switching power supply 2


Posted on Feb 7, 2014    5995

This circuit will double almost any DC input voltage as well as handling plenty of current. 12 to 24V is just an example. With a few changes, it can also supply any desired output voltage. There are many possible applications. One I can think of would be to get the 28V for the ADC connector on Gigabit Ethernet and later Power Macintosh G4s from th


switching power supply 2
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e +12V on a standard PC ATX power supply. Basically any time you need more voltage than what you`ve got. Possibly on camping trips when you need 12-14 volts but only have 6V cells. Also you can use it to boost the cooling power of the fans in your computer if they can handle the extra voltage. Some can`t. Keep reading for more on this. What I use it for is to increase the speed and thus the airflow of a standard 80mm DC brushless fan. White-LED backlights are gaining acceptance because they offer higher reliability and simpler drive circuitry than those based on CCFL and EL technology. As a result, the white-LED backlight is increasingly common in PDAs, cell-phones, digital cameras, and other portable devices. A design in which the display is backlit (or frontlit) for extended periods needs an efficient circuit that drives the LEDs with a controlled current, and eliminates the wasted power associated with current-limiting resistors. A flyback converter implements a current-limited power supply to charge lead-acid batteries. The MAX773 current-mode controller limits the output current and the flyback transformer provides isolation and flexibility for input voltages both above and below the battery voltage. The MAX471 current-sense amplifier monitors the charging current and feeds back to a threshold detector so that below a designed threshold the flyback converter can switch to a lower charging voltage for trickle-charge mode. The circuit shown in Figure 1 charges lead-acid batteries in the conventional way: A current-limited power supply maintains a constant voltage across the battery (2. 4V/cell or so, as specified by the battery manufacturer) until the charging current decreases below a current threshold defined by the capacity of the battery. At this point, the charger is placed in a trickle-charge mode. The current threshold is typically 0. 01C, where C refers to the battery capacity, which is specified in ampere-hours. When charging a battery, the term C rate  refers to the current required, in theory, to charge a battery to its full battery capacity C in one hour. In actuality, power lost during the charge cycle ensures that all batteries charged at their C rate take more than an hour to reach full charge. Ideally, you could charge a 5A-hr battery in one hour if the charge current is 5A. Also, ideally, a C/10 charge rate (500mA) charges the same battery in 10 hours. However, the power loss mentioned previously increases these charge times beyond the two time spans stated above. In conventional applications, switching-regulator ICs regulate VOUT by controlling the current through an external inductor. The IC in Figure 1, however, driving a diode-capacitor network in place of the inductor, offers comparable performance for small loads. Made of readily available components, the network can double, tripple or quadruple the input voltage. Though somewhat less efficient than inductor-type regulators, the Figure 1 circuit offers equivalent line and load regulation. The supply works by shorting the inductor across the 12 volts through the regulator. This stores energy in the inductor. When the internal switch in the LT1170 goes off, the inductor is placed in series with the 12 volts, adding to it. This voltage pulse is stored in the output capacitor and smooths the output. The diode is used to keep the output capacitor from discharging during switching. It contains a 100 khz current based oscilator whose output is controled by feedback provided by R1 and R2. These make a voltage divider such that at the wanted output volta

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