PROTECTION CIRCUITRY

The protection circuits of the LM391 are very flexible and

should be tailored to the output transistor’s safe operating

area The protection V-I characteristics circuitry and resis-

tor formulas are described below The diodes from the out-

put to each supply prevent the output voltage from exceed-

ing the supplies and harming the output transistors The out-

put will do this if the protection circuitry is activated while

driving an inductive load

TURN-ON DELAY

It is often desirable to delay the turn-ON of the power ampli-

fier This is easily implemented by putting a resistor in series

with a capacitor from pin 14 to ground The value of the

Protection Circuitry with External Components

TLH7146 – 5

resistor is set to limit the current to less than 1 mA (the

absolute maximum) This resistor with the capacitor gives a

time constant of RC The turn-ON delay is approximately 2

time constants

Example

Amplifier with maximum supply of 30V like the 20W 8X

example in the data sheet requiring a delay of 1 second

1mA

So

a 30V rating

Protection Characteristics

TLH7146 – 6

Type of Protection

Current Limit

w

Not Required

Short

Not Required

Single Slope SOA

w

w

J

1kX

Not Required

Protection

Dual Slope SOA

Protection

w

w

J

1kX

b

1

(

Note w

transistors

6