HV9931 查看數據表（PDF） - Supertex Inc

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HV9931

Unity Power Factor LED Lamp Driver

Supertex Inc 

HV9931

Input Voltage Regulator

The HV9931 can be powered directly from its VIN pin, and

takes a voltage from 8V to 450V. When a voltage is applied

at the VIN pin, the HV9931 seeks to maintain a constant

7.5V at the VDD pin. The VDD voltage can be also used as a

reference for the current sense comparators. The regulator

is equipped with an under-voltage protection circuit which

shuts off the HV9931 when the voltage at the VDD pin falls

below 6.2V.

The VDD pin must be bypassed by a low ESR capacitor

(≥ 0.1µF) to provide a low impedance path for the high

frequency current of the output gate driver.

The HV9931 can also be operated by supplying a voltage

at the VDD pin greater than the internally regulated voltage.

This will turn off the internal linear regulator and the HV9931

will function by drawing power from the external voltage

source connected to the VDD pin.

PWM Dimming and

Wall Dimmer Compatibility

PWM Dimming can be achieved by applying a TTL-

compatible square wave signal at the PWMD pin. When the

PWMD pin is pulled high, the gate driver is enabled and the

circuit operates normally. When the PWMD pin is left open

or connected to GND, the gate driver is disabled and the

external MOSFET turns off. The HV9931 is designed so that

the signal at the PWMD pin inhibits the driver only, and the

IC need not go through the entire start-up cycle each time

ensuring a quick response time for the output current.

The power topology requires little filter capacitance at

the output, since the output current of the buck stage is

continuous, and since AC line filtering is accomplished

through the middle capacitor rather than the output one.

Therefore, disabling the HV9931 via its PWMD or VIN pins

can interrupt the output LED current in accordance with

the phase-controlled voltage waveform of a standard wall

dimmer.

Oscillator

Connecting an external resistor from RT pin to GND programs

switching frequency:

FS

[kHz ] =

RT

25000

[KΩ ]+

22

Input and Output Current Feedback

Two current sense comparators are included in the HV9931.

Both comparators have their non-inverting inputs internally

connected to ground (GND). The CS1 and CS2 inputs are

inverting inputs of the comparators. Connecting a resistor

divider into either of these inputs from a positive reference

voltage and a negative current sense signal programs the

current sense threshold of the comparator. The VDD voltage

of the HV9931 can be used as the reference voltage. If more

accuracy is needed, an external reference voltage can be

applied. When either the CS1 or the CS2 pin voltage falls

below GND, the GATE pulse is terminated. A leading edge

blanking delay of 215ns (typ) is added. The GATE voltage

becomes high again upon receiving the next clock pulse of

the oscillator circuit.

Referring to the Functional Circuit Diagram, the CS2

comparator is responsible for regulating output current. The

output LED current can be programmed using the following

equation:

RCS 2

=

Io

+

1

2

∆IL2

7.5V

⋅ RREF 2

⋅ RS 2

where ∆IL2 is the peak-to-peak current ripple in L2. The CS1

comparator limits the current in the input inductor L1. There

is no charge in the capacitor C1 upon the start-up of the

converter. Therefore, L2 cannot develop the output current,

and the HV9931 starts-up in the input current limiting mode.

The CS1 current threshold must be programmed such that no

input current limiting occurs in normal steady-state operation.

The CS1 threshold can be programmed in accordance with

a similar equation:

RCS 1

=

I L1( PK )

7.5V

⋅ RREF 1

⋅ RS1

where IL1(PK) is the maximum peak current in L1.

MOSFET Gate Driver

Typically, the gate driving capability of the HV9931 is limited

by the amount of power dissipation in its linear regulator.

Thus, care must be taken selecting a switching MOSFET

to be used in the circuit. An optimal trade-off must be found

between the gate charge and the on-resistance of the

MOSFET to minimize the input regulator current.

Connecting the resistor from RT pin to GATE programs

constant off-time:

TOFF

[µ s ] =

RT

[KΩ ]+

25

22

5

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