I am building an appliance that should work in very wide range input voltage: In some scenarios input is 5VAC, in other scenarios it can be 250VAC.
It's not a problem to convert AC to DC, then convert it using converters to required 3.3V for the appliance. The appliance consumes current from 10mA to 150mA on 3.3V.
- Wide input voltages range.
- Small size as possible.
- Less components as possible (footprint, size, price).
- Less heat dissipation (efficiency in other words).
- Low current, very low voltage, low output power.
Till now I used 2 separated power supplies for low-voltage and high-voltage scenarios (switching between them mechanically):
There is not a risk of HV input on LV circuit: the input controlled by dual way relay. This approach has following disadvantages (for my point of view):
- Mechanical switching is not so nice.
- Waste of space in tiny appliance.
- Maintaining BOM with similar by function parts.
I looked for an alternative solution to merge 2 PSUs in one. Ready PSUs are huge in size: more than inch (25mm) in one of dimensions.
In this thread it was suggested so far "the best" solution based on wide range regulator LR8. Minimal input of 13.2V is not a problem, I can ignore lower input voltages...
Disadvantages for this approach are:
- No replacement parts for LR8 in case of short stock.
- Supply of 1 regulator is not enough. Connecting LDOs in parallel is tricky and not trivial for me. The avoiding overload one of them and lazy load on other is a big deal.
In this thread the idea of LED driver was suggested. In common, this is good idea except following:
- The most of LED drivers are working in range 80V and up. (At least, I didn't find lower input voltage LED driver).
- LED driver is build to maintain constant (limited) current. In my appliance, when current not required (10mA consumption) the driver will raise the voltage to reach the preset current. This will burn the appliance itself.
Additional idea to get wide input voltage PSU can be implemented (in science fiction :) by connecting sequentially 2 regulators LTC3639 of Linear. Each regulator can deal with 5-150V range. So 2 in a sequence can deal 10-300V which maybe enough. But I have no clue how to connect them... I think this is not possible. True?
So, I ran out of ideas to solve the problem of single wide input voltage range buck converter/circuit to get 3.3V output at 10-150mA. Please, help.
What can be better: develop new research direction or improve LR8 LDO regulator in parallel?