Hi, colleagues

I want to built an ESR tester, powered from a 2.4V Ni-Mh battery ( 2xAAA). The moving coil meter, 200uA 500 Ohm to read the value will be used.
Stucked with the rectifier stage. I'd like to avoid using of a special Opamps or special ICs. Can anyone point me to a circuit diagram ? Accuracy of 5% is acceptable. The previous cascade impedance is 10 kOhm, maximum output is 100mV, frequency is 100 kHz.
Circuits from a college books is out of interest, I need a real circuit diagram...

Thank you in advance

 

2.4 V is not much to work with, but it can be done. Can the 100 kHz be a square wave, or must it be a sine wave?

ak

 

Show us your proposed circuit for the measurement.

 

If you only have 2.4 volts which will drop to less than 2 as batteries deplete, a plain vainilla opamp won’t cut the mustard.

 

2.4 V is not much to work with, but it can be done. Can the 100 kHz be a square wave, or must it be a sine wave?

ak

sine

 

I want to built an ESR tester, powered from a 2.4V Ni-Mh battery ( 2xAAA)

Does it have to be 2.4 volts? A lot of the circuits I have seen draw very little current and a 9 volt battery would suffice without taking up any additional space.

 

Phase shift oscillator makes a decent sine wave with one transistor.

Phase shift oscillator

 

Beat me to it while I was off banging on another thread.

ak

 

Phase shift oscillator makes a decent sine wave with one transistor.

Phase shift oscillator

Everything clear with the oscillator to me.
Stucked with rectifier.

 

Show us your proposed circuit for the measurement.

Nothing special:

Sine w oscillator --- Cx----Amplifier-----Linear rectifier-----200uA meter

 

What do you mean by "linear rectifier"?

ak

 

I believe he means “precision rectifier”.
But that is only my guess.

 

What do you mean by "linear rectifier"?

ak

precision rectifier

 

If you've only got a 2.4V supply I'd be interested to see if anyone could could come up with a precision rectifier with 5% (or even 10%) accuracy. Even Schottky diodes would eat into that voltage allowance.

 

If you've only got a 2.4V supply I'd be interested to see if anyone could could come up with a precision rectifier with 5% (or even 10%) accuracy. Even Schottky diodes would eat into that voltage allowance.

No problem . I have some HF germanium transistors and small signal germanium diodes.
Some time ago I saw an ESR meter powered from a 1,5V battery on a forum. It was crystalradio.cn link , I guess. Sorry, can't find the circuit diagram at the moment

 

To give yourself a fighting chance of success with the circuit design, I’d recommend you power it from something like this, which claims to operate down to an input of 2V.

https://www.ebay.co.uk/itm/26533899...siFFlFJkLZOOJYxXtJPNvz2XU=|tkp:Bk9SR76jovunYg

 

If the op-amp is notionally operating at unity gain (with the feedback), and you want a voltage output swing of less than +1V then an op-amp with a 1MHz bandwidth should easily do the job. There are a number of fairly inexpensive op-amps with a 1MHz bandwidth – but I’d recommend you test the circuit design using LTspice.

 

If the op-amp is notionally operating at unity gain (with the feedback), and you want a voltage output swing of less than +1V then an op-amp with a 1MHz bandwidth should easily do the job. There are a number of fairly inexpensive op-amps with a 1MHz bandwidth – but I’d recommend you test the circuit design using LTspice.

Really ? A quite fast opamp OPA2211 ( slew ratio is 27 V/us , unity gain BW is 45 MHz), shows a clearly visible distortions at 100kHz :

Precision Full-Wave Rectifier, Dual-Supply

 

A quite fast opamp OPA2211 ( slew ratio is 27 V/us , unity gain BW is 45 MHz), shows a clearly visible distortions at 100kHz :

Precision Full-Wave Rectifier, Dual-Supply

Please indicate the figure or paragraph you are referencing.

If the author had run multiple generations of opamps through the same circuit, you might find that the distortions have more to do with the device's internal topology than simply its bandwidth. IOW, I wonder how an LM318 from the 1970's would perform at 50 kHz. Same for a current-feedback opamp from the 1990's.

Also, don't confuse simulation results with the real world. TI knows a lot about modelling, but I wouldn't trust anyone's models when chasing this kind of subtlety.

BTW, nice find on the article.

ak

 

A little while back I was experimenting with an LT1361 dual op-amp with a 50MHz bandwidth. Although having a maximum 36V rail, there is no way that the device can output a sine wave with peak to peak (0-36V) even at 10MHz unity gain.

The datasheet shows the undistorted output voltage swing limited to 10V (p-p) at around 5MHz. But I would be very surprised if the LT1361 would not be suitable in your application. I think I purchased 5 for around $15 including p&p from an ebay seller.