Friday, June 12, 2009

Electronic Earth Leakage Circuit Breaker

Differential CT is used to sense earth leakage current. Out put current of Differiantial CT will be difference of Phase current and Neutral current divided by turns ratio. This current is fed to current to voltage converter. One variable resistor is provided in the fee back path to audjest sensitivity. This signal is full wave rectified and given to relay driving circuit with a small delay.

SCR is used as relay drive for latched operation. Push to on switch is used for resetting the circuit. Test switch is used to check the working of the circuit by creating a artificial leackage current of 20mA. Another good referance design from Fairchild Semiconductor

Sunday, June 7, 2009

Electronic Transformer

Matix converter can be used with a high frequency ac link to make low frequency transformer.

The circuit presented here uses MOSFET as switches and EE70 ferrite core transformer as AC link. Transformation ratio is directly prepotional to turns ratio of EE70. If EE 70 have 1:1 turns ratio the curcuit will act as 1:1 isolation transformer. The main adventage of this topology is its low frequency response. We can use this electronics transformer DC to 200Hz.




Saturday, June 6, 2009

Multi Level Inverter

Multi Level Inverters are used to produce fine pwm wave forms with muliple voltage steps. It uses one or more power sources and multiple power switches. Main adventage of multilevel inverter is low switching component at output which will reduce the output filter components.
Multilevel inverters have very low switching loss but conduction losses are high. Another adventage is reduced voltage requirment of switching devices. The circuit given below is a three level inverter.The power supply is + - 400V connected as dual polarity bus ie 800V. Four 600V IGBT switches are connected in series and center point is taken as output. The levels are defined by shifting triangle wave above and belo GND (0V). 6V amplitude 50 hz sinewave is the input signal which is reproduced as 385V at output.Out put pwm have three levels 0V +400V and

Circuit of Multi Level Inverter

Input Sine Wave and level shifted Triangle Wave

PWM gate waveforms

PWM Out Put and Final Out Put

Have nice day