24Vdc to 220Vac 100 Watt, 50Hz Inverter- If, for example, three 220V / 20 W fluorescent lamps are to be switched over to a 24 Vdc emergency supply, they must still be operated from 220 V/50 Hz because the existing choke and normal starter must remain circuit. In mains operation a sinusoidal voltage is available. A 3.3uF capacitor connected parallel to the 20 W lamp compensates the corresponding inductive reactive current and the lamp only consumes a resistive power of 20 W plus the losses in the choke.
Choppers supply a square wave voltage that is not suitable for operating compensated fluorescent lamps. The parallel compensating capacitor causes considerable capacitive loading of the chopper, especially at the edges of the voltage waveform. The edge losses can be eliminated by omitting the compensating capacitor, but a high inductive reactive power remains that is 3 to 4 times higher than the lamp power rating. These reactive currents must be supplied by the emergency chopper and consequently by the transistors in it. A self-oscillating chopper can be ruled out when the three lamps are to be switched in individually because the chopper frequency increases with each lamp connected and the firing voltage decreases. As a result the lamp switched in does not fire or if at all only with appreciable delay.
A good solution is a sinewave generator that permits the compensated lamps to be switched in individually because any number of tuned circuits of the same resonant frequency can be connected in parallel as long as the generator power suffices. However, the transistors are loaded much harder in a class B push-pull sinewave generator than in a square wave generator.
24Vdc to 220Vac 100 Watt, 50Hz Inverter Circuit Diagram:
In the circuit diagram, the transformer output voltage is a square wave. The series capacitor of 10 uF (2 x 4.7 uF) forms with the choke a series resonant circuit with a sinusoidal voltage of about 220 Vac at terminals c-d. The square wave voltage at a-b is about 125V. The current is approximately sinusoidal. The square wave voltage minimizes the losses for the output transistors 2N3055. The control voltage consists of the IC TDB0555B, which delivers a frequency of 50 Hz adjustable by ±5 Hz.
The half cycle times are set to 10 ms by R2 and R4 respectively. The Zener diode BZY97C12 stabilizes the 12 V supply Voltage. The frequency remains stable at 50 Hz even when the 24 V emergency supply varies by ±15%. The BC177 acts as phase inverter. The transistors BD441 amplify the driver current for the output stages to 2 to 3A. The diodes type 1N4002 keep the transistor free of reverse current.
The 10uF/630V output capacitor is an AC type. Three 20W lamps can be connected sequentially or all together to this capacitor. A better solution would be a 3.3uF capacitor for each lamp. The lamp voltages then remain within close limits. However, when switching over to mains operation each lamp must have its own changeover switch and supply lead.
Battery voltage Vs = 24V ±15%.
Battery current Is = 5A
Oscillation Frequency f = 50Hz ±10% adjustable
Transformer M102 OL Dyn B1. 1V
n1 = 2 x 58 turns, 1.4mm dia. Enam. Cu (Bifilar wound)
n2 = 340 turns, 0.6 enam. Cu
if necessary with additional terminals:
+20 turns (.5 dia)
+20 turns (.5 dia)
List of components needed for the 24Vdc to 220Vac Inverter
- IC TDB 0555 B
- Transistors 2 N 3055
2 Transistors BD 441
- Transistor BC 117B
2 Diodes 1 N 4002
1 Zener Diode BZY 97C12
1 MKH Capacitor 10nF/250 V
1 MKH Capacitor 0.33u/100 V
1 MKH Capacitor 0.33u/250 V
2 MKL Capacitors 4.7u/630 V
1 Electrolytic Capacitor 22u/40 V
1 Electrolytic Capacitor 100u/25 V
2 Heat Sinks for 2N3055 Rth = 1 K/W