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Transformerless 5 Volt Power Supply

An increasing number of appliances draw a very small current from the power supply. If you need to design a mains powered device, you could generally choose between a linear and a switch-mode power supply. However, what if the appliance’s total power consumption is very small? Transformer-based power supplies are bulky, while the switchers are generally made to provide greater current output, with a significant increase in complexity, problems involving PCB layout and, inherently, reduced reliability.... [read more]

Ignition Coil Buzz Box

Here's a circuit to create a buzzcoil using a standard automotive ignition coil. A 556 dual timer is used to establish the frequency and duty cycle of the coil current. One of the timers is used as an oscillator to generate the 200 Hz rectangular waveform needed to control the (IRF740 MOSFET) while the second timer switches the oscillator on and off as the breaker points open and close (closed = on). The result is a steady stream of sparks from the ignition coil spaced about 5 milliseconds apart while the breaker points are closed.... [read more]

16 Stage Bi-Directional LED Sequencer

The bi-directional sequencer uses a 4 bit binary up/down counter (CD4516) and two "1 of 8 line decoders" (74HC138 or 74HCT138) to generate the popular "Night Rider" display. A Schmitt Trigger oscillator provides the clock signal for the counter and the rate can be adjusted with the 500K pot.... [read more]

48V Phantom (Microphone) Power Supply

48 V ‘phantom’ powering has become the standard for professional condenser microphones. The supply (or rather bias) voltage is applied over both wires of the balanced screened cable via two 6k8 resistors (see reference [1]) – the absolute value is not critical, since a variation of ±20% is permitted, but they must be matched to an accuracy of 0.4% or better [2]. Many microphones are fitted with an output transformer, and derive their power from a center-tap on the secondary.... [read more]

Interfacing 5 volt CMOS to 12 volt/ 25 Watt Loads

The circuit below is designed to be used with the bi-directional lamp sequencer shown above on this same page. Two additional transistors are used to increase the current from the 74HCT138 decoder to control 12 volt 25 watt lamps. A 6.8 volt/1 watt zener diode is used in series with the ground connection of all the CMOS ICs (74HC14, CD4516 and 74HC138s) so that the total voltage across the CMOS devices will be about 5.2 volts and the outputs will move from +12 to about +7 when selected.... [read more]

Op-Amp Booster Designs - PDF

Although modern integrated circuit operational amplifiers ease linear circuit design, IC processing limits amplifier output power. Many applications, however, require substantially greater output voltage swing or current (or both) than IC amplifiers can deliver. In these situations an output “booster,” or post amplifier, is required to achieve the needed voltage or current gain. Normally, this stage is placed within the feedback loop of the operational amplifier so that the low drift and stable gain characteristics of the amplifier are retained.... [read more]