9

Voltage Regulators

AN8032

s Application Notes (continued)

[2] Operation descriptions (continued)

1. Normal control (continued)

2) Control outline description (Refer to figure 2 and figure 3.) (continued)

(8) Switching device turn-on

By resonance, the turn-on signal is sent to the switching device, timed with the sub-coil voltage when

it swings from high to low.

(9) Continuation of operation

When the switching device is turned on, current flows in the inductor so that the above operation is

repeated.

<Summary>

• When the excitation energy of inductor is lost and the free resonance is started, the switching device turns on.

• The switching device will turn off when the following two elements cross each other: The product of the input

• The fluctuation of input voltage and load current is controlled by changing the peak value height of switching

device current.

• The purposes of mixing two signals by using the multiplier are:

 to stabilize the control system

 to reduce the number of components required

3) Description of each function

• Function

It detects the discharge of the excitation energy of the inductor (reset operation) and turns on the power

MOSFET at the next cycle.

• Method

When the inductor is reset, the sub-coil provided on the inductor (bias winding) starts free resonance.

It is difficult from the view point of withstanding voltage to input this voltage directly to the IC. For this

• Function of upper limit voltage clamper

Function of lower limit voltage clamper

case of monolithic IC, malfunction (such as latch-up) occurs when the terminal voltage decreases to a value

• IC inside

However, if the off signal has been given to the power MOSFET by the overvoltage protection func-

tion, this function precedes the former.

0 V

Power MOSFET

(1.5 V typ.)

OFF

ON

OFF