Hi Ladies and Gentlemen,

It is related to an existing post here from early 2019. Voltage to PWM Circuit, need to understand frequency

I am trying to make a simple 0-10V to PWM converter (idealy linear on it's full span).

It is pretty simple and I have in hand a reference module that was described in the previous mentioned post. I am trying to reproduce it's behavior and the ramp it generates.

In theory I understand that the Ramp signal generated by a 555 will sit between 1/3VCC and 2/3VCC due to the internal resistor network. And that's what I get from my BredBoard experiment.

Now How can I get the ramp to be between 0V and 2/3VCC? I know the question can be odd, but that is exactly what I get by monitoring the Ramp signal in the little board shown here. Yes the 0V is on the middle of the vertical axis. There is no extra parts like a (-1/3VCC supply to make a vertical translation on the signal). There is only what is shown on this module...

I know I am trying to retro-engineer a Chinese product :-/ But is there anybody that could have an insight that would help bring light on this?

Thanks in advance for your input.

Little board from LC Technology signal at the Trigger pin, and output of comp

enter image description here

  • \$\begingroup\$ 1) What is the output voltage of the AMS1117? 2) did you measure the peak voltage of the trigger pin? 3) Where is the supply voltage of the comparator connected to? \$\endgroup\$ – vtolentino Mar 17 at 22:14
  • \$\begingroup\$ 1) the Output voltage of the AMS1117 is exactly 5V, (same as Vmax of the PWM wave) screanshot revised with values. 2) The peak voltage at the trigger pin (pin2, pin 6 & pin 7) is 3.4V. 3) The supply voltage of the Comparator is connected to +5V from the regulator. Pictures and Screenshot will be updated with relevant information. \$\endgroup\$ – JF Ouellet Lamy Mar 18 at 13:15
  • \$\begingroup\$ "I am trying to make a simple 0-10V to PWM converter (idealy linear on it's full span)." <--- This calls for a cheap microcontroller, not an NE555. With any microcontroller with an ADC, this is literally 1 (one) decoupling capacitor for the microcontroller and 2 (two) resistors for a voltage divider to let the microcontroller sense the voltage above its VCC, and said microcontroller. Don't let the quite unsatisfactory NE555 get in the way of efficient development – even learning how to write software for a microcontroller will take less time than trying to tune 555 circuitry until it's linear. \$\endgroup\$ – Marcus Müller Mar 18 at 13:34
  • \$\begingroup\$ The sawtooth wave is exactly where I get confused. I really like that the lowest point of the wave is close to 0V. But in theory if I get to reproduce this circuit I get something more in the order of 1/3VCC. Which is logical considering the circuit of 3 x 5k resistors in series in the 555. So out of the weeds, how were those guys able to do the compare to 0V instead of 1/3VCC? That puzzle me. \$\endgroup\$ – JF Ouellet Lamy Mar 18 at 13:34
  • \$\begingroup\$ Are you sure that the pot is connected to ground? Just to confirm. \$\endgroup\$ – vtolentino Mar 18 at 14:03

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