LM2576-12

2

4

1

3

5

+

1N5820

+

2200 PF

Feedback

Output

100 PF

GND

100 PH

-5V to -12V

LOW ESR

ON/OFF

LM2576, LM2576HV

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SNVS107C – JUNE 1999 – REVISED APRIL 2013

Also, the maximum voltage appearing across the regulator is the absolute sum of the input and output voltage.

For a

−12V output, the maximum input voltage for the LM2576 is +28V, or +48V for the LM2576HV.

The Switchers Made Simple (version 3.0) design software can be used to determine the feasibility of regulator

designs using different topologies, different input-output parameters, different components, and so on.

NEGATIVE BOOST REGULATOR

Another variation on the buck-boost topology is the negative boost configuration. The circuit in Figure 29 accepts

an input voltage ranging from

−5V to −12V and provides a regulated −12V output. Input voltages greater than

−12V will cause the output to rise above −12V, but will not damage the regulator.

Typical Load Current

Heat sink may be required.

Figure 29. Negative Boost

Because of the boosting function of this type of regulator, the switch current is relatively high, especially at low

input voltages. Output load current limitations are a result of the maximum current rating of the switch. Also,

boost regulators can not provide current limiting load protection in the event of a shorted load, so some other

means (such as a fuse) may be necessary.

UNDERVOLTAGE LOCKOUT

In some applications it is desirable to keep the regulator off until the input voltage reaches a certain threshold. An

undervoltage lockout circuit which accomplishes this task is shown in Figure 30, while Figure 31 shows the same

circuit applied to a buck-boost configuration. These circuits keep the regulator off until the input voltage reaches

a predetermined level.

Complete circuit not shown.

Figure 30. Undervoltage Lockout for Buck Circuit

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