Regulated Power Supply

In the previous chapter, various methods of rectifying ac to become fairly smooth dc were described. However, the rectifiers studied in that chapter would deliver voltages that are too low, if the wall socket 120 volt ac were to drop somewhat in 

The reader is reminded of output into Giass 2 of Exampie A on page 36, and output into Meter 3 in Fig. 4.2 on page 38, which are simiiar to the emitter foiiower s Output 3.  

When constructing this circuit, the experimenter should use the 120V to 12V transformer, with a power cord soldered on, and insulated with tape. The 12 volt secondary is center-tapped with a thin black wire, and the 100 ohm resistor is attached to this, so the initial tum-on current does not rush into the empty capacitor too fast. (This is called in-rush current, and it can damage some components. It can also occur when heated filaments or electric motors are first turned on.) 

Initially, the switch is closed, (really just a clip lead attached), applying a IK load. When plugging into the 120V wall socket, just one diode is used, and half-wave rectified dc fills the capacitor, as was done in the previous chapter. The meter reads about +5.5 volts. 

As an optional experiment, an additional diode can be hooked up as shown by the dashed line. This makes full wave rectified dc, which works in a manner similar to that of the four-diode bridge used in the previous chapter. As discussed in Chapter 11, filters can do further smoothing of the output. The combination of a bridge, the transistor, and an LC filter can provide good enough dc for radios and computers. Even better results can be obtained with feedback, and that will briefly be covered in Chapter 23. 

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Fig. 3-2. A, Phosphor-photoelectric detector B, sample cell C, sample D, CA-5 x-ray tube and housing E, milliammeter F, amplifier and rectifier vacuum tubes G, regulated power supply for amplifier tubes and multiplier phototube H, control panel.

Observe how the voltage output of the regulated power supply can be controlled. To do this, touch the red multimeter lead to the output of the regulated power supply, either P42 or P43, and rotate the knobs of the potentiometers, first the coarse, then the fine. You should observe that this output can vary between -5 and +5 V. Record your observations and your comments in your notebook. 

FIGURE 7.10 Block diagram of a basic electrochemical detector. All three electrodes are controlled by a regulated power supply coupled to a potentiometer and a series of amplifiers. The output from the electrodes is fed into a data acquisition system. 

Consider now a situation where, instead of a measuring instrument, one inserts (Fig. 6.31) into the circuit a source of potential (e.g., an electronically regulated power supply). Here, the total potential difference across the cell must equal (in magnitude) that put out by the source.18 This is, in fact, the law of conservation of energy applied to an electrical circuit, or Kirchhoff s second law The algebraic sum of all potential differences around a closed circuit must be equal to zero. For the simple hypothetical system shown in Fig.6.32, one has... 

Power sources based on the zinc-mercuric oxide system are particularly suited to a wide range of applications, mainly concerned with miniature portable electronic equipment, where a relatively constant voltage is required throughout long discharge periods. In addition, such cells are used as voltage reference standards in regulated power supplies, potentiometers, chart... 

Usually, after a reaction is about 98% complete, a current of about 0.1 of the normal value is used. In the apparatus developed for coulometry of high accuracy, the voltage of the regulated power supply seldom changes by more than 0.001% in a day, the current is accurately measurable through the use of a standard resistor (known to better than 1 ppm) of high precision, and adjustment of the iR drop is made equal to that of a Weston cell. The time can be measured to an accuracy of 1 ppm or better. ... 

The lower-powered microwave signals used by communication transmitters are usually produced by solid-state devices. The Gunn diode is an example. When supplied with voltage from a well-regulated power supply these devices reliably produce a few watts of microwave signal. 

Fig. 1. Electrochemical cell for the removal of residual silver ion. The cathode is a cylindrical platinum net electrode (18 X 40 mm) and the anode is a 20 X 40 mm platinum sheet. A Kimble fine frit (porosity 4-5.5) separates the anode from the cathode compartment. The checker has added a vent to the anode compartment to remove H2. A self-regulating power supply such as the Tektronix PS 501-2 works well.

Several commercial power supplies for constant current exist. We found a low-cost, regulated power supply (Delta Elektronika BV, Zierikzee, the Netherlands) Type E 060-0.6 for 0—60 V or 0-600 mA entirely satisfactory. 

In summary, the following experimental conditions should be used for a successful dimerization of carboxylic acids. An undivided beaker type cell (Fig. 2) is used, equipped with a smooth platinum anode and a platinum, steel or nickel cathode at a close distance a current density of 0.25 A cm or higher should be provided by a regulated power supply a slightly acidic or neutral electrolyte, preferably methanol as solvent and a cooling device to maintain temperatures between 10 and 45 °C should be employed. With this simple procedure and equipment, yields of coupling product as high as 90% can be obtained, provided the intermediate radical is not easily further oxidized. 

Most modern lamps of this type contain deuterium unijjirc of a low-voltage type in which an, irc is formed between a heated, oxide-coated filament and a metal elecirode (see Figure 1,3 I la). The heated filament provides electrons to maintain a direct current when about 40 V is applied between the filament and the electrode. A regulated power supply is required for constant Intensities. 

Different types of photosensitive detectors have been used for spectral intensity measurements, including barrier layer photocells, vacuum and gas photodiodes, and multiplier phototubes. By far the most commonly used device is the multiplier phototube because of its extremely high sensitivity and precision when powered by a voltage-regulated power supply. A variety of multiplier phototubes are available that have maximum response in different wavelength regions. 

Two common approaches are illustrated in Fig. 5.30 and Fig. 5.31. If the screen power supply impedance is excessively high in the direction of reverse electron flow, the screen voltage will attempt to rise to the plate voltage. Note the emphasis on low impedance in the reverse electron flow direction. Most regulated power supplies are low impedance in the forward electron flow direction only. If the supply is not well bled, the reverse electrons will try to flow from anode to cathode in the regulator series pass element. As the screen voltage rises, the secondary... 

Unitrode. 1984. Unitrode Switching Regulated Power Supply Design Seminar Manual. Unitrode Corporation, Lexington, KY. 

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