Perpetual Candle – White LED Lamp on Ni-Cd

This is a easy to build LED lamp circuit for Learning and building skills. This is the first draft schematic V 1.0. It will need improvements for Higher Power Lighting.

Perpetual Candle Project

I will give a short summary, The LM317 here configured for around 6.4V DC. The Q3 BC547 limits the current, you can select R3 to suit, make it 1/2W. The Ni-Cd battery pack 1.2 * 4 will not get Over-Current or Over-Voltage due to this circuit.

The IRF540 Mosfet or any other equivalent you have around, along with Q2 BC547 forms a current source for the parallel 12 LED array. Ultra-bright White LED at 20mA each or use a 1W ready LED Chip. R4/R6 can be selected for the Max LED current. The voltage of LED is around 3.1 and 20mA * 12 = 240mA is the max current. You can Tweak the design for even 5A or more but then you will need a DC/DC High frequency converter in place of LM317. The Current source also needs to switch to improve efficiency. A PWM on the mosfet gives brightness control. The entire solution (switching) can be found in many chips with semiconductor vendors today.

One Single High Current LED may work well. 12 Matched LEDs also can be used. In LED Array some are dim, put min. resistor (3.9 ohm) for all 12 for current sharing. The resistor addition will impar the ability of Candle to work at lower battery voltages. Also resistor is less green, It wastes power, so use PWM and Single Die high current LED. Ni-Cd system may last over 5 Years if Candle is allways on Mains. Sealed Lead Acid system may go upto 2-3 years life but will have more punch. A SuperCap system may last more than 12 Years, i feel.

Source in Cadsoft Eagle format – candle.zip

Power Supply with Battery Backup

This is an incomplete version of the power supply used for the Alertness Monitor with hourly LED Display. This circuit used a Dual Color LED. Green meant Alert and Red meant No Alert or acknowledge press.

Power Supply with Battery Backup

I can write here only in “Electronic English”. Focus on the tech not grimmer. It may be like Pascal with a touch of Acronyms, codes and circuit axioms.

The top part is a 5V regulator with 0.7 Diode boost, means 5.7 V DC. The battery was floating on this point above the zener Z4, that connection comes from outside. A protection fuse maybe needed in case Zener draws more current. The Zeners were test selected to get above 6V along with the diode.

The second supply is to drive the LED array and Relay. This second battery supply was needed to prevent the RAM from losing data and also the CMOS logic getting reset, when the relay solenoid operates. Even when the Display Now switch is pushed, the current is large and the pulse could reset digital circuit.

The battery was used very less, it worked during the power failures for short duration between mains and generator switching. This circuit is not meant for in situations when battery drains are high.

WorkBench Dual Power Supply

I will just explain part of this circuit. D9 and D10 provide a low cost -1.4 from -5 V. This is needed to reach near 0.00 for LM317 Min. setting. An LED also can be used with proper bias. Note that there is a Temperature Coefficient in ppm, see The Unusual Diode FAQ. but it may not matter upto 8 bits accuracy.

TIP2955, TIP3055 (NPN), TIP2955 (PNP) Complementary Silicon Power Transistors. It is a Darlington, that means good current gain. See Darlington transistor – Wikipedia. When current in R1 10E goes more than 50mA a voltage of 50mA X 10E = 500mV is applied across Emmiter-Base junction. So lower than 500mV no bias the tap is turned off, 500mV-700mV the tap starts turning on depending on type of transistor. The transistor is like a water Tap. So TIP2955 carries the major current burden thru the load allowing LM317 to do the decision making when to turn-on or off. It is analog control, it is not On-Off but linear-proportional. The LM317 is very cool as the burden is passed off to TIP2955 who will need a heatsink to keep going and deliver the power you want.

WorkBench Dual Power SupplyPut the filter caps appropriately. The Hum-Noise will be filtered. The cap after the regulator should be a small guy. The main filter cap after the Bridge can be as big as your cabinet or budget.

If you build it and wire it without designing a PCB, then make all wiring and connection very sound. The test of this ability you can know easily, If your project stops working after the last screw of the cabinet is tightened, Then we need to improve.

LM317 based Regulated Power Supply

This is a Regulated Power Supply based on the LM317 IC. It will need a Boost Power Transistor and heatsink for higher currents. It is a versatile building block for stable instrumentation supplies. Consumer Electronic gadgets can use a SMPS chip. In case you wish to use a SMPS for a Precision Instrumentation Block, then take extreme care on Shielding and EMI-RFI.

LM317 based Regulated Power Supply

This is a General Purpose Chip, Series Regulation. It can be varied or trimmed. There is an Internal temperature compensated reference. The minimum trim value is around 1.2. In case you want a Low value voltage like 0.5 with a good current, then use a good negative supply to offset the 1.2 V.

The transformer can be s Split Bobbin with Pri-Sec copper shield foil. This can be earthed along with the metal enclosure. C4 sends any hi-freq components to earth. It is better if you do not earth the ground but use such capacitors. A Supply should simulate a a battery with both ends floating wrt Earth. A option to eartth the ground is fine. This also helps the user to configure his own dual supplies.

Q1 and R5 form a Short Circuit OR current fold back OR constant current mechanism. TP1 can be used to vary the output voltage. Better use something like a Bourns 10T trimpot. An open preset may introduce a noise due to dust and vibration. I don’t remember why i added a zener DZ1, a diode may suffice.

PDF file is here – LM317 – Variable Power Supply