Question regarding an IR2111 half bridge mosfet driver - Page 1
Forum section: electronics / projects

author: Unknown
author_rank: Unknown
timestamp: October 22, 2016, 11:57:36 pm
content: Hi all,I am trying to build a circuit which switches two opto-isolators 180° apart.The trigger is a 555 which sits nicely at 50% duty cycle. My problem has been transmitting that to the optos...Although I have never used one before, it seemed like a good idea at the time to try a half-bridge mosfet driver, seeing as they have both Hi and Lo outputs.So here I am, replicating the circuit in the datasheet (see attachment) only without the mosfets - and getting nowhere.With a 5v input on both pins 1(Vcc) and 8 (Vb) and Ground on pin 3, my Lo out is the same as Ground, whilst the Hi out and Vs are both around 5v.The input signal is 200hz at around 1.8 voltsWhat have I done wrong?

author: Andy Watson
author_rank: Super Contributor
timestamp: October 23, 2016, 12:06:52 am
content: There is an under-voltage lockout that requires Vb and Vcc to greater than about 8V.

author: Unknown
author_rank: Unknown
timestamp: October 23, 2016, 12:23:00 am
content: Ok, so gave it 12v but I have 0Hz frequency on any other pin.I am looking for two outputs of 200Hz 50% duty cycle to trigger two opto's 180° apartp.s. with 12v input it comes out 12v and the opto's don't take 12v

author: Andy Watson
author_rank: Super Contributor
timestamp: October 23, 2016, 12:30:30 am
content: Is your input voltage still 1.8V? It needs to swing between 38% to 64% of Vcc to trigger the input (see page 3 of the datasheet).

author: Unknown
author_rank: Unknown
timestamp: October 23, 2016, 12:36:21 am
content: Hang on then...Need to do some soldering....

author: Seekonk
author_rank: Super Contributor
timestamp: October 23, 2016, 12:38:43 am
content: Saying 555 is the perfect lead in to say IR makes a IR51HD420 which is a 500V, high speed, self- oscillating half-bridge, a high voltage 555 with built in FET output.

author: Unknown
author_rank: Unknown
timestamp: October 23, 2016, 12:50:18 am
content: Thanks for all the replies.Ok, with 8v in on the IR2111 and 3.2v out of the 555 it still does not work. No output at all on Lo out and no frequency passing through the device.Seekonk.. didn't understand what you were saying....An IR51HD420 removes the need for a 555?

author: Unknown
author_rank: Unknown
timestamp: October 23, 2016, 12:53:24 am
content: Need to increase the output voltage of the 555?

author: Andy Watson
author_rank: Super Contributor
timestamp: October 23, 2016, 12:58:50 am
content: Yes. Could you run the 555 from the same Vcc?

author: Unknown
author_rank: Unknown
timestamp: October 23, 2016, 01:05:23 am
content: Can do. In fact it was with 12v input that the 555 gave 3.2v out.Just looking at these IR51's... Maybe that could resolve my dilemma?

author: Seekonk
author_rank: Super Contributor
timestamp: October 23, 2016, 01:10:19 am
content: Even a IR51HD420 requires at least a 10V supply. 51 series has been replaced by 53, but old ones are probably on ebay. A neat part I have that I have never found anything useful to do with.

author: Unknown
author_rank: Unknown
timestamp: October 23, 2016, 01:13:28 am
content: I can easily give the input 12v and up to 15 with a bit of fiddling, it is more important for the output to trigger the opto isolators, which will blow at 10 or 12 volts.3 to 5 volts would be ideal

author: Unknown
author_rank: Unknown
timestamp: October 23, 2016, 01:43:45 am
content: No more ideas?

author: nuno
author_rank: Frequent Contributor
timestamp: October 23, 2016, 02:17:01 am
content: I guess you should look more carefully into the internal diagram of the chip, to see what can/cannot be done with Vb and Vs. (assuming the chip is good)

author: Unknown
author_rank: Unknown
timestamp: October 23, 2016, 02:47:47 am
content: Quote from: nuno on October 23, 2016, 02:17:01 amI think this chip is not capable of doing that which is needed. I need two opposing outputs which can trigger 4N25 opto couplers.

author: Seekonk
author_rank: Super Contributor
timestamp: October 23, 2016, 06:22:10 am
content: "the opto isolators, which will blow at 10 or 12 volts. " Which ones do that?? I am quite a fan of driving FETs directly with opto isolators. I refuse to ever use a 555 for anything, but if I remember you can never or easily 50% duty cycle. What about a flip flop divide by two. Don't forget that turn off speed is about 4 times longer than turn on.

author: Unknown
author_rank: Unknown
timestamp: October 23, 2016, 11:28:52 am
content: Well, I must be doing something right then, as I have a stable 50% duty cycle from the 555.As for the 'divide by two', why would I do that? That would divide the frequency. That is not the problem.I need to trigger one opto at 0 and the other at 1. 180° separation in the cycle.The circuit to is to run at 200 - 600 Hz with 50% duty cycle, triggering two opto's.The 555 is not essential, it is just that that part is working fine... As are the opto's... Just how to connect between the two?I'm gonna play around some more with the IR2111look into using an IR2151.Back to the opto voltage.... I have blown various opto's whilst experimenting with the input/protection circuitry and voltages. 5v is the input voltage which experience has shown me to be safe, but please feel free to correct me.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: October 23, 2016, 08:23:38 pm
content: I am puzzled of why you use a mosfet driver when you say you want to drive opto couplersI am also puzzels at how you managed to blow several opto couplers. This suggest to me you're quite a novice in electronics and probably connected them wrong. Hint: optocouplers are simple devices and have no internal current limting. Just as with normal leds always use a current limiting resistor for the Opto Led. The IR led's for optocouplers usually have a voltage drop of about 1V.In the past I've had succes with driving 2 optocouplers from a microcontroller ( @Vcc = 5V) by making intelligent use of the voltage drop over the opto coupler leds & other leds."Schematic:"Vcc -> Opto Coupler led -> Green Led -> Red Led -> Opto Coupler Led -> GND.All diode's connected in series. But because the combined minimum voltage is > 5V none of these devices conduct current in this "idle" state.Now connect a resistor between your driver circuit (ne555/ uC) and the connection between the 2 Red & Green Leds.If your output is High, The red Led wil light up (and the Opto to GND).If your output is Low, the Green led wil light up (and the Opto from Vcc).For a more general device tell us more about what you want to achieve with your opto coupler circuit.

author: Seekonk
author_rank: Super Contributor
timestamp: October 23, 2016, 08:49:21 pm
content: I'm thinking I can't help anybody that hangs around my arch enemy the 555. Why don't you use a chip that isn't crap like the TL494 that has two outputs out of phase.

author: Unknown
author_rank: Unknown
timestamp: October 23, 2016, 09:42:14 pm
content: Hahaha...Didn't realise that certain components had enemies.It is true that I am a relative novice, however, it is only by making mistakes that you truly learn why NOT to do things in a certain way. I am in no way afraid of making, nor ashamed of the mistakes I have already made whilst learning electronics.As for the TL494, I shall take your kind advice and have a look into it.If the circuitry can be simplified then I am all for it.As for the circuit. The output requirements are;Two opto couplers being switched 180° out of phase from each other, at somewhere between 100Hz to 1KHz whilst maintaining a fixed 50% duty cycle.It is surely not too difficult. The trigger (555) section is working fine as are the opto's (with diode, transistor, resistor protection), Currently trying something else here on the bench

author: Unknown
author_rank: Unknown
timestamp: October 24, 2016, 12:13:29 am
content: Anyway,cracked it!Reverted back to my original idea, which was aborted after a 'non-novice' technician told me it couldn't work.... Namely using a PNP and NPN on the 555 pin 3 to trigger the opto's.Thanks to all who tried to help.