Browse Prior Art Database

EMI inductor size reduction and control techniques in electronic ballast using Triac based dimming control interface

IP.com Disclosure Number: IPCOM000180631D
Publication Date: 2009-Mar-13
Document File: 5 page(s) / 89K

Publishing Venue

The IP.com Prior Art Database

Abstract

ID776710

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Page 1 of 5

EMI inductor size reduction and control techniques in electronic ballast

using Triac based dimming control interface

Inventors: Subramanian Muthu, subu.muthu@philips.com

Sree Venkit, Sree.Venkit@philips.com

Abstract

Large EMI inductors are needed in the electronic ballasts that use the popular triac dimming interface, which adds cost and

increases the size of the ballast. Specifically, in a universal mains voltage design (120V to 277V), the size of the inductor is too big

to fit into the ballast housing and makes it impossible to meet the product specification requirements. This disclosure describes a new invention for a control method that allows the use of smaller inductors.

Background

Triac  or  phase  cut  dimming  is  one  of  the  commonly  used  dimming  methods.  The  Traic  dimmer  is  connected in series with the ballast and the dimming control is derived from the conduction angle or the  conducting time of the ballast. 

 

Patent No. 4,39,086 and 5,604,411  describe the methods to design and operate an electronic ballast in  a single mains voltage. EMI filters are commonly designed for a single pole frequency (which is given by  

LC

1

= , 

 Where L is the inductance and C is the total capacitance of the emi filter. In order to minimize the value  and in turn, the size of the inductor, typically a large value of C is used in typical ballast designs.  

 

When the Triac turns on, the emi capacitor is charged and the emi filter and the emi capacitor form a  resonant network. The peak value of the capacitor charging current is given by  

L

f p π

2

=   ,  

where  Vmains_at_turnon  is  the  mains  instantaneous  voltage  when  the  Triac  turns  on.     Note  that  a  higher 

value of capacitor increases the peak value of the charging current. When this value is higher than the  PFC  input  current,  the  instantaneous  mains  current  (which  is  a  combination  of  PFC  input  and  the  capacitor charging current)  may becomes zero during the negative cycle of capacitor charging cycle. The  Triac turns off when the mains current falls below its holding current, which causes stability issues.  This  issue is overcome when emi components are selected such that the following condition is met. 

V

Ic turnon

at

mains

p _

_

C

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P

load >

C

2  ,  

where Pload is load.   

US patent No. 5,604,411 discloses methods in which a combination of smaller value of capacitor and a  larger value of inductor is used to keep the frequency of the pole constant. However, this method works  very well for the ballasts ...