gunrunnerjohn
Member
I have a little module that has a switching power supply module that operates from AC or DC (model train track voltage) of around 9 volts up to 18 volts. I'd like to be able to power this module from track voltage as low as 5 volts. It draws a maximum of 100ma at low voltages and drops to less than 50ma at higher supply voltages. The switching module is rated at 28 volts maximum input, and I can attest that it'll croak if you go higher!
The logical plan seemed to be a voltage doubler to raise the low voltage from 4-5 volts AC to a usable level. That appears to work great at low voltages, I can operate down to around 4 volts AC input power. The problem comes when the input power goes to 18 volts, the voltage doubler hits 40 volts on the output and smokes the switching power supply!
What I need to do is have a voltage doubler that operates normally at low voltage, but limits the maximum voltage to around 18-20 volts regardless of the input voltage. A key requirement is low cost and small size as this is going inside the model locomotive.
I've considered a simple resistor and Zener to limit the voltage, but that's the brute force method, and generates quite a bit of heat at high track voltages. I'm looking for something a bit kinder and gentler.
The floor is open for any ideas.
The logical plan seemed to be a voltage doubler to raise the low voltage from 4-5 volts AC to a usable level. That appears to work great at low voltages, I can operate down to around 4 volts AC input power. The problem comes when the input power goes to 18 volts, the voltage doubler hits 40 volts on the output and smokes the switching power supply!
What I need to do is have a voltage doubler that operates normally at low voltage, but limits the maximum voltage to around 18-20 volts regardless of the input voltage. A key requirement is low cost and small size as this is going inside the model locomotive.
I've considered a simple resistor and Zener to limit the voltage, but that's the brute force method, and generates quite a bit of heat at high track voltages. I'm looking for something a bit kinder and gentler.
The floor is open for any ideas.