Re: Advice on LG DVD player blown power supply
Aaaand I forgot to mention one of the most important aspects regarding APFC in PSUs: the voltage boost on the primary cap.
Why have the voltage boost?
Reason #1: it makes the PSU independent of line input voltage, thus being capable of taking full range 90-260V AC operation without the need for a voltage selector switch.
Reason #2 (and this is probably the bigger one): The amount of energy stored in a capacitor determines the hold-up time. The energy stored in a capacitor is equal to:
E = 0.5 * C * (V^2)
where C is the capacitance and V is the voltage preset at the capacitor terminals
Essentially, the energy increases proportionately with the capacitance and proportionately with the square of the voltage. So doubling the capacitance will double the energy storage. But doubling the voltage will *quadruple* the energy storage!
This allows PSU manufacturers to achieve the same hold-up time with smaller input bulk capacitors (lower capacitance, but higher voltage). Smaller input capacitors = lower cost. So in short, it is also cost-cutting measure.
Aaaand I forgot to mention one of the most important aspects regarding APFC in PSUs: the voltage boost on the primary cap.
Why have the voltage boost?
Reason #1: it makes the PSU independent of line input voltage, thus being capable of taking full range 90-260V AC operation without the need for a voltage selector switch.
Reason #2 (and this is probably the bigger one): The amount of energy stored in a capacitor determines the hold-up time. The energy stored in a capacitor is equal to:
E = 0.5 * C * (V^2)
where C is the capacitance and V is the voltage preset at the capacitor terminals
Essentially, the energy increases proportionately with the capacitance and proportionately with the square of the voltage. So doubling the capacitance will double the energy storage. But doubling the voltage will *quadruple* the energy storage!
This allows PSU manufacturers to achieve the same hold-up time with smaller input bulk capacitors (lower capacitance, but higher voltage). Smaller input capacitors = lower cost. So in short, it is also cost-cutting measure.
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