TL783: PWM Based Regulator Design

Hi Fatih,

Could you provide a schematic for your design, or TL783 resistor values and op amps used? That would be helpful to allow me to troubleshoot further. 

What behavior does the circuit exhibit? Can the output not be adjusted at all, or can it just not be brought to the expected 60V? 

There shouldn't be an issue using a single supply op amp in this application, but it will mean that the voltage offset can only be positive, and won't be able to drop all the way to 0V due to output swing limitations on the op amp's output. Depending on the resistor values chosen for the TL783's divider, the op amp's output current may be a limiting factor.

Best Regards,

Alex Davis

Hi Alex,

I am sharing the schematic below. I used LM324 as opamp. I can not adjust the output value with single supply opamp, but when I connect the TL081 with dual supply I can do it. Voltage output value must be normally ~60V when settting the pwm-anaog output as ~2V, but I can not adjust.

Thank you very much for your support.

Best regards,

Fatih ÇAVDARCI

Hi Fatih,

I suspect this may be due to output current limitations of the LM324. With an 82Ω R1, the op amp needs to sink ~15mA. From Figure 5-35 of the LM324 datasheet, under that load condition the lowest voltage the LM324 output could swing to would be approximately 2V. Since this swing is the offset above the VCC- supply, a dual-supply configuration provides additional negative headroom, allowing the op amp output to drop below the 2V limit in the single supply configuration.

If this is the case, a single-supply op amp with improved current sinking should solve the issue. We offer an LM324 variant, the LM324LV, which may be better suited for a low-voltage single-supply configuration like this. 

Best Regards,

Alex Davis