5

FN2898.4

November 19, 2004

Application 1

High power amplifiers and buffers are in use in a wide variety

of applications. Many times the “high power” capability is

needed to drive large capacitive loads as well as low value

resistive loads. In both cases the final driver stage is usually a

power transistor of some type, but because of their inherently

low gain, several stages of pre-drivers are often required. The

HA-2541, with its 10mA output rating, is powerful enough to

drive a power transistor without additional stages of current

amplification. This capability is well demonstrated with the

high power buffer circuit in Figure 3.

The HA-2541 acts as the pre-driver to the output power

transistor. Together, they form a unity gain buffer with the

ability to drive three 50

Ω coaxial cables in parallel, each with

a capacitance of 2000pF. The total combined load is 16.6

Ω

and 6000pF capacitance.

Application 2

VIDEO

One of the primary uses of the HA-2541 is in the area of

video applications. These applications include signal

construction, synchronization addition and removal, as well

as signal modification. A wide bandwidth device such as the

HA-2541 is well suited for use in this class of amplifier. This,

however, is a more involved group of applications than

ordinary amplifier applications since video signals contain

precise DC levels which must be retained.

The addition of a clamping circuit restores DC levels at the

output of an amplifier stage. The circuit shown in Figure 4

utilizes the HA-5320 sample and hold amplifier as the DC

clamp. Also shown is a 3.57MHz trap in series, which will

block the color burst portion of the video signal and allow the

DC level to be amplified and restored.

Suggested Offset Voltage Adjustment

HP2835

LOAD 16.6

Ω; 6000pF

OR 12.5

Ω; 6000pF

HP2835

+

HA-2541

-

100

Ω

50

Ω

1k

Ω

2N5886

532pF

FIGURE 3. DRIVING POWER TRANSISTORS TO GAIN

ADDITIONAL CURRENT BOOSTING

HA-2541

1k

Ω

1k

Ω

1k

Ω

1k

Ω

1k

Ω

75

Ω

3.57MHz

TRAP

FIGURE 4. VIDEO DC RESTORER

NC

NC

BAL

-IN

+IN

V-

NC

NC

NC

BAL

V+

OUT

NC

NC

1

2

3

4

5

6

7

14

13

12

11

10

9

8

+

-

1mV| minimum referred to output. Typical range is

HA-2541