Monday, February 15, 2016

Circuit Diagram Automotive Turn Signal Flasher with Lamp Outage Detection using LM393 and NE555 IC

RealAutoTips. - Here is Circuit Diagram Automotive Turn Signal Flasher with Lamp Outage Detection using LM393 and NE555 like in Figure 1 below. It has a built-in function of lamp-outage detection. In normal operation, it will flash at about 1.4Hz and when a lamp goes bad, the flash-rate is doubled. The flashers faster clicking sound and the dashboard indicators faster flashing attracts the drivers attention that one of the bulbs has gone out. A circuit of a flasher which I designed for automotive use.

Circuit Diagram

Description

Circuit diagram like in Figure 1 is Circuit Diagram Automotive Turn Signal Flasher with Lamp Outage Detection using LM393 and NE555 IC. According Zen22142.zen site that published this circuit describe that the circuit consists of two parts - the flashing unit and the lamp outage detection module. The flashing unit is built around 555 timer configured as an astable multivibrator. The resistors R12/R13 and capacitors C3/C4 sets the required frequency. Note that C3 is connected in parallel to C4 through BC547 an NPN transistor, acting as a switch. When there is positive voltage at the base of the transistor, it conducts and connects C3 to ground. C3 & C4 in parallel doubles the capacitance value i.e. 220nF + 220nF = 440nF. This capacitance value together with R12 and R13 result in frequency of about 1.4Hz.

In the lamp outage detection module, a shunt resistor (a thick wire) with a calculated minor resistance (30mΩ) is the key to detect the lamp outage. The voltage to lamps is fed thru this shunt. Hence, the shunt is connected in series to the network of the bulbs which are connected in parallel. The inverting input of the comparator U1 is also connected to the shunt. The non-inverting input is connected to a potential divider providing a reference voltage of 11.90V


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