When used with a minimum of external components, this device is ideal for a wide variety of applications including precision programmable voltage references, high speed amplifiers, comparators, linear series or shunt regulators, current sources or limiters, delay timers, voltage monitors, alarm circuits, and oscillators. This application note demonstrates the versatility of the AS in typical applications and presents data useful for gaining a complete understanding of its application. Figure 1 shows the schematic symbol and functional block diagram for the AS As indicated by the schematic symbol, the device can be thought of as a programmable zener diode.
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When used with a minimum of external components, this device is ideal for a wide variety of applications including precision programmable voltage references, high speed amplifiers, comparators, linear series or shunt regulators, current sources or limiters, delay timers, voltage monitors, alarm circuits, and oscillators.
This application note demonstrates the versatility of the AS in typical applications and presents data useful for gaining a complete understanding of its application. Figure 1 shows the schematic symbol and functional block diagram for the AS As indicated by the schematic symbol, the device can be thought of as a programmable zener diode. The functional block diagram, however, reveals a versatile IC consisting of a trimmed 2.
It is capable of shunting from 1 to milliamps and has an output voltage range of 2. Note that only one external resistor is required for an output voltage equal to VREF. For output voltages other than VREF, a simple resistor divider network is used. Fixed 2. A single resistor R is used to set the cathode current IK. The circuit can be made variable by using a potentiometer for R1.
Generally, R should be chosen to give about 10 mA of cathode current. This will keep the power dissipation low.
The voltage across R is 20 — 2. Thus, an R of 1. Programmable Output To program the output to any desired value between VREF and 30 volts, a simple resistor voltage divider is used as shown in Figure 2B. Figure 3 shows a simple linear voltage regulator. This circuit converts an unregulated DC source rectified AC or battery to a low-noise, low-ripple precision-regulated DC output. The output voltage can be set to any desired value between 2.
Its values should not be so low as to cause excessive power dissipation, nor too high that an error is introduced due to changes in IREF over temperature IREF is typically 0. A and deviates 0. A over the full temperature range. The network type and values are chosen so as to ensure stability and proper transient response. Note that there are many different types of switching power supply topologies having different compensation, isolation and PWM configurations.
The AS and associated circuitry, however, are essentially the same in all cases except for component values, the type of compensation network used and location it may be located on the primary side in some applications.
The AS may also be used for other functions in a switch mode power supply. Figure 6 illustrates several of these applications. A typical single zero-pole pair compensation network is shown in Figures 4 and 5. Due to the complexity of frequency compensation network design and the vast number of power supply topologies possible, a detailed discussion is beyond the scope of this application note.
However, the information provided is useful in determining the compensation needed for a particular application. The AS as a MagAmp Controller Post regulation is required in many cases for one or more outputs of a switch-mode power supply. Linear regulators incorporating the AS are adequate for most low current outputs. Generally speaking, a MagAmp is a pulse-width modulated buck regulator circuit that uses a saturable core inductor as the switching element.
The inductor initially has a high inductance that blocks a pre-determined number of volt-seconds. Upon saturation, the inductor reverts to a very low impedance, which allows current to flow to the output with little loss. The number of voltseconds blocked in each cycle is defined by the control circuitry and varies in accordance with changes in line and load, providing tight regulation at the output. The AS is an ideal low-cost MagAmp controller, for it contains all the necessary control functions needed precision reference, high gain Application Note 1 error amplifier and an output stage in a small package.
Since this circuit constitutes a closed loop system, frequency compensation of the error amplifier is necessary. Other Applications The AS also can replace an ordinary zener diode in any circuit where a higher accuracy and temperature stability is required.
Applications for this device are limited only by the imagination. Several practical applications are illustrated in Figure 6. Typical AS Applications ASTEC reserves the right to make changes without further notice to any products described herein to improve reliability, function, or design. ASTEC does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights or the rights of others.
ASTEC products are not authorized for use as components in life support devices or systems intended for surgical implant into the body or intended to support or sustain life. Milpitas, California ?
ADJUSTABLE PRECISION SHUNT REGULATORS
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