing to me too, but then I figured out the above, which I hope helps a little.

 

[bauer]

Re: clampers

A clamper is an electric circuit that prevents a signal from exceeding a certain defined magnitude. A diode clamp relies on a diode, which conducts electric current in only one direction; resistors and capacitors in the circuit can be used to alter the dc level at the clamper output.


Clamping for input protection

Clamping can be used to adapt an input signal to a device that cannot make use of or may be damaged by the signal range of the original input



In electronics, a clipper is a device designed to prevent the output of a circuit from exceeding a predetermined voltage level without distorting the remaining part of the applied waveform.

 

[Euler's Identity]

Re: clampers

"Clamping can be used to adapt an input signal to a device that cannot make use of or may be damaged by the signal range of the original input"

So you CLIP off the part of the signal that'll cause problems. You do this by tying a diode to the ref supply such that the diode conducts when the signal exceeds the working range of the following device that could be damaged.

Example 1:

A negative voltage spike is generated by a preceding differentiator*. To eliminate the spike, which would exceed Veb = 5v of a following NPN transistor in a CE confguration, you tie a diode (k to base) to gnd at the base. Hence, when the negative spike goes below -0.7, the diode becomes forward biased and limits the input to -0.7v or greater.

* vin ----- C ----- vo ----- R ----- Gnd

Example 2:

A positive voltage spike is generated by a preceding differentiator**. To eliminate the spike, which would exceed Vbe = 5v of a following PNP transistor in a CE
configuration, you tie a diode (k to Vref) to Vref at the base. Hence, when the positive spike goes above Vref+0.7, the diode becomes forward biased and limits the input to 5.7v or lower.

** vin ---- C ----- vo ---- R ----- Vref


The above isn't a clamp. Rather, it's a clip. True, some call it clamping, but it's really clipping. A clamper shifts a signal either positive or negative by adding a battery (using a capacitor of course) in series with the signal. The diode forces the capacitor to retain its charge.

h**p://hyperphysics.phy-astr.gsu.edu/Hbase/electronic/limiter.html

shows a simple clamper.

Also, h**p://www.tpub.com/neets/book9/37e.htm

is a good page on them.