Created by
Created September 22, 2013
Last modified September 30, 2013
Tags ramp   voltage  


Nearly Linear Voltage ramp-up from 0v to about 22v in one second. Stable output and low noise.


This is a design for a linear voltage ramp up. I'm using it to provide a soft power-up for a phantom power feed to a microphone I've built. The capacitor charges very slowly through the 'Throttle' resistor (RC Time constant of just under 5 seconds) The Transistor Q1 acts like an emitter-follower providing unity gain. The Collector voltage is the feed to my phantom power via a low-pass filter.

The Op Amp feeds the transistor's base and takes its feedback from the collector through a resistor network that ensures the voltage at the collector is about 5 times the voltage seen across the capacitor.

Why? Well I'm only using the first 20% or so of the capacitor's charging cycle. A small portion of the charging curve looks linear, and the total effect is a nearly linear ramp, over about 1 second, from 0v to just under the supply voltage.

I searched around for voltage ramp circuits but because I made this one I understand it and I'm very happy with the result. With the Low Pass filter at the output, and a load draw of about 30mA (which is what the rest of the circuit requires), my oscilloscope measures less than 0.1 mV voltage noise across a 22 V output, and the frequency spectrum of the noise looks quite 'White' so is probably resistor noise which I'm happy enough with.

Hope it's useful. It's probably naive. But it works..


No comments yet. Be the first!

Leave a Comment

Please sign in or create an account to comment.

Revision History

Only the circuit's creator can access stored revision history.