Switch Mode

Switching Power Supply 14V

In this small switching power supply, a Schmitt trigger oscillator is used to drive a switching transistor that supplies current to a small inductor. Energy is stored in the inductor while the transistor is on, and released into the load circuit when the transistor switches off. The output voltage is dependent on the load resistance and is limited by a zener diode that stops the oscillator when the voltage reaches about 14 volts...

12V 40A Switching Power Supply

The present trend is to use ever higher frequencies. But by doing so it becomes more difficult to filter out the RF noise inevitably generated by the switching. So I decided to stay at a low switching frequency of only 25 kHz for the full cycle, which due to the frequency doubling effect of the rectifiers results in 50 kHz on the output filter. For the main switching elements, bipolar transistors or MOSFETs can be used. Bipolars have lower conduction losses, while MOSFETs switch faster. As in this design I wanted to keep the RF noise at an absolute minimum, very fast switching was not desired, so I used bipolar transistors. But these tend to become too slow if the driving is heavier than necessary. ..

60 Watt switching Power supply

This paper gives a practical example of the design of an off-line switching power supply. Factors governing the choice of a discontinuous flyback topology are discussed. The design uses a pulsed-width modulation (PWM) control scheme implemented with a Unitrode UC3840 IC. This chip's voltage-feed-forward feature is used to achieve improved output regulation. The paper discusses closing the control loop to achieve both stability and adequate dynamic regulation, and provides guidelines for transformer design and component selection...

Pulsed Charger for Lead Acid batteries (NE555)

The object is to get the cell voltage high enough for the sulphate to dissolve without boiling or melting the battery. This is achieved by applying higher voltage for shorter periods and let the battery rest for a while. The pulses on short range is about 0.5s on / 3s off and the long pulse range is 1.4s on / 2s off. These times can vary depending on component tolerances. Start on long pulse and if you discover ?boiling? (more than with normal charging) in the electrolyte switch to short puls. Don?t leave the process unattended, at least until you know how your specific version of this project turns out. I built ver.1 of this circuit some 10 years ago and have experimented with it but I?m sure someone can improve it further...

If you`re an effects builder or repairer, you know by now that it`s a good idea to protect the circuitry in the effect from the consequences of a reversed battery. While many older effects can withstand a momentary reversal, some more modern components can be damaged if you accidentally touch the battery contacts the wrong way during replacement. Sometimes this is subtle damage...

This page provides basic information about voltage comparator integrated circuits and is to act as reference material for other circuits. The circuits shown are based on the LM339 Quad Voltage Comparator chip or the LM393 Dual Voltage Comparator chip. These devices are functionally identical. The LM311 Voltage Comparator can be used for these applications as well and also has a number of unique features...

One of the main features of the regulated power supply circuit being presented is that though fixed-voltage regulator LM7805 is used in the circuit, its output voltage is variable. This is achieved by connecting a potentiometer between common terminal of regulator IC and ground. For every 100-ohm increment in the in-circuit value of the resistance of potentiometer VR1, the output voltage increases by 1 volt. Thus, the output varies from 3.7V to 8.7V (taking into account 1.3-volt drop across diodes D1 and D2)...

Many applications require current sources rather than voltage sources. When you need a high-current source, using a linear regulator is inadvisable, because of the high power dissipation in the series resistor. To solve the wasted-power problem, you can use a switch-mode regulator. The circuit of Figure 1 uses IC1, an LM2576 adjustable regulator. It needs only a few external elements and has an adjustable sensing input, which you use for controlling the output current. Resistor RSC is a current sensor...

This Design Note describes how to generate five separate output voltages using the LTC®1538-AUX, a dual synchronous switching regulator controller with internal circuitry adaptable to many additional configurations...

Most switch-mode power supplies rely on a PWM (pulse-width-modulated) output that is controlled via voltage feedback. A 555-timer IC can inexpensively perform PWM. The circuit in Figure 1 shows how to turn a 555 PWM circuit into an switch-mode power supply with only one simple equation. The design uses two 555s. IC1, in astable mode, triggers IC2 in PWM mode. IC1 is set to oscillate at approximately 60 kHz at a high duty cycle...

Start-up is a stressful time for the power driver section of a switching power supply. Because the output voltage is initially zero, the feedback error initially jumps to its maximum. The large feedback error then drives the loop filter to its limit, which drives the power switching transistors in the driver section of the power supply at their maximum rating. This condition continues until the output voltage of the power supply approaches its nominal value...

A D.C. power supply is usually regulated by some type of feedback circuit that senses any change in the D.C. output and develops a control signal to compensate for this change. This feedback maintains an essentially constant output. In a monolithic regulator, the output voltage is sampled and a high-gain differential amplifier compares a portion of this voltage with a reference voltage...

In Figure 1 , a basic and versatile 5V supply uses a zener diode and an emitter-follower transistor. You must calculate and design the transformer such that Q1 is close to saturation at low mains voltages and nominal output current. Additionally, you must choose R1 to ensure proper bias for the zener diode...

Figure 1 shows the LT®3439, one of several low noise switchers available from Linear Technology. Ultralow noise and low EMI are achieved by controlling both the output switch voltage and current slew rates. This switching architecture is particularly well suited to noise-sensitive systems such as industrial sensing and control, data conversion and wideband communications...

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...