EMI inductor size reduction and control techniques in electronic ballast using Triac based dimming control interface
Publication Date: 2009-Mar-13
The IP.com Prior Art Database
EMI inductor size reduction and control techniques in electronic ballast
using Triac based dimming control interface
Inventors: Subramanian Muthu, email@example.com
Sree Venkit, Sree.Venkit@philips.com
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.
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
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
f p π
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.
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 ...