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 IC2in PWM mode.
Click here to download the full size of the above Circuit.
IC1 is set to oscillate at approximately 60 kHz at a high duty cycle. The output is low for only approximately 2. 5 µsec to trigger the PWM circuit and then goes high for the rest of the period. The PWM circuit has a maximum pulse width of approximately 85 µsec, and it becomes shorter, depending on the control voltage from the feedback circuit. You can reduce the chip count by using a 556 or another continuous-trigger source. The input must be (1. 5VOUT+Margin), so for 5V output you need 9V minimum input. If you use CMOS chips and small timing capacitors C1 and C2, you can keep the operating current low. Thus, you can use a simple zener-diode regulator for the 555 and increase the input voltage to more than 30V. The input-voltage limit is a function of how much power the zener supply can handle while delivering 5 to 10 mA to the 555s. Q1 has low RDS(ON) and low VGS and can handle more than 40V. D1 clamps any voltage spikes, such as those that occur when a large current flow ceases, causing a large magnetic field to be left in the inductor. You should select D1 according to the output voltage you need. For 5V output, use a 5. 6V zener diode, for example. IC3, R1, R2, and V1 form the feedback circuit to set the output voltage. The output-voltage equation is VOUT=V1(R1/R2+1). The TL431 is a popular part for setting a voltage reference and can easily create the 1. 25V shown for V1. You can supply 5V at 1. 5A with an input of 9...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
characters left: