Hello,I'm working with a National Semiconductor
LM334 Current Source in 3 terminal configuration with a 27 Volt source. I
am using an Optocoupler in series with the voltage source and LM334 to
create a square pulse of no greater than 1kHz across a load of roughly
We choose the set resistor to set the current of the LM334 to about
.1 mA, and are noticing that each time the optocoupler triggers a pulse,
the transient turn-on/off response of the current source creates a
large voltage spike across our load before settling to the proper level.
Any suggestions on how we can kill this transient spike? Is there some common
method or configuration of the LM334 that would attenuate or eliminate
this spike altogether?Thanks,
I would suggest removing the opto-coupler from the series connection and, instead, connect the collector/emitter connections across (i.e. in parallel with) the 5k load. This way the 100uA (.1mA) is going either though the 5k resistor (Opto-Coupler is Off) or through the opto-coupler transitor (Opto-Coupler is On).
The upside is that the LM334 is always running at the set current, so the transient behavior is no longer an issue.
The downside is that the collector to emitter impedance of the opto-coupler transistor will prevent getting a low level signal of zero when it is on. Check your Opto-Coupler datasheet for Typical Performance behavior curve(s) for "Collector-Emitter Saturation Voltage vs. Forward Current" to determine how close to zero you might get.
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