Make a very simple ESR meter.

Thread Starter

bob2

Joined Jun 15, 2019
212
I will try to measure the frequency.
Hopefully, by selecting the circuit modes, it will be possible to get a frequency of 80-100 kHz.
Regarding the operational amplifier, then the choice is not great. So far I have only TL062,072.
 

MrAl

Joined Jun 17, 2014
8,136
I will try to measure the frequency.
Hopefully, by selecting the circuit modes, it will be possible to get a frequency of 80-100 kHz.
Regarding the operational amplifier, then the choice is not great. So far I have only TL062,072.

It looks like both of those op amps are specified with a +/- 15 volts power supply so it is unlikely they will work.
The 062 has common mode input range of Vpos-4 and Vneg+4 so with a 5v power supply there is no input range left. That is typical for JFET input op amps. The 062 also has a power supply spec of minimum of +5 and -5 volt supplies.

Find an op amp that is spec'd at 5v and has at least 4MHz gain bandwidth and decent slew rate.

I checked the TI site they have a large number of op amps that will work at 5v and have 5MHz or better gain bandwith. You should tske a look see what you like.
 
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Thread Starter

bob2

Joined Jun 15, 2019
212
Here I found more information on the use of operational amplifiers in this circuit.
The Op Amp
Note that I also used a TL082 instead of a TL062 or even TL072. It still works. Since it's in a socket I'll see what happens with other op amps such as LM358, LM1458, and maybe even an LM6142 RRIO which is probably overkill. Why did I use a TL082? because I have a bunch of them... And a lot of LM1458's... Maybe I should have used dual 741's because I have a boatload of those along with LF355 and LF356... I wish I had a few LM358 and LM324, these op amps should be pretty good. Only a few LM6142's unfortunately. I think I may also have a TS512AN's... I have a few RRIO TLV2374 too...

The LM1458 oscillated at a lower than expected frequency and apparently the amplifier stage did not work. It figures, it's an ancient dual unit. It probably does not like being run at 5V. After noticing the LM358 not working well, the LM6142 will likely have the same problem. It wasn't until I compared the datasheets of my op amp stockpile until it was clear - the input impedence of the rail-capable opamps is not nearly as high as the non rail-to-rail op amps. The LM6142's inputs are just atrocious. I suppose you can look for other JFET or CMOS op amps like LF353 or (I don't have any CMOS op amps to suggest), just don't try to sub in bipolar op amps without circuit modification.

You do know what, after studying the circuit a bit more, it leaves a bit to be desired. Due to the amplifier biasing I would imagine that there's no reason why any op amp wouldn't work here, except for the fact that the AC voltage in the original design seems to be biased strangely, though it still works for the TL062/TL082/TL084. The other issue is the fact it runs off of 5V: for many older op amps, this is on the low end borderline of the usable operation region, hence not getting enough voltage swing to drive the meter.

http://www.vanade.com/~blc/html/hardware/esr/
After reading the information on this link, there were questions about the capacitors C1, C2, C3.
C1. What are the requirements for this capacitor? Or any one?
C2, C3. I understand that it is necessary to select these capacitors with the lowest ESR.
 
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MrAl

Joined Jun 17, 2014
8,136
Hi,

None of these are a good choice:
LM358 and similar,
TL062,72,82,84, etc.

The LM358 only has 1MHz GBP so at 100kHz the max gain would be 10. One of the op amps in the circuit has a gain of 39.
The TL series above has JFET inputs, which means a minimum power supply of plus and minus 5v, and that is two supplies not one.

The only one you mentioned that will work properly is the LM6142 op amp. That's because it looks like it can work at 5v just one supply as this circuit has. This is very important as the other op amps might appear to be working when really they create too much distortion.

Another possibility is to generate a minus 5v power supply too using a boost inverter circuit that produces -5v. That's been done before and allows the use of the TL084 but the input range is still limited.
 

Thread Starter

bob2

Joined Jun 15, 2019
212
Hi,
Thanks.
The situation is more or less clear.
What do you think about the capacitors C1, C2, C3?
 

Thread Starter

bob2

Joined Jun 15, 2019
212
C1.Any type of capacitor can apply?
In this case, can it be better to use instead of electrolytic capacitors C2, C3 ceramic capacitors with low ESR?
 

Thread Starter

bob2

Joined Jun 15, 2019
212
C1 ceramic.
In addition to the ceramic capacitor, can I use a different type? Polypropylene or polystyrene? Does the quality of this capacitor have any meaning?
I will show one.
His capacitance is different, but this is just for example. In my opinion, very high-quality capacitors.
 

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MrAl

Joined Jun 17, 2014
8,136
In addition to the ceramic capacitor, can I use a different type? Polypropylene or polystyrene? Does the quality of this capacitor have any meaning?
I will show one.
His capacitance is different, but this is just for example. In my opinion, very high-quality capacitors.
Ceramic should be fine.
If you are worried then use silver mica for the oscillator.

Next a simulation would be good.
 

Thread Starter

bob2

Joined Jun 15, 2019
212
I finish making the test PCB.
Regarding C1, C2. In different versions of the circuit, electrolytic capacitors of 1-10uf are used.
I think this is not so important.
Thanks for the info. Any information is very important.
 

Thread Starter

bob2

Joined Jun 15, 2019
212
Transformer used ready from the old monitor.
R5, R6-1Ohm.
We actually have a fairly good range of 0.02-20 Ohm.
 

Thread Starter

bob2

Joined Jun 15, 2019
212
Yes. I have already said that I will do the original circuit with a transformer.
And I will do your circuit later, because I do not have the necessary operational amplifiers.
Are you going to make your scheme or not?
 

MrAl

Joined Jun 17, 2014
8,136
Yes. I have already said that I will do the original circuit with a transformer.
And I will do your circuit later, because I do not have the necessary operational amplifiers.
Are you going to make your scheme or not?
What scheme? I already posted one way back in this thread.

I just wanted to make sure we were still looking at the same circuit (with the transformer) and that other readers could see the circuit you are talking about without going way back in the thread and downloading a pdf. It's really better to post an image for a circuit if that is all that is being posted.
 
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