Okay, so bare with me on this one please… First post on this stack and still refreshing my memory on electronics in general.
So basically i'm working on a project which generates a varying AC voltage from as little as 15 volt to in excess of 400 volts. To make it familiar, it is very similar to a wind mill generator.. So below 15volts would be a shut off
- Input: 5vac to 400vac
- Output: 15vdc to 48vdc regulated
- Current: at least 1amp at lowest 15vdc output
The desired output is DC and regulated between 15 and 48 volts to keep it in a workable range with simpler circuits / anything i want to power of it.
Biggest issue i have had is trying to make use of the whole range, as in the lowest AC input from at least 10 volts all the way up to 400 volts… But the lowest range being most vital with the highest still be required as well. (Rotate of the blade can vary a lot)
While electronics is not my skill in most sense, generally i have been able to build most items given time and a fair bit of googling.. I just need a little feedback and guidance to what is the most practical, cheapest, smallest design.
What i have tried / tested / using so far?
- Simple full-wave rectifier (4 diodes) – Still using this mostly
- 78xx regulators, They would be simple if i get to the lower DC range.. not used atm
- Transformers multi-tap transformers with rectifier(s)/regulator(s).. still needs control
What i currently am looking at, But i could be way of target??
- PWM type control, prototyping with a arduino…
- Other SMPS chips/ic's that offer a large voltage difference
- Some other form of a feedback loop to regulate
- Buck converters, these still have a limited v range?
While i could simply use a AC wall socket charger rated from 110 to 240vac.. This would remove the range from 20 to 110vac and this is absolute necessary. From my understanding, using PWM i should be able to control the voltage, but this will still need current control.. But if i am not mistaken, this would be the simplest approach for the above requirements?
As for current, well ideally in the whole range at least 1 amp at the regulated DC voltage, the current generator is able to produce 15vdc @ 1.2amp using a simple 7815.
And as before, i am not asking anyone to build it for me or draw schematics.. Just to give me some general guidance with something that will suit this need?
== Sorry for the long post / question.. Just want people to be sure of the need and that i have physically tested and tried approaches with research.
Best Answer
The AC to DC part will be simple, just use bridge or full wave rectification and one or possibly several filter caps in series, it depends on how much current you need at that voltage. Then, use a buck converter to scale down the voltage to what you need. You might have an issue with having a buck converter with the full voltage range and current output you need, depending on whether or not you want to use a single IC switching solution or build up your own. Is it critical that the voltage on the output changes immediately? Can it lag a few milliseconds?
The tricky part is trying to scale the voltage on the output. Since supplies that use switching use "sensing" on the output to ensure stability and proper output voltage as well as setting the voltage on the output, you can use this to manipulate the voltage to what you want. The trick is figuring out how you want to do the math to compare the input and output voltages. You could use a voltage divider on the input and output to scale the voltage to something usable by an op-amp, have it go into a buffer first then have it compare the two voltages and use the error signal to drive the switching circuit (likely through a transistor if you need the voltage to be high on the sense input). The problem is you will need to tweak the resistor values of both the input and output dividers to get it to represent the proper output voltage across the whole range. The advantage is that it's closed loop feedback so you will get basically instantaneous response to voltage changes. Also you will need to bypass the crap out of the op-amps and most likely use the input buffers with a low pass filter to prevent wild oscillations or fluctuations in voltage which could be... very very bad. Also be wary of the switching signal possibly adding some noise, hence the low-pass filtering.
The other solution for controlling the voltage is simply using a microcontroller to compare the voltages, do the math, output a certain voltage (which will likely drive a transistor which in turn drives the voltage sense on the switching circuit) which then changes the output. The disadvantage is the programming, sensitivity to voltages if something goes horribly amiss, and response time of the microcontroller. The advantage is you can read in actual voltages and set up parameters you want to control, or even control the rate you want the voltages to change on the output etc. Offers some flexibility to you.