Fullscreen HTML5Med Res (??MB)HTML4

High efficiency fluoro inverter wanted I have constructed three 20W fluoro light inverters, as described in the February 1991 edition of SILICON CHIP. All perform brilliantly and have cut power consumption by nearly 50% on our solar power system. I have also built the 40W inverter, described in the same article but this has not performed to expectations. While power­ing a 40W tube, the inverter would not draw more than 2.8A when fully warmed up and the secondary voltage measured up to be around 600VAC. When powering a 36W tube only 2.6A could be drawn. The transformer consisted of 500 turns of 0.25mm enamelled copper wire, wound on an ETD29 bobbin, for the secondary and 12 turns of 0.5mm ECW, centre tapped at 6 turns, for the primary plus the base windings. The cores used were made from F44 material rather than N27 stuff and were gapped at 0.6mm to achieve the results above. I tried larger air gaps but the inverter would only fire the tube three years ago, in another Australian electron­ ics magazine. That design might be of interest if you do need a generator that can store the waveform on board. High power light dimming Just recently the need has arisen for a high power (1200W) incandescent lamp dimmer and delving through and settle drawing nearly 4A, with the tube glowing dimly. So I wound another transformer, this time with the second­ary consisting of 5 full layers of 0.25mm enamelled copper wire. The instructions aren’t particularly clear for winding the 40W transformer. Winding 5 layers of 0.25mm will make 400 turns all up. I tried this transformer and ran a 36W tube at 700VAC, with the inverter drawing 2.2A. The transformer cores were gapped at 0.44mm, just like the instructions said. The ballast capacitors are rated at 500VAC but still work. Could you please advise me on what to do to make this cir­ cuit work properly? (N. R., via email). • It is impossible to produce a high efficiency inverter for a 40W fluoro using bipolar power transistors such as TIP3055s. Their gain is low and so is their Ft which means that they cannot switch efficiently at high frequencies. The only way to get high efficiency is to use Mosfets and run at frequencies of 100kHz or more. We produced such a design in the November 1993 issue. my library of SILI­CON CHIP magazines I found the article on a Heat Controller in the July 1998 issue and a High Power Dimmer in the August 1994 issue. Now I realise the Heat Controller is clearly not designed for the job of lamp dimming but I am very attracted to the sim­pler design (there is no transformer for a start). Would it be possible to adapt your circuit to lamp dimming duty by increasing the operating frequency LE of the oscillator or are there other complications that would make this too difficult? (R. M., via email). • The Heat Controller cannot be used to dim lights although your thinking is on the right track. The problem is that the mains frequency is fixed at 50Hz and the heat controller varies the power by applying bursts of 50Hz sinewave to the appliance. The minimum burst is one 20ms cycle. So no matter what you do with the burst rate, a heat con­troller like this, relying on zero voltage switching, will always cause really severe flicker if used to control power to lights. However, if the mains frequency is increased to 400Hz, as it is on aircraft, then this system of light dimming does become prac­tical. Notes & Errata LP Doctor, January 2001: The LM833 op amps that perform the treble filter and output buffer functions for the right channel are referred to in brackets as IC7a & IC7b. These should read IC9a and IC9b, respectively. The left channel IC numbers (IC5a & IC5b) are correct. PIC TestBed, January 2000: The overlay diagram on page 79 shows two resistors with the value 4.kΩ; these should read 4.7kΩ. The circuit diagram on page 78 is correct but shows a 4.7kΩ resistor connected to pin 7 of CON3/4: it should connect to pin 6. The overlay diagram is correct. VHF FM Receiver, June 2000: The circuit diagram on page 28 shows the incorrect pinouts on both the 2N7000 and LM336Z isometric drawings. Reading from the left, the 2N7000 should read “D G S” rather than “G D S” and the LM336Z has the “Adj” and SC “-” pins reversed. WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 100  Silicon Chip