12V Regulated Inverter Circuit Diagram & Build Guide

Description

When powering electronic devices utilizing 12V electrical systems from lead-acid battery arrays, the voltage delivered to the equipment can fluctuate considerably, ranging from below 11V when the batteries are depleted, to exceeding 14V during recharging. Numerous devices are intolerant of such a broad variation and may exhibit diminished performance or suffer damage.

This step-up converter, alongside a 12V steady regulator, represents an effective resolution. Q1 & Q2, along with the ferrite pot-core transformer, form a DC-to-AC inverter. The transformer’s turns ratio reduces the input voltage approximately by 30%. The resulting square wave voltage is rectified and combined with the input DC voltage. The amplified DC voltage is then channeled to a 7812 12V regulator (REG1).

7812 Regulator

The 7812 is a three-terminal positive voltage regulator integrated circuit. It’s a low-dropout (LDO) regulator that maintains a constant output voltage of 12V, even with variations in the input voltage or load current. It's widely used in various electronic circuits where a stable 12V supply is required. Its compact size and ease of use make it a popular choice for numerous applications.

Circuit diagram:

The designated regulator is capable of supplying 1.5A at 12V output, from any input into the inverter between 9V and 15V, with the inverter contributing the remaining current. Current needs are minimized by avoiding the inverter’s provision of the total current.

By replacing the linear regulator with a higher rated model, up to 5A can easily be supplied by this uncomplicated circuit. The transistors can be any standard general-purpose power transistor while the twin diode (D4/D5) is a fast-switching device often found in obsolete computer power supplies. Standard rectifier diodes can be used with a slight decrease in efficiency. The same applies to D2/D3. D6 is a protection diode and any 3A type will suffice.

By adjusting the transformer’s turns ratio and replacing the linear regulator, 24V devices can be powered from a 12V supply. Laptops requiring around 18V can also be operated.

This diagram illustrates the winding process for the transformer. L1 & L2 are six turns bifilar-wound, utilizing 1mm-diameter enameled copper wire, while L3 & L4 are four turns bifilar-wound.