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Beginners / Re: Convert US standard 115V to International 230V
« Last post by Jwillis on Today at 10:34:26 pm »I agree that the statement is a simplified explanation of how a SMPS works. But if you look at main stream switching power supplies on the market they are designed for a broad range of frequencies and input voltages. You need to choose a power supply rated for the application to which it is intended. There are SMPS's rated for medical applications. So why reinvent the wheel just get a power supply rated for your application.You are missing my point. It has nothing to do with SMPS. The point is that a bridge rectifier followed by a capacitor is highly dependent on frequency because the capacitor needs to hold enough energy to power whatever it powers during a longer time, until the next pulse to recharge it comes along. Lower the input frequency and you increase the ripple, decreasing the voltage level to which it falls. If you reduce the frequency by 50% you need to double the capacitance in order to maintain ripple and not increase voltage drop. It does not matter what follows, SMPS, linear or whatever. I have dealt with adapting 120 V, 60 Hz machines to 220 V 50 Hz, including linear PSU, motors and transformers and I am quite familiar with the issues. That was long time ago, in a previous life.
Electrolytic's standard testing is between 100Hz 20Co and 120Hz at 25Co. The DC ripple in a SMPS after rectification is either 100Hz or 120Hz.
Electrolytic capacitors show very little change to behaviour between 10Hz and 1kHz depending on temperature. So to say that there would be any significant change in behaviour between 50Hz and 60Hz at an ambient temperature of 20Co to 25Co is over thinking that a problem can occur. https://www.cde.com/resources/technical-papers/AEappGuide.pdf
The frequency of mains supply after rectification 100Hz or 120Hz depending on where you live. AND THERE IS NO SIGNIFICANT BEHAVIOUR CHANGE OF AN ELECTROLYTIC CAPACITOR BETWEEN 100Hz AND 120Hz AT 20 to 25Co It makes no damn difference whether it's on a linear supply or an SMPS. That tiny change in Value and ESR between 100Hz and 120Hz won't make a damn bit of difference to the ripple voltage. Electrolytic capacitors have as much as 20% tolerance in value and your saying that a fraction of a uF can make a significant difference to ouptut ripple? That's absurd! Just to reduce the output ripple voltage by half, the capacitance needs to double.