AN3009 Datasheet, PDF (9/36 Pages) M/A-COM Technology Solutions, Inc. – S-Parameter S2P File Format

AN3009
Designing a transition mode PFC
● Maximum output voltage (Vdc):
V_OVP = 430 V
(7)
The mains frequency generates a 2 f_L voltage ripple on the output voltage at full load. The
ripple amplitude determines the current flowing into the output capacitor and the ESR.
Additionally, a request for a certain hold-up capability can be sent to the PFC in case mains
dips occur, in which case the output capacitor also has to be dimensioned taking into
account the required minimum voltage value (Vout min) after the hold-up time (t_Hold) has
elapsed.
● Maximum output low frequency ripple:
∆V_out = 20 V
(8)
● Minimum output voltage after line drop (Vdc):
V_{out min} = 300 V
(9)
● Holdup capability (ms):
t_Hold = 10 ms
(10)
The PFC’s minimum switching frequency is one of the main parameters used to dimension
the boost inductor; here the switching frequency is considered at low mains at the peak of
the sinusoid and at full load conditions. As a rule of thumb, the switching frequency must be
higher than the audio bandwidth to prevent audible noise. Additionally, it must not interfere
with the L6564’s minimum internal starter period (reported in the datasheet). On the other
hand, if the minimum frequency is too high, the circuit shows excessive losses at a higher
input voltage and probably skips switching cycles not only at light loads. The typical
minimum frequency range is 20 - 50 kHz for wide-range operation.
● Minimum switching frequency (kHz):
f_{sw min} = 40 kHz
(11)
To properly select the power components of the PFC and dimension the heatsinks if they
are needed, the maximum operating ambient temperature around the PFC circuitry must be
known. Note that this is not the maximum external operating temperature of the entire
equipment, but rather the local temperature at which the PFC components are working.
● Maximum ambient temperature (°C):
T_ambx = 50°C
(12)
Doc ID 16032 Rev 4
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