YOUR CART 0 items 
Hot Search:  th-f8 vhf  41-103-9R  bateria baofehg  case surecom  XwhS  DCsS  MKkZ  hf tunner  boefeng power switch  casesurecom  4-083y 4-079  icom ic- 7410  ct 118  kenwood round 8 pin  4-083y+4-079  
Code/Search:    Home  |   All Products  |   How to Buy  |   Payment Method  |   Post Tracking  |   My Address   |   Contact Us
  Hot News - A Power Supply Works

A Power Supply Works

How power supplies work

A power supply is used to reduce the mains electricity at 240 volts AC down to some thing more useable, say 12 volts DC. There are two types of power supply, linear and switch mode.

A linear power supply uses a transformer to reduce the voltage. The ratio of primary windings (connected to the mains) to the number of secondary windings (connected to the output) would give the ratio of how much the voltage reduced by, in this case a ratio of 20:1 reduces the 240 volts AC input in to 12 volts AC on the secondary windings.

A switch mode supply works by turning the mains electricity on and off very quickly to reduce the voltage. In this case the reduction in voltage depends upon the ratio of the on time and off time. Switching takes place very fast, at 10,000 times a second or quicker. Using this technique the bulky transformer found in a linear supply can be replaced with a smaller one.

Below is a block diagram of a switch mode power supply. The AC signal is rectified and regulated to produce a high DC voltage. This is then switched on and off rapidly by a FET. Then the switched signal goes through a transformer, although this can reduce the voltage it isolates the output from the mains electricity (for safety reasons). Feedback of the output is then used to control the mark space ratio of the switching so that the output stays at the required voltage. The transformer used in a switch mode supply is much smaller and cheaper than the type used in linear supply, but must be able to handle the higher switching frequencies.


We have already mentioned that there are two types of transformer, those used at low frequencies (50Hz) in a linear power supply and the high speed (>10KHz) version used in switch mode supplies. The linear power supply transformer typically uses a steel core. Because eddy currents would occur in a solid steel core and reduce the efficiency the core is made from insulated steel plates stacked next to each other with the windings wrapped around them

Regulated supplies

A regulated supply uses an IC, where the IC monitors the output voltage relative to a reference voltage and adjusts the output accordingly. Regulators have a much lower ripple and often include over current and over temperature protection, whereby they automatically shut down making them and the rest of the supply indestructible. The part shown right is a 7805, a common 5 volt regulator.
In the block diagram of the switch mode power supply, the final stage was to smooth out the pulses by adding a large capacitor. Depending upon how accurate the supply needs to be this solution may be adequate. In this design the output will have some ripple; it will vary from the required voltage by a small amount, maybe a few percent.

Case types

The most common case type is the plastic case. This is because it can be easily made using an injection moulding process and features such as PCB mounting holes or clips, holes for cable entry exit etc can be included in the design at virtually no extra parts cost. The more expensive alternative is a metal enclosure; however these must be grounded for safety reasons.


Search keyword does not accept symbols . , " ; .../ !   

  Antenna Parts


Accessory for Walkie-talkie
  SURECOM Product Line
  foot-earpiece foot-speaker-mMic foot-adaptor foot-power-supply
foot-repeater repeater cable foot-power-supply foot-dummy-load
SURECOM new Product line how-to-choose-earpiece   how-to-order-from-409shop
lexuma Shipping post  


Why Choose

    -Over 10,000 Radio products
    -Extremely low prices
    -Timely refunds and replacements
    -Worldwide free shipping (except F.O.B.)


Follow us on:

409shop-facebook 409shop-you-tube SKYPE-409shop 

Our Company

Learn & Support

Customer Service

Partner With Us


Software Downloads

PAY Method

Reseller Contact

About Us

Technical Support MAP

Post Tracking

Supplier Contact

My Company


Privacy Policy

Affiliate Program



Repair Return Address


Authority of AllSit Map

Tax Policy

Contact Us



   409shop Group: SURECOM | DAXSHINE | 409shop-TWO-WAY-RADIO | 409shop-moibleHKTDC | 對講機香港代 409shopradio 
   Quick buy: Buy Earpiece | Buy Speaker/Mic | Buy Antenna | Buy Adaptor | Buy UV5R 3800MAH battery | Buy SURECOM PRODUCT 
   Friendly Links 

walkie-talkie ,對講機牌照,DMR數碼對講機,cb對講機,motorola對講機香港 ,motorola數碼對講機,香港合法對講機,motorola對講機香港代理,motorola, t8對講機 ,motorola對講機耳機, 免費諮詢 , 409shop專業無線對講機生產 

google-site-verification: google6cffa68deb0f3230.html

Copyright © 2021 409shop,walkie-talkie,Handheld Transceiver All Rights Reserved.