POWER SUPPLY MODEL XP-720 Instruction Manual Elenco Electronics, Inc. Copyright © 1997 Elenco Electronics, Inc.
SPECIFICATIONS ON XP-720 POWER SUPPLY Input Voltage Current Protection 110-130VAC 1A Output Voltage (at 120V input) 1) 2) 3) 4) 1.5-15VDC @ 1A 1.5-15VDC @ 1A 5VDC @ 3A 6.3, 12.6CTAC @ 1A Output Regulation 200mV each supply Line Regulation 100mV each supply Ripple Max 5mV RMS Current Protection 1A limit 2-15VDC 3A limit 5VDC Short Protection 1A limit 2-15VDC 3A limit 5VDC Output Impedance .025Ω each supply CAUTION: The maximum output current for the AC section is 1 amp.
CIRCUIT DESCRIPTION Introduction Congratulations on your purchase of a very versatile power supply. Our engineers have carefully designed the XP-720 to give you years of trouble-free performance. 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.
In practice, the current through the diodes is not as shown in Figure 2C. Because capacitor C5 has a charge after the first cycle, the diode will not conduct until the positive AC voltage exceeds the positive charge in the capacitor. Figure 5 shows a better picture of what the current flow looks like, assuming no loss in the diode. It takes a few cycles for the voltage to build up on the capacitor. This depends on the resistance of the winding and diode.
The 5 Volt Power Supply In the previous discussion of the variable voltage regulators, the ICs can handle about 1A of current. In the design of the 5V supply, we need 3A of current. To meet this current requirement, we must add an external pass transistor capable of delivering 3A. Figure 7 shows a simplified 5V regulator with an external PNP pass transistor. In this circuit, transistor Q1 is a power transistor capable of delivering over 3A. Transistor Q2 is biased off until the LM-7805 IC draws about .2A.
PARTS LIST QTY 1 2 2 2 DESCRIPTION RESISTORS .18Ω 3W 2.
SCHEMATIC DIAGRAM -6-
Elenco Electronics, Inc. 150 W. Carpenter Avenue Wheeling, IL 60090 (847) 541-3800 http://www.elenco.com e-mail: elenco@elenco.
