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Switchable transformer turns ratio in DC-DC-converter comprised in HID lamp driver

IP.com Disclosure Number: IPCOM000028089D
Publication Date: 2004-Apr-23
Document File: 2 page(s) / 73K

Publishing Venue

The IP.com Prior Art Database

Abstract

ID614305

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ID614305

Switchable transformer turns ratio

in DC-DC-converter comprised

in HID

lamp driver

Lamp drivers for HID

lamps are generally equipped with

a DC-DC-converter

such as an

up-converter or a

flyback-converter. Immediately

after ignition of the lamp, before

the discharge

has become stable, the output voltage

of

the DC-DC- converter needs

to be

much higher than later during stable operation.

In order to be able to generate the high output voltage immediately

after ignition, DC-DC- converter is usually equipped with

a transformer. This transformer enables the DC- DC-converter to generate a high output voltage. However,

the turns ratio

of the primary winding

and secondary winding

of the

transformer also determines

the duty cycle of the

switching element (Ml) during stable

operation, when the output voltage of the

DC-DC-converter is much lower.

In practise the duty cycle during stable operation is often such that

the efficiency of the

DC-DC-converter is adversely affected.

This problem

can be

     overcome by shunting the diode (Dl) comprised in the DC-DC-converter

by

a series arrangement

of second secondary winding (L3),

a

diode (D3)

and

a switching element (M4). Immediately

after ignition, switching element M4 is

controlled in the

conductive state, so that L2 and L3

together form the secondary winding

of

the transformer. Later, when the discharge

has become stable, switching element

M4

is rendered non-conductive

so that

the secondary winding

of

the transformer is form...