Does anyone know how I could protect a load from exceeding two different voltages...
I have a load that I want to keep within +1.6V and -0.6V.... I can't exceed these values, and have to be within 200mV of them
I thought about putting a 1.6V zener across my load, that way in one direction it wouldn't go over 1.6V and in the other direction it would be limited to about 0.6V... but I can't find any 1.6V zeners...
Does anyone know another way I could pull this off?
- much thanks
How much current must one absorb when clamped?
...Jim Thompson
How accurate do those voltages have to be ?
Graham
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
Then you'd better check the diode drop over temperature.
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.
A " 'load' of 100 qua?" two silicon signal diodes and one germanium should be 1.5 volts.
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...
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