cd00173891

AN2640
Application note
Intelligent multipower digital ballast for
fluorescent lamps
Introduction
Fluorescent lamps are highly popular due to their luminous efficiency, long life and color
rendering. These lamps need external circuitry to compensate for their negative resistance
characteristic. This circuitry is called "ballast". The simplest ballast is a magnetic inductor
connected in series at the lamp. The electronic ballast with respect to the magnetic one
offers the following advantages:
■
Better efficiency
■
Increased lamp life
■
Lightweight with smaller dimensions
■
Better lamp power control
For these reasons, in the last years there has been a shift in the market towards the use of
electronic ballasts with dedicated drivers and controllers. Today, thanks to microcontrollers,
it is possible to add intelligence into the circuit. Instead of having a dedicated circuit for each
lamp with a single ballast it is possible to drive many different lamp groups. This application
note describes an electronic ballast that is able to recognize lamps within the T5 fluorescent
family such as 24 W, 39 W, 54 W and 80 W. It consists of two main blocks:
■
A boost converter (Power Factor Controller PFC) working in transition mode (fixed TON
and variable frequency)
■
An inverter in half-bridge configuration working in zero voltage switching
Both ballast and PFC stages are controlled by the ST7FLIT19B that offers its entire signal to
the L6382D5 which provides the right voltage and current levels for the Power MOSFET.
This system after tube recognition sets the right parameter and drives the lamp correctly.
Figure 1 shows the ballast block diagram.
Figure 1.
January 2008
Ballast block diagram
Rev 1
1/36
www.st.com
Contents
AN2640
Contents
1
PFC section design criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2
Boost inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3
PFC devices selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3.1
Power switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.2
Rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2
Half-bridge design criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3
ST7LIT19BF1 - 8-bit MCU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4
5
3.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2
Use of the pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
L6382D5 - power management units for microcontrolled ballast . . . . 18
4.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.2
Use of the pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Recognition technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.1
6
Code implementation on microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . 23
Board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.1
Electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.2
Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.3
Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.3.1
From system switch on to ballast run . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.3.2
PF, THD and ballast efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.3.3
Electromagnetic compatibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
9
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2/36
AN2640
List of figures
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.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Ballast block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
The step-up "Boost" regulator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Inductor current waveform and MOSFET timing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
24 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
39 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
54 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
80 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
ST7LITE1xB general block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
ST7LITE1xB 20-pin SO and DIP package pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
PFC overcurrent detection circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
PFC Vout sense circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
PFC Vin waveform circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Average current circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Lamp type detection circuit (a) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Lamp type detection circuit (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Peak lamp voltage circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Average lamp voltage circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Lamp detection circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Zero-current detection circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
L6385Dx block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Typical L6385Dx use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Circuit connected at CSI pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Ballast operation sequence flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
STEVAL-ILB004V1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
L6382 startup sequence and ballast start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
24 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
39 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
54 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
80 W lamp power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Test equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
24 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
39 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
54 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
80 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3/36
PFC section design criteria
AN2640
1
PFC section design criteria
1.1
Introduction
The following data are needed to calculate the input and output capacitors and the boost
inductance:
●
Mains range (Virms(min) and Virms(max))
●
Regulated DC output voltage (Vo)
●
Rated output power (Po)
●
Minimum switching frequency (fswmin)
●
Maximum output voltage ripple (∆Vo)
●
Expected efficiency (η)
●
Maximum mains RMS current (Irms)
●
Rated output current Io
Input capacitor
The input capacitor that has been chosen is 470 nF. Using this value good performances in
terms of power factor and current distortion have been obtained with the lamps that can be
driven.
Output capacitor
The output bulk capacitor (Co) selection depends on the DC output voltage and the ripple on
it. For lighting applications the ripple, 2*∆Vo, is typically 5% of the output voltage.
The output bulk capacitor has been calculated using the following formula:
Equation 1
Io
Po
C o ≥ ---------------------------------------- = -----------------------------------------------------4 ⋅ π ⋅ f ⋅ ∆V o 4 ⋅ π ⋅ f ⋅ V o ⋅ ∆V o
Where:
●
f= 50 Hz (mains frequency)
●
Vo= is the output voltage (420V)
●
∆Vo= (½ ripple peak-to-peak value at 5%) is 10.5 V
●
Io= is the output peak current capacitor
●
Po(max)= (lamp specifications)
therefore
4/36
●
Co ≥ 30.7 µF
●
Co was selected as 47 µF
AN2640
1.2
PFC section design criteria
Boost inductor
To define the PFC inductor several parameters are involved. The formula used to obtain the
inductance value is:
Equation 2
2
V irms ( min ) ⋅ ( V o – 2 ⋅ V irms ( min ) )
L = ---------------------------------------------------------------------------------------------2 ⋅ f sw ( min ) ⋅ P i ⋅ V o
Where
●
fsw(min)= 35 kHz
●
Virms(min)= 185 V
●
Pi= Po/η
●
Po is the lamp power
●
η is the estimated efficiency (0.9)
For multipower ballast the inductance calculation must be performed adopting the maximum
lamp power (85 W).
Using these parameters L = 1.95 mH.
An inductance value of 2 mH ± 5% is chosen.
The switching frequency of PFC power transistor can be obtained using the following
formula:
Equation 3
2
V irms ⋅ ( V o – 2 ⋅ V irms ⋅ sin Θ)
1
f sw = -------------------------- ⋅ -----------------------------------------------------------------------------------------Vo
2 ⋅ L ⋅ Pi
Notice that increasing the inductance value L decreases the PFC switching frequency.
1.3
PFC devices selection
The PFC is a step-up "Boost" regulator, therefore in normal operation the energy is fed from
the inductor to the load and then stored in the output capacitor
Figure 2.
The step-up "Boost" regulator
5/36
PFC section design criteria
Figure 3.
1.3.1
AN2640
Inductor current waveform and MOSFET timing
Power switch
It must be:
●
VDSS > Vout
●
ID > IT(pk)
Equation 4
V out = 420 V
Equation 5
P omax = 85 W
Equation 6
η = 0.9
Equation 7
P omax
P imax = ---------------- ≅ 95 W
η
Equation 8
V imin ( rms ) = 185 V
Equation 9
P imax
I Lmax ( rms ) = -------------------------- ≅ 510 mA
V imin ( rms )
Equation 10
I L ( pk ) = 2 ⋅
6/36
2 ⋅ I Lmax ( rms ) ≅ 1.5 A
AN2640
PFC section design criteria
For safety reasons we must choose a device with:
●
VRRM 20% more Vout, that is, 504 V
●
IF(av) 3 times more Iout, that is, 4.5 A (to be considered transient current)
The STP6NK60Z, a Zener-Protected SuperMESH™ MOSFET, satisfies these
specifications.
Table 1.
1.3.2
STP6NK60Z general features
VDSS
RDS(on)
ID
600 V
< 1.2 Ω
6A
Rectifier
It must be:
Equation 11
V RRM > V out = 420 V
Equation 12
P omax
I F ( av ) > I out = ---------------- ≅ 200mA
V out
For safety reasons we must choose a device with:
●
VRRM 20% more Vout, that is, 504 V
●
IF(av) 3 times more Iout, that, is 600 mA
The STTH1L06, a turbo 2 ultrafast, high-voltage rectifier, was selected because it is
especially suitable as a boost diode in discontinuous or critical mode power factor
corrections.
Table 2.
STTH1L06 general features
IF(AV)
VRRM
VF(typ)
trr(max)
1A
600 V
1.05 V
80 ns
7/36
Half-bridge design criteria
2
AN2640
Half-bridge design criteria
The design of the half-bridge section involves dimensioning the resonant components:
ballast inductor and startup capacitor. The component design is not an easy matter and
several parameters must be considered, especially when different lamps must be driven
with the same resonant components. The main parameters to be considered are preheating
current and voltage, maximum preheating voltage, maximum ignition voltage and run lamp
voltage. For each lamp the transfer function was plotted in order to evaluate the operating
point in terms of preheating and run frequency. The resonant inductor has been chosen as
1.2 mH and the startup capacitor has been chosen as 10 nF.
8/36
Figure 4.
24 W lamp power
Figure 5.
39 W lamp power
AN2640
Half-bridge design criteria
Figure 6.
54 W lamp power
Figure 7.
80 W lamp power
During the preheating phase in this system the half-bridge works at fixed frequency and the
selected preheating frequency is the best choice according to the selected lamp
specifications.
This working frequency guarantees the right preheating current for all lamps that can be
driven by this system.
After tube recognition the microcontroller sets the right run frequency for the connected
lamp.
9/36
ST7LIT19BF1 - 8-bit MCU
3
ST7LIT19BF1 - 8-bit MCU
3.1
Introduction
AN2640
The ST7LIT19BF1 is a member of the ST7 microcontroller family.
All ST7 devices are based on a common industry-standard 8-bit core, featuring an
enhanced instruction set.
Figure 8.
ST7LITE1xB general block diagram
The ST7LIT19BF1, moreover, is a microcontroller designed for lighting applications.
10/36
AN2640
ST7LIT19BF1 - 8-bit MCU
The following are a few main features that make this microcontroller suitable for this scope:
●
Internal RC oscillator with 1% precision at 8 MHz CPU frequency
●
32 MHz timer counter clock with two independent counters for half-bridge and PFC
management
●
Analog PFC zero-current detection and half-bridge dead time generation
●
Analog comparator
●
10-bit A/D Converter with 7 channels and the possibility to use an amplifier (fixed gain
8) between the input and converter
●
2 timers with 1 ms or 2 ms time base to provide timing to the system management
Figure 9.
3.2
ST7LITE1xB 20-pin SO and DIP package pinout
Use of the pins
●
Pin 1: GND
●
Pin 2: VCC. The microcontroller is supplied by means of this pin. The voltage is
generated by the L6382D5 device. To prevent noise in this pin a 100 nF capacitor must
be soldered as close as possible between this pin and GND.
●
Pin 3: reset (not used). It is advisable to connect a small capacitor to avoid undesired
reset of the micro between this pin and GND.
●
Pin 4: COMPIN+. This pin is used to protect against overcurrent on the PFC Power
MOSFET and inductor. When the current exceeds 2 A, the comparator inside the MCU
stops the ballast without using the MCU core. Figure 10 shows the detection circuit.
11/36
ST7LIT19BF1 - 8-bit MCU
AN2640
Figure 10. PFC overcurrent detection circuit
●
Pin 5: AIN1 - PFC Vout sense. This pin is used to perform the PFC Vout voltage
protection and regulation. Figure 11 shows the circuit for the PFC Vout sense.
Figure 11. PFC Vout sense circuit
In this pin the MCU reads the voltage on the C6 capacitor and converts this value to a
digital one which is proportional to the DC bus voltage.
●
12/36
Pin 6: AIN2 - PFC Vin waveform. The circuitry shown in Figure 12 measures the input
voltage and the voltage across R5-C4 is used by the MCU to understand the
instantaneous main voltage.
AN2640
ST7LIT19BF1 - 8-bit MCU
Figure 12. PFC Vin waveform circuit
●
Pin 7: AIN3 - average current. In the ballast during the run state the inductor current is
controlled by monitoring the voltage across Rsense.
Figure 13. Average current circuit
The voltage across C22 is proportional to the current that flows in the Power MOSFET which
is related to the discharge current in the tube.
When ballast frequency is changed, a current regulation is performed.
●
Pin 8: AIN4 - lamp type detection. This circuit is used to distinguish between lamps
having different cathode resistances. When the NPN transistor Q5 is in the cutoff
region, the PNP transistor Q4 is also, producing a voltage close to zero at pin 8 "Lamp
Type Detection". When the NPN transistor Q5 is in the saturation region, the PNP
transistor Q4 is also, producing at pin 8 "Lamp Type Detection" a voltage that depends
on the resistor of the lamp electrodes. Normally the NPN transistor Q5 is kept in the
cutoff region so that the whole circuit is disabled. This circuit is enabled just to
recognize the lamp family, after recognition, it is disabled.
13/36
ST7LIT19BF1 - 8-bit MCU
AN2640
Figure 14. Lamp type detection circuit (a)
Figure 15. Lamp type detection circuit (b)
●
14/36
Pin 9: AIN5 - peak lamp voltage. Using the circuit shown in Figure 16, it is possible to
measure the voltage across the lamp.
AN2640
ST7LIT19BF1 - 8-bit MCU
Figure 16. Peak lamp voltage circuit
The resistors R31 ÷ R34 form a voltage divider and the voltage across R36-C23 is
used to control the voltage on the lamp during all lamp phases.
●
Pin 10: AIN6 - average lamp voltage
Figure 17. Average lamp voltage circuit
The circuit shown in Figure 17 is used to detect asymmetrical lamp voltage when lamp
rectification happens.
●
Pin 11: PA7 - lamp detection
15/36
ST7LIT19BF1 - 8-bit MCU
AN2640
Figure 18. Lamp detection circuit
The circuit shown in Figure 18 connected at this digital input is used to detect the lamp
presence. If the lamp is present, the cathode is in parallel to R30 and C17 and the
voltage across C17 is low. The low voltage is used by the micro to sense the lamp
presence. If the lamp is not present or the cathode is broken, the voltage across C17 is
high (5 V) and the MCU stops the ballast.
●
Pin 12: PA6 (not used). This pin is connected at micro VCC voltage by means of a 10 kΩ
resistor because this pin is also used as ICCCLK and during normal operation it must
be pulled up, internally or externally (external pull-up of 10 kΩ is mandatory in noisy
environments).
●
Pin 13: PWM3 - PFC gate driver. This pin is connected to the L6382 driver in order to
control the PFC PMOS.
●
Pin 14: PA4 (not used). This pin is connected to micro VCC voltage by means of a 10 kΩ
resistor because an unused pin must be kept at a fixed voltage. It can be left
unconnected if it is configured as output (0 or 1) by the software.
●
Pin 15: PWM1 - High side input. This pin is connected to the L6382 driver and the
signal is used to drive the High side PMOS.
●
Pin 16: PWM0 - Low side input. This pin is connected to the L6382 driver and the signal
is used to drive the High side PMOS
●
Pin 17: PA1 - CSO. This pin is connected to the CSO pin of the L6382 and can be used
to lock the ballast when the CSI pin is high.
●
Pin 18: LTIC - Zero-current detect
Figure 19. Zero-current detection circuit
16/36
AN2640
ST7LIT19BF1 - 8-bit MCU
The zero-current detection circuit switches the external MOSFET ON as soon as the voltage
across the boost inductor reverses or the current through the boost inductor goes to zero.
This feature allows the transition mode operation. The signal for ZCD is obtained with an
auxiliary winding on the boost inductor. The secondary winding is connected to the LTIC pin
by means of a resistor. The MCU detecting negative dv/dt gives the turn-on signal to the
driver for the Power MOSFET commutation.
●
Pin 19: PC1 (not used). This pin is connected to micro VCC voltage by means of a 10
kΩ resistor because an unused pin must be kept at a fixed voltage. It can be left
unconnected if it is configured as output (0 or 1) by the software.
●
Pin 20: Lamp Type Detection Circuit Enable. This pin is used to enable the "Lamp Type
Detection Circuit".
17/36
L6382D5 - power management units for microcontrolled ballast
4
L6382D5 - power management units for
microcontrolled ballast
4.1
Introduction
AN2640
This driver allows powering efficiently all the ICs (PFC, microcontroller, driver) in all
conditions and allows the microcontroller to drive the MOSFET (both half-bridge and PFC)
without using numerous different drivers.
Figure 20. L6385Dx block diagram
The L6382D5 ICs (Figure 20) include 3 MOSFET driving stages (for PFC, for the halfbridge, for the preheating MOSFET) plus a power management unit (PMU) able to supply
the microcontroller in any condition by means of a voltage reference available at a pin. It has
a precise reference voltage (5VDC ±2%, overall temperature range) able to provide up to
30 mA to supply the microcontroller.
The L6382D5 also integrates a function that regulates the IC supply voltage without the
need of any external charge pump and optimizes the current consumption (Figure 21). The
L6382D5 reduces the application bill of materials because many different tasks (regarding
drivers and power management) are performed by a single IC, which of course improves
application reliability.
18/36
AN2640
L6382D5 - power management units for microcontrolled ballast
Figure 21. Typical L6385Dx use
Another feature of the driver is the internal interlocking that avoids cross-conduction in the
half-bridge FET's. If by chance both HGI and LGI inputs are brought high at the same time,
then LSG and HSG are forced low as long as this critical condition persists.
A current sense is also available in this driver. When the voltage on pin CSI overcomes the
internal comparator reference (0.56 V, typ), the block latches the fault condition. In this state
the OCP block forces both HSD and LSD signals low while CSO is forced high so that it can
be sent to an input pin of the microcontroller that, based on its programming, starts the
proper protection sequence. The CSO output remains latched high until LSI and HSI are
simultaneously low (e.g. during dead time) and CSI is below 0.5 V. This function is suitable
to implement an overcurrent protection or hard-switching detection by using an external
19/36
L6382D5 - power management units for microcontrolled ballast
AN2640
sense resistor. As the voltage on pin CSI can go negative, the current must be limited below
2 mA by external components.
4.2
Use of the pins
A short description of each pin function is given below.
20/36
●
Pin 1: PFI. This pin receives a digital input signal from the ST7 micro to control the PFC
gate driver. We advise connecting a capacitor for noise filtering between this pin and
GND. In this application a 33pf capacitor is used.
●
Pin 2: LSI. This pin receives digital input signal from the ST7 to control the low side
switch in the ballast.
●
Pin 3: HSI. This pin receives digital input signal from the ST7 to control the high side
switch in the ballast.
●
Pin 4: HEI (not used). This pin receives digital input signal from the ST7 to control the
HEG driver.
●
Pin 5: PFG. This pin is able to drive an external MOSFET with a sink current capability
of 120 mA and a source current capability of 250 mA. A 10 Ω resistor is connected
between this pin and the Power MOSFET gate to reduce the peak current.
●
Pin 6: not connected
●
Pin 7: TPR. This pin is connected by means of an RC net to the half-bridge midpoint in
order to form a charge pump circuit charging the capacitor connected to the VCC pin. In
this application a capacitor of 1 nF at 630 V and a resistor of 44 Ω (2 x 22 Ω) have been
mounted. The high voltage capacitor in this connection also performs the snubber
function in the half-bridge section limiting the slope during the voltage variation.
●
Pin 8: GND. On the GND traces it is better to keep separate power traces from the
signal and a star connection of these tracks is advisable.
●
Pin 9: LSG. This pin is connected to the Power MOSFET gate of the low side of the
half-bridge. This pin has 120 mA as source and sink current capability. A 33 Ω resistor
is connected between this pin and the MOSFET gate to limit the peak current. At turnoff
a net composed of a diode and a 33 Ω resistor reduces the resistance which decreases
the turnoff time.
●
Pin 10: VCC. This pin provides the supply voltage to the driver. A capacitor of 47 µF is
connected between this pin and GND and in parallel another small capacitor is
mounted.
●
Pin 11: BOOT. This pin provides the supply voltage at the high side gate driver. A
100 nF capacitor is connected between this pin and the out pin of the driver. This
AN2640
L6382D5 - power management units for microcontrolled ballast
capacitor is supplied thanks to a patented structure that replaces an external diode
connected between this capacitor and VCC.
●
Pin 12: HSG. The same as pin 9 but is able to drive the half-bridge high side Power
MOSFET gate.
●
Pin 13: OUT. This pin is the high side floating ground and it is connected at the midpoint
of the half-bridge.
●
Pin 14: not connected
●
Pin 15: HVSU. This pin allows driver startup and two resistors of 10 Ω are connected at
the DC bus according to the Vref current requirement.
●
Pin 16: not connected
●
Pin 17: HEG (not used)
●
Pin 18: CSO. This pin is the output of the current sense comparator. During normal
operation this pin is forced low, but if the voltage on the CSI pin exceeds 0.55 V this pin
is high with 5 V logic level.
●
Pin 19: CSI. This is the input of the current sense comparator.The circuit that is
connected at this pin is shown in Figure 22. During the operating mode if overcurrent
occurs in the half-bridge, the voltage on the R28 resistor increases and when it
exceeds 0.55 V, the L6382 forces both half-bridge drivers low. This condition remains
until the input signals LGI and HGI are low simultaneously (dead time) or Vcc is below
the undervoltage lockout.
Figure 22. Circuit connected at CSI pin
The capacitor C20 is used to filter the voltage on the CSI pin.
●
Pin 20: Vref. This pin provides a precise voltage reference of 5 V with a current
capability up to 30 mA. This voltage is used to supply the ST7 microcontroller which
avoids adding external components. To ensure voltage stability and prevent noise, a
220 nF capacitor is recommended between this pin and GND.
21/36
Recognition technique
5
AN2640
Recognition technique
To identify the connected lamp, the power must be evaluated by measuring both the lamp
voltage and current.
In this way, by multiplying these measurements, it is possible to obtain the lamp power:
Equation 13
P lamp = V lamp ⋅ I lamp
With the evaluation board based on STMicroelectronics' ST7FLIT19BF1 MCU and L6382D5
driver, the lamp power measurements can be easily calculated. Our proposal is based on a
patented method that evaluates the PFC TON. The PFC is a boost converter working in
transition mode (TM). In the transition mode operation the boost converter works with a fixed
switch conduction time, TON, and variable frequency.
To measure the lamp power the constant TON is evaluated and moreover the TON is
proportional at the load power as shown in the following relationship:
Equation 14
2⋅ L⋅ P
T ON = ---------------------------o2
V inr
Where:
●
TON is the PFC switch conduction time
●
L is the PFC inductor value
●
Vinrms is the RMS AC input voltage
●
Po is the load power, that is, the lamp power
This technique provides a key advantage of obtaining the lamp power information by directly
reading the PFC conduction time without multiplier evaluations in the board.
When the mains is switched ON the microcontroller performs a measurement on the AC
input voltage. After this phase it starts the half-bridge. The PFC is activated during this initial
phase to distinguish the family type and a cathode resistance measurement is performed to
select the lamp type.
After this selection, the preheating phase is performed until the ignition phase turns the
lamp on.
After the ignition the connected lamp is recognized and starts the run phase.
Using the described technique it is simple to calculate the lamp power. Experimental results
have confirmed this data.
22/36
AN2640
5.1
Recognition technique
Code implementation on microcontroller
Figure 23. Ballast operation sequence flowchart
Start
Clear previous error information
Oscillator Init
Enable Interrupts
Port Init
VIN Recognize
Analog Comparator Init
ADC Init
Lamp Detection
Lite Timer Init
Ballast Control
Auto Reload Timer Init
PFC Control
PFC Init
Is the lamp
connected?
No
Yes
23/36
Board description
6
Board description
Figure 24. STEVAL-ILB004V1
24/36
AN2640
1n
275VAC
C2
J5
2
1
R28
820
AverageCurrent
PFC VinWaveform
PFC Vout Sense
PFC OC
10nF
C10
AverageLampVoltage
PeakLampVoltage
LampTypeDetection
RESET
VDC-5V-programm.
CSI
AverageCurrent
AC
L
N
PE
J1
C9
220nF
C20
1n
C22
470n
Out pin
1nF
630V
C8
3
+
+
+
+
+
J3
C3
+
+
+
+
+
2
4
6
8
10
R5
18k
R4
750k
R3
750k
R46
0.6W 22
R16
0.6W 22
ST7LITE1B 20pin
RESET
C27
10p
C26
10p
100p
C4
20
19
18
17
16
15
14
13
12
11
R43
10k
10k
1
2
3
4
5
6
7
8
9
10
C12
100nF
10k
R45
10p
C25
C11
+ 47uF
35V
R44
D4
T2
VREF
CSI
CSO
HEG
NC
HVSU
NC
OUT
HSG
BOOT
LampPresence
PFC Gate Driver
High Side Input
Low Side Input
10p
2
1N4007
D12
2.0mH
20
19
18
17
16
15
14
13
12
11
R22 33
10
R7
27k
C28
R6
L6382
PFI
LSI
HSI
HEI
PFG
NC
TPR
GND
LSG
VCC
U2
PFC Mosfet Gate
PFC VinWaveform
PFC Zero Current Detect
PFC Mosfet Gate
Low Side Input
High Side Input
PFC Gate Driver
470n 275VAC
OSC1/CLKIN/PC0
OSC2/PC1
PA0(HS)/LTIC
PA1(HS)/ATIC
PA2(HS)/ATPWM0
PA3(HS)/ATPWM1
PA4(HS)/ATPWM2
PA5(HS)/ATPWM3/ICCDATA
PA6/MCO/ICCCLK/BREAK
PA7(HS)/COMPOUT
ICC-programmer
1
3
5
7
9
U1
D13
STTH1L06A
RsenseCurrent
Vss
Vdd
RESET
COMPIN+/SS/AIN0/PB0
SCK/AIN1/PB1
MISO/AIN2/PB2
MOSI/AIN3/PB3
COMP-/CLKIN/AIN4/PB4
AIN5/PB5
AIN6/PB6
DC5V
1
2
3
4
5
6
7
8
9
10
1
RsenseCurrent
2x47mH
3
1
3k9
R27
T1
4
2
J4
jump-prog/run
10k
R24
R2
1M
350V
4
+
2
BRIDGE RB156
CSO
4n7
1.8k
R52
R21 10
R19 10
1k
R14
R51
47k
R47
47k
RsenseCurrent
2
STTH1L06
D14
0.6W 0
R18
2n7
C5
C6
PFC OC
NTC1
10
LampTypeDetection Circuit
1k
Lamp Type Detection Circuit Enable
10n
C14
1
PFC Vout Sense
R10
CSO
C13
50V 100nF
CSI
R9
0.5
2
STTH1L06
D2
STP6NK60Z
1
PFC Zero Current Detect
DC5V
Q1
1
R8
47k
1
8
1
D7
3
5
R1
1M
350V
1
2
3
1
2
2
3
C1
220n
275VAC
R49
10k
Q5
BF420
Q4
BF421
R13
10k
R12
750k
R11
750k
10k
R54
22uF 450V
C7
R23
1
2W,1%
1.2mH
L1
C23
68n
C30
330n
R36
22k
PeakLampVoltage
Out pin
R48
3.3k
Vcap
470n
C18
AverageLampVoltage
LampTypeDetection Circuit
Q3
STP6NK60Z
Q2
STP6NK60Z
+
DC400V
1M
R29
R40
2k2
R39
220k
R38
220k
1N4148 SMD
D6
C19
4n7
100V
LampPresence
DC5V
LampTypeDetection
C17
10n
R30
10k
R53
100nF
400V
C15
75k
R35
R41
2k2
1M
DC5V
R37
220k
Vcap
1
4
FUSE
2
T5 Lamps
3
J2
R34
120k
R33
330k
R32
330k
R31
330k
Vcap
C16
10n
1600V
6.1
F1
AN2640
Board description
Electrical schematic
Figure 25. Electrical schematic
25/36
Board description
AN2640
6.2
Bill of materials
Table 3.
BOM
Item Qty
Reference
Part / value
Voltage Watt
Type
275 Vac
EPCOS - order code B32922C3224K
1
1
C1
220 nF
2
1
C10, C14
10 F
3
1
C11
47 µF
35 V
Electrolytic
4
2
C12, C13
100 nF
50V
Ceramic
5
2
C16
10 nF
1600 V
EPCOS - order code B32653A1103J
6
1
C15
100 nF
400 V
Polyester
7
1
C17
10 nF
50 V
Ceramic
8
2
C18, C22
470 nF
50 V
Ceramic
9
1
C19
4.7 nF
100 V
Ceramic
10
1
C2
1 nF
275 Vac
Y2 capacitor
11
1
C20
1 nF
50 V
Ceramic
12
1
C23
68 nF
50 V
Ceramic
13
3
C25, C26, C28
10 pF
50 V
Ceramic
14
1
C27
10 pF
50 V
Ceramic
15
1
C3
470 nF
275 Vac
Polyester
16
1
C30
330 nF
50 V
Ceramic
17
1
C4
100 pF
50 V
Ceramic
18
1
C5
2.7 nF
50 V
Ceramic
19
1
C6
4.7 nF
50 V
Ceramic
20
1
C7
47 µF
450 V
Electrolytic
21
1
C8
1 nF
630 Vdc
Polyester
22
1
C9
220 nF
50 V
Ceramic
23
1
D12
1N4007
1 A 1000 V
General purpose rectifier
24
3
D2, D13, D14
STTH1L06A
1 A 600 V
ST Microelectronics turbo 2 ultrafast
high-voltage rectifier
25
2
D4, D6
1N4148
200 mA 100 V
Small signal diode
26
1
D7
BRIDGE RB156
27
1
F1
Fuse 2 A, 250 V
28
1
L1
1.2 mH ± 5%
29
1
NTC1
10
30
3
Q1, Q2, Q3
STP6NK60Z
26/36
Ceramic
Bridge rectifier
250 V
VOGT PFC choke EVD25
Part nr. SL0606302101
1 Ω / 6 A 600 V
STMicroelectronics
Zener-protected SuperMESH™
MOSFET
AN2640
Table 3.
Item Qty
Board description
BOM (continued)
Reference
Part / value
Voltage Watt
Type
31
1
Q4
BF421
500 mA 300 V
Small signal PNP transistor
32
1
Q5
BF420
500 mA 300 V
Small signal NPN transistor
33
3
R1, R2, R29
1 MΩ
34
2
R10, R14
1 kΩ - 1%
35
5
R13, R24, R30,
R49, R54
10 kΩ - 1%
36
2
R16, R46
22 Ω
37
1
R18
0Ω
38
1
R22
33 Ω
39
1
R23
1 Ω - 1%
40
1
R27
3.9 kΩ - 1%
41
1
R28
820 Ω - 1%
42
4
R3, R4, R11, R12
750 kΩ - 1%
43
3
R31, R32, R33
330 kΩ - 1%
0.25 W
44
1
R34
120 kΩ - 1%
0.2 5W
45
1
R35
75 Ω - 1%
0.25 W
46
1
R36
22 kΩ - 1%
47
3
R37, R38, R39
220 kΩ - 1%
0.25 W
48
1
R40
2.2 kΩ
0.25 W
49
1
R41
2.2 kΩ - 1%
50
3
R43, R44, R45
10 kΩ
51
1
R48
3.3 kΩ
52
1
R5
18 kΩ - 1%
53
1
R52
1.8 kΩ
54
1
R53
1 MΩ
55
1
R6
27 kΩ
56
3
R7, R19, R21
10 Ω
57
3
R8, R47, R51
47 kΩ
58
1
R9
0.5 Ω - 1%
59
1
T1
2x47 mH at 0.5 A
EPCOS Current-compensated D core
choke Or. code B82731-M2501-A30
60
1
T2
2 mH ± 5%
VOGT PFC choke EVD25
Part nr. SL0606301101
0.6 W
1W
1W
27/36
Board description
Table 3.
Item Qty
AN2640
BOM (continued)
Reference
Part / value
Voltage Watt
Type
61
1
U1
ST7FLIT19BF1B
6
STMicroelectronics 8-bit MCU
62
1
U2
L6382D5
STMicroelectronics power
management unit for microcontrolled
ballast
6.3
Experimental results
6.3.1
From system switch on to ballast run
The identification tests have been performed using T5 tubes having 24, 39, 54 and 80 W
lamp power ratings. Tests have been performed across the entire European mains (185 V ÷
230 V / 50 Hz) input range.
Figure 26. L6382 startup sequence and ballast start
The following results have been obtained with 230 V at 50 Hz as mains.
28/36
AN2640
Board description
Figure 27. 24 W lamp power
Figure 28. 39 W lamp power
29/36
Board description
AN2640
Figure 29. 54 W lamp power
Figure 30. 80 W lamp power
In Figure 27, 28, 29, and 30 it can be seen that the ballast identifies each lamp and that after
the recognition phase it adjusts and regulates the half-bridge working frequency to supply
the correct current to the lamp.
30/36
AN2640
6.3.2
Board description
PF, THD and ballast efficiency
The power factor, total harmonic distortion of current and ballast efficiency are measured
and the results are shown in Table 4, 5, 6, and 7.
Table 4.
Mains
PF
THD
η%
185 V at 50 Hz
0.968
17.6
88.2
230 V at 50 Hz
0.949
20.0
89.3
265 V at 50 Hz
0.923
22.0
89.9
Mains
PF
THD
η%
185 V at 50 Hz
0.983
13.5
90.4
230 V at 50 Hz
0.970
15.7
90.6
265 V at 50 Hz
0.956
17.4
90.6
Mains
PF
THD
η%
185 V at 50 Hz
0.989
11.3
94.1
230 V at 50 Hz
0.982
13.0
94.4
265 V at 50 Hz
0.972
14.4
94.6
Mains
PF
THD
η%
185 V at 50 Hz
0.992
10.9
97.6
230 V at 50 Hz
0.988
11.1
98.0
265 V at 50 Hz
0.980
14.6
98.2
Table 5.
Table 6.
Table 7.
6.3.3
24 W lamp power
39 W lamp power
54 W lamp power
80 W lamp power
Electromagnetic compatibility
The EMC tests have been performed according to the EN55015 standard (Limits and
methods of measurement of radio disturbance characteristics of electrical lighting and
similar equipment).
The Agilent E7401A EMC Analyzer has been used as test equipment.
31/36
Board description
AN2640
Figure 31. Test equipment
Agilent 6812B
AC Power Source / Analyzer
Agilent E7401A
EMC Analyzer
Figure 32, 33, 34, and 35 show the results.
Figure 32. 24 W
Figure 33. 39 W
32/36
STEVAL-ILB004V1
T5 Tube
AN2640
Conclusion
Figure 34. 54 W
Figure 35. 80 W
7
Conclusion
The proposed microcontrolled multipower ballast has several advantages. Design and
production cost are reduced as there is no need for different circuits to drive different lamps.
Moreover, by using the microcontroller, the systems' present flexibility from a design point of
view respects that of an analog circuit. With the use of STMicroelectronics' Power MOSFET
and diodes, the circuit shows good overall efficiency results.
33/36
References
8
34/36
AN2640
References
1.
AN966: L6561, Enhanced Transition Mode Power Factor Corrector
2.
STMicroelectronics ST7LITE1xB (8-BIT MCU with single voltage flash memory, data
EEPROM, ADC, 5 Timers, SPI) datasheet
3.
STMicroelectronics L6382D5 (Power management unit for microcontrolled ballast)
datasheet
AN2640
9
Revision history
Revision history
Table 8.
Document revision history
Date
Revision
28-Jan-2008
1
Changes
Initial release
35/36
AN2640
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