TOUCH SWITCH

ELECTRONIC ON-OFF  TOUCH SWITCH

 

You can give sophisticated and good look to many electronic equipments such as Inverters, Battery chargers, UPS and D.C. power supplies to name a few. 

The working of this circuit is very simple as shown in schematic diagram.  When power supply is connected initially the relay L3 remains in de-energise (off) mode and voltage across the relay coil will be same i.e. +12V.  Therefore, the base of transistor Q3 will be high through resistor R7 to keep it in cut off state.  When push to on switch S2 is pressed momentarily Q4 start conducting and relay is latched and the base of Q3 will be pulled down and LED L2 will glow indicating power is on. The voltage available at the collector of Q3 will keep the transistor Q4 in on state through resistor R8.  Now, when push to on switch S1 is pressed momentarily the base of Q3 is pulled up and high base biasing will cut off transistor Q3 and the LED L2 will go off.  This will cause pull down base of Q4 through resistor R8 which will result in de-energising the relay L3.

The power to the equipment (connected through circuit) will be available through N/O & common points of the relay.  If you want to use it with an Inverter the relay contacts will be placed in series with the D.C. line to Inverter card. To use it with UPS, you have to use double contact relay, one contact will be used to cut A.C. 230 V line to the load and second contact will be in series with D.C. line to inverter card.  If D.C. 12 V is not available in the equipment in which you intend to use it.  You can built a 12V supply  by adding a 12 V 300 milliamp transformer, a bridge rectifier and a 470 Mfd. electrolytic capacitor.