MP110 – 900V OFFLINE SWITCHING REGULATOR

OPERATION

The MP110 incorporates all the necessary

features required by a reliable switch mode

power supply. The proprietary 900V monolithic

integration enables a highly integrated power

supply solution. It has burst mode operation to

minimize the stand-by power consumption at light

load. Protection features such as auto-recovery for

over-load protection (OLP), short-circuit protection

(SCP), over-voltage protection (OVP), and thermal

shutdown for over-temperature protection (OTP) -

contribute to a safer converter design with minimal

external components. .

PWM Operation

The MP110 employs peak current mode control.

On the secondary side, the output voltage is

divided down by a voltage divider network. This

voltage is fed back to the primary side as voltage

on the FB pin using an opto-coupler and a shunt

regulator. The voltage at the FB pin is compared to

switching current. The integrated MOSFET turns

on at the beginning of each clock cycle. The current

in

the

transformer

magnetizing

inductance

increases until it reaches the value set by the FB

voltage, and then the integrated MOSFET turns off.

Initially, the IC is driven by the internal current

source which is drawn from the high-voltage

Drain pin. The IC starts switching and the internal

high-voltage current source turns off as soon as

typical value). At this point, the supply of the IC is

taken over by the auxiliary winding of the

typical value), the regulator stops switching and

the internal high-voltage current source turns on

again.

The lower threshold of VCC UVLO decreases from

value) when fault conditions happen, such as SCP,

OLP, OVP, and OTP.

Soft-Start

The MP110 implements an internal soft-start

circuit in order to reduce stress on the primary

side MOSFET, secondary diode and smoothly

establish the output voltage during start-up. The

internal soft-start circuit gradually increases the

primary

current

sense

threshold

which

determines the MOSFET peak current during

start-up. The pulse width of the power switching

device is progressively increased to establish

correct operating conditions until the feedback

control loop takes charge.

Figure 3: Soft Start

Switching Frequency

The switching frequency of MP110 can be set by

FSET pin. The frequency can be set by a resistor

between FSET pin and GND pin. The oscillator

frequency can be attained below:

S

9

12

FSET

FST

1

f

R

200 10

112.5 10

V

−−

=

×

+

×

×

Hz

Over Voltage Protection (OVP)

constant filter allows the MP110 to enter OVP

during an over-voltage condition, typically when

operation after the fault disappears.

MP110 Rev. 1.01

www.MonolithicPower.com

12

6/4/2014

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