SG3525 Inverter Circuit with Output Voltage Correction

In this post you will learn how to build a reasonably powerful SG3535 inverter circuit with output correction and also with other protection features such as battery regulation and mosfet overheat protection.

The discussed inverter is actually a system that enables power equipment needing 220V AC during the circumstances of a power outage or scenarios that result in virtually no accessibility to it.

The many included features of this inverter will be liked by folks spending vacation in a outdoor tents or bivouac.

The proposed SG3535 inverter circuit with output correction has been tested practically and worked well with outstanding accuracy.

The prototype was tested with the below mentioned appliances:

• televisions and radio
• bulbs, fluorescent lamps,
• circulation pumps furnace CO,
• power tools (drills, grinders)
• computers,
• Power.

SG3525 Inverter Circuit with Output Voltage Correction


Schematic diagram of the inverter exhibits the Fig.1. Voltage 220VAC acquired by means of alternately switching windings of the transformer TS1.

The crucial job is peformed by a couple of MOSFET power transistors from the n channel – T2 and T3. These are operated specifically by the IC US3 (SG 3524).

This set up is IC PWM generator intended specifically for use in voltage converters. The frequency with which it runs correctly is fairly wide and varies from 10 Hz to 300 kHz.

In the scenario explained in this article, this frequency inverter is 50Hz, or responds to the frequency from the power main grid.

This frequency is determined by by the parts R15 and C6. Variable pulse width US3 created through the technique has been employed for voltage stabilization 220VAC output.

Among the voltage stabilizing stages are components D6, D7 and divider Resistance R12 and R13, through which voltage signal moves to the input of the amplifier error (ending IN-) of the US3.

This specific voltage is analyzed with an suitably a divided reference voltage located on the Vref port. This lets “Self Adjust” the generator into the terminal voltage of the battery.

An additional clamping circuit tend to be components D8, R6, PR1, US2, R7, R8, and C4, that happen to be in control of offering a feedback signal relative to load malfunction applicable at the output of the inverter. Inverter with no stabilization might allow the output voltage depend directly soon load power and the degree of discharge of the battery.

The voltage might range from 170V to 270V ~ ~. As a consequence of these protection circuits the unit is able to stabilize voltage at the inverter output in practically any conditions enabling a constant 220 V ~.

Supposing essentially the most undesirable scenario, which may be partial discharge the battery as well as the load of the inverter at 100 % power of 250 W output voltage is probably not going to tumble under 220 V ~.

Switching transistors T2 and T3 are blocking capacitors in the form of C8 and C9, whose job would be to limit the voltage spikes created during the switching of T2 and T3. Further safeguard is delivered by the in-built configurations of the MOSFET diode reverse.

With a load of the order of 200W or 250W, the transistors tend to work with significant amounts of current, causing notable rise in temperatures. For that reason, the inverter is geared up with an active cooling system. As soon as the temperature extends to 40 ° C (which often roughly signifies that the core temperature of the device is 70 ° C), causes the resistance of the sensor which is a PTC thermistor to increase.

This in turn cause the comparator US5 alter the status of the output towards the to a triggering of the transistor T4 whose collector is attached with a cooling fan installed near the heatsink.

Converter system protected against incorrect connection battery terminals. This particular safeguard is accomplished using a diode D1 in the control relay PK1. This circuit stage is additionally utilized as collateral protection against abnormal battery discharge.

In case the value of the input voltage the power supply drops beneath 10.5 V at the end of the 6 US1 voltage begins to develop, thus inhibiting the operation of transistor T1 and, this results in the disconnection of the relay contacts PK1.

LED D5 indicates the triggering of the inverter, while the D4 notifies that the battery is actually overly discharged. Forced to quit in the situation, the inverter system now begins operating only with a single load whose power is optimized appropriately. while protection against short-circuit by means of fuses B1 and B2 appears to be adequate. INSTALLATION AND COMMISSIONING OF WARNING!! The inverter generates AC voltage 220V, which can be extremely hazardous to life and health. The inverter system is assembled on one single printed circuit board which can be found in Fig.2. Figure 3 exhibits the distribution of components.

Switching transistors T2 and T3 are placed on a plate yet needs to be mounted on a individual heat sink and coupled to the transformer.

Immediately within the heat sink is actually fitted is a PTC thermistor. It appears like with regard to fuses B1 and B2, which may be accessible externally. The inverter is built with quality and standard components so that they work optimally after connecting wth the battery.

All manipulations to the system pertains to your setting potentiometers PR1 and PR2. By using PR1 set output of the inverter voltage to precisely 220V ~. It has to be taken into account that the criticality of right measurement associated with RMS voltage 220V from the inverter is vital.

Because the output waveform will not be a sine wave nevertheless in close proximity to rectangular A number of appliances might have difficulties coping with the RMS value of the output voltage.

For that reason, to measure the voltage go for the meters equipped with “True RMS” measurement feature or employ the oscilloscope. The subsequent potentiometer PR2 needs to be set for the heat sink at a temperature of about 40 ° C. in order to switch ON the connected cooling fan.

The transformer which is used is a toroidal transformer with a couple of set of winding having symmetrical V 10 (secondary winding) and a 220 V (the primary winding).

The inverter no-load really should charge at the rate of current of approx. 300 mA. In case the current drawn tends to be much higher that could indicate asymmetrical winding activation of the transformer TS1 or causing varyations in the triggering of the switching transistors T2, T3.

At the conclusion a few words on the compatibility of the inverter battery. Finding the right battery for the inverter must be paid consideration regarding two parameters.

The first being the highest current drawn from the battery, which might depend on the equipment powered by the inverter.

Each load 10 converter means 1A current usage through the battery. The 2nd aspect is battery capacity or the AH which determines the operating period of the inverter and this must be taken into consideration too.

PCB track and component overlay designs for the proposed SG3535 inverter circuit with output correction can be seen in the following diagrams



Parts List for the 220V inverter circuit using SG3525 and output voltage correction feature

parts list