sawtooth LM324 generator

[ichibindigi]

sawtooth generator

Hello everyone,

Im using this ckt, its basically a sawtooth generator using a LM324. It works okay. my problem is that the ckt doesn't oscillate when i input 5,4,3,2,1 volts but its fine @ 6volts up to 15V. @ 5,4,3,2,1volts the ckt outs a DC voltage. Ive tried to use schottky diodes and reduced resistor values but still no progress/change.

So my last option is a change of opamp, got any suggestions on a op amp i could use preferably have the same pin configuration and can used running with only a single supply. Plz help

ichi

**broken link removed**

 

[VVV]

lm324 sawtooth

I cannot see any component values, but I think the problem is that with lower supply voltages, the output cannot trigger the comparator. That could be because the LM324 output is about 1.5V below the supply rail. So if you power it at say, 3V, then the output can only go to 1.5V. If the comparator's threshold is higher than 1.5V, then the circuit stops operating.
This is just one possible explanation that comes to mind.

To fix it, try using the LMV324, also from Nations, which has a rail-to-rail output. It should operate down to 2.7V. The pinout is the same, so you do not need to change anything.
The dual version is LMV358.

 

[ichibindigi]

sawtooth generator circuit

R1=111.11Kohm
R2=205Mohm
R3=47Kohm
R4=30Kohm
R5&R6=10Kohm
C1=0.3µF

 

[VVV]

op-amp sawtooth generator

OK, so look at the comparator: R5, R6 will produce Vcc/2 at pin 6.
To have the comparator switch, you need a little more than 2.5V at pin 5. Since the voltage at this pin is the output voltage divided down by R3, R4, you get:
Vpin5=R3/(R3+R4)*Vout≈0.61*Vout.

So: 0.5*Vcc=Vout*0.61=(Vcc-1.5)*0.61

0.11*Vcc=0.915

From this, the minimum Vcc for reliable operation is:
Vccmin=0.915/0.11=8.32V.

That means you are lucky it works at 6V.
Solve the equation now to see the actual drop of your IC:
0.11*6=x x=0.66

That means the IC you used actually has a drop of:

0.66/0.61=1.082V

To test the validity of this, reduce the voltage until the oscillation stops and measure the output DC voltage. It should be about Vcc-1.082V


So, using the LMV324 I suggested, which has a drop of only 0.1V, you can ensure reliable operation down to:
0.5*Vcc=(Vcc-0.1)*0.61
Vccmin=0.061/0.11=0.55V (theoretical limit)

In reality, you can say the circuit will operate down to 2.7V, which is the minimum Vcc specified for the LMV324.

 

[ichibindigi]

op amp sawtooth generator

thank you kind sir

 

[ichibindigi]

comparator sawtooth generator

Hi

Ive been using a non-inverting amplifier to reach 10Volts but when i use a DMM it reads 10V but when i look at it on a Oscilloscope the sawtooth is being clipped. what is the reason for the sawtooth being clipped? Im using a differnt IC(IC2) another LM324 w/ a supply of 15V for the non- inverting amplifier. on the sawtooth ckt im using a different LM324 as well.

ichi

 

[VVV]

sawtooth generator using op amp

Can you post a picture of the clipped waveform?

 

[ichibindigi]

op amp sawtooth

actually it starts out as a perfect tipped sawtooth waveform. Ive put a variable resistor on the non-inverting amp ckt so i can adjust it both on the R2 and R1. As soon i adjust the potentiometer it clips at it reaches the 9.++volts mark



**broken link removed**

 

[VVV]

lm324 triangle wave generator

At first glance, it seems the amplifier you added clips because the gain is too high and its supply voltage too low for it to swing higher.

First, Can you check that the input sawtooth is correct?

Then, please post the actual DC voltages for this amplifier, including input sawtooth DC average and power supply.

 

[ichibindigi]

lm324 generator

First, Can you check that the input sawtooth is correct?

yes, the input sawtooth is correct

Then, please post the actual DC voltages for this amplifier, including input sawtooth DC average and power supply.

Power supply = 15V
Input sawtooth DC average by this do u mean the voltage of the sawtooth goin into the amplifier? then it is 8.14V

 

[VVV]

lm324 pinout

I believe now that the amplifier is clipping.
If you the power is 15V, then the signal can only swing up to about 13.5-14V. If the DC output voltage (as measured with the DMM) is 10V, then the signal can only have and amplitude of 8Vpp.
If you try to get a signal with an amplitude larger than this, you will get clipping.

Try to AC couple the amplifier. Use a divider on the + input, set to about 6V (make it adjustable). That will center the output's DC voltage, such that the output can swing both ways, allowing a maximum amplitude of 12-13Vpp.

 

[ichibindigi]

lm324 op amp + vcc pin

Try to AC couple the amplifier. Use a divider on the + input, set to about 6V (make it adjustable). That will center the output's DC voltage, such that the output can swing both ways, allowing a maximum amplitude of 12-13Vpp.

So ill put a capacitor on +?but where do i put the 6V.

 

[VVV]

op amp as sawtooth generator

Also at the + input. Just build a divider with two resistors, to obtain about 6V at the + input of the opamp. Then feed the signal through a large enough capacitor to the same + input.