The s1206 series is a positive voltage regulator with ultra low current consumption, low dropout voltage, highaccuracy output voltage, and 250 ma output current developed based on cmos technology. The current through the shunt regulator has diverted away from the load and flows uselessly to the ground, making this form usually less efficient than the series regulator. Circuit diagram of transistor series voltage regulator. Zener controlled transistor series voltage regulator such a circuit is also named an emitter follower voltage regulator. The transistor works as a variable resistor regulating its collector emitter voltage in order to maintain the output voltage constant. In this circuit however, they are used to provide a stable voltage reference v z at the base of tr1. The series regulator is based on the use of one or more pass transistors that possess a variable voltage that is in series with the output voltage. The purpose of load regulation is regulating output voltage when theload changes.
Because the total load current passes through this transistor, it is sometimes called a pass transistor. There are two kinds of zener controlled transistor voltage regulators. Transistor series voltage regulator the circuit is shown in fig. They are exceptionally easy to use and require only 2 resistors to set the output voltage. Controlled transistor series regulator with overload and. Zener controlled transistor series voltage regulator. Shunt voltage regulator is connected in shunt with the load. High precision voltage regulator features input voltage up to 40 v output voltage adjustable from 2 to 37 v positive or negative supply operation series, shunt, switching or floating operation output current to 150 ma without external pass transistor. This provides a simple form of feedback system to ensure the zener voltage is. Transistor zener diode regulator circuits tricks and tips for the lm78xx series voltage regulators. The l200 is a positive variable voltage regulator which includes a current limiter and supplies up to 2 a at 2. Series voltage regulators 2 voltage reference formed by the shunt regulator, r1 and d1.
March 8 lm78xxlm78xxa 3terminal 1a positive voltage. The circuit uses a single pass transistor in the form of an emitter follower configuration, and a single zener diode or other voltage regulator diode driven by a resistor from the unregulated supply. The output of the opamp drives the series pass transistor. The figure below shows the transistor series voltage regulator. Transistor seriesvoltage regulator or emitter follower voltage regulator emitter follower. Transistor series voltage regulator electronics post. The l78 series of threeterminal positive regulators is available in to220. In the shunt voltage regulator the output dc voltage is constant. Such a circuit is also named an emitter follower voltage regulator. This regulator has a transistor in series to the zener regulator and both in parallel to the load.
Here, the control element is the npn transistor, often called the pass transistor because it. Different types of voltage regulator and working principle. You may work ahead if you like, but do not fall behind. The load current i l flows through resistor r 5, causing a voltage. The series regulator circuit using opamp is shown below. It is also called emitterfollower regulator because the voltage at the emitter follows the base voltage. This provides a simple form of feedback system to ensure the zener voltage. The npn transistor was replaced with a pnp transistor, and the polarity of the zener diode and 100uf capacitor were reversed. The circuit of a transistor series voltage regulator with foldback current limiting facility is illustrated in the figure. This handbook describes on semiconductors voltage regulator products and provides information on applying these products. Voltage regulators,circuits,types,working principle. A voltage regulator generates a stable output for the variations in input or load. The lm 337 series of adjustable voltage regulators is a complement to the lm 317 series devices. Although designed primarily as fixed voltage regulators, these devices can be used with external components to obtain adjustable voltage and currents.
Since the zener voltage is constant, the increase in v o causes v be to decrease. Contents1 line regulation2 load regulation 3 linear and switching voltage regulator3. In line regulation output voltage is regulated when the input voltage changes. They are series voltage regulators shunt voltage regulators. Transistor series regulator since q 1 is an npn transistor, v o is found as. Output transistor safe operating area protection general description the lm78xx series of three terminal positive regulators are available in the to220 package and with several. A single transistor may be used instead of a darlington pair. The voltage drop of the diode is approximately equal to the transistor base emitter voltage. The three transistors and r2 and r3 form a high gain amplifier that is a very simple version of an operational.
Difference between shunt voltage regulator and series. The decrease in v be reduces conduction through the pass transistor. The schematic for a typical series voltage regulator is shown in figure 434. Note that in a transistor the current required by the base is only 1hfe times the emitter to collector current. Voltage regulation is classified into line regulation and load regulation. So a low power rated zener diode can regulate the base voltage of the bjt that can pass a huge current through it. There are different types of voltage regulators like zener, series, shunt, fixed. Study of transistor series voltage regulator, when input voltage. Transistor seriesvoltage regulator or emitter follower voltage regulator emitter follower voltage regulator. The voltage divider consisting of r1 and r2 is the sample and adjust circuit. Finally, the circuit design is tested after part eight is completed.
The s35 series, developed by using the cmos technology, is a positive voltage regulator ic of 150 ma output current, which has low dropout voltage, highaccuracy output voltage and softstart function. Other relevant topics include tradeoffs of linear versus switching regulators, series. The negative adjustable voltage regulators are available in the same voltage and current options as the lm 317 devices. Maturity status link l78 positive voltage regulator. That completes this introduction to zener diode based voltage regulation. In the figure below, you can see a simple series voltage regulator that is using a transistor and zener diode.
Lm8 and lm338 5amp adjustable regulators datasheet rev. A series regulator controls the voltage drop between input and output nodes by actively controlling the value of the series resistance. It actually controls the input voltage magnitude and. On this channel you can get education and knowledge for general issues and topics. A zener controlled voltage regulator is used when the efficiency of a regulated power supply becomes very low due to high current. Z1 should be rated at a quarter watt and a few volts above the desired voltage if the main linear regulator that will follow.
Basic linear regulator theory and switching regulator topologies have been included along with practical design examples. Discrete transistor series voltage regulator here from the block diagram, we can see an unregulated input is first fed into a controller. Simple series regulators, zener diode action, feedback, current limiting and. Notice that this regulator has a transistor q1 in the place of the variable resistor found in figure 432. Power supplies and linear regulators university of kansas. In the series voltage regulator the output dc voltages is not constant. Series voltage regulator circuitseries voltage regulator circuit shunt voltage regulator. Power supplies and linear regulators our objective is to examine characteristics, schematics, analysis, design and limitations of practical power supplies with ic regulators. Series voltage regulator has not so good voltage regulation at high load currents. To that end, an active device such as a bipolar junction transistor or field effect transistor. Transistorized low voltage regulator circuits and design. Pdf transistor seriesvoltage regulator or emitter follower.
Referring to figure1, the circuit works as follows. The emitter voltage of tr1 will be typically about 0. In some cases, the zener diode connected to the base of transistor. All the load current passes through the transistor q2 and thats why it is called a pass transistor. Negative feedback regulator control transistor series regulator duration. Lm78xx series voltage regulators general description the lm78xx series of three terminal regulators is available with several fixed output voltages making them useful in a wide range of applications. Series regulator using opamp analogintegratedcircuits. Series feedback voltage regulator electronics post. The output voltage is fixed with two resistors or, if a continuously variable output voltage. The collector current of q1 is controlled by the feedback voltage. The video shows how to make a 123 transistor series voltage regulator. Basic series regulator using a zener diode and emitter follower. Lm78xxlm78xxa 3terminal 1a positive voltage regulator. Constant current regulators battery chargers available packages typical application circuit 3 description the lm8 series of adjustable 3terminal positive voltage regulators is capable of supplying in excess of 5 a over a 1.
1185 608 655 1083 283 197 1055 822 931 757 796 882 960 1193 273 818 693 1088 800 1464 632 412 761 185 1070 1138 1033