Modeling and Analysis of A Novel Igniter for HID Lamps
Weiping Zhang, Dongyan Zhang, College of Information Engineering North China of University Technology,
Beijing, P.R. China 100144 Email: [email protected]
Qiang Cheng
Datang MobileCommunications Equipment Co.,LTD Beijing, P.R. China 100083
Email:[email protected]
Abstract—Based on the special application of electronic ballast in movie and television industry, a novel electronic igniter for HID lamps has been investigated in this paper. Compared with the traditional magnetic igniter, the circuit has many good performances such as substantially less volume and weight.
The main contributions are as the followings: (1) A model of the igniter has been put forward to analyize the electronic properties; (2) Based on the proposed model, theoretical analysis and design consideration are also given; (3) A prototype for 575W HID lamp has been built . The proposed theory and approaches have been verified by the results of the experiments and computer simulation given in this paper. The experimental results show that the volume and weight of the prototype has reduced by at least 80% than of the magnetic igniter.
Keywords-novel ignite; modeling; HID lamp;
I. INTRODUCTION
High-Identity-Discharge (HID) lamps are widely used in automobile ,film industry and commercial lighting applications nowadays due to their excellent color rendering properties, high efficiency and compact size. The typical starting-up characteristics of HID lamps is shown in Fig.1. During the process of ignition, the current decreases and the voltage increases owing to the negative increment impendence of HID lamps. So, ballast should be connected in series with the lamp to limit the current in ignition process. The circuit diagram of the electronic ballast is illustrated in Fig.2. Power-Factor- Correction (PFC) circuit is a typical Boost Power factor correction circuit. DC-DC converter is a Buck step-down circuit to make sure the realizable ignition and provide the constant power control for stable operation. To eliminate the acoustic resonance, DC-AC converter is a full-bridge circuit to get a low-frequency square-wave power signal to drive the lamps. In additional, an igniter has to be required to provide a high voltage to discharge the high pressure gas in the tube when the HID lamps start up.
The conventional magnetic igniter circuit and interconnection required are illustrated in Fig.3.
When the switch S is turned on, the AC signal is applied to the input step-up transformer T1, the secondly side of T1 charge the capacitor C2 quickly. When the spark gap SG break
series resonant circuit. Because of the high resonant frequency (about 2 to 4 MHz), the voltage applied to C1 is equal to zero.
These high-frequency high-voltage pulses are stepped up in voltage through transformer T2 and then applied to the lamp terminals. An arc is struck in the HID lamp, and when suitable voltage is available across the lamp's electrodes, the lamp will ignite. When the switch S is turned off, the ignition circuit does not work and the electronic ballast provides a low-frequency constant power signal to realize the reliable operation.
The magnetic igniter has paid little attention in medium and small power application because of the great weight and bulk in low frequency operation mode.
Fig.1 Electrical characteristics of HID lamp’s igniting process
Fig.2 the diagram of the electronic ballast
Fig.3 the diagram of the magnetic ballast t/min
%
Moreover, when the switch S is interrupted to cause the multiple ignition of the lamp, the electrode loss is excessive to reduce the working life of the lamp.
In this paper, a novel electronic igniter model for HID lamps has been proposed. The weight and volume has been reduced immensely for the high frequency operation mode of T1 and T2. Furthermore, the stability of the circuit has been improved for the automatic ignition in accordance with the voltage of lamp to avoid multiple ignitions.
II. THE ELECTRICAL MODELS OF PROPOSED ELECTRONIC IGNITER FOR HID LAMPS
The diagram of the proposed electronic igniter circuit has been shown in Fig. 4.
When the lamp does not ignite, the DC-AC inverter of the ballast is no load and the output is a low frequency square AC voltage signal with 300V(RMS). By use of a bridge rectifier, the AC voltage can be transformed to DC voltage to supply power to IC with depressurizing of the zener diodes. IC is a square generator to produce high frequency pulse to drive the switch Q.
When Q is turned off, the DC voltage VDC charges the capacitor C1 via the resistor R and the primary side of T1. The C1 is almost short for the initial voltage of C1 is zero and the initial current of the primary inductor L1 of T1 is VDC/R.
Because the resistor R (≈ 1K) is greatly larger than the characteristic impedance 2 L C1 1 , the circuit is over- damped oscillation circuit and can be approximately considered as capacitor charging circuit.
When Q is turned on, the series resonant circuit consisting of the primary of the T1 and C1 transfers the energy to the secondary side of the T1 by the magnetic field coupling. The diodes D1,D2 and the capacitor C2,C3 are used to compose the half wave voltage double rectification circuit. When the voltage of the C1 increases to the breakdown voltage of spark gap, it is shorted and the series resonant circuit consisting of the C3 and the primary side of T2 transfers the energy to the secondary side of the T2 to ignite the HID lamps by the magnetic field coupling.
When the lamp has broken down in steady operation, the AC voltage is low (<100VRMS) and IC stops the pulse output.
The overall circuit of igniter also stops working immediately.
After that moment, the ballast starts to operate and provide the energy for the lamp.
Fig.4 the diagram of the proposed electronic igniter circuit
III. THE ANALYSIS OF ELECTRONIC CHARACTERISTICS In order to simplify analysis, we suppose that the start time point is the moment of the switch Q to turn off. Three models for igniter have been put forward to analyze the operation principle.
A. Model 1
Mode 1, shown in Fig.5, is an equivalent circuit for the capacitor charging.
In Fig.5, resistor R presents is the current-limiting resistance, the winding resistance of the T1 and the ESR of C1.
The rectified DC voltage Vin charges the capacitor C1 via R and L1. The voltage of the C1 grows exponentially and the output. Voltage U3 can be approximately considered as zero for the inductor L1 is almost short. After the period of
t,
0 1
1( )0 (1 )
t RC
U t =Vin −e− , where t0 is the turn-off time of the switch S.
B. Model 2
Mode 2, shown in Fig.6, is an equivalent circuit for the resonance circuit.
In Fig.6, resistor R1 presents the winding resistance of the L1, the ESR of C1 and the turn-on resistance of switch Q.
Resistor R2 presents is the winding resistance of the L2 and the ESR of C2. In fact, R1 is usually small (<1ohm) and R2 is greater than 100ohm. The second order series resonance circuit of the primary and secondary side of the transformer T1 are consisted ofC1,L1,R1 and C2,L2,R2. The initial voltage of C1 is U t1( )0 . For C2≤10C3, the circuit in Fig.6 can be further simplified as the following circuit, shown in Fig.7.
Fig.5 an equivalent circuit for the capacitor charging
Fig.6 an equivalent circuit for the resonance circuit
Fig.7 an simplified equivalent circuit for the Model 2
The following equations can be derived based on the simplified Model 2.
2 2
1 2 1
1 1 2 2 2 1 1 1
2 2
2 1
2 2 2 1 2 2
( ) 0 ( ) 0
d u d u du
L C MC R C u t
dt dt dt
d u d u
L C MC u t
dt dt
+ + + =
⎧⎪
+ =
⎨
+
⎪
⎪⎪⎩
(1)
The initial values are as the followings:
0 ) 0 ( ) 0 ( , 0 ) 0 ( , 0 ) 0 ( ) 0 ( ), ( ) 0
( 1 0 1 1 1 2 2 2 2
1 + =U t u′ + =i + C = u + = u′ + =i + C =
u L L
From the reference[1], we know that when the L C1 1=L C2 2 , the efficiency of energy transformation
η=1 and the maximum output voltage can be obtained when the coupling coefficient:
2
2 1
( 0,1, 2, 3 )
2 2 1
k n n
n n
= + = ⋅⋅⋅
+ +
The maximum output voltage of C3 is:
3 max 2 max 1 0 2
1
( ) 2 ( ) 2 ( ) L
u t u t U t
= = L .
C. Model 3
Mode 3, shown in Fig.8, is an equivalent circuit for the capacitor charging.
In Fig.8, resistor R2 presents the winding resistance of the L3, the ESR of C3 and the turn-on resistance of spark gap. The secondary L2 of the transformer T1 charges the capacitor C3 via the half wave voltage double rectification circuit. When the voltage of the C3 reach the breakdown voltage of SG, SG is shorted and C3 ， L3 and R2 form a second order series resonance circuit. C4(10~50PF) is a capacitor of the both electrodes of the HID lamp. The following equations can be derived based on Model 3 in Fig.8.
2 2
3 4 3
3 3 2 4 2 2 3 3
2 2
3 4
4 4 2 3 2 4
( ) 0 ( ) 0
d u d u du
L C MC R C u t
dt dt dt
d u
L C d u MC u t
dt dt
⎧ + + + =
⎪⎪⎨
⎪ + + =
⎪⎩
(2)
Because the structure of equation (1) and (2) is similar, it is necessary to satisfy the following conditions: L C3 3 =L C4 4 to
obtain the maximum efficiency of energy transformation and k=0.6 to get the maximum output voltage.
So, the conclusion is also agreed with model 2.
Fig.8 an equivalent circuit for lamp that has broken down
IV. SIMULATION RESULTS AND EXPERIMENTAL RESULTS After the text edit has been completed, the paper is ready for the template. Duplicate the template file by using the Save As command, and use the naming convention prescribed by your conference for the name of your paper. In this newly created file, highlight all of the contents and import your prepared text file. You are now ready to style your paper; use the scroll down window on the left of the MS Word Formatting toolbar.
Based on the theoretical analysis, the electric property of igniter has been simulated with the Pspice software.
A. A. Simulation result for model 1
Employ Model 1 do simulation to analyze the electric property of igniter. The main parameters are the followings:
C1=0.033u/630V, C2=150p/4KV, C3=1500p/4KV, L1=20uH, L2=20mH, k＝0.6, R1=0.5ohm, R2=150ohm, R=1K/5W. The simulation results are exhibited in Fig.9.
As can be seen from Fig.9, the voltage of C1 grows exponentially to DC 300V.
In fact, the duty cycle of switch Q is small (≈1.3%) and it can be simplified as capacitor charging circuit. The conclusion is consistent with theoretic results in section 3.1.
B. Simulation result for model 2 and 3
When Q is turned off, the voltage of C2 grows exponentially to DC 300V. The simulation results are shown in Fig.10.
As can be seen from Fig.10, the frequency of the series resonant circuit consisting of the L1 and C2 is approximate to
1 2
1 0.2
2 MHz
π L C = . The conclusion is consistent with theoretic results in section 3.1.
C. The relationships of output voltage of C2 and C3 with R The value of R plays an important role in the circuit.
Comparisons on voltage with different R are shown in Table 1.
TABLE1. Comparisons on the voltage with different R
R(Ω) 1 2 3 4 5
UC2(kV) 25.5 11.4 7.3 5.4 4.2
UC3(kV) 5.4 2.6 1.6 1.2 0.9
The table shows clearly that R hurts the output voltage very much, so we should keep R as small as possible.
For the real implementation, a prototype in 575W lamp in Fig. 11 with the proposed circuits has been build and tested.
Fig.10 Simulation result of model 2
Fig.11 the top view of the traditional igniter and the proposed igniter
The Fig.11 depicts the actual circuit comparison with the dimension between the traditional igniter and the proposed igniter.
The experimental results are given out from Fig.12 to Fig.14, which show orderly the driven waveform of Q, the output voltage waveform of L1, and the output voltage waveform of L4.
As can be seen from Fig. 12, the duty cycle of driven signal of Q is small (d=1.3%, f=14 kHz) to achieve the maximum voltage of C1.
Fig.12 the driven waveform of Q
Fig.13 the output voltage waveform of L1
Fig.14 the output voltage waveform of L4 The voltage waveform of L1
The voltage waveform of C3
From Fig.13 and Fig.14, it can be seen that the waveform across L1 and L4 are damped oscillation signal. When the lamp is broken down, the voltage of L4 decays immediately to avoid multiple ignitions.
V. CONCLUSIONS
A novel electronic igniter for HID lamps has been deeply studied in this paper. A few of equivalent circuits has been proposed to analyze its electric properties A prototype for 575W lamp has been made up. The proposed theory and approaches have been verified by the computer simulation and experimental results. The experimental results show that the volume and weight of the prototype has reduced by at least 80% than of the magnetic igniter. Compared with the traditional magnetic igniter, the circuit has many good performances such as substantially less volume and weight.
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