LM2903B: Output low to high transition

With the open-collector output, the signal is pulled high only by the resistor.

Figure 6-37 in the datasheet shows how the output should behave. Do you get a different curve?

Hi,

Yes, rise time takes seconds. There is different questions at my message above.

Clemens 

thanks as always for your support. 

Gokhan

sorry to hear about the problem. We’re on holiday break until Monday so we will review again on Monday. If you could include a scope shot of inputs, output and VCC, this will help us diagnose. You did a good job describing your circuit but an actual schematic is always nice. Hopefully you have a localized bypass capacitor for the comparator.

Chuck 

Hi Gokhan,

in such situations always replace the chip in question by a fresh one and check again. Also check the cabling.

If the issue persists, think of output oscillations caused by hum, EMI or else being superimposed to the slowly varying DC voltage at the -input. Imagine that only the top of superimposed hum will make the comparator toggle. Then, when the DC level at the -input is slowly changing this would result in an output oscillation with a varying duty cycle, looking like a slowly varying DC voltage when being measured by a slow and averaging (!) DC voltmeter.

You could additionally low pass filter the signal at the -input of comparator. Not to furtherly slow down the input signal but to remove noise and hum.

But the best remedy is to add hysteresis. Keep in mind that comparators urgently need hysteresis when the input signal is very slowly changing. Never omit hystersis when the input signal is such slowly changing as in your case.

Kai

Thanks Kai

Good points and suggestions. 

Chuck