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At that current level, you will need to select capacitors with low ESR to avoid self-heating. You could perhaps use a few capacitors in parallel to share the load current, and reduce the overall ESR. With some doubts, I have used multi-layer capacitors in half-bridges. The doubts were the result...
I don't disagree, but the decision can be based upon labour costs alone.
Anyway, the LF411 has a long pedigree of working as described, but accuracy with a small value sensing resistor may not be adequate.
One obvious solution is to use a charge-pump or some other means to increase the supply...
There is an inconsistency between the text and the chart. That is not uncommon.
The text says:
"The amplifier will operate with a common-mode input voltage equal to the positive supply; however, the gain bandwidth and slew rate may be decreased in this condition. When the negative common-mode...
The EDN circuit is here
**broken link removed**
This will work well, I expect.
It will not be any easier to change the range or sensitivity of this circuit than the other, and still needs an op-amp with inputs that can be at the rail voltage.
The LF411 is not guaranteed to have this capacity...
Reviving this thread again:
Well I finally did go for the high side voltage sensing.I was looking for some help on making the circuit have a programmable gain.I could add a relay and switch the value of R3 so that I get different amplifications.But is there any other more elegant way, using...
I think that 1% over such a range will be difficult. Let's say that you supply the op-amp with +30V, obtained with a zener diode, and use resistors to reduce the common-mode voltage.
Even if the sensing resistor is shorted out, there will be an output due to common-mode errors, that changes as...
Hello Phaedrus,
I don't know that it has a name. It was in use long before Zetex packaged it.
As for the op-amp, 45V is probably not available outside of specialised devices.
The sensed voltage is 'impressed' across the collector resistor, and virtually independent of the common-mode voltage...
Thanks to Powermos for the simulations.
I don't think it is a matter of whether the designs will actually work, but the relative cost and ease of achieving the same result.
Dividing the common-mode voltage with resistors will work of course, but the sensed voltage is also divided by the same...
Phaedrus,
It is difficult to answer these general-yet-specific questions and not mislead, but here we go.
Resistors are available in almost any tolerance, but price becomes an issue. 1% tolerance is now virtually standard, and therefore inexpensive. However, even using 1%, the divider bridge...
high side current measurement
Hello Phaedrus,
It would be difficult to achieve 1% with this design unless you are willing to use high precision resistors, and even then...
Perhaps I can recommend the method used by Zetex in their devices.
The basic idea is shown in the datasheet;
**broken link...
shunt resistor for ina139
Some of the older JFET op-amps are also very cheap, but have the advantage that the positive common-mode voltage can exceed the supply rail; at least enough for this application.
The LF411 is one such device, but there are many others.
Re: Simple sensing circuit?
FvM is quite right, but it will always be necessary that some current flow in the switch, so it is a case of mimimising this current. Perhaps the base current of a BJT is too high, but an FET is a possibilty. It is likely that the array will be scanned, but unless...
how to use uln2803
Pin 10 is often connected to the supply, but not as a pull-up. If the load is inductive, the terminal voltage will rise when it is switched off. The diodes provide a path for the inductor's current, while clamping the output to the voltage at pin 10, plus the forward voltage...
Re: Simple sensing circuit?
srgrelic,
If the details of the phone are not known, it limits the range of possibilities.
Perhaps a simple circuit that relies on the current through the switch, rather than detecting the voltage, would be better. I have included a schematic as a general guide...
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