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

Perpetual Candle - White LED Lamp on Ni-Cd

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.

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The input impedance of this module is very high, if U1 is OP07 it is in mega ohms, use CA3140 or LF356 fet input opamps to get 1 tera ohm input impedance, but for high gains OP07 is better as it is ultra low offset, this is a good amplifier for sensor outputs, as in a DC Circuit.

Non-Inverting Opamp Interactive Simulation

Non-Inverting Amplifier - Op-Amp Circuits

Vout = Vin * (Rf + Ri) / Ri

The Spice in Analog Design

The zener diodes protect the opamp inputs, R1 limits current during high voltage inputs and R1 and C1 form a filter to remove ac components C1 should be a plastic type as ceramic and electrolytic caps are leaky. A large C1 will slow the response time, the sum of Ri + Rf should be greater than 5k so that output is not loaded. also do not connect output to voltages more than vcc/vdd it will blow Opamp.

This supply gives both positive and negative outputs. Appropriate Fuses should be used to protect from fire hazard and overload of transformer.

Voltage Regulators LM7812 and LM317

You could use LM7824 or LM7815 or LM7812 for 24V, 15V and 12V respectively. You could use LM7924 or LM7915 or LM7912 for -24V, -15V and -12V respectively.

Dual Polarity Power Supply

The Filter capacitor C1 4700uF has an impedance of Xc = 1 / (2 * 3.14 * f * C) which comes to 0.6 ohms at 50 Hz.

Power Electronic Circuits

The impedance of the load at 2A for 24V is R = V / I that is 12 Ohms which is more than 20 times the impedance of the capacitor at 50 Hz. That means less than 1 / 20 of ripple current will flow thru the load. The Regulator also reduces the ripple a little.

This is a Test arrangement for Leakage Testing of Diodes on Reverse Bias. The leakage current indicates the ability of the diode to withstand higher voltages. An AutoTransformer or Variac can be used to vary the test voltage. Even Plastic capacitors can be tested for leakage this way.

High Resistance Indicator – del50004

Diode Reverse Bias Leakage Tester

Safety Precautions –
Use a Isolation 1:1 transformer for safety. This circuit has to be enclosed in a insulated cabinet. A Jig or Acrylic Safety Plate with clamp can be used to connect the diode. The voltage is only applied as long as a Mains two way push switch is pressed. This adds to the safety.

Build a DMM or Digital Multi Meter

Caution Instruction –
Use this with Low voltages like 24V AC for Learning. Do not Use it with High Voltage AC. If you are learning, first work with other circuits using batteries or Low Voltage Mains Adapters.

Voltage multipliers are used to obtain low current high voltage, from an existing AC Source. Step up transformers can be used, but the insulation problems and care that has to be taken for HV above 1kV, make it difficult. After SMPS technologies and Ferrites were developed, HV for CRTs was generated by blocking oscillators and step up Transformers at High Frequency AC.

Mains Voltage and Power Circuits

Voltage Doublers and Multipliers

Caution Instruction –

Use this with Low voltages like 24V AC for Learning. Do not Use it with High Voltage AC. If you are learning, first work with other circuits using batteries or Low Voltage Mains Adapters.
This circuit uses Diodes and Capacitors, just like the text book circuits.

More Reading –

Voltage Multipliers – The Creative Science Centre

Here is the circuit of a Op-Amp based Square Wave Generator. One of the main application of this is in a Simple PWM circuit and Triangle Opamp Oscillator. The Slope of the Triangle wave is compared with a DC Level to derive a pulse width or On-Time proportional to a Voltage.

Op-amp Oscillator delabs

This On-Time proportional to voltage is for a fixed oscillation rate based on C2-C3 and R15. The C2-C3 form a Unpolarized cap, This type is also used in crossover networks in speaker boxes. This is because, a plastic 4.7 uF (2 * 10uF series) is big and costlier, but a plastic cap is very stable and closer to an ideal cap.

Square and Triangle Opamp Oscillator

First you need to know that most opamps in such circuits can give a square wave, but very few can swing to the rails (+/-5). For designing take 75% of Vcc. CA3130 is one that can swing to rails like a CMOS gate.

Op Amp Triangle-Wave Generator

Assuming the swing of output is around +/- 4V, the pin 10 + input will be at +/- 2V. When the cap is discharged at 0 V, let us take that the output is +, the cap charges to a little above +2, – input becomes dominant, so output swings negative. This discharges the cap to 0 and then charges it negatively upto -2. This in turn flips the output to + as pin 10 turns dominant. Hence this continues as a oscillation, with a nice triangle across the cap for the PWM comparator.

Dominant means more +, 0 is positive compared to -2V. Also -2.5 is negative compared to -2.2.

This is the Display Circuit and PCB part of of section Temperature Control.

The above circuit is powered by +5 and -5 from a LM7805 and LM7905 pair. If +/- 12V or +/- 7.5V is used in opamp or digital parts, then use below circuit for the DPM section.

5 V Dual Supply with Zeners

The PCB for above

The PDF Circuit for above Display Card STC1000

The Circuit below is a paper design and not tested. It can be used for education and information, this can help you make your own design. Please do not just wire it up and expect it to work.

Regulated High Voltage Power Supply

Now let me see if i can explain the circuit, This is a regulated AC power supply. This circuit uses the Mosfet to turn off when voltage goes beyond a reference point. That means it just chops the Sine wave above a point, that also implies that the output may not be pure sine and may have harmonics. The Transformer if well designed may smoothen the chops. Even a Series Inductor or Resonant Circuits may reduce harmonics.

The opto coupler 4N50 Provides isolation and good Current Transfer Ratio. That may mean you may not get a shock and that even a small current signal in Opto-LED will give a saturated or Low Impedance in Opto-Transistor. The Mosfet is used like a Impedance Control switch turned On-Off by Opto. The Optocoupler diode is controlled by the Opamps which work Closed loop. The transformer output is compared with reference to drive opto-led.

Regulated High Voltage Power Supply – del20032

This Circuit is based on Teledyne Solid State data book application note. They may not be making these parts anymore but they are available from others.