ACT30AYT datasheet(4/10 Pages) ACTIVE-SEMI

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ACT30

Rev 5, 05-Jun-09

Active-Semi

Innovative Power

- 4 -

www.active-semi.com

ActiveSwitcher

TM is a trademark of Active-Semi.

FUNCTIONAL BLOCK DIAGRAM

VDD

REGULATOR

GND

FREQ1

DRV2 2

BIAS

& UVLO

OSC &

RAMP

CURRENT

PFWM

SWITCHING

CONTROL

LOGIC

SLEW

GND

DRV1

HICCUP

CONTROL

200k

4.75V

10µA/V

ILIM VC

GENERATOR

ERROR

COMP

20k

56X

3.6V (ACT30A/C)

4.6V (ACT30B/D)

FUNCTIONAL DESCRIPTION

As seen in the Functional Block Diagram, the main

components include switching control logic, two on-

chip medium-voltage power-MOSFETs with parallel

current

sensor,

driver,

oscillator

and

ramp

generator, current limit VC generator, error

comparator, hiccup control, bias and under voltage-

lockout, and regulator circuitry.

As seen in the Functional Block Diagram, the

design has six internal terminals. VVDD is the power

supply terminal. DRV1 and DRV2 are linear driver

outputs that can drive the emitter of an external

high voltage NPN transistor or N-channel MOSFET.

This emitter-drive method takes advantage of the

high VCBO of the transistor, allowing a low cost

transistor such as ‘13003 (VCBO = 700V) or ‘13002

(VCBO = 600V) to be used for a wide AC input range.

The slew-rate limited driver coupled with the turn-off

characteristics of an external NPN transitor result in

lower EMI.

The driver peak current is designed to have a

negative voltage coefficient with respect to supply

voltage VVDD, so that lower supply voltage

automatically results in higher DRV1 peak current.

This way, the optocoupler can control VVDD directly

to affect driver current.

Startup Sequence

Figure 1 shows a Simplified Application Circuit for

the ACT30. Initially, the small current through

resistor R1 charges up the capacitor C1, and the

BJT acts as a follower to bring up the DRV1

voltage. An internal regulator generates a VVDD

voltage equal to VDRV1 – 3.6V for ACT30A (VDRV1 –

4.6V for ACT30B) but limits it to 5.5V max. As VVDD

crosses 5V, the regulator sourcing function stops

and VVDD begins to drop due to its current

consumption. As VVDD voltage decreases below

4.75V, the IC starts to operate with increasing driver

current. When the output voltage reaches regulation

point, the optocoupler feedback circuit stops VVDD

from decreasing further. The switching action also

allows the auxiliary windings to take over in

supplying the C1 capacitor. Figure 2 shows a

typical startup sequence for the ACT30.

To limit the auxiliary voltage, use a 12V zener diode

for ACT30A or a 13V zener diode for ACT30B (D1

diode in Figure 1).

Even though up to 2MΩ startup resistor (R1) can be

used due to the very low startup current, the actual

R1 value should be chosen as a compromise

between standby power and startup time delay.

: FREQ terminal wire-bonded to VDD in ACT30C/D (TO-92)

: DRV2 terminal wire-bonded to DRV1 in ACT30B/D (TO-92)

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