how to make a low voltage clamp or limiter

How much current must one absorb when clamped?

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food

If it's signal level, there are some "clamp-amps", opamps with auxiliary Vh and Vl limiting pins. HFA1130 is one; Analog Devices has a similar one.

John

Self-made 1.6V zener : two or three diodes in series. Then a diode in reverse parallel and you have your limiter.

ahhh.... I like this 2 or 3 diode solution... sounds promising, thanks

my accuracy has to be within +/- 200mV

and my load will be pulling around 100uA

d

Now, if the supply voltage goes over 1.6V ( or below -0.6V ) the current thru the diodes could destroy them, so you sould limit the supply current somehow.

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food

Then you'd better check the diode drop over temperature.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Meaning, that the signal has to accurately track an input up to

200 mV of those limits? Or, that the limits can vary from +1.6 +0.200V to +1.6 - 0.200V?

How accurate? What input drive is available, and what output current is required? Is this an analog signal with accuracy requirements, or just a logic level ON/OFF?

One way is to buffer with an op amp with rail/rail output, and voltage-divide the output down to the range you want. The slew rate will suffer, and you need to have a reference voltage to bias the center off ground. There are also amplifiers (LM13700) which can be accurately current-limited, and a load resistor to the midpoint of your selected range will accomplish the same thing, with better recovery times after clipping, and better slew rates.

There aren't any good Zeners in the low range you want, of course. The best environment for diode/Zener clippers is the old analog

+/- 24V power regime. With lotsa volts to start with, circuitry gets less complex.

Low voltage zeners are as bad as a forward-biased diode, meaning crappy. An adjustable voltage refrence would give excellent results

*providing* you do not need to shunt large currents. For the reverse direction, an ordinary silicon diode would do; again check the shunt current needs. Then again, if the output uses a series pass transistor, current limiting and voltage sensing would help.

Prolly better off with an adjustable voltage reference (sharp transition) and a single small-signal diode or two schottky diodes in series. The diode(s) will be temp sensitive...