Adjustable Negative Voltage regulator ICs

The LM 337 is the negative output counterpart of the LM 317 and is a good example of this type of IC regulator. Like LM 317, IC LM 337 requires two external resistors for output voltage adjustment as shown below.


The output voltage can be adjusted from -1.2V to -37V depending on the external resistor values. The capacitors are for decoupling and do not affect the dc operation.

1) Output voltage : -1.2V to -47V
2) Output current :1.5A
3) Load regulation: 0.3%
4) Line regulation: 0.01%
5) High ripple rejection: 77dB
6) Internal short circuit protection.
7) Thermal shutdown.

The output voltage equation is
∴Vo=-Vref [1+R2/R1 ]+(-Iadj R2 )
∴Vo=-1.25[1+R2/R1 ]+(-Iadj R2 )
Iadj is almost negligible and hence output voltage is
∴Vo=-1.25[1+R2/R1 ]
Advantages of adjustable voltage regulators over fixed voltage regulators:

1) Improved line and load regulation by a factor 10 or more
2) High value of load current can be drawn over a specific temperature range.
3) Highly reliable.

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