Hi,

I must have been confused about your application. Instead of light sensor I should have wrote light switch.

I did not realise there was no permanent power supply available.

This capacitor amp depends on an external supply of current that will not be available for my current application, . . . however it could be obtained from a battery pack powered version . . . right?

In a way, yes. But powering it from a battery pack would mean the camera was effectively powered from said pack.

It would still be possible to run it off a large capacitor bank. The cap bank powers the cap multiplier. The time constant of the cap multiplier must be less than the cap bank. The cap bank must provide at least 7.5V. If designed correctly the output would appear to have a fast rise time.

I am using linear rectifier (7v 800mA P.S.) so that helps with the ripple, but more filter is always welcome.
- Does it help with ripple & noise or just ripple?

It reduces ripple and noise. Think of it like adding a 10,000µF cap across the supply rails. It's not identical, but it's similar.

Wow 5 watts, why so big?
I like the idea of the 'fuse'. The regulator is protecting the cam too, right? (unless of course it fails, which makes a case for the zener)

The zener goes in parallel with the supply output.

If the supply output is less than about 4.5V the zener does not conduct.

When it exceeds 4.7V it starts conducting. (Between 4.5V and 4.7V it conducts a very small current.) The zener shorts out the supply hopefully blowing a fuse somewhere. It needs to be big because it might have to short out for 5 seconds or more before something goes.

A) If I am right about your impression of my installation environment than the circuit you are describing would be much better suited for a battery operated unit since it is so power efficient. How hard would it be to drop in a PIR sensor that powered the camera for say 4-5min when motion was detected?

Yes it would also work with a battery and PIR sensor.

 

Here is a circuit which may do what you want.

It is normally powered by the 7V supply but the cap bank is attached.

In the simulation I reduced the cap bank to 30 millifarads because otherwise the simulation would take too long. You would attach your large cap bank where this cap is.

The op-amps U1 and U2 are powered by the 7V supply line even during cap charging. They should be LM324 op-amps which work from 3V to 32V.

When first switched on the cap bank charges and the comparator (an op-amp) U1 compares the supply voltage to a 4.5V reference. The 4.5V reference is formed from a zener-resistor combination powered from the 7V line. The 4.5V reference is not accurate before about 5.5V supply voltage, but it still works as intended due to the configuration of the op-amp.

When U1 switches on, it charges up the small cap and this initiates U2's purpose, which is as a voltage regulator.

When the supply voltage is removed the cap bank slowly discharges and this alerts U1 which goes low. Then the output is slowly ramped down by the capacitor on the output, but slightly ahead of the cap bank discharging. This allows the camera to perform a controlled shut down before all power is lost. Eventually the cap bank will discharge below 3V and then the behaviour is not guaranteed but usually it will mean the supply output will drop to 0V or so. This should happen long after the camera has been shut down.

The output is nominally regulated to 3.9V using the 3.9V zener diode, which should be a 500mW type. The 4.7V zener (for the 4.5V supply) should be a <500mW type.

Some values will need to be tweaked to get the desired effect. Try 22μF, 100μF and 220μF caps for the timing capacitor until the camera has enough time to perform its shutdown.

The comparator output could also be used to alert other devices of an imminent supply failure. Just remember not to load the output too much - a maximum of 10-15mA.

Due to a bug/limitation in the simulator when the output is off the supply rises to ~500mV. This is because the op-amp is, in the simulation, powered by an indepenent supply.

$ 1 5.0E-6 23.47059216675035 44 5.0 50
c 208 272 208 336 2 0.03 1.4743886790550151
g 208 336 208 352 0
R 64 272 32 272 0 0 40.0 7.0 0.0 0.0 0.5
O 208 224 208 176 1
a 384 432 480 432 1 7.0 0.0 1000000.0
x 217 327 270 330 0 12 Cap bank
t 832 304 832 272 1 1 -0.4788188064420349 0.6448685827898266 100.0
c 608 432 608 496 0 2.2E-5 0.35071282383551494
g 608 496 608 512 0
r 672 432 672 496 0 100000.0
g 672 496 672 512 0
w 672 432 608 432 0
z 736 496 736 432 1 0.805904783 3.9
g 736 496 736 512 0
w 736 432 672 432 0
w 880 272 848 272 0
a 736 416 832 416 0 15.0 -15.0 1000000.0
r 944 448 944 272 0 22.0
w 944 272 880 272 1
g 944 448 944 464 0
w 944 272 944 240 0
w 944 240 736 240 0
w 736 240 736 400 0
O 944 272 992 272 1
r 288 272 288 448 0 10000.0
z 288 512 288 448 1 0.805904783 4.7
g 288 512 288 528 0
g 352 512 352 528 0
r 352 512 352 464 0 10000.0
w 352 464 352 416 0
w 352 416 384 416 0
r 352 416 352 272 0 3900.0
r 832 304 832 416 0 1000.0
d 544 432 608 432 1 0.805904783
r 480 432 544 432 0 470.0
w 352 272 816 272 0
x 240 559 323 562 0 12 ~4.5V regulator
w 384 448 288 448 0
w 288 272 352 272 0
w 208 272 288 272 0
s 128 272 208 272 0 0 false
x 134 290 199 293 0 12 Light switch
w 208 224 208 272 0
r 64 272 128 272 0 1.0
x 436 471 466 477 0 24 U1
x 758 375 788 381 0 24 U2
x 5 0 57 6 0 24 hello
o 3 64 0 34 5.0 9.765625E-5 0 -1
o 23 64 0 34 5.0 9.765625E-5 1 -1

 

One thing I should add. There should probably be a 100µF cap on the output to suppress any oscillations from the op-amp. Also, remember to ground the inputs of all unused op-amps.

 

Tom, This really looks like it could work!
I am ordering the op- amps and zeners.

One camera behavior that may need to be addressed here is the hang that the camera experiences when re-energized in a relatively short period. (or even long period, see below)

Depending on what value of capacitor I go with will determine how long it will take before the circuitry following the capacitor continues to be energized.
(this could be a window of 20 minutes to >1hour depending on capacitor value!)
The camera requires the current to be COMPLETELY shut off before it can be re-energized successfully (a power cycle) [see flow chart]

Knowing my camera's behavior, this circuit seems like it would successfully save the first video, but then none after it. (please correct me if I am wrong)

I've tested it before where overnight I let the capacitor discharge and even with 10mV the camera was not satisfactorily discharged to safely re-start. (i'm not even joking, it's really bad)

The simulation shows current still active a long time after the camera is off.

Need to shorten the re-energize window
​

Perhaps a zener or some other component can be used to power isolate the camera after the substantial capacitor voltage has subsided?

Thank you for your diagram and highly detailed explanation, it's even easier to understand than your last diagram explanation. Very helpful to an aspiring novice!

 

One camera behavior that may need to be addressed here is the hang that the camera experiences when re-energized in a relatively short period. (or even long period, see below)

Depending on what value of capacitor I go with will determine how long it will take before the circuitry following the capacitor continues to be energized.
(this could be a window of 20 minutes to >1hour depending on capacitor value!)
The camera requires the current to be COMPLETELY shut off before it can be re-energized successfully (a power cycle) [see flow chart]

Knowing my camera's behavior, this circuit seems like it would successfully save the first video, but then none after it. (please correct me if I am wrong)

I've tested it before where overnight I let the capacitor discharge and even with 10mV the camera was not satisfactorily discharged to safely re-start. (i'm not even joking, it's really bad)

It might still work. The output should drop down to a few microvolts (1 microvolt = 1 µV = 1 millionth of a volt.) I highly doubt the camera will work on a few microvolts. If it doesn't, some kind of supply discharger may need to be added. Perhaps using another channel of the op-amp.

Perhaps a zener or some other component can be used to power isolate the camera after the substantial capacitor voltage has subsided?

It could, but this would require an external power source to control a transistor.

A better way would be a relay. The relay is connected to the 7V power supply (choose a 6V (coil rating) relay.) When the output drops the relay turns off, switching off the camera completely. The other output of the relay could connect to a load dump resistor or could be left floating. The 100µF cap I mentioned should go before the relay.

Thank you for your diagram and highly detailed explanation, it's even easier to understand than your last diagram explanation. Very helpful to an aspiring novice!

I am happy to help. I was a novice once and people on the 'net helped me out so giving things back is always nice.

 

Also, remember to add a diode across the relay's coil, to prevent an EMF spike damaging the op-amps. The diode should be reverse biased normally, it only conducts when the relay disengages to reduce the voltage. The diode should be a 1N4148 type.