HA17385HRP View Datasheet(PDF) - Hitachi -> Renesas Electronics

Part Name

Description

Manufacturer

HA17385HRP

High Speed Current Mode PWM Control IC for Switching Power Supply

Hitachi -> Renesas Electronics 

HA17384SPS/SRP, HA17384HPS/HRP, HA17385HPS/HRP

Features and Theory of Current Mode Control

Features of Current Mode Control

• Switch element current detection is performed every cycle, giving a high feedback response speed.

• Operation with a constant transformer winding current gives a highly stable output voltage (with

excellent line regulation characteristics, in particular).

• Suitable for flyback transformer use.

• External synchronous operation is easily achieved. (This feature, for example, is applicable to

synchronization with a forizontal synchronizing signal of CRT monitor.)

Theory of Current Mode Control

In current mode control, a PWM pulse is generated not by comparing an error voltage with a triangular

wave voltage in the voltage mode, but by changing the current limiter level in accordance with the error

voltage (COMP terminal in this IC, that is,output of the error amplifier output) which is obtained by

constantly monitoring the current of the switching device (power MOSFET) using source resistor RCS.

One of the features of current mode control is that the current limited operates in all cycles of PWM as

described by the above theory.

In voltage mode, only one feedback loop is made by an output voltage. In current mode, on the other hand,

two loops are used. One is an output voltage loop and the other is a loop of the switching device current

itself. The current of the switching device can be controlled switch high speed. In current mode control,

the current in the transformer winding is kept constant, resulting in high stability. An important

consequence is that the line regulation in terms of total characteristics is better than that in voltage mode.

AC

input

Transformar

OSC

S

RS

Flip flop

R

DC

output

Current sense

comparator

IS

2R

VCOMP

Vref

R

Error amplifier

Figure 5 Block Diagram of Current Mode Switching Power Spply

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