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## Make this Simple Delay ON Timer Circuit - Application Note Included

The post explains a simple delay ON timer circuit which allows the connected load at the output to be switched ON with some predetermined delay after power switch ON.

The explained circuit can be used for all applications which calls for an initial delay ON feature for the connected load after the mains power is switched ON.

The shown diagram is pretty straightforward yet provides the necessary actions very impressively, moreover the delay period is variable making the set up extremely useful for the proposed applications.

The functioning can be understood with the following points:

Assuming the load which requires the delay ON action being connected across the relay contacts, when power is switched ON, the 12V DC passes via R2 but is unable to reach the base of T1 because initially, C2 acts as a short across ground.

The voltage thus passes through R2, gets dropped to relevant limits and starts charging C2.

Once C2 charges up to a level which develops a potential of 0.3 to 0.6V (+ zener voltage) at the base of T1, T1 is instantly switched ON, toggling T2, and the relay subsequently....finally the load gets switched ON too.

The above process induces the required delay for switching ON the load.

The delay period may be set by appropriately selecting the values of R2 and C2.

R1 ensures that C2 quickly discharges through it so that the circuit attains the stand by position as soon as possible.

D3 blocks the charge from reaching the base of T1.

Parts List

R1 = 610K
R2 = 330K
R3= 10K
R4 = 10K
D1 = 3V zener diode
D2 = 1N4007
D3 = 1N4148
T1 = BC547
T2 = BC557
C2 = 33uF/25V
Relay = SPDT, 12V/400 Ohms

Application Note

Let's learn how the above delay ON timer circuit becomes applicable for solving the following presented issue by one of the keen followers of this blog, Mr. Nishant.

Hello Sir,
I have a 1KVA automatic voltage stabilizer.It has one defect that when it is switched on, very high voltage is outputted for about 1.5s (therefore cfls and bulb got fused frequently) after that the voltage becomes OK. I have opened the stabilizer it consist of an auto-transformer,4 24V relay each relay connected to a separate circuit(each consisting of 10K preset,BC547,zener diode,BDX53BFP npn darlington pair transistor IC,220uF/63v capacitor,100uF/40V capacitor ,4 diodes and some resistors).These circuits are powered by a step down transformer and output of these circuit are taken across corresponding 100uF/40V capacitor and fed to corresponding relay.What to do in order to tackle the problem.please help me.Hand drawn circuit diagram is attached.

Solution:

The problem in the above circuit might be due to two reasons: one of the relays is switching ON momentarily connecting the wrong contacts with the output, or one of the responsible relays is settling down with the correct voltages a little while after power switch ON.

Since there are more than one relay, tracing out the fault and correcting it can be a bit tedious......the circuit of a delay ON timer explained in the above article could be actually very effective for the discussed purpose.

The connections are rather simple.

Using a 7812 IC, the delay timer can be powered from the existing 24V supply of the stabilizer.

Next, the delay relay N/O contacts may be wired in series with the stabilizer output socket wiring.

The above wiring would instantly take care of the issues as now the output would switch after some time during power witch ONs, allowing enough time for the internal relays to settle down with the correct voltages across their output contacts.

•  Stumble

1. Hello Sir,
1.What is the power rating of each resistor?

http://evelta.com/index.php?route=product/product&path=158_81&product_id=58

3.Can I power the above circuit with the same 12 0 12 step down transformer which is already there in the stablizer used to power 4 above hand drawn circuits.

If yes then how?
connecting 24v ac to bridge rectifier (using 1N4007) then a filter capacitor(please tell the best value preferred ), also tell the preferred value for filter capacitor(ceramic or electrolytic?) to be connected at input and output of 7812,Is this power supply will comfortably run the delay circuit?

1. Hello Nishant

1) All resistors are 1/4 watt CFR

2) Yes the shown relay will work.

3) you will have to use the 0-12 tap and connect a bridge rectifier/capacitor(1000uF/25V) with it and then the output would become OK for the above circuit.

Alternatively you may use a 7812 IC and feed its input with the existing 24V DC...the output of the 7812 would then become applicable for the above circuit.

2. hello sir,
i tried ur above circuit with 2 transistor in simulation software but its not working.......plz help me out....

1. helo rocky, try it practically, it will work.

3. I have tryed it practically and mine doesen't Work.

1. I have tried this circuit and it works just as explained.

4. hi mr swagatam,

I am graduating engineering student can u help me to have a piece of idea for what i am going to invent as my theses please?
thank you more power

5. hi mr swagatam please help me i am going to do a project for my theses i am just run out of time please provide me an idea to have a starting point in doing a ece project as my theses thanks. more power

1. Hi Sandy, It will be difficult for me to suggest any particular project, you can choose any one from this blog, it has plenty neat stuffs of all levels.

6. What is the formula for determining the delay time from R2 and C2? I need about 1 second of delay. Thank you

1. the formula is complicated, Google "RC time delay formula", you'll get an idea

2. ...you can set it with some trial and error.

7. sir! if want to use this circuit with two relays, how to connect it?
i have an 15v 150mA adapter can i use it to supply this circuit? if can, do i need a regulator or 12v zener to step down it?

1. you can connect the relay coils in parallel in the above circuits.
you can connect 15V directly, no need to step it down.

8. The circuit works fine, thanks for the article. I have a requirement where I need delay ON and delay OFF. The required delays are very small, about 10 ms. How can I modify the above circuit to achieve ON and OFF delays?

1. connect another capacitor right across the base and ground of T1, let's call it C1.

Dimension C1/C2 for getting the 10ms delay,

9. hi swagatam.
i want a delay of 3-8 seconds. will it work? by the way what are is the time delay of this circuit in this configuration?
i want to run this directly on 220V. but dont want to use transformer or power supply. can you please give me a link or suggest me a capacitor diode based simplest power supply as an addon.
thanks. waiting for your reply as you have not replied me before.

1. Hi Muhammad, any delay between 1 second and 1 minute can be achieved from the above circuit by varying R2/C2 accordingly.

you can try the following transformerless power supply:

http://1.bp.blogspot.com/-9MKa1nQydEY/U6fgPJheSeI/AAAAAAAAHVA/FQbUQOL1qa8/s1600/simple+1+watt+LED+driver+circuit.png

Remove the shown LEDs, and use the transistor emitter as the positive supply for the delay circuit. You can also remove the 56 ohm resistor, it's not required.

10. sir,
i want to use above circuit work for 10 min
is it possible by changing R2 and C2????????

1. yes it's possible by increasing R2/C2 and also by increasing D1 voltage rating

11. Hi Swagatam,

I am looking for a circuit for the following application:
My pellet stove has a control board which I am not capable of modifying. It controls the pellet feed rate by activating a 115vac .5amp motor driving a feed auger. The control board allows me to adjust the time that the motor is powered from 3 sec to 8 sec. in a 15 sec cycle. I need to be able change the lower limit to 1 sec. I can do it in a couple ways with a circuit between the control board and the motor:
either 1. Apply a two second delay each cycle (when the board activates the motor)
--or-- 2. Only allow one of every three 15 sec cycles to activate the motor

I think I prefer option one, but could use either.

Could you provide a circuit to accomplish this?

1. Hi Jencliff, from the explanation what I could understand is that you basically want an intermediate stage that would allow you to transform the existing 3 to 8 sec feature into 1 to 8sec, (right?)

If that's the case I could recommend you a IC 555 monostable timer stage to be inserted in between the motor power device and the control board output.

2. Hi Swagatam,

Thanks for the quick response. I do have a few questions after looking at various circuits on your blog which use the IC 555.
1. I assume I will need a relay in the circuit to handle the 120ac. That being the case, how does the IC 555 get triggered, since the only I have is the 120ac and the IC 555 seems only to handle low (5-9dc) voltage?
2. I assume the circuit when completed could be placed between the motor and control board on the neutral leg from the relay.
3. Are the above assumptions correct and could you point me to a circuit like those on your blog which shows the whole circuit I need?

3. Hi Jencliff,

The trigger input will need to be taken from the DC output of the control board which may be responsible for activating its relay.

If you don't wish to disturb the control unit circuit, then you can think about installing a separate 12V AC/DC power supply for feeding the IC 555 circuit and use another external relay at the output of the IC for controlling the motor.

The above set up could then be powered from the 120V relay output from the control board.

You could try out the following design for the monostable:

12. Hi Swagatam,

Can I connect a push button between R2 to instantly switch the circuit on?

Thanks,
Vijay

1. Hi Vijay,
you mean parallel to R2? Yes you can do it but make sure that the switch has a 1K resistor in series otherwise the BC547 will get damaged instantly on pressing the button.

2. Hi sir can you give me please any electrical project for my theses...thank you

3. Hi Naldz, It'll depend on your preferred difficulty level, there are plenty of circuits from easy to the most difficult

13. hi ,i am a big fan of yours. i want to build a circuit like.. when power is present- relay on(relay got power) then off (relaxed) automatically after few seconds..please reply..thanks

1. thanks skl, you can use the above explained circuit with a slight modification.

replace T2 with another NPN....remove R3 and let the base of T2 connect directly with the T1 collector....now, T2 emitter will connect with the ground, and the relay assembly will need to be fixed across the collector of T2 and the positive line.

I hope you got it!!

14. thanks for reply, i redraw the circuit as you said. should i connect R4 with base of T2 or remove that too? i am little curious to know how 'delay on' circuit become 'delay off' by replacing a transistor ? actually i wanted to know the working principle... thanks again.

1. without R4 your T2 (NPN) will never conduct, so it's required.

By changing T2 into a NPN transistor we are inverting the process (the driver stage) and making delay ON into delay OFF, T2 is now doing the opposite of T1, previously with a PNP it was following T1

15. sorry to disturb you again. actually i want to use this circuit replacing a push button switch. in my circuit relay coil needs a positive spike for a second to start. your circuit providing negative spike for relay...can i use a pnp transistor as T2 ? hope you got my question.

1. there is no push button in the discussed design, the spike is received by R2 from the positive line...or you can disconnect R2 from the positive and use it across any source which generates the spike

2. sorry it won't to a spike...the input must be consistently present for R2.

A PNP at T2 will make it delay ON, as it's in the existing diagram.

16. I have a battery charger circuit (you post a circuit like this with main ac on-off by relay; but i want to cut the 12 dc supply), its like - a push button switch turns on the whole circuit by giving (12v) positive supply to a relay - relay on - circuit on. now relay stay on by the circuit. when battery got full charge - relay off.
i just want to replace that push button switch so that battery got automatically connected with charger when i;m not in home. or
when the electricity come after loadsheding i do'nt want to push that button to give charge to the battery

1. your application has nothing to do with a delay timer....I think you are referring to the following post:

make the second circuit from the following article it will do exactly what you are looking for:

17. hello again. recently i was working with delay off circuits and i configured a circuit like this(by mistake) https://farm1.staticflickr.com/757/21205145188_74edc18489_m.jpg , a pnp transistor's collector goes to (+), base to gnd with a 2200uf capacitor, relay coil connected with emiter through gnd.
this circuit worked exactly like what i asked you for...like when transistor got power- relay on , then goes off automatically. although this circuit worked as my expectation,but i am confused. how it is working ? can you please explain that for me.. can i trust this circuit for my project? this circuit is also working https://farm6.staticflickr.com/5789/21402515961_8aea73735b_m.jpg

1. hello, you can trust the second circuit...not the first one.

18. thanks for reply.hope resistor values are ok in my second circuit.

1. the 10k,and the 10uF will need to appropriately calculated for getting the required delay for your application, rest is OK

19. Engr swagatam. Please where can I put an LED in the circuit such that it will indicate that delay timer is on and then switches off as soon as the timer is up

1. holawaleh, you can connect an LED right across T1 collector/emitter for the response

20. Dear Sir,
Can i use 5v instead of 12v?

Thanks.

1. yes you can use 5V, but the relay will also need to be changed with a 5V relay.

21. Hai, is there any circuit for "simple delay OFF" for 10-15 mins?
Means that after switch off the power , they relay should deactivate after 10-15 mins.

1. It can be implemented using a set/reset kind of circuit, where the "set" button switches ON the circuit and the load, and the reset button switches OFF the load and the circuit after the specified amount of delay...

presently I do not have this circuit in my blog.

22. can this circut made with 2n3904 npn transistor, i also use 555 ic bit after some time it work again

1. you can 2n3904 for the BC547 transistor, and a 555 IC can be also be used for getting an identical delay effect.

23. plzz send info for 555 ic on 6v and 2n3904 transistors

24. Hi Swagatam. Glad I found your site, and I'm impressed! I wanted to see if you could make an ON Delay circuit similar to your 12V one posted, only with 24VAC input power. Also the relay will have a 24VDC coil (.87 watt). I read that I may need to adjust the resistor and capacitors values to achieve the delay time desired, however, I am looking to be at 5 to 10 seconds on delay. This will be for a safety delay when switching motor directions in a motor control unit. Please let me know if you need any more information from me. Thanks!

1. Thanks startup, for 24V you will just need to make R3/R4 twice the shown value, and upgrade the capacitor and the relay voltages accordingly....rest everything can be as is.

you may have to experiment a bit with the capacitor value for getting the specified time delay, you may start with a 100uF, and get closer to the required value by referring to the 100uF results.

2. Thanks! Would it matter if I used 1/2 watt resistors instead of 1/4?

3. you can use 1/2 watt, but 1/4 watt would also work without issues.

4. Hi again Swagatam! So I put together this circuit on a bread board, but for some reason all I get is an instant 9-10Vdc on the relay coil side. I haven't yet hooked up any relay/load yet. Please note that due to availability issues, I had to change some components: T1= BC547CTA and T2= BC557BTA, D1= 1N5913BRLG and R1=620K. Maybe this is where I went wrong? Or maybe my connections are off? Any help would be appreciated. Thanks.

5. Hi startup, the BC547 orientation looks to be incorrect....it should be the otherway round

6. I see that now, thanks. I've turned T1 around. For some reason I keep blowing the T2 though(shorted between Base/Emitter) I'm getting 10.5VDC at the T2 Base and Ground. The only other thing different is that I'm using a 33uF 50V cap. That and my input voltage is 24VAC instead of DC.

7. T2 will burn only if its collector is shorted to ground or if its base is shorted to ground or connected with the collector of T1 without a resistor...otherwise there's no way it can get damaged....so you can check for these issue.

the base voltage should be measured across base emitter of the BC557...not across base and ground.

8. Hi swagatam,
i need a on delay timer circuit of 10 second, after timer on a relay will be actuated and after 1 second delay the capacitor used for the first on delay circuit must be auto reset.
i see a circuit in your page which include 610k resistor for discharge the capacitor, but it takes time. i need quicker discharge.
kindly help me.

9. Hi Ravi,

if 610k is causing longer discharge time, then you try reducing it to some lower value and make the discharge quicker.

25. hi sir,

i want to make a delay mains switch.
so when electricity comes, it will block it for 30 seconds to get voltage stablise. after 30 seconds mains is turned on.
please work on this. it will be very useful to protect home electronics from burning.
please find simple and solid way to do it.

thanks.

1. Hi Gopal,

you can try the following concept:

http://makingcircuits.com/blog/2015/08/simple-time-delay-relay-protector-circuit-for-refrigerators.html

26. Hello sir,

I too want to make a 10 second to 5 minute adjustable power delay circuit for the refrigerator and couple of other gadgets in the house. I did check the circuitry for the refrigerator delay circuit. But was hard to figure out as its a bit hazy. It'll be great help if you could guide me in some other way.

Thanks

1. Hello Anirudh, the above explained circuit is perhaps the right one for your requirement. you can configure the circuit with a capacitive power supply and then connect the relay with the fridge...this will ensure a delay switch ON each time the fridge is powered ON and it will never respond to sudden power failurers or ON/OFF fluctuations.

2. Thanks a lot sir for guiding me. But i would like to ask you, which components decide the time delay? So as i can change the delay time.

For one circuit i need the time delay to be 10 seconds. And for another i need it to be 5 minutes. Kindly guide me.

3. C2, and R2 are responsible for the delay effect.

27. Sir i want to give input 5v and use 5v relay . Is it possible in your circuit if yes then which part i need to change . Please send a quick repose .

1. Satya, it is possible without any change.....you can use the same circuit as given.

28. Hello folks,

It's working 100%. I used BC327 + BC337, 220uF/63v cap, 5V1 zener diode in to a circuit as above. R1 is to large, I replaced with 100K because it takes to long to reset the capacitor.

30sec @ 14.4V
40sec @ 11.0V

1. Thank you Jason, yes the above circuit is quite handy as a delay ON circuit but I am sorry this circuit cannot be modified for an alternate delayed ON/OFF toggling, a schmitt trigger with flip flop is the only minimum way of achieving the feature that you have mentioned, the flip flop enables s single button ON/OFF function while the schmitt trigger facilitate the required delays in the ON/OFF cycles.

30. Currently using night light circuit to turn stair lights on and off. However at dusk they flicker on and off until it becomes dark enough for lights to stay on permanently. Will this time delay circuit work for this? A have my circuit drawn but not sure how to send to you.

1. you can use the above explained delay timer for correcting the issue however an easier solution could be to simply add a high value capacitor across base/emitter of the transistor which is driving the relay or the triac, this would also solve as effectively.

2. Nightlight circuit is made up of SCR, LDR, and 2M resistor, there is only anode, cathode, gate

3. that's a very crude circuit, and there's no way to solve the issue in it.... I have already used it.

In this design remove the LEDs and replace with a 1K resistor, disconnect the emitter and connect it with triac gate

31. Dear Sir.
I' d like to use this very helpful circuit with a little difference.
I have a constant 12V and a 12V trigger (I could turn it to adry contact by using an other relay or tranzistor.
One of the use is the one you suggested: 12V (trigger) applied and have few seconds delay before a relay powered on.
The other need is when 12V (trigger) are turned off an other relay powered on by the same delay.

Forgive my English, I hope its clear. I'm sure you have an answer!

1. Thanks Giakoumis,

the same circuit which is shown above could be used for getting equal ON/OFF delays...and its output could be modified for any desired application.

just remove R1, and replace D3 with a jumper link...and the circuit will start producing equal ON/OFF delays...

2. Dear Swagatam

First of all Id like to thank you for the quick response.
Also thank you for the new tip about the on/off delays.
My question was about a different relay, in order to replace an "on/off/on button.
Something like that: https://www.evakw.com/1395-home_default/xic111-button-with-arrow-spring.jpg.pagespeed.ic.pCp6nOprN3.jpg

Im sure that you have an Idea to suggest
Thanks again.

3. Thanks Glakoumis....OK I think I got it now.

in that case you can make two identical circuits as given in the above article, and disconnect their R2 ends from the positive line, and connect them to an SPDT switch (outer terminals)...and connect the center terminal of the switch with a 12V trigger..toggling this SPDT would result in two alternate delayed relays across the two circuits

4. Thanks again for the response.
That's what i thought...
Two different circuits to do the same thing by the opposite trigger (apply 12V, cut off 12V).
Do you agree?

5. Yes that appears to be the only legitimate way of implementing the proposed application....

32. Dear Swagatham Can this circuit add features a start up delay of about 4 minutes to prevent frequent switching on and off during fluctuations and to save on down time means that when the mains returns to normal after any event, the checks the duration of the OFF time, if the circuit has been off for more than 4 minutes then it will switch on within 10 seconds rather than the standard 4 minutes. If however, the circuit has been off for less than 4 minutes, will ensure that it will remain off up to 4 minutes and then restarts automatically.

1. Hi Seby, yes definitely it can be used for the mentioned delay and protection against fluctuations....I have already discussed one such application in the following article: