K78XX = switch-mode LM78XX

December 10, 2013 | 14:37
K78XX = switch-mode LM78XX
K78XX = switch-mode LM78XX

For decades, the linear voltage regulator of the 78 series and its variants have been extremely popular, because these three-legged ICs allow stable supply voltages in the low voltage range to be created in a cost effective way. However if the difference between input and output voltage is considerable, efficiency decreases and the wasted heat must be dissipated which is not only costly and space consuming, but also a source of problems with thermal drift in sensitive and precision electronics. The use of switching regulators on the other hand generally requires more external parts and greater board surface. A modern replacement for the popular 3-pin voltage regulator would therefore make life easier for many electronic designers and engineers.


In addition to various conventional DC / DC converters, Chinese manufacturer Mornsun now also supplies non-insulating 3-pin voltage regulators that almost ideally meet the requirements for replacement of a linear regulator by a switching controller. The K78XX-YYY series is available with different output voltages (XX) and different maximum output currents. The range offers output voltages from 3.3 V to 24 V and currents of 500 mA to 2 A. The typical properties are:


  • Efficiency up to 97%

  • Voltage accuracy of up to 2%

  • Fixed voltages: 3.3 / 5 / 6,5 / 9 / 12 / 15 / 24 V

  • Maximum current: 0.5 / 1 / 1.5 / 2 A

  • Input voltage: 4.75 - 72 V, depending on type

  • Output voltage ripple 10 mV

  • Quiescent current 1 - 10 mA depending on type

  • Load regulation <0.5%

  • Built-in protection against short-circuit

  • Thermal shutdown at 150 °C

  • Operation to 85 °C


For stable operation most versions of the series K78XX need a decoupling capacitor (10 uF) at the input and output, similar to linear regulators. Interestingly negative output voltages may be obtained from a positive input voltage by connecting pin 3 (out) to the circuit ground. Pin 2 (GND) of the IC then supplies the negative voltage. In addition to the 3-pin regulators in a SIP package, there are also versions in a SMD package.

Because of the integrated components in the modules they are somewhat bulkier than their linear counterparts.



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