Generate positive linear voltage ramp from single sided supply

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... or go look at my suggested micro with on board DAC. It is a one chip answer.

If you are using a micro and a logic output, you likely can do better than the PWM circuit that is in the micro. The trick would be a "delta mod" like action so that the bulk of the noise would be higher than clock/N as it would be with just a PWM. Perhaps using the PWM hardware and dithering the count would do it.

No matter what you do, some percentage *will* be inserted backwards. Some are fused for this reason. Some radials had three or four leads so they couldn't be inserted backwards. ;-)

With 24 bits of counter and DAC (or however big they make DACs these days; in the 1980's, they had 12 - do they go up to 24 yet?) you could make it pretty darn smooth, I'd think.

Use synchronous counters, of course. ;-)

Cheers! Rich

In addition, use some RC filtering after the DAC.

If the fall time is critical, use a digital output to reset the capacitor voltage.

Even with a low bit count DAC, one or two digital signals could be used to switch out part of the series resistance in the RC filter after the DAC.

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Now that is retro. About 30 years ago we used a gear motor to ramp a

On Dec 5, 2:22=A0pm, Paul Keinanen wrote: [... DAC and counter ...]

A transistor can get you down to within a few mv of ground. If you design the filter so that all of the filter nodes are at ground when the output is at ground a multi-pole filter can be used.

Since the steps from the DAC are of equal size and spacing, the spectrum has a few tall peaks in it. The filter could be designed to place zeros right on those frequencies. The filter and grounding transistors can be designed so that the line comes off the zero volts point at almost the exact right slope instead of no slope until the early capacitors take on their initial charge.