Power Supply Model XP-720 Instruction Manual
The Model XP-720 Power Supply features three solid-state DC power supplies and a 12.6VAC center tapped output. The first two DC supplies consist of one positive and one negative 1.5 to 15 volts at 1 ampere. The third has a fixed 5V at 3 amperes. All DC supplies are fully regulated. A special IC circuit keeps the output voltage within .2V when going from no load to 1 ampere. The output is fully protected from short circuits. The AC section has 6.3VAC @ 1A and a 12.6 center tapped @ 1A. This supply is ideal for use in school labs, service shops or anywhere a precise DC voltage is required.
Transformer
The transformer T1 serves two purposes. First, it reduces the 120VAC input to 17VAC to 8VAC to allow the proper voltage to enter the rectifier stages. Second, it isolates the power supply output from the 120VAC line. This prevents the user from dangerous voltage shock should the user be standing in a grounded area. AC to DC Converter
The AC to DC converter consists of diodes D1 and D3 and capacitor C5. Transformer T1 has two secondary windings which are 180 degrees out of phase. The AC output at each winding is shown in Figure 2A and 2B. Diodes are semiconductor devices that allow current to flow in one direction. The arrow in Figure 3 points to the direction that the current will flow. Only when the transformer voltage is positive will current flow through the diodes. Figure 3 shows the simplest possible rectifier circuit. This circuit is known as a half-wave rectifier. Here the diode conducts only half of the time when the AC wave is positive as shown in Figure 2C. Use of this circuit is simple but inefficient. The big gap between cycles require much more filtering to obtain a smooth DC voltage.
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