MITSUBISHI SEMICONDUCTOR < STANDERD LINEAR IC >
M62281P/FP
GENERAL PURPOSE CURRENT MODE PWM CONTROL IC
Even if the timer function is not needed, latch function operates, that is, IC becomes inoperative when
the voltage of CT terminal is forced to be high voltage. Therefore, CT terminal can also be used for
OVP(over voltage protection).
When only OVP function is needed(timer latch function is not necessary), connect the resistor between
CT terminal and GND. In this case, the above mentioned charge current cannot make the voltage of CT
terminal rise up to "H" threshold, thus latch function does not operate. (Refer to Fig.5-1, 5-2)
Vcc
Vcc
OVP function operates
when photo-coupler is ON.
CT
OVP function operates
when photo-coupler is ON.
CT
Fig.5-1 Method to use timer type latch and OVP
Fig.5-2 Method to use only OVP
(3) SOFT(DUTY SET-UP) TERMINAL
The voltage of SOFT terminal determines the maximum duty.
Maximum duty can be set by connecting the resistor as in Fig.6
because the constant current compensated for temperature flows
out of this terminal.
And by connecting the capacitor between the terminal and GND,
soft start function operates. That is, we can get the gradual
increase of maximum duty at start-up.
Maximum duty is represented as:
Duty(max.)
≈
(42 * VSOFT) - 59 (%)
,where VSOFT=ISOFT * RSOFT (V), ISOFT=43µA(typ.)
If the voltage of SOFT terminal is higher than 3.53V(typ.)(upper limit
voltage of the oscillation waveform), maximum duty is internally decided
to be 90%.
Soft start time (TSOFT) is represented as:
TSOFT
≈
CSOFT * 31 * 103 (sec)
TSOFT means the time from start-up until the voltage of SOFT terminal
goes up to higher than 1.4V(typ.) (lower limit voltage of the oscillation
waveform).
Discharging circuit operative before start-up at Vcc is internally equipped
so that the soft start never fail to operate at the restart of voltage supply.
SOFT
CSOFT
VSOFT
Fig.6
Method to set up duty
and SOFT start function.
(6/9)
MITSUBISHI [ MITSUBISHI ELECTRIC SEMICONDUCTOR ]
