Friday, 8 March 2013

DC Power Supply 12



Voltage multipliers

 A special rectifier circuit voltage multiplier output which is theoretically an integer times the AC peak input, for example, 2, 3, or 4 times the AC peak input. Therefore, it is possible to get 200 VDC from Vpeak AC source using duplicate 100, 400 VDC from quadrupler. Any load in a practical circuit will lower these voltages.An application of DC voltage doubler power supply capable of using either 240 VAC or 120 VAC source. Supply using a switch selected full-wave bridge to produce about 300 VDC from a 240 VAC source. Position 120 V switch rewires the bridge as a duplicate of producing about 300 VDC from 120 VAC. In both cases, 300 VDC is produced. This is the input to the switching regulator producing lower voltages for powering, say, a personal computer.Half-wave voltage in Figure below (a) consists of two circuits: a clamper at the detector (b) and peak (half-wave rectifier) ​​in Figure prior, shown in modified form in Figure below (c). C2 has been added to the peak detector (half-wave rectifier).



 the half-wave voltage doubler (a) consists of (b) clamper and (c) a half-wave rectifier.

Refer to Figure above (b), C2 charges to 5 V (4.3 V considering the diode drop) on the negative half cycle of the AC input. Is based on the right end of the run D2. The left end is charged at the negative peak AC input. This is the operation of the clamper.
During the positive half cycle, half-wave rectifier comes into play at Figure above (c). D2 diode circuit since it is reverse biased. C2 is now in series with the source voltage. Note polarity generator and C2, series help. Thus, rectifier D1 view of 10 V at the top of the sinewave, 5 V from generator and 5 V from C2. D1 run wave v (1) (Figure below), charging C1 peak sine wave riding on 5 V DC (Figure below v (2)). Wave v (2) is a duplicate output, stable at 10 V (8.6 V with diode drops) after a few cycles of sinewave input.

DC Power Supply 11

Regulator Transistor
In the simplest case emitter follower is used, the base of the control transistor is directly related to the reference voltage:


 
Stabilizer uses the power source, having voltage UIN may vary from time to time. It delivers Uout voltage constant. Output load RL can also vary from time to time. For such a device to work properly, the input voltage must be greater than the output voltage and voltage drop must not exceed the limit of transistor used.
Stabilizer output voltage is equal to the UZ - Ube Ube which is about 0.7 V and depends on the load current. If the output voltage drops below the limit, this increases the voltage difference between the base and emitter (Ube), opening the transistor and delivering more current. Delivering more current through the same output resistor RL increase voltage again. When the output voltage increases, because the base-emitter voltage is reduced BJT will run less and regulations will be maintained.


Rv values ​​limit the maximum output current Iout, which have upper limits. Rv (a rough estimate) should not be greater than (UIN - UZ) / IB, where IB is the maximum Iout current ratio dividing the transistor amplification.
 
Regulator with operational amplifier

 
Stability of the output voltage can be increased significantly by using operational amplifiers:


 
In this case, the operational amplifier drives the transistor with more current if the voltage at the inverting input drops below the output voltage at the input reference is not inverted. Using a voltage divider (R1, R2 and R3) allows choice of arbitrary output voltage between Uz and UIN.  


LM317


Attribute
Value
Vout range
1.25 V – 37 V
Vin – Vout difference
3 V – 40 V
Operation ambient temperature
0 – 125
Output Imax
less than 1.5 A (assuming factory-suggested heat sinking)
Minimum Load Currentmax
10 mA

operation
LM317 is a linear voltage regulator is used in a DC to DC converter applications. Overall function similar LM317 regulators LM78xx series. While the 78XX series regulators have set the output voltage (eg 7805 has an output 5V), LM317 can be adjusted to any voltage (within limits).