Power Inverter using transformer

prayami · Joined: 22 Dec 2004 Posts: 78

Hi...

We are making Power Inverter for getting variable output from 12V to 30V with 12V input. Everything working fine but when we connect some register at the output, the output voltage does not go to desire voltage but little bit less than desire. For example if desire output is 25V the actual output is 24.4V and does not go above that even continuous pulses are applied. The pulses coming out from MOSFET are having spikes and noise. We are using 18F2420 microprocessor.

One analog chanel I used as current voltage and one variable register to another analog chanel for desire voltage. When current voltage goes above desire voltage the pulses applied to MOSFET are stopped. And if current voltage is less than desire voltage then pulses are given continuosly.

Pulse frequency is around 20Khz. There is 5us delay between turning ON and OFF of both the MOSFET.

Is there any intelligent advice.....

Thanks...

Ttelmah · Guest

First, ignore the processor.
You are saying that if the pulse train is continuously applied, then the voltage still does not reach the required level. If this is the case, then you need to reconsider your hardware design. You give no detail of the hardware, but from your mention of 'MOSFETs' (plural), it sounds as if this is a push-pull inverter?. You then give no mention of the transformer used. Ferrite?. Ratio?. How are the FETs driven?. How are you snubbing the off period?. What current are you attempting to deliver?. How is the output rectified?. What are the wire thicknesses on the transformer?. 20KHz, is a very low frequency for any significant power with a small core. Are you sure that your transformer core is actually able to deliver the required power at this frequency.
Then looking at the 'control loop', You will find it very hard indeed to get smooth control with just on/off switching of the waveforms. Remember also that the ADC input, has significant capacitance, and unless well buffered, this will introduce significant delays in the control loop.

Best Wishes