HV9805 230V
AC
Off-Line LED Driver Evaluation Board User’s Guide
DS50002347A-page 18
2015 Microchip Technology Inc.
The output voltage of the control amplifier provides the on-time reference for the boost
converter control circuitry, according to
EQUATION 2-4:
THE ON-TIME REFERENCE FOR THE BOOST CONVERTER
CONTROL (T
ON
)
2.4
BOARD TESTING, TEST POINTS WAVEFORMS AND OVERALL MEASURED
PARAMETERS
2.4.1
Board Testing
To start testing the evaluation board, follow these steps:
1. Power the board at 230V
AC
.
2. Check that the voltmeter indicates the LED load voltage (do not exceed 440V
DC
).
3. With a power supply of 230V
AC
, verify if the current regulated through the LED
strings is about 90 mA (by means of an ampere-meter connected in series with
the LEDs).
The following steps are possible if a variable AC power supply or an autotransformer
is available:
4. Set the power supply to 190V
AC
and verify if the output current on the LED side
stays regulated (I
OUT
~90 mA).
5. Set the power supply to 270V
AC
and verify if the output current on the LED side
stays regulated (I
OUT
~90 mA). Also, check that the voltage stays regulated on
V2 near the value 415V.
2.4.2
Test Points Waveforms
The board has several test points that help engineers to analyze the switch node's
waveforms of HV9805 device output:
The regulated headroom voltage is approximately 8V in order to reduce the losses on
the linear regulator.
TON KHVR VHVR
=
Where:
T
ON
=
On-time reference signal from the headroom voltage regulator
K
HVR
=
On-time modulator gain
V
HVR
=
5V
K
HVR
=
2.2 µs/V
T
ON
=
5 × 2.2 µs = 11 µs
TABLE 2-1:
TEST POINTS
Test Point
Description
TP1
Boost inductor (L3) voltage
TP2
Rectified line voltage V
DC
TP3
Bus voltage sense (BVS pin voltage)
TP4 (SW)
Voltage on switching node (DRV pin) of the HV9805 device
TP5
Inductor current sense voltage
TP6
V
DD
voltage on IC (V
DD
pin voltage), (6.5 to 8V)
TP7
Gate control voltage (CRG pin) of the linear regulator
TP8
LED current sense (CRS pin)
TP10
GND
TP11 – TP12 LED string voltage
TP13
High-voltage sense (HVS pin voltage)
