27.02.2015

Dc voltage regulator types

A negative fixed voltage regulator is same as the positive fixed voltage regulator in design, construction & operation. An adjustable voltage regulator is a kind of regulator whose regulated output voltage can be varied over a range. In this circuit, the value of Vref is the reference voltage between the adjustment terminals and the output taken as 1.25 Volt. The LM 337 series of adjustable voltage regulators is a complement to the LM 317 series devices. The resistor R2 shown in the figure is not an external component connected to the IC, but an internal resistor that is built inside the IC during manufacture. This shows that the output of the regulator can be controlled by putting desired values for R1 and R2. The IC has a series pass transistor that can handle more than 1.5 A of load current provided that enough heat sinking is provided along with it.
When there is quite a distance (in cms) from the IC to the filter capacitor of the unregulated power supply, there may occur unwanted oscillations within the IC due to lead inductances within the circuit. Any device in the LM 340 series needs a minimum input voltage at least 2 to 3 V greater than the regulated output voltage. Switching regulators differ in design,construction & operation compared to linear voltage regulators.
As shown in the figure above, the rectangular pulses are given to the base of the transistor. As shown in the figure above, when the transistor is saturated, the current flows through the inductor.
When the output voltage increases, the comparator circuit produces a higher output voltage and thus the inverting input of the triangle to pulse converter will have high value. Switching regulators are available in different configurations like the flyback configuration, feed-forward, push-pull, and non-iso­lated single-ended or single-polarity types. The LM 1578A IC was also developed by National Semiconductors and is used as a switching regulator for applications like dc-dc voltage converters, inverting configurations and buck-boost converters. From the functional diagram we can see that the IC has a comparator circuit with an inverting and on-inverting input along with a 1 volt internal reference to each input, which clearly simplifies the circuit design and PCB layout. Multi tap ic chip with verying input voltage from 12 v dc down to 3vdc with option to tap in at a voltage output level to match less than 12 volts and usuable voltage down from this for low drain circuits, Prototype made at Bond university Gold Coast Australia. The circuit has been constructed to provide an in-circuit system that will test the integrity of electronic components such as Silicon Controlled Rectifiers, diodes, and PNP or NPN transistors. The circuit was designed for the purpose of creating a voltmeter with high impedance that would measure Direct Current voltages across any types of circuits. Shown in the figure is an IC voltage regulator (also known as stabilizer), designed to increase its current output with the use of an outboard pass transistor. The circuit has been designed using a single CMOS integrated circuit of model 4069 to produce a frequency that is twice of the input signal by functioning as a frequency doubler.
The circuit illustrates the function of a switch that responds sensitively by means of a touching mechanism with the utilization of two CMOS with models 4027 and 4011. ATMega162 based homemade digital oscilloscope project with a sampling rate of 40MSPS and 5MHz maximum input frequency.
The circuit was designed to create ten different frequency bands to be handled by a single graphic equalizer to produce and maintain a predetermined area of frequencies. The project was built around the Hitachi lateral power MOSFETs to create high fidelity Class AB amplifier. Next to the voltage is the amount of current needed to make the microcontroller to work properly. Therefore is a good practice to run your microcontroller at the half of the maximum current allowed by its electrical specification and make sure you are sourcing or sinking the microcontroller’s ports within its electrical specification.
By knowing your microcontroller voltage, operating current and summing all the total current needed by the other supporting peripheral on the project such as LEDs, Motors, Relay, LCD, etc; now we could determine the right power supply to the project. All the microcontroller circuit needs a direct current (DC) in order to operate and the perfect source for this current type is a battery. The best widely available battery for the microcontroller project is the AA type battery which available both in NiMH (Nickel Metal Hydride) rechargeable and Alkaline type; I always recommend this type of power source especially when you are doing your first microcontroller project.
You could also experiment with various battery types such as the 3 Volt CR2 lithium used for powering the photo camera or 3.7 Volt cell phone batteries for powering your project.
Before continuing, I would like to remain you about working directly with the electricity, that you should always take extra precaution and extremely aware to the danger of the electrical shock. From the time diagram above we could learn how this AC to DC converter circuit work; the AC wave form is a 50 Hz sinusoidal wave form and the AC voltage value is always presented in its effective value which is equivalent to the DC value or we could say that the AC effective voltage value will give the same amount of energy as the DC voltage value does.
On the first-half cycle (red color), the D2 and D4 diode will be on (forward bias) while the D3 and D1 diodes will be off (reverse bias), this will charge the capacitor and when the AC wave is falling down then the capacitor will discharge its energy through the load; on the second-half cycle (blue color), the D3 and D1 diode will be on (forward bias) while the D2 and D4 diodes will be off (reverse bias), again this will charge the capacitor and when the AC wave is falling down, the capacitor will discharge its energy through the load. This cycle will continue repeating every 100 Hz (twice the AC frequency) and the result we have the DC output where its voltage value will almost equal to the AC maximum voltage value minus the diode forward bias voltages. As you notice from the AC to DC converter circuit, the DC voltage produce by this circuit is depend on the load; the heavier the load (more current to the load) means the capacitor discharge time will be more faster and as a result the DC voltage output level will be drop. The first one is the analog voltage regulator, this type of regulator operate the transistor in its linear region (current gainer). The second one is the most efficient voltage regulator as this type of voltage regulator operates the transistor in its saturate region or known as a switching voltage regulator.
Now as we understand the basic of how this voltage regulator work, its time to make our own voltage regulator.
Below is the picture showing the LM 2940 IC circuit is use to power to the microcontroller’s board. This is my favorite voltage regulator, although it’s required more component compare to the analog one and of course more expensive but the result is worthy.


The bridge is use to ensure the correct polarity supplied to the LM 2576 IC, below is the JazzMate 2576-5V board from the ermicro powering the microcontroller board. The other advantage of using the switching voltage regulator, that it’s more immune to the noise compare to the analog one especially when you control the device that generate noise such as DC motor with the microcontroller. The LM317 is the classic and widely available adjustable voltage regulator which is suitable especially for the experimenter where we need to change the voltage output regularly for example to test the brown out voltage level of the microcontroller. The following picture shows the LM 317 IC circuit powering the microcontroller’s board. You should always be aware of the power dissipation (power lost as heat) when you are working with the analog voltage regulator; therefore it would be wise to put the heat sink to the IC especially when you drain lot of current from it. Do you think it is possible to get a symmetrical +-5V supply from 2 AA batteries and a couple of MAX756 ?
I want to ask you if I use this source using MAX756 for Mini Line Follower Robot and driving a motor?May we use heatsink for remove heat dissipation? Remember the MAX756 maximum current on 5 volt is less than 200mA and on 3 volt is less than 300mA.
Controlling the Motor is one of interesting topics in the embedded world especially for the robotics enthusiasts, on the next post we will learn the basic of motor electronic circuit as well as how to control it with microcontroller.
The block diagram of basic series DC voltage regulator is shown in figure, which is consisting of four stages. In the figure of basic op-amplifier series voltage regulator , the op-amp is used as comparator . Over years we have published a handful of voltage regulator circuits in this website – which serve many purposes. Some circuits based on LM317 voltage regulator Few useful circuits using the voltage regulator IC LM317 is shown here. A regulated voltage (without fluctuations & noise levels) is very important for the smooth functioning of many digital electronic devices. A common type of classification is 3 terminal voltage regulator and 5 or multi terminal voltage regulator. There are two variations of the same; known as positive adjustable voltage regulator and negative adjustable regulator.
Right now we shall discuss how an LM317 adjustable positive voltage regulator IC is connected.
This means that the output voltage varies only 0.01 percent for each volt of input voltage. The negative adjustable voltage regulators are available in the same voltage and current options as the LM 317 devices.
Thermal shutdown is a feature that will turn off the IC as soon as the internal temperature of the IC rises above its preset value. In order to remove this unwanted oscillation, the capacitor C1 has to be placed as shown in the circuit.
During each cycle of the pulse the transistor changes between saturation and cut-off.When the transistor is saturated the current flows through the inductor. When the transistor switches to cut-off a large voltage will be induced across the inductor coil because of the sudden collapse of the magnetic field around it. By controlling the duty cycle of the pulse generator, the duty cycle of the input voltage to the LC filter is controlled. This voltage is then fedback to the comparator circuit where a reference voltage Vref is compared with the output voltage and passed on to the negative input of the triangle to pulse converter. Since the error voltage to the comparator is near zero, the voltage across R2 is approximately equal to Vref. Both these IC’s are known for their minimum component fabrication, and simple to use facilities. This IC is known for its high efficiency and will clearly replace all 3-terminal linear voltage regulators.
Both the IC’s are available fo different voltage levels like 12 volts and 15 volts and are adjustable.
The IC is known for its flexibility in design by providing output pins for the collector (Pin 6) and emitter (Pin 5). An oscilloscope is one of the most important tools that should take place on a electronics hobbyist’s workbench. Sometimes we take it for granted the important of having an adequate power supply to our microcontroller project and this can lead to the unexpected result or behavior from the circuit.
Nowadays most modern microcontroller only needs a tiny direct current (in micro ampere order) to operate as introduced by Microchip with their nanoWatt PIC microcontroller families or Atmel with their pico-technology AVR microcontroller families.
Today modern battery is evolve to be more compact yet more powerful to provide the power required by the sophisticated gadget such as cell phone, iPod, MP3 player, PDA, camera, etc.
Most of electronics devices use the direct current (DC) and lower voltage level to operate; consequently we have to convert AC to DC and the voltage level as well.
The circuit above is called unregulated AC to DC converter; because it could not maintain its voltage output level, this kind of power source could not be use in electronic circuit that required constant voltage level in order to operate properly such as in digital and microcontroller circuit. The current supplied to the transistor base lead is depend on the voltage different between the reference voltage and output voltage apply to the error amplifier input; for example when the output voltage is greater than the reference voltage, than the error amplifier will make the transistor to conduct less, this mean the voltage drop across the collector and emitter (Vce) will be increase this will make the output voltage to decrease and vice verse. The working principal is the same as the analog one, but instead of using the constant current to the transistor base lead; this voltage regulator type use pulse current or known as PWM (Pulse Width Modulation) to the transistor base lead and this make the transistor to turn on and off according to the PWM duty cycle supplied by the error amplifier.
Today there are plenty choices of the voltage regulator IC on the market and we will just explore some of them. Also another consideration; it would be better to separate the power circuit (voltage regulator) from your microcontroller board as it will be more flexible for you to use many type of the power source. In the shunt voltage regulator, the reference voltage unit produces constant voltage to the error detector stage.


In the series voltage regulator the controlling element (Q) is connected in series but in shunt regulator the transistor is connected in parallel. MSK5012 is a highly reliable adjustable voltage regulator.Whose output can be programmed using two resistors. Switching regulators work by drawing small amounts of energy from the input source and transferring it step by step to the output.
We need styles that are quick and easy to maintain without having to wake up at the break of dawn every morning to get it right. A common case is with micro controllers, where a smooth regulated input voltage must be supplied for the micro controller to function smoothly. An example of IC based voltage regulator available in market is the popular 7805 IC which regulates the output voltage at 5 volts. A fixed voltage regulator can be a positive voltage regulator or a negative voltage regulator. LM317 is a classic example of positive adjustable voltage regulator, whose output voltage can be varied over a range of 1.2 volts to 57 volts. This rise in temperature may mostly be due to excessive external voltage, ambient temperature, or even heat sinking. Though they are chosen for different purposes, they do have a disadvantage of high power dissipation of the series pass transistor. Thus the current keeps flowing in the same direction.Since the transistor is cut-off, the only path is through the capacitor. Since the duty cycle is lower, the filtered output voltage is less, which tends to cancel almost all the original increase in the output voltage. These IC’s also have the advantage of internal frequency compensation and fixed frequency oscillator. In this tutorial we will learn the principal of powering our microcontroller and how we could provide the microcontroller circuit with a good and yet simple power supply. The same principal also applies to our microcontroller when we drive the microcontroller with higher clock speed in order to increase the execution time speed, we certainly need more power. This type of microcontrollers makes them suitable for used as the portable devices in the remote area where the power is limited to the portable power source such as battery or the solar cell. The LED and the 1 K current limiter resistor is use as the power indicator as well as the discharge circuit to the capacitor when we unplugged this circuit from the electricity power outlet. Therefore we need what is called Voltage Regulator Circuit and at the same time works as the DC to DC voltage step down. With output voltage being continuously compared to the reference voltage (close loop feedback) by the error amplifier, this kind of circuit could maintain its voltage output level constantly.
Therefore by changing the PWM duty cycle we could change the average voltage drop across the collector and emitter (Vce). This kind of step-up power is widely use on digital and microcontroller circuit that powered by low input voltage battery such as micro alkaline 1.5 volt battery. When the input voltage-different high, the output current will also be high, notice that the consumption should not be too high. The main reason is because the series pass transistor is used as a Class A power amplifier which is known for its low efficiency and power loss in the form of heat. That is, instead of the transistor working in the active region, it is made to switch between the saturation region or cut-off region.
The ac components of the input voltage to the filter is blocked and the dc component is allowed to pass through the filter. If the direction of charging current through the capacitor is checked, output voltage is found to be negative. The square wave is given as input to the integrator and produces an output triangular wave. It means that any attempted increase in output voltage generates a negative feedback voltage that almost eliminates the original increase. According to the type of use of the IC, an external current limit terminal may be referenced to either the Ground terminal(Pin 4) or the the Vin terminal (Pin 8). Therefore we have to consider wisely and balancing between the speed and the power consumption.
The disadvantage of using this type of voltage regulator is the power dissipation (power lost as a heat) on the transistor is high especially when we want to use 5 Volt output from 11.33 volt from the unregulated DC source or drain lot of current from it. It is an integrated circuit whose basic purpose is to regulate the unregulated input voltage (definitely over a predefined range) and provide with a constant, regulated output voltage. Because of thermal shutdown and current limiting, devices in the LM 340 series are almost indestructible.
Thus, the power dissipation is lessened and thus can carry heavy load currents at low voltages with less bulky heat sinks.
As the transistor keeps switching, the average value will always be lesser than the input voltage.
The following graph is the example of some popular microcontrollers with their operating voltage and frequency (for detail please refer to their respectively datasheet).
In addition, the LM 1578 A has an on board oscillator, which sets the switching frequency with a single external capacitor from < 1 Hz to 100 kHz (typical). Such linear regulators will also need a step-down transformer which again increases the size of the overall circuit. The large ripples produced by the circuit should be eliminated and this requires large sized filter capacitors.




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