MIC9130 datasheet(9/19 Pages) MICREL

9 / 19 page

April 2005

M9999-040805

MIC9130

Micrel, Inc.

Functional Description

Micrel’s MIC9130 is a high voltage, high speed current mode

switching power supply controller. It uses a BiC/DMOS pro-

cess to achieve a high voltage input, low quiescent current

and very fast internal delay times. The MIC9130 is designed

to drive an external low side N-channel MOSFET, which

makes it suitable for controlling Boost, Flyback and Forward

converter topologies. The high voltage startup pin eliminates

the requirement for an external start up circuit. This makes

it ideal for use with Telecom converters.

Ablock diagram of the MIC9130 is shown in Figure 1. The de-

scription of the controller is divided into 6 basic functions:

• Power and bias circuitry

• High voltage start-up circuit

• VCC and bias supplies

• Enable and undervoltage monitoring circuits

• VCC and VIN UVLO

• Enable

• Oscillator and sync circuitry

• Soft-start and soft-start reset circuits

• MOSFET gate drive circuits

• Control loop operation

• Current sensing & overcurrent protection

• Slope compensation

• Error ampliﬁer

High Voltage Start Up Circuit

Many conventional Off-Line and Telecom power supplies

use an external bias resistor and zener diode to supply the

initial start-up voltage for the control IC. The control IC gets

its supply voltage from a bias winding once the power sup-

ply is running. This method has the disadvantages of extra

components (diode and power resistor), continuous power

dissipation in the resistor and a large bias capacitor, used to

supply the IC until the bias winding takes over.

The MIC9130 eliminates these problems by using an internal

depletion mode MOSFET as a pre-regulator to provide the

start-up bias voltage from the high voltage input of the power

supply. This approach eliminates the need for external start

up components and reduces the size of the controller’s bias

supply capacitor.The MOSFETis turned off once the external

bias winding takes over, which eliminates power dissipation

in the start-up circuit. In some cases, the MIC9130 may be

run directly from the input voltage rail, eliminating the need

for an external bias winding.

Transformer

Bias

Winding

VIN

180V

DEPLETION

FET

Internal

Circuitry

MIC9130

VCC

Line

THERMAL

SHUTDOWN

1.21V

VCC

UVLO

∆VPR

VPR(OFF) Depletion FET Pre-Regultor turn-off threshold

Depletion FET turn-on threshold

∆VGLO VCC Gate Lockout Hysteresis

VCC voltage when powered from VLINE

VGLO(ON) VCC gate lockout turn on threshold

Figure 2

MIC9130 Datasheet(PDF) 9 Page - Micrel Semiconductor

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