Power Supply
APPLICATION NOTE
POWER SUPPLY DESIGN BASICS by P. ANTONIAZZI
Aimed at system designers whose interest focusses on other fields, this note reviews the basic power supply design knowhow assumed in the rest of the book.
In mains-supplied electronic systems the AC input voltage must be converted into a DC voltage with the right value and degree of stabilization. Figures 1 and 2 show the simplest rectifier circuits. In these basic configurations the peak voltage across the load is equal to the peak value of the AC voltage supplied by the transformer’s secondary winding. For most applications the output ripple produced by these circuits is too high. However, for some applications - driving small motors or lamps, for example - they are satisfactory. If a filter capacitor is added after the rectifier diodes the output voltage waveform is improved considerably. Figures 3 and 4 show two classic circuits commonly used to obtain continuous voltages starting from an alternating voltage. The Figure 3 circuit uses a center-tapped transformer with two rectifier diodes while the Figure 4 circuit uses a simple transformer and four rectifier diodes. Figure 1 : Basic Half Wave Rectifier Circuit. Figure 3 : Full Wave Rectified Output From the Transformer/rectifier Combination is filtered by C1.
Figure 4 : This Circuit Performs Identically to that Shown in Figure 3.
Figure 2 : Full Wave Rectifier Wich uses a Center-tapped Transformer.
Figure 5 shows the continuous voltage curve obtained by adding a filter capacitor to the Figure 1 circuit. The section b-c is a straight line. During this time it is the filter capacitor that supplies the load current. The slope of this line increases as the current increases, bringing point c lower. Consequently the diode conduction time (c-d) increases, increasing ripple. With zero load current the DC output voltage is equal to the peak value of the rectified AC voltage. Figure 6 shows how to obtain positive and negative outputs referred to a common
POWER SUPPLY DESIGN BASICS by P. ANTONIAZZI
Aimed at system designers whose interest focusses on other fields, this note reviews the basic power supply design knowhow assumed in the rest of the book.
In mains-supplied electronic systems the AC input voltage must be converted into a DC voltage with the right value and degree of stabilization. Figures 1 and 2 show the simplest rectifier circuits. In these basic configurations the peak voltage across the load is equal to the peak value of the AC voltage supplied by the transformer’s secondary winding. For most applications the output ripple produced by these circuits is too high. However, for some applications - driving small motors or lamps, for example - they are satisfactory. If a filter capacitor is added after the rectifier diodes the output voltage waveform is improved considerably. Figures 3 and 4 show two classic circuits commonly used to obtain continuous voltages starting from an alternating voltage. The Figure 3 circuit uses a center-tapped transformer with two rectifier diodes while the Figure 4 circuit uses a simple transformer and four rectifier diodes. Figure 1 : Basic Half Wave Rectifier Circuit. Figure 3 : Full Wave Rectified Output From the Transformer/rectifier Combination is filtered by C1.
Figure 4 : This Circuit Performs Identically to that Shown in Figure 3.
Figure 2 : Full Wave Rectifier Wich uses a Center-tapped Transformer.
Figure 5 shows the continuous voltage curve obtained by adding a filter capacitor to the Figure 1 circuit. The section b-c is a straight line. During this time it is the filter capacitor that supplies the load current. The slope of this line increases as the current increases, bringing point c lower. Consequently the diode conduction time (c-d) increases, increasing ripple. With zero load current the DC output voltage is equal to the peak value of the rectified AC voltage. Figure 6 shows how to obtain positive and negative outputs referred to a common