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Circuit protector

IP.com Disclosure Number: IPCOM000014363D
Original Publication Date: 2000-Apr-01
Included in the Prior Art Database: 2003-Jun-19
Document File: 2 page(s) / 73K

Publishing Venue

IBM

Abstract

Disclosed are circuits to avoid big rush current at power-on. Hot plugging or power-on by mechanical switch causes big rush current to de-coupling capacitor. And it could result in damage of the capacitor.

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Circuit protector

    Disclosed are circuits to avoid big rush current at power-on.
Hot plugging or power-on by mechanical switch causes big rush current to de-coupling capacitor.
And it could result in damage of the capacitor.

This protector is effective to avoid the dangerous rush current being used between DC power supply
and the main circuit..

It is applicable to Hard Disk Drive or any circuits that allows hot plugging or power-on by
mechanical switch.

Fig.1 shows one of the circuit protectors.
C1 is the de-coupling capacitor.

Even if the power voltage Vin rises in no time, Ic, the current through C1, is suppressed by Q1, Pch
enhancement type power MOS FET, that gradually becomes "ON" according to time constant determined by
R1, R2 and C2.

+12V C 2 => M ain C ircuit

VinR 1

G S R 1: 24KΩ

Q1 R2: 12KΩ

          Ic +C1: 10μF/20V R2 C 1 C2: 0.1μF

Q1: P ch Enhancem ent

P ow er M O S FET

Fig1. C ircuit P rotector 1

Fig.2 shows another example.
As same as the circuit of Fig.1, Ic, the current through C1, is suppressed by Q1, Pch enhancement
type power MOS FET.

In addition to above, this circuit can protect the main circuit from surge voltage caused at Vin
during power-on.

The surge voltage is absorbed by the FET and Vin2 rises gradually according to time constant
determined by R1, R2 and C2.

+12V Iin S D => M ain C ircuit VinR1 C 2 G Vin2

Q 1 R1: 24KΩ

                           R2: 12KΩ +C1: 10μF/20V x 2 R2 C 1 C2: 0.1μF

Q1: Pch Enhancem ent

Pow er M O S FET

Fig2. C ir...