Peak detector circuit with 10k resistors, 1uF/10uF cap, IN914 diode, 15V op-amp not working

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Why doesn’t my op-amp peak detector circuit produce an output with 10 kΩ resistors, a 1 µF/10 µF capacitor, a 1N914 diode, and a 15 V supply?

Your circuit needs a few fixes: move the anode of D2 from ground to the junction of the 741’s inverting input and the 10 kΩ resistor, and add an output capacitor of about 100 nF [#21665843][#21665842] Make sure the circuit is being driven with an AC signal rather than DC, because a peak detector only works on AC input [#21665836] Check the LM741 datasheet as well, since one reply notes its input range is about ±12 V minimum and its output swing is less than the rails even on a ±15 V supply [#21665838] If the input frequency is high, a 10 µF capacitor may be too large because the op-amp’s internal resistance and the capacitor form an RC time constant that can prevent proper operation [#21665837]

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#1 21665834 09 Jan 2013 15:46

furious 555 furious 555

Anonymous
Post #1
21665834 09 Jan 2013 15:46

I tried the circuit below, but i couldn't make the output.. Plz help me with corrections.
In schematic:
Resistors - 10k
capacitor - I tried both 1uf and 10 uf
Diode - IN914
I applied 15v to the op-amp

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#2 21665835 09 Jan 2013 15:53

Eugene Lisovy Eugene Lisovy

Anonymous

Post #2
21665835 09 Jan 2013 15:53

See page 13 into this application note.
#3 21665836 09 Jan 2013 15:55

David Adams David Adams

Anonymous

Post #3
21665836 09 Jan 2013 15:55

at what carrier frequency ??? Unity gain is 1 at 100 KHz ???

Remember peak detector is for AC not DC
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Peak detector needs grounded input and lower capacitance
#4 21665837 09 Jan 2013 16:21

Earl Albin Earl Albin

Anonymous

Peak detector needs grounded input and lower capacitance
Post #4 21665837 09 Jan 2013 16:21

What were you expecting? What is your input voltage and is it grounded to the reference return? This is essentially a 1/2 wave rectifier, referred to as a peak detector so if say you have a sine wave (doesn't have to be) of 1V peak (+) then of course it would be 1V peak (-) as well. The output cap should charge to iV peak assuming that the frequency isn't too high. I say that because the opamp has an internal resistance which forms an R/C time constant with the output cap. In the case say 1MHz, it may not work at all with a 10uF cap.
#5 21665838 09 Jan 2013 17:30

Steve Lawson Steve Lawson

Anonymous

Post #5
21665838 09 Jan 2013 17:30

Also consider that the input voltage range for an LM741 is, at minimum, +/-12 volt ( +/-13 volts typical), and the output swing will be less than +/-15 volt (depending on output load).

Check the datasheet!
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Possible latch-up from input overvoltage
#6 21665839 09 Jan 2013 17:36

Earl Albin Earl Albin

Anonymous

Possible latch-up from input overvoltage
Post #6 21665839 09 Jan 2013 17:36

Ah good point about the input voltage. Some ICs (this may not be one, haven't checked the spec) will latch up if the input voltage exceeds the bias supply voltage by more than a diode. Latched up means it is either at the +V rail, or it is at the -V rail, and does nothing no matter what the input is. This is corrected when power is reset, but will come back if the original latch conditions exist.

Surely check this.
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#7 21665840 09 Jan 2013 17:39

Steve Lawson Steve Lawson

Anonymous

Post #7
21665840 09 Jan 2013 17:39

I forgot about latch-up -- I checked the datasheet and the LM741 claims "no latch-up".
Requesting scope traces at op-amp inputs and output
#8 21665841 09 Jan 2013 18:38

Earl Albin Earl Albin

Anonymous

Requesting scope traces at op-amp inputs and output
Post #8 21665841 09 Jan 2013 18:38

Curious 555, when you say you get nothing what exactly is nothing? Also trace out the signals and show where the nothing begins. For instance what does the positive (+) terminal of the opamp look like on a scope (assume you have one) or even an AC voltmeter. Second what does the negative terminal (-) look line, then what does the output of the opamp look like. You need to furnish more that just, "Nothing."
#9 21665842 27 Apr 2013 15:21

Safwan RAJAB Safwan RAJAB

Anonymous

Post #9
21665842 27 Apr 2013 15:21

Sorry for the late I haven't seen the question till now
yes this schematic has an error a capcitor at the output of op-amp must be put
100nf is match

and I have a scheme perfect for Mic
this schematic can give 5V output "level" at 50 mv peak to peak input
1V at 10mv peak- peak input - directly connect your Mic and measer the level of sound at output using DC-Voltmeter
#10 21665843 06 Jun 2018 23:48

PeterTraneus Anderson PeterTraneus Anderson

Anonymous

Post #10
21665843 06 Jun 2018 23:48

Move the anode of D2 from ground, to the junction of the - input of the 741 and the 10K resistor.
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Topic summary

A peak detector circuit using 10k resistors, 1µF or 10µF capacitors, an IN914 diode, and a 15V powered op-amp (LM741) was not producing the expected output. Key issues discussed include the importance of input signal frequency and amplitude, as the peak detector functions for AC signals and may fail at high frequencies (e.g., 1MHz) due to the op-amp's internal resistance and RC time constant with the output capacitor. The LM741 op-amp's input voltage range and output swing limitations were highlighted, with a reminder to consult the datasheet to avoid input voltages exceeding supply rails, which can cause latch-up in some ICs (though LM741 claims no latch-up). A suggested correction involves adding a 100nF capacitor at the op-amp output to stabilize the circuit. Another modification recommended moving the diode anode from ground to the junction of the op-amp's inverting input and the 10k resistor. The circuit was noted to behave like a half-wave rectifier, charging the output capacitor to the peak input voltage if conditions are met. Proper grounding and signal tracing with an oscilloscope or AC voltmeter were advised to diagnose the issue further.
AI summary based on the discussion. May contain errors.

Peak detector circuit with 10k resistors, 1uF/10uF cap, IN914 diode, 15V op-amp not working

Why doesn’t my op-amp peak detector circuit produce an output with 10 kΩ resistors, a 1 µF/10 µF capacitor, a 1N914 diode, and a 15 V supply?

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