Switching

     Modifiers DC-DC power (DC-DC Converter) with the title chopper DC (DC Chopper) is used mainly to supply DC output voltage that varies the amount in accordance with demand on the load. Power input from DC-DC process is derived from the DC power source which typically have a fixed input voltage. Basically, the income of the DC output voltage is to be achieved by regulating the length of time the connection between the output and input side on the same circuit. Components used to perform a liaison function is none other than the transistor. In general there are two functions of the operation of the chopper DC (DC Chopper) that is raising the voltage where the resulting output voltage is higher than the input voltage, and a decrease in voltage where the output voltage is lower than the input voltage.

     To better understand the benefits of this type of transition, can be seen the principle of DC-DC power conversion of linear type as shown in Figure 1.

Figure 1 Modifiers linear type.

 

 

     In the linear type, the output voltage regulation is achieved by adjusting the current in the load depends on the large amount of current on the transistor base:  V₀ = I_L . R_L  

      Thus the linear type, the transistor functions like prisoners who can be changed also quantified as shown in Figure 1. Furthermore, the transistors that are used can only be operated on the linear constraints (linear region) and not exceed the limit cut-off and saturated regions (saturation region). Therefore this type is known as the linear type. Although the linear type is the easiest way to achieve varying output voltage, but less attractive in power applications because of the high power loss (power loss) at the transistor (VCE * IL) resulting in low efficiency. As an alternative, it appears the transition type, which in principle can be seen in Figure 2.

Figure 2. Modifier type transition.

 

      On the type of transition, visible transistor functions as electronic switches that can be opened (off) and closed (on). Assuming that the switches are ideal, if the switch is closed, the output voltage will equal the input voltage, whereas if the switch is opened, the output voltage will be zero. Thus the output voltage pulse generated will be shaped as in Figure5.

Figure 3. Voltage switching.

 

     The amount of the average or DC component of the output voltage can be derived from the following equation: 

 

     From the equation above shows that the DC output voltage can be quantified by adjusting the parameter D. The parameter D is known as the duty ratio is the ratio between the length of time the switch is closed (tons) with period T of the output voltage pulse, with 0 <D <1. Parameter f is the switching frequency (switching frequency) used in operating the switch. Unlike the linear type, the type of transition no power is absorbed in the transistor as a switch. This is possible because the switch is closed when no voltage is dropped on the transistor, while during the switch is opened, there was no electric current flows. This means that all power is absorbed in the load, so power efficiency to 100%. But remember, in practice, no switches are ideal, so it will stay there the slightest power loss in the switch components and the efficiency is very high though, will never reach 100%.

Series Rectifier with Capacitor Filter

     To provide a stable DC output, the filter circuit to smooth the DC voltage. Half-wave rectifier is rarely used because it is inefficient and requires a grading capacitors are relatively large.

Picture 1. Wave rectifier with filter C

Figure 1 is a series of full wave rectifier with filter capacitor C is parallel to the load R. By adding this filter output voltage waveform becomes more flat. Figure 2 shows the DC voltage output from a series of half wave rectifier with capacitor filter

Picture 2. Wave output with filter C

Rectifier Diodes

     Diodes are the connection PN material that serves primarily as a rectifier. P-type material into the anode side while the N-type material into the cathode. Depending on the polarity of the voltage given to him, the diode can act as a switch is closed, if the anode gain a positive voltage while katodenya get a negative voltage. And apply as a switch opens when the anode have a negative voltage while the cathode get a positive voltage. This condition occurs only in the ideal diode-conceptual. In diode factual (real), it is necessary voltage greater than 0.7 V (for diodes made ​​of silicon) on the anode to the cathode for the diode to conduct electrical current. Voltage of 0.7 V is called a barrier voltage. Semi-conductor diode there are two kinds of silicon and germanium. In general that is used is silicone, which is not a conductor material and not insulators but have properties between them. A diode is divided into two parts, namely N-type silicon and silicon-type P. N-type manufacturing process with a chemical process called doping, this material is made ​​to have the free electrons in larger quantities. P-type doping is obtained by a different process in order to get a lot of holes. Hole shift from one atom to another atom in the silicon material. It is common to assume a free electron in a silicon N (anode) and holes in silicon P (cathode) as the carrier flow.

Picture 1. Meeting P-N is an insulator

 

     Regional meetings between P and N called the meeting to form a PN diode. At the meeting, free electrons from silicon material to fill holes in material N P, so this area is no more free electrons and holes so that the silicon becomes an insulator.

Picture 2. Symbols and physical form diodes

Picture 3. Given diode reverse bias

     If the diodes are reverse bias (+ to the N and - to P), see figure 3, the diode does not deliver because of the expanding PN meeting, see Figure 3. When the diodes are forward biased (+ to P and - to N), see figure 2.5a, then the insulating area does not appear that deliver diode, see figure 4.

Picture 5. Given diode forward bias