I am having a harder time than anticipated locating a step down DC-DC converter that I can control with a PWM signal.
This is going to be part of a project that non-enthusiasts may try to replicate/build, so I am ideally looking for something that can be pretty simply wired up instead of building my own converter from scratch. I found this description of a buck converter, which leads me to believe that a buck converter is the correct choice for this application: http://www.learnabout-electronics.org/PSU/psu31.php
The application: I have a small, what is essentially a battery powered radio. The battery is a nominal 7.5V and lasts for about 1 day. As the battery voltage drops at the end of life, some strange things begin to happen. For training, I want to be able to simulate the dying battery stage on demand over the course of 30 minutes to an hour.
The device: The device that takes 7.5VDC with a max input of 8VDC (damage occurs above 8 volts and it's about $250 so I don't want to have any possibility of more than 8V being applied). I would like to use a 7.5-8V power supply, run through a PWM controlled converter that is essentially transparent (or close to it) at 100% PWM, and then can ramp the power down. I don't know what the minimum voltage will be, but I envision it's somewhere between 4-6 volts so as long as the converter can drop the voltage below that level, we are good.
All the variable buck converters I have been able to find are manually set with a pot, which is not what I am looking for. Does anyone here know of something that might work for this application?