HV9911DB1 - Electronic component Microchip - Free user manual and instructions

USER MANUAL HV9911DB1 Microchip

High Brightness Step-Down LED Driver Demoboard with Excellent Current Regulation

General Description

The HV9911DB3 is an LED driver capable of driving up to 25 one-watt LEDs in series from an input of 130 - 200VDC. The demoboard uses Supertex's HV9911 in a buck topology with the HV7800 used for high side current sensing. The converter has a very good initial regulation (+/-5%) and excellent line and load regulation over the entire input and output voltage range (<+/-2%). The full load efficiency of the converter is typically greater than 85%.

The HV9911DB3 is protected against open LED and output short circuit conditions. It is also protected from input under voltage conditions. It has a very good PWM dimming response, with typical rise and fall times of less than 5.0 s, which will allow high PWM dimming ratios.

The switching frequency of the HV9911DB3 can be synchronized to other HV9911 boards or to an external 150kHz clock by connecting the clock to the SYNC pin of the HV9911DB3.

Specifications

Parameter Value
Input voltage (steady state): 130 - 200VDC
Output LED string voltage: 20V	min - 100V max
Average output current: 350mA	+/-5%
Output current ripple: 5% typical
Switching frequency: 150kHz
Full load efficiency: 90% (at 150V input)
Output short circuit protection: Included
Input under voltage protection: Included
PWM dimming performance:	5.0μs (rise time)5.0μs (fall time)
Dimensions: 53.7mm x 38.1mm

Board Layout and Connection Diagram

Green printed circuit board with components like capacitors, resistors, and connectors (no readable text or symbols)

Actual Size: 53.7mm X 38.1mm

Input - The input is connected between the VIN+ and GND terminals as shown.

Output - The output is connected between the VO+ and VO terminals as shown, with the ANODE of the LED string to VO+ and the CATHODE to connector VO-.

Enable/PWM Dimming - To enable the board, short pins PWMD and VDD of connector J1 as shown. To use the PWM dimming feature of the board, connect an external push-pull square wave source between terminals PWMD and GND of connector J1 as shown by the dotted lines.

SYNC - To synchronize two or more boards, connect the SYNC pins of all the boards. To synchronize the HV9911DB3 to an external 150kHz clock, connect the clock between the SYNC pin and the GND pin of connector J1.

Note:

During PWM dimming, the PWMD pin of connector J1 should be left open. Also, the PWM signal must have the proper polarity, with the positive connected to the VDD pin of connector J1. Note that the GND pin of connector J1 is internally connected to the return path of the input voltage.

Demoboard Testing:

Normal Operation: Connect the input source and the output LEDs as shown in the connection diagram and enable the board. The LEDs will glow with a steady intensity. Connecting an ammeter in series with the LEDs will allow measurement of the LED current. The current will be 350mA +/- 5%.

Current Regulation: While the converter is operating, change the input voltage within its specified input voltage range. The current output of the HV9911DB3 will remain very steady over the entire line range. With the supply turned off, change the number of LEDs in the string within the specified limits and turn the power supply back on. The current will still be regulated at 350mA.

Open LED Test: The buck converter is inherently protected against open LED conditions since the maximum output voltage is limited to the input voltage. If the LED string is disconnected during operation, the output voltage of the converter will rise and stay at the input voltage level.

Short Circuit Test: When the HV9911DB3 is operating in steady state, connect a jumper across the terminals of the LED string. Notice that the output current will immediately go to zero and the converter will shut down. To restart the HV9911DB3, recycle the input power to the demoboard.

PWM Dimming: With the input voltage to the board disconnected, apply a TTL-compatible, push-pull square wave signal between the PWMD and GND terminals of connector J1 as shown in the connection diagram. Turn the input voltage back on and adjust the duty cycle and/or frequency of the PWM dimming signal. The output current will track the PWM dimming signal. Note that although the converter operates perfectly well at a 1kHz PWM dimming frequency, a wider PWM dimming ratio can be obtained at lower frequencies, like 100Hz or 200Hz.

Effect of the High Side Disconnect Switch

The high side disconnect switch included in the HV9911DB3 disconnects and reconnects the load during PWM dimming. This prevents the output capacitor from having to charge/discharge every cycle, leading to shorter PWM dimming rise and fall times. It also limits the surge current through the output sense resistor during output short circuit conditions. However, the level translator needed to drive the disconnect FET consumes power during normal operation and reduces the overall efficiency of the converter by about 3% at full load. The decision to include or exclude the high side driver should depend on which factor is more important, high PWM dimming or converter efficiency. The following typical results section will show the results for both cases.

Typical Results

1. Efficiency: The efficiency of the converter at various LED string voltages is shown in Fig.1 (measured at the nominal input voltage of 150V). Fig.2 shows the full load efficiency of the converter at varying input voltages. The minimum efficiency of 93% for the converter occurs at 21V input and full load output.

Fig. 1 Efficiency vs Output Voltage

Fig. 2 Efficiency vs Input Voltage

1. Current Regulation: Fig.3 and Fig.4 show the output current regulation vs. output voltage and load voltage, respectively. The total current regulation (line and load combined) is found to be less than 1%.

Fig. 3 Output Current vs Input Voltage

Fig. 4 Output Current vs Output Voltage

1. Normal Operation: Figs.5a, 5b, and 5c show the drain voltage and output current waveforms during normal operation.

Fig.5a Waveforms at V_IN = 150V and V_o = 100V