/diy/ - Do It Yourself

I'm trying to build a lamp flasher circuit that can switch off during the day and start flashing in the night. The quiescent current should be as low as possible during "off" state. This circuit will deliver pulses into the |ON/OFF pin of an LM2575 IC which drives a small light bulb.

The CD4093 quad NAND seemed perfect for the task so I decided to make a prototype with it. It has wide operating voltage range suitable for battery use (3..15 V) and very small current consumption (<1 µA).

I breadboarded and measured the circuit in pic related with a 5 V supply. It consumes a constant 0,43 mA of current during daylight. In dark the consumption fluctuates between 0,90 and 1,20 mA. The consumption of the LM2575 is not included in this measurement. According to the data sheet its standby consumption is around 80 µA.

Do you think there's anything to optimize in this design? If anything, I will probably choose a much larger value resistor R104 + slightly smaller capacitor C101 for a slower flashing cycle. Also the resistor divider formed by R101, RV101 & R102 always pulls certain amount of current depending on the trimmer pot setting and the light falling on the LDR. Would be good if the divider could be somehow switched off during the day.