Troubleshooting Inverter Output Voltage Drop Issue

The post presents a discussion regarding the troubleshooting of a 4047 IC based inverter output voltage drop problem on connecting a load. The solution was requested by Mr. Isaac Johnson.

The Issue

Good day sir, I am a reader of your blog and an electronics hobbyist.

I constructed a square wave inverter with a filter capacitor(ceiling fan capacitor 2.2uf 400v) at the transformer out. I noticed on no load, i sometimes get 200-215v but when i connect a 200w bulb the output Voltage drops to 186v. I used a 12v 7A battery.

Pls is the FET not conducting fully? I get around 2.5v at pin 10 and 11 of my oscillator. Even same at emitter load resistor feeding the Gates of my fets (is the volt too small to cause the fets to switch fully?).

Pls check my Circuit, and Advice me. Also is the 8v regulator necessary? If no, wont the battery current damage the cd4047 (oscillator) and c1815 (driver) directly? My transformer is gotten from a old 2kv ups so it cant be having regulation issue or been small. Pls assist me.

Isaac Johnson.

Solutions:

The battery Ah is way too insufficient for handling a 200 watt load. In order to achieve 200 watts of power without dropping the output voltage, a minimum 40 AH would be required from the battery.

The FEts are conducting correctly and fully, the 2.5V is roughly the 50% of the supply since the outputs are switching at 50% duty cycle, the peak voltage would be close to the supply DC of the IC.

The voltage regulator shouldn't be removed as it's presence will not harm the circuit in anyway, but should be replaced with a 12V (7812) regulator for a better response.

The 1K at the collector can be removed (shorted), and the emitter resistor should be replaced with a 1 K.

The transformer primary must be rated at slightly lower than the battery voltage for optimal performance, for example with 12V battery it could be a 9-0-9V rated. This will ensure a normal output voltage within the required range even while the battery voltage drops to a relatively lower level.

Feedback from Mr. Isaac

Thanks alot for that urgent response and eye-opener. I am cleared.

Pls, in a Circuit such as the inverter oscillator section Where i used a 8v regulator, what would be the effect if i were to connect the circuit directly to a battery say 12v 100A?

Will the circuit draws only her required current (mA) needed to function or will the battery (high Amps) damage the i.c's?

From my little basic knowledge of electronics, it should be ok having it connected directly to the battery irrespective of the Amps provided the i.c's rated Voltage is not exceeded. Pls correct me if i am wrong.

Am having doubts in that regard.
Thanks so much.
Isaac Johnson

My Reply:

Since the IC4047 is specified to work with higher voltages than 12V, it won't affect its performance even if no regulator is used, but a regulator is always recommended for better safety. Amp of the battery becomes immaterial as long as the IC maximum voltage rating is not exceeded.

Higher Ah values will not affect the circuit at all. The inverter will consume only what it is supposed to consume, according to the output load current specifications.