Part # Application Note General Purpose Products Microcontrollers AN1476 datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: MCUS - LOW-COST POWER SUPPLY FOR HOME APPLIANCES


Part Details:

AN1476 APPLICATION NOTE LOW-COST POWER SUPPLY FOR HOME APPLIANCES INTRODUCTION In most non-battery applications, the power to the microcontroller is supplied by using a step- down transformer, which is then rectified, filtered and regulated. However, in many smaller low-cost applications, the cost of the transformer becomes the key factor in the system. Under these circumstances, the step-down transformer is normally not used in order to reduce the cost as well as the size. The power supply is a simple one-way rectifier with very few compo- nents. The output voltage is regulated by using a 5.6V zener diode. Despite its simplicity and low cost, it is still able to deliver enough current to the microcontroller and application circuits. The purpose of this application note is to present the basic principle and cost analysis of the various power supply circuits for home appliance applications. AN1476/0904 1/8 1 LOW-COST POWER SUPPLY FOR HOME APPLIANCES 1 BASIC CIRCUITS 1.1 TRANSFORMER POWER SUPPLY Figure 1. Transformer Power Supply Diagram T1 1N4003*4 N 1 3 U2 VCC 78L05 4 2 IN OUT D L 2 4 C1 GN C2 C3 C4 3 100nF 470uF/35V 10nF 100uF/16V Figure 1. describes how to obtain a 5V DC voltage from the AC power line. In this circuit, the AC voltage drops down on the transformer s secondary winding. A rectifier bridge with 4 di- odes is used to convert the alternating AC voltage to a continuous DC voltage supply. A filter capacitor is added after the rectifier bridge in order to decrease the DC voltage ripple. The 78L05 triple terminal voltage regulator provides a very stable output and high current. The advantages of this solution are: Power Supply is isolated from the AC line voltage, Power Supply can deliver high current (up to 100 mA for 78L05),


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Application Note General Purpose Products Microcontrollers AN1476.pdf Datasheet