Hobby Projects - Insulation tester, LED Circuits, Meters.

Saturday, December 18, 2010

Drive a LED with a Constant Current

Constant Current Source LED Drive

This is a Constant Current Source LED Driver, When the LED driver Upper-NPN is driven by a voltage thru 4.7K the LED lights up. Assume that the Lower-NPN at bottom is absent. The current via LED and NPN is limited by R. 20mA may be ok 15mA even better. Or LED blows even transistor goes.


BC547 is like 100mA-40V-200b, Limit collector current to 60mA, use it at less than 25V and depending on the individual transistor you may get a DC current amplification of 200 times. That is 1uA of base-emitter current could give a whooping 200uA of collector-emitter current.

Still Thinking we do not have the Lower-NPN we calculate the resistor. Vcc - ( 2 LEDs * 1.7) - Vce = Vr that is the voltage across the resistor. You know ohms law and the current needs to be 15mA for a bright and long lasting LED. Lastly 1.7 the forward drop of a green LED and 0.6 a saturated or Turrned-On NPN Vce.

Now you use the Lower-NPN, The above calculations do not hold anymore. Let us think a small current is flowing in the LED. Then the voltage across R is less than 0.7V, that means base-emitter diode of the Lower-NPN will not get to conduct. The Collector does not draw any current away. Now think that more current flows in LED, the voltage across R builds up above 0.7V the Lower-NPN is biased. The collector of Lower-NPN starts drinking current from the base of the Upper-NPN. So The Upper-NPN starts losing its bias. This lowers the LED current and contains, regulates or controls the LED current as shown in the formula.

BC847/BC547 series; 45 V, 100 mA NPN general-purpose transistors
LEDMUSEUM.ORG-THE LED MUSEUM-Reviews of LEDs

FET Current Source

This is a constant current source using a FET. This is the most simple replacement to series resistor to limit current. The N-Channel FET BF256C can give 15mA current.

More at - Schematics of delabs: LED-Circuits

LM555 Voltage Doubler and More 555

This circuit shows the voltage doubler working with a 555. LM555 has good drive 200mA, both Vcc and Gnd.

LM555 - Timer -o- LM555 Timer Circuits

More about Voltage Multipliers

My 555 Circuits here - Schematics of delabs: 555-Circuits

Friday, December 17, 2010

Ni-Cd and Li-ion Battery charger Generic

This is a Generic charger that is made by many brands, the circuit is an approximation of all. Some improvements suggested. Some brands in europe and usa also use this circuit. This works well, but may not be in the best interest of battery life. The cost of the charger needs to be low. So this design or configuration is popular.

Battery Level Indicator 

Ni-Cd and Li-ion Battery charger Generic

The more care you show in the charger's battery charging and discharging; the longer its life. Today i manage my UPS batteries manually, both charge and discharge. The batteries are expensive, there is no better way, that is affordable.

Switching Battery Charger with L296 - del20031

Take batteries seriously - this is the source of transportation, power, solar energy reservoir etc. More so in the Future - start here Battery University.

Analog Op-Amp Tutors with Gadgets

I have made some iGoogle Gadgets with canvas view, these are analog opamp tutors. Interactive Tutorial with Simulated Meters and Potentiometers, demonstrating how Operational Amplifier functions in different configurations.

Interactive Tutorials using Virtual Electronic Components 

Slide the Potentiometers just like you would operate a Sliding Control. Drag the Knob on Pot to increase or decrease the resistance. The Resistance is shown is blue letters and dynamically alters value as you slide the pot.

The mV Source is varied by just moving mouse pointer over the two buttons, no clicking. This reduces finger strain and also you have a long lasting mouse. The mV buttons are special, the variation picks up speed if you let the mouse pointer remain on the button. This is Ramp-up and Ramp-down. This enables you to set it faster with just two buttons.

Finally you have a DVM a Digital Volt Meter that just Displays the Voltage at any Point, this readout value has to be noted down.

Op-Amp Simulation using Javascript

From Soldermans Basic Electronics

If you wish to examine the code - Analog Tutorials Project Page

Introducing a new delabs icon - Elektrick the Power Jedi

I am also attempting a Toy Scope or a waveform display.

Mains Voltage Stabilizer Circuits

Mains Voltage Stabilizer Circuits

These circuits were drawn for a person in Africa. See the thread here… stabilizer circuit. They were not tested by me, but are quite close to a practical design.

Stabilizer Step up 230V AC 500VA

This circuit is a design i did, not tested by me as yet. It can Stabilize Mains voltage to around +/- 10% . It can be used for both 110V AC or 220V AC inputs with modifications. The Output is 220V AC. There is an overload, under voltage and over voltage trip circuit. With some tweaks and modifications it might work.

Solid-State Stabilizer Step up 110V AC

This circuit is a design concept, not tested by me and i did it just to explain some ideas. The circuit uses opto-coupler MOC3041 of Motorola and the Triac BTA-16-600 of ST as a solid state switch or relay. It also uses the LM324 quad opamp from National Semiconductor which is low power and single supply. As the MOC3041 switches the Triac at zero crossover there is no inter-winding short of transformer on crossover hopefully, the control circuit is designed in such a way that more than one triac will not be turned on at a time, i would like you to give feedback.

EEVblog – Electronics Engineering Video Blog

Off-the-cuff video blog and Podcast of interest to anyone involved in electronics design. Electronics professionals, hobbyists, hackers, and makers will find something of interest here.

EEVblog - Electronics Engineering Video Blog
David L. Jones is an electronics design engineer based in Sydney Australia. He has over 20 years experience in the electronics design industry.
If you are into electronics, computers, or anything else remotely technical, then I'm sure there will be something of interest for you here. There are various electronic projects,
TRONNORT Technology - Electronics Resourse Site

Thursday, December 02, 2010

Perpandle has been UpGraded Again

The Center piece is a bamboo tube. The bottom of this pipe is a brass part. A autotransformer dial is the big washer. The LED array is from a Failed China Lamp and The Enclosure is a 10 CD Box. The Top Byzantine Structure is a Pepper Cap from Africa and a Furniture Knob.

Perpetual Candle - White LED Lamp on Ni-Cd

From Hobby Hound - DIY Electronics


Read Earlier Post - Perpandle Design