AN3372
Application note
STEVAL-ILH004V1: 70 W HID digital ballast
By Sebastiano Messina
Introduction
This note describes digital ballast for 70 W HID lamps (sodium or metal halide) used in
general lighting applications. The ballast is composed of a boost converter (power factor
controller PFC) working in transition mode and an inverter composed of a half bridge that
drives the lamp in low frequency square wave.
Both the half bridge and the PFC stage are managed by the ST7LITE49K2 that controls the
L6382D5, activating all the power switches.
The tests have been conduced using a 70 W metal halide lamp. With test results some
design criteria are given.
Figure 1.
STEVAL-ILH004V1 image
January 2013
Doc ID 018625 Rev 1
1/37
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Contents
AN3372
Contents
1
2
3
4
5
6
General circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Lamp power calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
STEVAL-ILH004V1: electrical scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
STEVAL-ILH004V1: layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
STEVAL-ILH004V1: BOM list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
PFC design rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1
6.2
6.3
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Power components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.3.1
6.3.2
6.3.3
6.3.4
6.3.5
Input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Boost inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Power MOSFET selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Boost diode selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7
8
9
10
11
12
Auxiliary power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
ST7 microcontroller application pin use . . . . . . . . . . . . . . . . . . . . . . . . 20
Half bridge operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Half bridge design criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Lamp operating point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
STEVAL-ILH004V1: experimental results . . . . . . . . . . . . . . . . . . . . . . . 30
12.1
12.2
12.3
Half bridge section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
PFC section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Conducted emission pre-compliance tests . . . . . . . . . . . . . . . . . . . . . . . . 33
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Contents
13
14
15
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
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List of figures
AN3372
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
STEVAL-ILH004V1 image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
150 W HID ballast block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Inductor current during charge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Inductor current during discharge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
PFC electric scheme. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Half bridge electric scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Auxiliary power supply electric scheme and microcontroller pin use . . . . . . . . . . . . . . . . . 10
Bottom view (not to scale) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Top view (not to scale) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Auxiliary power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
ST7FLITE49K2 pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Reset circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
PFC Vout sense. Resistor divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
PFC Vlamp measurements. Resistor dividers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Isense measurement circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Half bridge ZCD circuitry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Enable/disable igniter circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
PFC ZCD circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
PFC OC circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Steady-state phase: lamp current, voltage and lamp power. . . . . . . . . . . . . . . . . . . . . . . . 30
Steady-state phase: inductor current and lamp voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
STEVAL-ILH004V1: power factor vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
STEVAL-ILH004V1: THD% vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
STEVAL-ILH004V1: efficiency% vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
STEVAL-ILH004V1: peak measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
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General circuit description
1
General circuit description
The block diagram of the ballast is shown in
Figure 2.
The complete circuit is composed of
two stages:
●
●
The boost converter which regulates the DC bus voltage and corrects the power factor.
The inverter stage composed of a full bridge that converts the DC current coming from
the PFC stage into an AC current for the lamp.
Operation mode of the full bridge realizes a buck converter. The full bridge, moreover,
supplies the igniter block to generate the high voltage pulses.
Figure 2.
150 W HID ballast block diagram
To generate a square wave current in the lamp, the circuit is driven in the following way:
When low-side PMOS Ls is switched ON, the current increase linearly, the voltage across
the inductor L is:
Equation 1
V
L
=
V
dc
−
V
lamp
where:
●
●
●
V
L
= inductor voltage
V
dc
= DC bus voltage
V
lamp
= lamp voltage.
The duty cycle D is established by a current mode control circuit (see
Figure 3).
Doc ID 018625 Rev 1
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