© Semiconductor Components Industries, LLC, 2003

June, 2003 - Rev. 1

1

Publication Order Number:

AND8098/D

AND8098/D

Low−Cost 100 mA

High−Voltage Buck and

Buck−Boost Using NCP1052

Prepared by: Kahou Wong

ON Semiconductor

INTRODUCTION

This application note presents low-cost high-voltage

100 mA non-isolated power supply using NCP1052 by

buck and buck-boost topology. The NCP1052 is one of the

latest low-cost switching controllers with integrated 700 V/

300 mA power switch from ON Semiconductor. It is

primarily designed for isolated 10 W-range

flyback

converter. If isolation is not needed, the IC can also be used

as stepping-down buck and buck-boost converter for

further cost saving by removing optocoupler and replacing

the transformer by an inductor. The output current capability

is 100 mA. The possible operating range is from input range

between 20 Vdc and 700 Vdc to output range of 5.0 V or

above with 100 mA. Typical efficiency around 65% is

obtained in the 12 V buck demo board.

Advantages of the proposed circuits include:

optocoupler and replaces transformer by an inductor for

cost saving.

switches comparing to flyback. It minimizes the

switching loss and increases efficiency.

voltage with wide range between 20 Vdc and 700 Vdc.

It needs no extra supply circuit.

accommodates low-cost components such as aluminum

electrolytic capacitors and powered-iron core magnetic.

electromagnetic inference (EMI).

protection.

concerned.

The proposed buck and buck-boost converters are very

similar to each other. Their major difference is that buck

provides a positive output voltage but buck-boost provides

a negative output voltage referring to the input ground.

PRINCIPLE OF OPERATION

Figure 1 shows the proposed buck and buck-boost

converters. The rectifier circuit, which consists of capacitor

voltage. Then, the NCP1052 is self-powered up from the

When the switch inside the IC is opened, there is a voltage

across Drain (D) and Source (S) pins of the IC. If this voltage

up for the operation of the IC. Comparing to the switching

frequency jittering features to minimize EMI and

short-circuit fault timing function.

Input

Output

D

L

C

FB

DS

1

(a) Buck

Input

Output

D

L

C

FB

DS

(b) Buck-boost

Figure 1. Proposed Circuit Using NCP1052

In Figure 2a it is noted that in the buck topology the input

voltage powers up the IC through the path across the

inductor L and capacitor C. This charging path passes

APPLICATION NOTE

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