SG2524, SG3524

REGULATING PULSEWIDTH MODULATORS

SLVS077D – APRIL 1977 – REVISED FEBRUARY 2003

9

POST OFFICE BOX 655303

shutdown circuitry

COMP also can be employed to introduce external control of the SG2524. Any circuit that can sink 200

µA can

pull the compensation terminal to ground and, thus, disable the SG2524.

In addition to constant-current limiting, CURR LIM+ and CURR LIM– also can be used in transformer-coupled

circuits to sense primary current and shorten an output pulse should transformer saturation occur. CURR LIM–

also can be grounded to convert CURR LIM+ into an additional shutdown terminal.

current limiting

A current-limiting sense amplifier is provided in the SG2524. The current-limiting sense amplifier exhibits a

threshold of 200 mV

±25 mV and must be applied in the ground line since the voltage range of the inputs is limited

to 1 V to –1 V. Caution should be taken to ensure the –1-V limit is not exceeded by either input, otherwise,

damage to the device may result.

Foldback current limiting can be provided with the network shown in Figure 7. The current-limit schematic is

shown in Figure 8.

VO

Rs

R2

R1

EMIT 2

EMIT 1

SG2524

I

O(max) +

1

Rs

200 mV

)

V

O

R2

R1

) R2

I

OS +

200 mV

Rs

CURR LIM+

CURR LIM–

11

14

5

4

Figure 7. Foldback Current Limiting for Shorted Output Conditions

Constant-Current Source

CURR LIM+

COMP

CT

Comparator

Error Amplifier

CURR LIM–

Figure 8. Current-Limit Schematic

† Throughout these discussions, references to the SG2524 apply also to the SG3524.