5VDC Single Polarity to 12VDC Dual Polarity Converter

Tue, 08 Sep 2015 13:36:02 +0000

During the on-time of the switching cycle, the inductor (L1) is charged by applying the supply voltage across the inductor. During this time the output capacitors (C2 and C3) are supplying the load. During the off-time of the switching cycle, the energy stored in the inductor is transferred to the output capacitors and the loads. The LM2595 is regulated off of the negative output. The positive output is regulated because of the coupling between the windings of the inductor. The diode D4 prevents the ?12V output from the going positive above a diode drop during the turn-on of the circuit. The diode D1 is used for providing isolation between the output and the input. LM2595 operates at a switching frequency of 150 kHz resulting in small inductor and capacitor sizes.

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This is the circuit diagram of 5VDC single polarity to 12VDC dual polarity converter based on IC LM2595-12 from National Semiconductor. This circuit will convert 5V DC single voltage (+) become 12V DC dual polarity output (+), GND, (-).

Many electronic devices need a ?12V power supply. Typical examples include analog circuits or RS-232 driver power supplies. The ?12V typically needs to be generated from a 5V system bus. The solutions normally used involve a multiple secondary transformer or multiple switching regulators. These solutions can be complicated, may require custom transformer design and may have poor efficiency and poor regulation. The 5VDC single polarity to 12VDC dual polarity converter circuit shown in above image is simple, uses only one switching regulator IC, uses a small number of components, and provides good regulation at a high efficiency. Additionally, all the components used in this circuit are off the shelf components.

The converter circuit in above image uses an LM2595-12 (buck SIMPLE SWITCHER?) based switching regulator to generate both the +12V and the -12V outputs from 5V input. The LM2595 is configured as an inverting buck-boost converter to obtain the negative output. The positive output is generated using an additional winding in the off-the-self inductor (CTX250-4 from Coiltronics) used in this circuit. Only one additional diode (D3) and a capacitor (C3) are needed to generate the positive output.

This circuit come from Application Note #1118 by National Semiconductor about Simple Regulator Provides ?12V from 5V Source using LM2595-12.
Download the application note AN-1118:

AN-1118 - 5V to 12V DC Converter

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DC to DC Converter | Electronic Schematic Diagram

5VDC Single Polarity to 12VDC Dual Polarity Converter

AN-1118 - 5V to 12V DC Converter

DC to DC Converter +5V to +12V