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HVLED805TR
Off-line LED driver with primary-sensing up to 5W
October 2010 Doc ID 18077 Rev 1 1/29
HVLED805Off-line LED driver with primary-sensing
Features 800 V, avalanche rugged internal power
MOSFET 5% accuracy on constant LED output current
with primary control Optocoupler not needed Quasi-resonant (QR) zero voltage switching
(ZVS) operation Internal HV start-up circuit Open or short LED string management Automatic self supply Input voltage feed-forward for mains
independent cc regulation
Applications AC-DC led driver applications LED retrofit lamps (i.e. E27, GU10)
Table 1. Device summary
Figure 1. Application diagram
Contents HVLED8052/29 Doc ID 18077 Rev 1
Contents Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125.1 Power section and gate driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.2 High voltage startup generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.3 Secondary side demagnetization detection and triggering block . . . . . . . 15
5.4 Constant voltage operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.5 Constant current operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.6 Voltage feedforward block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.7 Burst-mode operation at no load or very light load . . . . . . . . . . . . . . . . . . 22
5.8 Soft-start and starter block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.9 Hiccup mode OCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.10 Layout recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
HVLED805 Description
Doc ID 18077 Rev 1 3/29
1 Description
The HVLED805 is a high-voltage primary switcher intended for operating directly from the
rectified mains with minimum external parts to provide an efficient, compact and cost
effective solution for LED driving. It combines a high-performance low-voltage PWM
controller chip and an 800V, avalanche-rugged power MOSFET, in the same package.
The PWM is a current-mode controller IC specifically designed for ZVS (zero voltage
switching) fly-back LED drivers, with constant output current (CC) regulation using primary-
sensing feedback. This eliminates the need for the opto-coupler, the secondary voltage
reference, as well as the current sense on the secondary side, still maintaining a good LED
current accuracy. Moreover it guarantees a safe operation when short circuit of one or more
LEDs occurs.
In addition, the device can also provide a constant output voltage regulation (CV): it makes
the application able to work safely when the LED string opens due to a failure.
Quasi-resonant operation is achieved by means of a transformer demagnetization sensing
input that triggers MOSFET’s turn-on. This input serves also as both output voltage monitor,
to perform CV regulation, and input voltage monitor, to achieve mains-independent CC
regulation (line voltage feed forward).
The maximum switching frequency is top-limited below 166 kHz, so that at medium-light
load a special function automatically lowers the operating frequency still maintaining the
operation as close to ZVS as possible. At very light load, the device enters a controlled
burst-mode operation that, along with the built-in high-voltage start-up circuit and the low
operating current of the device, helps minimize the residual input consumption.
Although an auxiliary winding is required in the transformer to correctly perform CV/CC
regulation, the chip is able to power itself directly from the rectified mains. This is useful
especially during CC regulation, where the fly-back voltage generated by the winding drops.
In addition to these functions that optimize power handling under different operating
conditions, the device offers protection features that considerably increase end-product’s
safety and reliability: auxiliary winding disconnection or brownout detection and shorted
secondary rectifier or transformer’s saturation detection. All of them are auto restart mode.
Maximum ratings HVLED805
4/29 Doc ID 18077 Rev 1
2 Maximum ratings
Table 2. Absolute maximum ratings Limited by maximum temperature allowed.
Table 3. Thermal data
HVLED805 Electrical characteristics
Doc ID 18077 Rev 1 5/29
3 Electrical characteristics
TJ = -25 to 125 °C, Vcc=14 V; unless otherwise specified.
Table 4. Electrical characteristics
Electrical characteristics HVLED805
6/29 Doc ID 18077 Rev 1 Parameters tracking each other
Table 4. Electrical characteristics (continued)
HVLED805 Pin connection
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4 Pin connection
Note: The copper area for heat dissipation has to be designed under the drain pins
Figure 2. Pin connection (top view)
Pin connection HVLED805
8/29 Doc ID 18077 Rev 1
Table 5. Pin functions
HVLED805 Pin connection
Doc ID 18077 Rev 1 9/29
Note: The measured IDSS is the sum between the current across the 12 MΩ start-up resistor (62.5
µA typ. @ 750 V) and the effective MOSFET’s off state drain current
Figure 3. COSS output capacitance variation
Figure 4. Off state drain and source current test circuit
Pin connection HVLED805
10/29 Doc ID 18077 Rev 1
Figure 5. Start-up current test circuit
Figure 6. Quiescent current test circuit
HVLED805 Pin connection
Doc ID 18077 Rev 1 11/29
Note: The circuit across the DMG pin is used for switch-on synchronization
Figure 7. Operating supply current test circuit
Figure 8. Quiescent current during fault test circuit
Application information HVLED805
12/29 Doc ID 18077 Rev 1
5 Application information
The HVLED805 is an off-line all-primary sensing switching regulator, specific for offline LED
drivers based on quasi-resonant ZVS (zero voltage switching at switch turn-on) flyback
topology.
Depending on converter’s load condition, the device is able to work in different modes
(Figure 9 for constant voltage operation): QR mode at heavy load. Quasi-resonant operation lies in synchronizing MOSFET's
turn-on to the transformer’s demagnetization by detecting the resulting negative-going
edge of the voltage across any winding of the transformer. Then the system works
close to the boundary between discontinuous (DCM) and continuous conduction
(CCM) of the transformer. As a result, the switching frequency will be different for
different line/load conditions (see the hyperbolic-like portion of the curves in Figure 9).
Minimum turn-on losses, low EMI emission and safe behavior in short circuit are the
main benefits of this kind of operation. The resulting constant current mode fixes the
average current also in case of a short-circuit failure of one or more LEDs.
2. Valley-skipping mode at medium/ light load. Depending on voltage on COMP pin, the
device defines the maximum operating frequency of the converter. As the load is
reduced MOSFET’s turn-on will not any more occur on the first valley but on the second
one, the third one and so on. In this way the switching frequency will no longer increase
(piecewise linear portion in Figure 9).
3. Burst-mode with no or very light load. When the load is extremely light or disconnected,
the converter will enter a controlled on/off operation with constant peak current.
Decreasing the load will then result in frequency reduction, which can go down even to
few hundred hertz, thus minimizing all frequency-related losses and making it easier to
comply with energy saving regulations or recommendations. Being the peak current
very low, no issue of audible noise arises. Thanks to this feature, the application is able
to safely manage the open circuit caused by an LED failure.
Figure 9. Multi-mode operation of HVLED805 (Constant voltage operation)
HVLED805 Application information
Doc ID 18077 Rev 1 13/29
5.1 Power section and gate driver
The power section guarantees safe avalanche operation within the specified energy rating
as well as high dv/dt capability. The Power MOSFET has a V(BR)DSS of 800V min. and a
typical RDSon of 11 Ω.
The gate driver of the power MOSFET is designed to supply a controlled gate current during
both turn-on and turn-off in order to minimize common mode EMI. Under UVLO conditions
an internal pull-down circuit holds the gate low in order to ensure that the power MOSFET
cannot be turned on accidentally.
5.2 High voltage startup generator
Figure 10 shows the internal schematic of the high-voltage start-up generator (HV
generator). It includes an 800 V-rated N-channel MOSFET, whose gate is biased through
the series of a 12 MΩ resistor and a 14 V zener diode, with a controlled, temperature-
compensated current generator connected to its source. The HV generator input is in
common with the DRAIN pin, while its output is the supply pin of the device (Vcc). A mains
“UVLO” circuit (separated from the UVLO of the device that sense Vcc) keeps the HV
generator off if the drain voltage is below VSTART (50 V typical value).
With reference to the timing diagram of Figure 11, when power is applied to the circuit and
the voltage on the input bulk capacitor is high enough, the HV generator is sufficiently
biased to start operating, thus it will draw about 5.5 mA (typical) from the bulk capacitor.
Figure 10. High-voltage start-up generator: internal schematic
Application information HVLED805
14/29 Doc ID 18077 Rev 1
Most of this current will charge the bypass capacitor connected between the Vcc pin and
ground and make its voltage rise linearly.
As the Vcc voltage reaches the start-up threshold (13 V typ.) the chip starts operating, the
internal power MOSFET is enabled to switch and the HV generator is cut off by the Vcc_OK
signal asserted high. The IC is powered by the energy stored in the Vcc capacitor.
The chip is able to power itself directly from the rectified mains: when the voltage on the VCC
pin falls below Vccrestart (10.5V typ.), during each MOSFET’s off-time the HV current
generator is turned on and charges the supply capacitor until it reaches the VCCOn
threshold.
In this way, the self-supply circuit develops a voltage high enough to sustain the operation of
the device. This feature is useful especially during CC regulation, when the flyback voltage
generated by the auxiliary winding alone may not be able to keep Vcc above VCCrestart.
At converter power-down the system will lose regulation as soon as the input voltage falls
below VStart. This prevents converter’s restart attempts and ensures monotonic output
voltage decay at system power-down.
Figure 11. Timing diagram: normal power-up and power-down sequences
HVLED805 Application information
Doc ID 18077 Rev 1 15/29
5.3 Secondary side demagnetization detection and triggering
block
The demagnetization detection (DMG) and Triggering blocks switch on the power MOSFET
if a negative-going edge falling below 50 mV is applied to the DMG pin. T o do so, the
triggering block must be previously armed by a positive-going edge exceeding 100 mV.
This feature is used to detect transformer demagnetization for QR operation, where the
signal for the DMG input is obtained from the transformer’s auxiliary winding used also to
supply the IC.
The triggering block is blanked after MOSFET’s turn-off to prevent any negative-going edge
that follows leakage inductance demagnetization from triggering the DMG circuit
erroneously.
This blanking time is dependent on the voltage on COMP pin: it is TBLANK = 30 µs for VCOMP
= 0.9 V, and decreases almost linearly down to TBLANK = 6 µs for VCOMP = 1.3 V
The voltage on the pin is both top and bottom limited by a double clamp, as illustrated in the
internal diagram of the DMG block of Figure 12. The upper clamp is typically located at 3.3
V, while the lower clamp is located at -60mV. The interface between the pin and the auxiliary
winding will be a resistor divider. Its resistance ratio as well as the individual resistance
values will be properly chosen (see “Section 5.5: Constant current operation on page 18”
and “Section 5.6: Voltage feedforward block on page 20”.
Please note that the maximum IDMG sunk/sourced current has to not exceed ±2 mA (AMR)
in all the Vin range conditions. No capacitor is allowed between DMG pin and the auxiliary
transformer.
The switching frequency is top-limited below 166 kHz, as the converter’s operating
frequency tends to increase excessively at light load and high input voltage.
A Starter block is also used to start-up the system, that is, to turn on the MOSFET during
converter power-up, when no or a too small signal is available on the DMG pin.
The starter frequency is 2 kHz if COMP pin is below burst mode threshold, i.e. 1 V, while it
becomes 8 kHz if this voltage exceed this value.
Figure 12. DMG block, triggering block
