Making a pin-base CFL light

The circuit shown in Inductor picture uses a dedicated integrated circuit type FAN7710 from our friends at Fairchild. As illustrated in Figure 4, this device combines one high-side 625-V gate driver circuit, two 550-V MOSFETs, afrequency control circuit and a shunt regulator –– plus active ZVS control and an open lamp detection function, all crammed into one ultra-compact 8-way DIP package. Its high functionality and built-in protection features save board space, reduce power dissipation and guarantee enhanced reliability in end systems. Good!

The AC line input voltage (here, 230 VAC 50 Hz) is rectified to provide a bus voltage of approximately 320 volts DC. Startup resistor R1 supplies initial (micro-) power to the FAN7710 IC. The IC begins to oscillate and the charge pump circuit consisting of C2, D2 and D7 supplies the current to the VDD pin, which gets regulated through the internal 15-V shunt regulator.

The FAN7710’s oscillator circuitry employs three discrete frequencies: one to pre-heat the CFL gas; one to ignite it and one for the on state — see the inset for the associated (simple) maths. In addition to this, it protects the ballast circuitry from low AC as well as lamp removal conditions.


Making the inductor
The bare PCB, FAN7710N IC and the 2.5-millihenry inductor used in the circuit come as a set from the Elektor Shop. However we would not discourage anyone from purchasing the inductor parts and making it yourself.


Let’s first carefully write down the specifications:

Inductance: 2.5 mH
Core material: Epcos N19 or equivalent
Core size: 20 / 10 / 6
Bobbin: E19
Gap: 1.5 mm
Wire gauge: 0.2 mm (SWG #32)
Number of turns: 280

Now look at the construction details.
First, wind the 280 turns of enamelled copper wire (ECW) on the E19 bobbin. Bare the wire ends for about 5 mm by scratching with a scalpel, then pre-tin. Check continuity of the coil. Put the Ecore halves over the bobbin as shown, then insert and adjust the spacers to get the required air gap of 1.5 mm which is essential to achieve the required inductance. The final step is to wrap electrical isolation tape around the core frame.


Ballast for Energy-Saving Lamps Printed Circuit Board )PCB)
Elektor labs have designed a circut board for the project; the component mounting plan is shown in PCB. The copper track layout is available as a free .pdf file from our website at Elektor for those wishing to etch their own circuit board. Reflected and non-reflected artwork is included in the .pdf file for your convenience. Component stuffing is a breeze as only normal size leaded components are used on a spacious board. The wiring to the mains and the lamp, and all connections and connectors in between, should comply with electrical safety guidelines. (Author: T. A. Babu, Elektor Magazine, 2008)

The alarm circuit transmits on MW (Medium Wave) (this is the small problem with the police). IC1a, together with a sensor (try a 20cm x 20cm sheet of tin foil) oscillates at just over 1MHz. This is modulated by an audio frequency (a continuous beep) produced by 4093 CMOS IC1b. When a hand or a foot approaches the sensor, the frequency of the transmitter (CMOS IC1a) drops appreciably.

Suppose now that the alarm circuit transmits at 1MHz. Suppose also that your radio is tuned to a frequency just below this. The 1MHz transmission will therefore not be heard by the radio. But bring a hand or a foot near to the sensor, and the transmitter's frequency will drop, and a beep will be heard from the radio.

More for RF Alarm

The oxygen sensor simulator as built on a protoboard. Note the cigarette lighter plug used for power source. The adjustment knob is at the left, and the switch is on the right. The red indicator LED is in the middle. Only use red, because the voltage drop of the LED is part of the circuit!



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