With outputting burst switching control pulse from IC, burst enegize of the TRANS is carried out.
Voltage stabilized also at the time of a light load can be supplied.
It is the optimum IC for constituting the power-supply system for minute electric-power supply.
By this IC, the burst time of switching control pulse is decided by level of output ripple of a power-supply system.
As for the terminal 4 which is carrying out the monitor of the power-supply output-voltage value, another side is
connected to the comparator.
The standard voltage value of this comparator has hysterisis, 2.5 V and 3 V fixation. (inside IC)
Since output DC voltage of a power supply is stabilized, power-supply output voltage is detected and it feedbacks
for the terminal 4 (FB IN terminal).
When the voltage value of a terminal 4 tends to become more than 3 V, switching control pulse of a terminal 7
(pulse out) is stopped.
If pulse is stooped, in order not to control power-supply TRANS, it will stop supplying energy supplied to the output
of a power supply, and the output DC voltage of a power-supply will descend.
If output DC voltage tends to become less than (V/2.5), switching control pulse of a terminal 7 (pulse out) will be
Power-supply TRANS is made to drive and PULSE supplies energy to a power-supply output.
Then, output DC voltage rises.
Burst electric supply is realized by repeating the above-mentioned operation.
Vref 2.5 V/3 V
Figure 2 Ripple Voltage Establish (example)
Hereafter, calculation using ripple level as an example
Voltage of Vout and the terminal 2 is set output DC voltage to Vref.
Vout = Vz + VF + 1/CTR ´ R2/R1 ´ Vref
*CTR = IC/IF
*IZ = IF + IS, R3 is set up.
For example, R1 = 10 kW, R2 = R3 = 1 kW, CTR = about 1, Vz = 3.9 V, VF = 0.7 V
Vref (minimum) = 2.5 V fixation and Vref (maximum) = 3 V fixation.
Vout (minimum) = 4.85 V
Vout (maximum) = 4.9 V.
Ripple in an output is 0.05 V.
Internal oscillation circuit for obtaining output PULSE is built in.
Oscillation frequency of output PULSE can be set up by outside attachment resistance to a terminal 2.
Duty about 50% of output PULSE has been obtained.
Oscillation frequency is calculation from f = i/2 CV (Hz), I = 1 (V) /R/10, and it will be set to 25 kHz, if 20 kW is
attached to a terminal 2 outside.
Terminal voltage and R are outside attachment resistance in 1 (V).
10 is a current ratio, sets current of a terminal 2 to 1/10, and makes it the charge/discharge current of a internal
50 pF capacitor. C = 50 (pF) (built-in capacitor value) V = 2 (V) (oscillation amplitude)