Ramping a reference voltage up from, or down to, 0V, over ~200us

[Flyback]

Hi,
Please assist us in ramping a reference voltage down to zero volts, or back up to the reference voltage. This being done at random times, on demand. The ramp should be over some 200us. It should be linear, but its not too bad if its not that straight….it could even be say in 10 steps (up or down).

The reference voltage could be any level from 0V to 0.5V.

….So eg it could be at, say, 0.23V…and every now and again we would need to ramp it down to zero volts….then some time later, ramp it back up to 0.23V.

Would you agree that the attached method is the best way?

It just uses a microcontroller to PWM the buffered reference voltage…(please ignore RC values) variable PWM to make it ramp over 200us…as discussed, it could be 10 steps, so 10 different duty cycles inside the 200us ramp time.
Please confirm there are no nice analog modules which do this, and no nice sub circuits which can do it better than this?

 

[Flyback]

Hi

Actually , now i think that 200us is too small a time for a micro to do the ramp….so I have done the attached circuit…however, it needs a +/-5v supply and the ramp is a little less linear than I’d like.

(LTspice sim and pdf schem attached)

Any improvements much appreciated?

 

[alec_t]

At any point during the ramp, does the ref voltage need to be accurately known/predictable, or is just the fact that it changes sufficient?

 

[Flyback]

Thanks, it just has to change...gradually up from, or down to, zero volts.

 

[alec_t]

Then wouldn't a simple RC (integrator) circuit suffice?

 

[ChrisP58]

I would use a microcontroller with a DAC function.

Microchip has devices with 5 bit (32 steps) or 8 bit (256 steps). The DACs are implemented with a stack of resistors in series, so the source impedance changes through the range, so I always buffer the output with a opamp follower.

I'm sure other processor manufacturers have similar parts.

 

[rjenkinsgb]

How about this - just a fast rail to rail opamp working as an integrator.
It gives a linear ramp between 0V and the positive supply, you can divide that to whatever level you need.

The voltage divider that sets the input bias should be adjusted for the mid voltage of the logic signal that switches it.
The ramp speed is adjusted by the integrator capacitor and resistor, and/or the voltage swing on the opamp + input by changing the input divider ratio. It's 10:1 as shown, using 5:1 would half the ramp time (subject to the opamp speed).