Peak voltage detector...

[ikelectro]

You cannot buy modern high frequency parts and you cannot measure the level of the input signal.
You don't even have an oscilloscope.

yes you are absolutely right in that case. I don't have any. It does not mean I shall stop to make a peak voltage detector.

 

[alec_t]

The LT1195 opamp should be ok for square waves up to ~2MHz.
I'm curious as to why you want to measure the peak voltage of square waves?

 

[ikelectro]

The LT1195 opamp should be ok for square waves up to ~2MHz.
I'm curious as to why you want to measure the peak voltage of square waves?

Ok... I have to find out LT1195 whether it is accessible or not here in local market........
some days ago I just found that my multimeter can't able to the accurate voltage peak voltage in high frequency... so just think why not to a build one......... if i'm able to do it it'll be great for me as my project instrument...

 

[Grossel]

I'll say that if you really don't know the nature of the input (what you refer as square wave), then you should expect readings of output voltage being higher than input voltage.
Especially since you cannot tell how the input curveform actually looks like.

I'm tempted to state the input you have is a close to a sinus curve since the output reading is pretty close to v.in * √2. And with your equipment I'll say it's within the margins of error too

 

[ikelectro]

I'll say that if you really don't know the nature of the input (what you refer as square wave), then you should expect readings of output voltage being higher than input voltage.

my input will be always square wave.......

here is one of the circuit where I have to test peak voltage................

 

[audioguru]

The IC in your circuit to be tested has no part number! Then we cannot look up its output current.
Also, you forgot to tell us the function of the circuit.

 

[ikelectro]

The IC in your circuit to be tested has no part number! Then we cannot look up its output current.
Also, you forgot to tell us the function of the circuit.

sorry for the less informative .......
that's the RT9238 VRM IC.....

 

[audioguru]

Your circuit is a switching voltage regulator that operates at 200kHz. The signal you are measuring goes high for only about 2us or less so you need an extremely fast circuit to measure the peak voltage. Use an oscilloscope.

The peak will be almost the same as the 5.0V supply voltage.

 

[Grossel]

Nevertheless, I assume the slow peak detector eventually will reach an output level that will match the highest spikes, but not THE highest spike.

 

[ccurtis]

A good, fast peak detector can be made with a high speed comparator driving a latch and a known variable reference voltage used to compare with the input peak to be detected. With this method, peaks as short as 4.5 ns (depending on the comparator used) can be determined with high accuracy and cheaply.

 

[ikelectro]

A good, fast peak detector can be made with a high speed comparator driving a latch and a known variable reference voltage used to compare with the input peak to be detected. With this method, peaks as short as 4.5 ns (depending on the comparator used) can be determined with high accuracy and cheaply.

Hi ccurtis.. It's a long time!!!!
Do you mean to convert the analog voltage into binary and do what you have said????

 

[ikelectro]

Your circuit is a switching voltage regulator that operates at 200kHz. The signal you are measuring goes high for only about 2us or less so you need an extremely fast circuit to measure the peak voltage. Use an oscilloscope.

The peak will be almost the same as the 5.0V supply voltage.

An oscilloscope is pretty expensive for me at this moment, but I can use my college's.....

 

[patrickabella851]

laser alarm

Works by sensing the light from the laser hitting the photoresistor which lowers the resistance, once the beam is broken the
Resistance increases and the 741 chip senses that the resistance is now higher than the 1k resistor. This results in the chip sending a
Pulse to the 4017, which sets off the buzzer and turns off the power to the photo-resistor so the buzzer will not stop when the beam is
Back on the sensor. To reset the circuit the laser must be back on the photo-resistor while you push the reset button.



please help.....

 

[ccurtis]

Hi ccurtis.. It's a long time!!!!
Do you mean to convert the analog voltage into binary and do what you have said????

Hi there. No, not anything complicated like that. Just apply a variable DC voltage that you supply, say from a power supply, to the - input of a good comparator. Label that voltage Vref. Apply the signal you want to test to the + input of the comparator. Label that voltage Vin. Start out with Vref set to a voltage greater than Vin (within the allowable levels for the comparator device, of course). As long as Vin is lower than Vref, the output of the comparator will be low. Now, slowly lower Vref just until the output of the comparator output goes high. Then measure Vref to find the peak voltage at Vin. If the peak occurs too quickly (or too infrequently) to notice at the output of the comparator, the rising edge of the comparator can be used to drive a latch, storing the event so you can see it. The latch, you could say, takes the place of a capacitor as a peak memory device.

 

[audioguru]

Works by sensing the light from the laser hitting the photoresistor which lowers the resistance, once the beam is broken the
Resistance increases and the 741 chip senses that the resistance is now higher than the 1k resistor. This results in the chip sending a
Pulse to the 4017, which sets off the buzzer and turns off the power to the photo-resistor so the buzzer will not stop when the beam is
Back on the sensor. To reset the circuit the laser must be back on the photo-resistor while you push the reset button.

View attachment 71540
WHY DID YOU HIJACK THIS THREAD INSTEAD OF STARTING YOUR OWN THREAD?
We are not talking about your 741 opamp that is biased completely WRONG!

 

[ikelectro]

to the - input of a good comparator. Label that voltage Vref.

good comparator like LM393 or more ????
I cant understand the "Lebel that voltage Vref'' do you suggest to fixed the voltage at VRef point????

 

[ccurtis]

good comparator like LM393 or more ????
I cant understand the "Lebel that voltage Vref'' do you suggest to fixed the voltage at VRef point????

I say to label it Vref only so that I can quickly type "Vref" instead of continuing to type "variable power supply voltage" multiple times. The LM393 can detect peaks lasting 300 nS, or more, using the method.

 

[ikelectro]

I say to label it Vref only so that I can quickly type "Vref" instead of continuing to type "variable power supply voltage" multiple times. The LM393 can detect peaks lasting 300 nS, or more, using the method.

ok. i'll first use LM358 and then LM393 and then you suggest what should i use.
first let me see if Im draw the circuit correctly or not. I'm not very good on that....