Current in the primary winding decreases and negative voltage is applied to JFET gate, which finally switches off the JFET. This peak voltage that switched off JFET falls back to zero, that is, secondary winding current reaches zero value and gate terminal gets rid off the negative voltage earlier applied across it.
Again, JFET gets turned on and the procedure repeats, thus oscillation process gets started.
Main advantage of this circuit is in ultra-low-voltage applications. This circuit has a forward mode of operation. Energy is transferred to output during on phase, which avoids the collapse of the switch-gate voltage oscillations during off-phase (a case of fly-back operation mode).
The self-oscillating ultra-low-voltage converter circuit simulated in LTspice is shown in Fig. 6. For simulation:
1. Download LTspice version 4 for Windows or MAC OS: click here
2. After installing the setup file, click on ultra_stepup_converter.asc file given at the end of the article. It will automatically open in the software and you will find the schematic capture window (Fig. 6).
3. Run the schematic by clicking the icon on the left-hand corner and you will get the results.
A self-oscillataing converter is capable of boosting 0.6V to approximately 5V. Output power is around 22mW and input power around 23.4mW. Simulation output of the system is shown in Fig. 7. Overall converter efficiency is about 92 per cent in simulation environment.
Energy storage. Energy storage will supply power to the sensor, microcontroller or data transreciever module. Advantages of the super capacitor make it ideal for energy storage. However, it takes a lot of time to charge and discharge.
Some semiconductor manufacturers have already introduced ultra-low-power ICs, which are capable of boosting as low as 10µW of input power. At such low input power, efficiency, noise immunity and stabilty of a power converter become questionable. But advancements in technology would definitely help future implementation of the IoT easy and reliable.
Download ultra_stepup_converter.asc file for Ultra-low-power Converter Circuit
Rohan Kadam is passionate about electronics and new technologies. He likes reading articles on application of power electronics and embedded systems, writing technical and non-technical articles