# Under-voltage lockout and a 555 (astable 50% duty cycle) lets LED flash – now save more power

The following project is built:

• A 9 V battery is used – no socket required. This is important to gain experience for future projects.
• There is an under-voltage lockout, which switches off when the battery becomes weak.
• A 555 timer, wired as an oscillator and with a 50% duty cycle, makes a red LED flash.
• The circuit is designed to save power.
• Unfortunately, the circuit is not yet power saving enough.

When I do the math: I buy this 9 V battery with 1200 mAh, and the circuit consumes 20 mA, then it runs for 60 h – so less than 3 days. I have to change that. The point is that this is the first milestone. Later, the circuit will be extended. I want to connect a microprocessor to the same battery later.

I only work with PSpice for TI 2022; this is a cut-down version of PSpice; in other words, I only have models from PSpice and Texas Instruments available.

By the way: the operational amplifier in the UVLO gets its own 9 V battery. This way the voltage is always the same, as it consumes very little current.

Current consume

• You may find that "working in SPICE" is, in this instance, rather counter-productive. If you want to save power, you'll need some sort of switching power conversion, so that the resistive energy losses will be minimized. You'll want to use a CMOS 555, if a 555 is even appropriate for this application (I doubt it is). Commented Aug 22, 2022 at 16:29
• I see you are using a 375 ohm resistor to represent an LED drawing 20mA. An LED will give substantial brightness even when drawing 2 or 3 mA. Couldn't you increase the value of the 375 ohm resistor so it represents an LED being driven with a smaller current.
– user173271
Commented Aug 22, 2022 at 16:48
• Why do you need the Q2? The 555 can source or sink 200 mA. Commented Aug 22, 2022 at 19:42
• First thing to look at is - obviously - where is the power going?? how much of that 20mA is the LED, how much is U1, how much is U2, etc. Don't just guess - find out! Commented Aug 22, 2022 at 22:24
• Ra seems much lower than it needs to be, especially compared to Rb, especially if you don't need a close-to-50% duty cycle. Commented Aug 22, 2022 at 22:25