ML4812

6

OUTPUT DRIVER STAGE

The ML4812 output driver is a 1A peak output high speed

totem pole circuit designed to quickly drive capacitive

loads, such as power MOSFET gates. (Figure 3)

ERROR AMPLIFIER

The ML4812 error amplifier is a high open loop gain,

wide bandwidth, amplifier.(Figures 4-5)

GAIN MODULATOR

The ML4812 gain modulator is of the current-input type

to provide high immunity to the disturbances caused by

high power switching. The rectified line input sine wave is

converted to a current via a dropping resistor. In this way,

small amounts of ground noise produce an insignificant

effect on the reference to the PWM comparator. The

Figure 5. Error Amplifier Open-Loop Gain and

Phase vs Frequency

Figure 7. Gain Modulator Linearity

5V

EA–

4

3

–

+

8V

0.5mA

EA OUT

Figure 4. Error Amplifier Configuration

the output of the error amplifier. When the error amplifier

is saturated high, the output of the gain modulator is

modulator output current is converted into the reference

voltage for the PWM comparator through a resistor to

ground on the gain modulator output. The gain modulator

output is clamped to 5V to provide current limiting.

Ramp compensation is accomplished by subtracting 1/2

of the current flowing out of RAMP COMP through a

resistor.

UNDER VOLTAGE LOCKOUT

On power-up the ML4812 remains in the UVLO

condition; output low and quiescent current low. The IC

drops below 10V, the UVLO condition is imposed.

making it usable as a “flag” for starting up a downstream

PWM converter.

6

2

7

16

CT

RAMP COMP

GM OUT

ISINE

ERROR CURRENT

9V

5V

IRAMP COMP

ISINE × ERROR CURRENT

– IRAMP COMP/2

Figure 6. Gain Modulator Block Diagram

500

400

300

200

100

0

SINE INPUT CURRENT (µA)

0

200

300

500

400

100

4.5

4.0

3.5

3.0

2.5

2.0

1.5

FREQUENCY (Hz)

10

1k

1M

100

10k

10M

100k

100

80

60

40

20

0

-20

0

-30

-60

-90

-120

-150

-180

GAIN

PHASE