Surrendering to the 555 Timer Option

On Monday, May 11, 2020 at 2:21:46 PM UTC+10, Ricky C wrote:

them to my will because they are not very good oscillators or they aren't r eally amenable to simulation in LTspice.

Try this one. It's a vastly slowed down version of a low current 100kHz ast able that I dreamed up back in 2008 and posted here in response to a rather silly request.

John Fields came up with an equally silly solution, and I made his work wit h parts that you could actually buy.

The point was that the BFR92 has very low internal capacitances, so it swit ches quite fast at very low current levels.

Version 4 SHEET 1 2848 1240 WIRE -576 576 -736 576 WIRE -112 576 -576 576 WIRE -576 608 -576 576 WIRE -112 608 -112 576 WIRE -576 704 -576 688 WIRE -464 704 -576 704 WIRE -384 704 -464 704 WIRE -240 704 -320 704 WIRE -112 704 -112 688 WIRE -112 704 -240 704 WIRE -736 720 -736 576 WIRE -464 736 -464 704 WIRE -240 736 -240 704 WIRE -576 832 -576 704 WIRE -112 832 -112 704 WIRE -496 880 -512 880 WIRE -464 880 -464 816 WIRE -464 880 -496 880 WIRE -448 880 -464 880 WIRE -384 880 -320 704 WIRE -320 880 -384 704 WIRE -240 880 -240 816 WIRE -240 880 -256 880 WIRE -208 880 -240 880 WIRE -176 880 -208 880 WIRE -208 912 -208 880 WIRE -496 928 -496 880 WIRE -576 1008 -576 928 WIRE -496 1008 -496 992 WIRE -496 1008 -576 1008 WIRE -208 1008 -208 976 WIRE -112 1008 -112 928 WIRE -112 1008 -208 1008 WIRE -736 1040 -736 800 WIRE -576 1040 -576 1008 WIRE -112 1040 -112 1008 FLAG -112 1040 0 FLAG -576 1040 0 FLAG -736 1040 0 SYMBOL RES -592 592 R0 SYMATTR InstName R1 SYMATTR Value 1000K SYMBOL res -128 592 R0 SYMATTR InstName R2 SYMATTR Value 1000K SYMBOL cap -384 864 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C1 SYMATTR Value 270n SYMBOL cap -256 864 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C2 SYMATTR Value 820n SYMBOL VOLTAGE -736 704 R0 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL npn -176 832 R0 SYMATTR InstName Q1 SYMATTR Value BFR92A SYMBOL npn -512 832 M0 SYMATTR InstName Q2 SYMATTR Value BFR92A SYMBOL res -256 720 R0 SYMATTR InstName R3 SYMATTR Value 4700K SYMBOL res -480 720 R0 SYMATTR InstName R4 SYMATTR Value 4700.1K SYMBOL cap -512 928 R0 SYMATTR InstName C3 SYMATTR Value 68n SYMBOL cap -224 912 R0 SYMATTR InstName C4 SYMATTR Value 330n TEXT -768 1176 Left 0 !.tran 0 20s 10s startup TEXT -776 1224 Left 0 ;This example schematic is supplied for informational /educational purposes only. TEXT -480 1176 Left 0 !.model BFR92A NPN(IS=0.1213E-15 VAF=30 BF=94.7

3 IKF=0.46227 XTB=0 BR=10.729 CJC=946.47E-15 CJE=10.416E-15 TR =1.2744E-9 TF=26.796E-12 ITF=0.0044601 VTF=0.32861 XTF=0.3817 R B=14.998 RC=0.13793 RE=0.29088 Vceo=15 Icrating=4m mfg=Infineon )

--
Bill Sloman, Sydney

bend them to my will because they are not very good oscillators or they aren't really amenable to simulation in LTspice.

pulse is good as I'm using a driver FET even if it's not needed just to maximize the voltage range. The circuit needs to be enableable with your choice of polarity from a totem pole driver. The circuit needs to be low power, preferably less than 100 uA when operating and lower when disabled. It has to work over a voltage range of 2 to 5 volts, lower is better. With a current drive of mA from the enabling signal, I could just interrupt the ground to disable the circuit. That would be low power standby for sure!

CD4060 does an execellent low power oscillator, 3:1 can be got with a pair of diodes, but 2V is a bit low.

ICM7555CBAZ 40uA at 5V

--
  Jasen.

Correct. The CD4060 is not spec'd below 3V but the 74HC4060 is most definitely spec'd from 2V to 6V. Assuming a osc frequency can be found where the HC4060 runs at low enough Idd to satisfy the OP then something like this might suffice ....

I drew a 2n7002 for the gate but that part will have too high Vgson for

2V use and a better choice substituted.

piglet

On 11/05/2020 05:21, Ricky C wrote:

Here's an offer:

Simulates in LTSpice except for some oscillatory strangeness in the supply current (but nowhere else which is odd !). Uses LTC1441 dual micropower comparator. I haven't tried it over voltage but shouldn't be too awful. I haven't bothered to tune it for you - not enough time while having lunch - but you'll work it out. Maybe Bill will derive a nice formula for R1, R2, R5 (set mark space) and R3, C1 and the others to set F.

MK

Version 4 SHEET 1 1092 680 WIRE -16 -176 -144 -176 WIRE 208 -176 -16 -176 WIRE 304 -176 208 -176 WIRE 624 -176 304 -176 WIRE 208 -128 208 -176 WIRE -144 -112 -144 -176 WIRE 208 -16 208 -48 WIRE 336 -16 208 -16 WIRE 432 -16 400 -16 WIRE 544 -16 512 -16 WIRE 768 -16 544 -16 WIRE 16 32 -80 32 WIRE 128 32 96 32 WIRE -16 80 -16 -176 WIRE 304 80 304 -176 WIRE -80 96 -80 32 WIRE -48 96 -80 96 WIRE 208 96 208 -16 WIRE 272 96 208 96 WIRE 128 112 128 32 WIRE 128 112 16 112 WIRE 480 112 336 112 WIRE -144 128 -144 -32 WIRE -48 128 -144 128 WIRE 272 128 160 128 WIRE -144 160 -144 128 WIRE 160 160 160 128 WIRE 160 160 -144 160 WIRE 208 192 208 96 WIRE -144 208 -144 160 WIRE 16 208 -144 208 WIRE 128 208 128 112 WIRE 128 208 96 208 WIRE -80 224 -80 96 WIRE 624 224 624 -176 WIRE 768 224 768 -16 WIRE -144 352 -144 288 WIRE -80 352 -80 288 WIRE -80 352 -144 352 WIRE -16 352 -16 144 WIRE -16 352 -80 352 WIRE 208 352 208 272 WIRE 208 352 -16 352 WIRE 304 352 304 144 WIRE 304 352 208 352 WIRE 624 352 624 304 WIRE 624 352 304 352 WIRE 768 352 768 304 WIRE 768 352 624 352 WIRE 304 400 304 352 FLAG 304 400 0 FLAG 544 -16 DISABLE FLAG 480 112 OUT SYMBOL Comparators\\LTC1441 -16 48 R0 SYMATTR InstName U1 SYMBOL voltage 624 208 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 124 Left 2 SYMATTR InstName V1 SYMATTR Value 3 SYMATTR SpiceLine Rser=0 SYMBOL res -160 192 R0 SYMATTR InstName R1 SYMATTR Value 1e6 SYMBOL res -160 -128 R0 SYMATTR InstName R2 SYMATTR Value 5e6 SYMBOL res 112 16 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 1e6 SYMBOL cap -96 224 R0 SYMATTR InstName C1

SYMBOL res 112 192 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 1e6 SYMBOL Comparators\\LTC1441 304 48 R0 SYMATTR InstName U2 SYMBOL res 192 -144 R0 SYMATTR InstName R6 SYMATTR Value 5e6 SYMBOL res 192 176 R0 SYMATTR InstName R7 SYMATTR Value 1e6 SYMBOL diode 400 -32 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL res 528 -32 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R8 SYMATTR Value 100k SYMBOL voltage 768 208 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value PULSE(0 3 10 1u 1u 10 20) TEXT -24 440 Left 2 !.tran 30 startup

Change D2 to BAT54 and R8 to 50k and works from 2.5V to 5V with about

2.5% change in F.

MK

d them to my will because they are not very good oscillators or they aren't really amenable to simulation in LTspice.

stable that I dreamed up back in 2008 and posted here in response to a rath er silly request.

ith parts that you could actually buy.

itches quite fast at very low current levels.

al/educational purposes only.

.73 IKF=0.46227 XTB=0 BR=10.729 CJC=946.47E-15 CJE=10.416E-15 TR =1.2744E-9 TF=26.796E-12 ITF=0.0044601 VTF=0.32861 XTF=0.3817 R B=14.998 RC=0.13793 RE=0.29088 Vceo=15 Icrating=4m mfg=Infineon )

Kind of sluggish looking, a good chance it will hang.

Why not use an ATTINY13A microcontroller chip? It is truly micropower, can be programmed in C, and has 5 general-purpose I/O pins. Your program should only be a couple lines of code. This chip casts about $0.50 in low quantity, a programmer can be had on eBay for about $10 and the development software is all free.

Very slow timers are problematic in analog circuitry.

Jon

555 timers goes for around 10 cents.

Only problem is selecting accurate capacitors. You can pre-select caps with freq counter.

This should do 0.25 Hz at 25%:

+----- VCC T(8) CNTL T(5) | RESET T(4) | -> R --- C R T(3) OUT --+ 1 \ / R +----+---- THR T(6)

The 555 model that comes with LTSpice is behavioral and not very good, I don't think it models current draw very well for one thing. Get a full transistor-level model it's a simple chip shouldn't slow down sim time too much. Looks like maybe someone posted one...

I have a gate-driver behavioral model from TI that doesn't work with a negative offset to the supply, e.g. +12 on Vcc and GND on Vee it works fine, but GND on Vcc and -12 on Vee and everything necessary referenced to Vee instead the model doesn't work at all - WTF

Plus at least 3 additional components, including a pretty large, low-leakage capacitor. the ATTINY13A only requires a decoupling cap, and maybe will run without. Also, getting large asymmetry of the on/off time can be an issue with the 555. With the micro, you can get any time you want. I am not one of those "put a micro in everything" guys, but this particular case does seem to warrant it. In general, I don't like seeing RC timers with delays over a second.

Jon

,

age

run

e

ne

s

Normally I *am* one of the "digital is great" guys. But in this case the d esign is for a ventilator which is mostly made of off the shelf electronics . I am shooting for no use of anything that might not be so available down the road and the circuits should be easy to make in low tech processes. S o while programming MCUs are not exactly state of the art, I prefer to not use it if I can avoid it. There's also the issue of power supply. When th e thing is first powering up there is no voltage on the supercap. I suppos e I could use a couple of diodes to multiple source the MCU power. I did l ook at the idea a while back since it is an obvious route. I need at least two comparators which is not hard to find in MCUs either.

The remaining part of the circuit is a constant current source to charge up the supercap. I suppose that could be done by the MCU and a pass transist or. If a PNP were used would that provide reverse current flow protection? I suppose if the base were held at the collector voltage it would reverse bias the BE junction and prevent flow. Otherwise the CB junction would be forward biased and the PNP would act as a very poor transistor still, no?

I think the hard spec would be for the MCU to continue to work down to 2.0 volts or below. I suppose a watch CPU would work at very low voltages, but then we are back to hard to source components. How many MCUs are built to work over 2.0 to 5.25 volts with two comparators and/or an ADC?

--

  Rick C. 

  + Get 1,000 miles of free Supercharging 
  + Tesla referral code - https://ts.la/richard11209

The main problem, is parts count. It takes something like three op amps to get a long risetime by feeding 15 mV into a 1 Mohm/ 0.1uF integrator and detect both the 1/4 time level-crossing, and do the reset at the

4/4 time point. Half a dozen resistors. There's just a lot of components to pick-and-place. Then there's the power problem: an LT6002 micropower quad amp isn't bad, but isn't cheap, either.

..

Not sure what that circuit would be doing. One of the first circuits I tri ed was a comparator with about half a dozen passives. A positive feedback resistor moves the Vth up and down on a voltage divider threshold at the po sitive input. To get different duty cycles a diode and resistor are parall eled with a resistor for the negative feedback to the cap. This is essenti ally the same as the two inverter loop, but instead of two inverters to pro vide different polarities to the resistor and cap a single comparator with two inputs do the same job. Instead of reversing the polarity of the cap r elative to the single input, the comparator uses positive feedback to move the threshold.

I would probably be using a comparator oscillator but I can't get them to s imulate properly in LTspice. The cap should be charging to the positive in put, but at lower Vcc it trips much sooner and mucks up the duty cycle a lo t. I can't figure this out at all. I've tried every single comparator in the LTspice library thinking a voltage reference was getting in the way or something. None of them work properly at the low end of the specified volt age range.

--

  Rick C. 

  -+ Get 1,000 miles of free Supercharging 
  -+ Tesla referral code - https://ts.la/richard11209

I reviewed the ventilator schematic that one company made public, you'll be happy to know it uses a 555 timer!

Other than that the business-end of the main board is not too complicated; H-bridges to drive the blower motors and a bit of glue logic.

The rest of the commercial ventilator design is power supplies, a relatively antiquated microprocessor board, display and display driver/lighting circuitry, and boards with the chips for all the external sensors that integrate mass airflow, velocity, O2 level, respiration rate, and such into the microprocessor.

In a fairly pedestrian way tho, generating a clock for the motor-driver H-bridges I believe.

He could use a microcontroller to run a digital model of an old-fashioned compressed-air-fed ventilator, detailed design schematics and timing diagrams are available online for e.g. the Bird respirator variants

The '555 feeds full power supply voltage into its RC 'integrator'; if you use an op amp and R and C for the integrator, you can get 100x time periods by dividing the power supply voltage down by a factor of 100, and integrating THAT instead.

So, within the limits of 1M max resistor, and 0.1uF (fairly cheap) capacitor, you can get the four second time constant. The integrator has low-Z output, so it feeds any comparators you want, with its triangle wave. An OC reset transistor (or maybe something with a diode) finishes each cycle. LP324 wants 3V or more, though.

er,

m

eakage

ll run

ssue

t one

es

lays

he design is for a ventilator which is mostly made of off the shelf electro nics. I am shooting for no use of anything that might not be so available down the road and the circuits should be easy to make in low tech processes . So while programming MCUs are not exactly state of the art, I prefer to not use it if I can avoid it. There's also the issue of power supply. Whe n the thing is first powering up there is no voltage on the supercap. I su ppose I could use a couple of diodes to multiple source the MCU power. I d id look at the idea a while back since it is an obvious route. I need at l east two comparators which is not hard to find in MCUs either.

e up the supercap. I suppose that could be done by the MCU and a pass tran sistor. If a PNP were used would that provide reverse current flow protect ion? I suppose if the base were held at the collector voltage it would rev erse bias the BE junction and prevent flow. Otherwise the CB junction woul d be forward biased and the PNP would act as a very poor transistor still, no?

2.0 volts or below. I suppose a watch CPU would work at very low voltages, but then we are back to hard to source components. How many MCUs are buil t to work over 2.0 to 5.25 volts with two comparators and/or an ADC?

.

Sounds a lot like what these guys are doing. I don't know what they are us ing for the important sensors. They have some kit type temperature sensor boards like they sell at the hobby shops. Same for the H bridge, L298N. F unny you can get modules from aliexpress cheaper than the chip at Digikey! They seem to be using an Arduino Uno for the device controller. Not sure what they are using for the display or controls yet.

--

  Rick C. 

  + Get 1,000 miles of free Supercharging 
  + Tesla referral code - https://ts.la/richard11209

The commercial vent design looked both over-engineered and antiquated simultaneously like a lot of medical/aerospace stuff. A lot of swish $2 op-amps and comparators (maybe because it was designed to run off battery-power for a while but for low frequency/DC tasks like they were in not really necessary) doing pedestrian things plus an obscure processor using external RAM and ROM like an embedded device from the early 90s.