1, a zener diode voltage regulator circuit
Zener diode, also known as Zener diode, until a critical reverse breakdown semiconductor device having a high voltage resistance before. In this critical breakdown point, reverse resistance is reduced to a small value, a large change in current flowing through the low-resistance region although the diode, and the voltage across it changes little and this phenomenon is repeated very good, and thus play the role of regulator. Because of this characteristic, the regulator is used primarily as a regulator or a voltage reference element.
Wherein, Us is the unregulated DC input voltage, U. A regulated DC voltage, Rs is the resistance of the current limiting protection in Dz, voltage regulation action underway, D2 is the zener diode, R is the load resistance. Its working principle is: the circuit characteristics of the main regulator using a zener diode, which remains substantially constant pressure drop across the reverse conducting i.e. Dz. When Rs of Us due to the increase, the current increases, but the U. I.e., the voltage across the D remain constant, increase amount such Us drop over Rs of all, to maintain the U. Unchanged, and vice versa. R in practical applications and D2 intrinsic properties play a key role for the entire regulation process.
This working range is limited by the voltage regulator circuit regulator maximum power, Iz not exceed a certain value. The key is: Us, R and U. Under conditions are given, the selected value of Rs should ensure maximum at the maximum input voltage USmax, stable current Iz and the regulator allowing no more than a predetermined power; the input voltage is the minimum value, and Iz ensure stability of not less than the minimum current.
2, regulator circuit shunt transistor
Solid type semiconductor device is a transistor, it can be used for detection and rectification, amplification, switches, regulators, signal modulation and many other functions. A variable transistor as a switch, based on the input voltage, the control current flowing, the transistor can be used as a current switch.
Where T is the adjustment pipe, D2 is a reference regulator, Rs is a current limiting resistor in Dz, R. It is the load. The output voltage of the regulator circuit is approximately equal to the Zener voltage of Dz (T actually add to the emitter voltage, germanium tube generally take 0.3V, silicon tube take 0.7V). This is because the power at work, T emitter is turned on, the emitter voltage and the base connected to a voltage consistent Dz and the base voltage is stabilized at a fixed value. This circuit may be viewed as T Dz regulator role magnified B times, corresponding to the access regulator is a regulator tube Dz voltage value, voltage regulation to voltage regulation of B times D2.
Shunt regulator regulator circuit performance has improved, the line is not complicated, the advantages are: there overload protection performance, does not damage the regulator output circuit; changes in the load hours, better regulator performance; instantaneous change better adaptability. Shunt regulator circuit but also have relatively large drawback: low efficiency, especially at light loads, the power consumption in almost all of the current limiting resistor and the regulator; visible small output voltage regulation; easy to do very high stability. These inherent drawbacks difficult to improve, it is now the widespread use of a series regulator circuit.
A simple series transistor regulator circuit. Adjusting tube T with the load resistor R. In series, or when the power supply changes since the circuit causes the output voltage ripple, it can be adjusted in a timely manner, the output voltage remains substantially stable, so it is called the regulator. Regulator tube Dz provided for the adjustment of the reference voltage, the base potential regulator unchanged. R. D2 is a protective resistor to limit the current through D2, the zener protective role.
The principle of the self-excited power supply analysis (typically four DC circuit)
This process regulator circuit paradox: if the input voltage Us is increased, the output voltage U. Is increased, since the fixed U. = U, set between the base-emitter voltage regulator Uo = UU:. The reduced base current I. Decreases, the pressure drop U. increases, offsetting Us enlarged portion, so U. Basically stable. If the load current I. Increases, the output voltage U. When reduced, since the U. Fixed, U "will increase, U. Reduced, so that similarly U. Basically stable.
Analysis can be seen from the above, as both the regulator is an automatic variable resistance: When the output voltage increases, its "resistance" is increased, a large share of the voltage out; when the output voltage is reduced, its "resistance" is reduced, make up a little down the voltage. In either case, the output of the circuit to maintain a stable voltage. Such stabilizing circuit can output a large current, and low output resistance, good regulator performance; circuit is also easy to fabricate, but it also has disadvantages such as the output voltage is not adjustable.
4, switching regulator circuit
Radiator, greatly reduced size and weight, small size, high efficiency advantages. This switching circuit has been widely used in various electronic devices.
Switching power supply to the control mode is divided and FM modulation width of Formula two, in practical applications, the use of too large width adjustment formula, currently developed and used in a switching power supply integrated circuits, but also for the vast majority of pulse-width modulation.
Based on the above-described linear power supply circuit may be small linear regulator circuit structure is simple, reliable, but it has a low efficiency (only 30% -50%), bulky, copper and iron consumption, high operating temperatures and the adjustment range and other shortcomings. To solve the linear regulator power dissipation major disadvantages, the development of the switched-mode power supply. Conversion rate of the switching regulator up to 60% to 85%, and the basic frequency transformer circuit may be omitted and the tremendous switching power supply block diagram shown in FIG. The rectified AC voltage rectifier filter circuit and filter circuit, into DC voltage ripple component contains a certain amount, the voltage-frequency converter into a square wave is converted into a desired voltage value, then finally the square-wave rectified voltage filter into a DC voltage required. The control circuit is a pulse width modulator which is mainly composed of a sampler, a comparator, an oscillator, a pulse width modulation circuit and the reference voltage or the like. This part of the circuit has been integrated to produce a switching power supply integrated circuit. A control circuit for adjusting the proportion of high-frequency switching time of the switching element, in order to stabilize the output voltage.
The method commonly used to realize switching control; self-excited switching regulators, pulse width modulation switching regulator and switching regulator DC converter and the like. Switching regulator circuit of small size, high efficiency, but the more complex control circuit. With the rapid development of electronic self-turn-off devices and the electricity power integrated circuits, the switching power supply has been more widely used.
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