Flowcode Support Board

Afternoon All,

Following another post on here that needed to know a low power supply voltage and trigger an event.
This got me thinking .....

I came up with this circuit - please see attached

The incoming supply DC voltage 7 - 9 V DC is monitored and if low the comparator output goes low, this could then be connected to an Interrupt pin on the micro and used to trigger a "Event"
The 3 x 470 uF Capacitors hold up the supply hopefully long enough to the "Event" to take place

This is only a rough and ready test circuit R1 & R2 possibly need looking at at the output went low when the DC input voltage was at around 4.9 V DC

Hope somebody finds this useful

Steve

Noticed last night if anybody wanting to have a go with this i have put the voltage reference in the wrong place
I would normally place it after the voltage regulator

The circuit works on a bread board as described above, R1 & R2 may need adjusting experience shows that voltage dividers on breadboards tend to give incorrect results due to the connections resistance.

I plan to have a further look at this circuit later and draw it up properly.

Steve

Edit : Change the 2K2 resistor on the TL431C to 390 Ohms when powered from the 5 Volt Rail
The Resistors i used are MF25 Series From Farnell

Afternoon All,

Done a few tests with various capacitors using A PIC16C710 monitoring a DC voltage and turns on or off some transistors to drive a relay (@12V) nothing too spectacular. This current was measured at 3.9mA with a fluke meter. = 0.0195 W.

so using an electronic load in constant Power mode set at 0.02W and a timer circuit to start and stop on a low voltage detect, and disconect the incoming supply. Supplying the various capacitors at varying voltages (Pre Regulator)

1 x 1000uf

Test 1 @ 7.5 Volts

0.32 seconds

Test 2 @ 9 Volts

0.02 W 0.41 seconds

Test 3 @ 12 Volts

0.02 W 0.60 seconds

Test 4 @ 15 Volts

0.02 W 0.87 seconds

====================================

2 x 1000uf

Test 5 @ 7.5 Volts

0.36 seconds

Test 6 @ 9 Volts

0.55 seconds

Test 7 @ 12 Volts

0.87 seconds

Test 8 @ 15 Volts

1.27 seconds

====================================

3 x 1000uf

Test 9 @ 7.5 Volts

0.50 seconds

Test 10 @ 9 Volts

0.69 seconds

Test 11 @ 12 Volts

1.16 seconds

Test 12 @ 15 Volts

1.66 seconds

====================================

4 x 1000uf

Test 13 @ 7.5 Volts

0.64 seconds

Test 14 @ 9 Volts

0.92 seconds

Test 15 @ 12 Volts

1.49 seconds

Test 16 @ 15 Volts

2.10 seconds

====================================

1 x 10,000 uf

Test 17 @7.5 Volts

11.69 seconds

Test 18 @ 9 Volts

20.46 seconds

Test 19 @12 Volts

33.56 seconds

Test 20 @ 15 Volts

51.33 seconds

Steve

Hello Steve
Pls have a look at the schematics I changed.
What do you think?

Hi Viktor

What do you want it to do / measure ?

The circuit works by comparing 2 x 2.5 volt signals. Vref from the voltage reference and the voltage divider network.

If the non-inverting (+) input is greater than the inverting (-) input the output will be high.
If the inverting input (-) is greater than the non-inverting (+), the output will be low.

I originally made a mistake and put the TL431 before the voltage regulator, this should be after the regulator ideally.

:edit

In normal operation the output is high.

Its not desirable to have circuits energising on faults.

Steve

Hi Viktor

Welcome to the Dark Side (v10 forum colour scheme versus v8).

Regards

Hello Steve, ChipFryer
Re:The circuit works by comparing 2 x 2.5 volt signals. Vref from the voltage reference and the voltage divider network.

Morning Viktor,

The circuit arrangement is a common arrangement that i used to employ on some battery monitoring boards for deep discharge protection.
This voltage is any where from 48 to 254 V DC this is where the voltage divider came from.

I just used the same input method for ease as i took the supply voltage to 15 Volts (see above tables) and altered the voltage divider to suit.

Steve

Edit:

just replied quickly previously, and didn't give it much thought.

Using a voltage divider allows you to better control the operating point of the comparator by setting the divider network to suit your voltage.