Need a 5V to 15V conversion with 555

[imsmooth]

I have a 555 running off of 5v. I want this signal to control another IC running off of 15v so the output toggles between 0 and 15v. I tried a 4069 hex inverter, but when it runs of 15v the 555 running off of 5v does not reach the logic HIGH threshold. I tried using a FOD3180 coupler, but did not work. Is it that the 555 does not have enough output current to drive the 3180?

I have 1k resistor coming off of pin3 on the 555. Is there a hex inverter that has a sub-5v threshold for logic HIGH that would work?

Thanks.

 

[berkeman]

Do you already have both 5V and 15V rails available, and are asking about how to do a logic level conversion between those two voltage domains? Or do you also need to chop a 15V supply from your 5V circuit?

 

[imsmooth]

I got it to work using a 150R resistor off of the 555. I would think it should have worked with a higher resistor, but I have to go to work now and can't play with it.

I have a 15v power source going to a breadboard. I am getting the 5v supply using a 7805 regulator off of the 15v.

As far as your question, I am doing a logic conversion from 5v to 15v. Is there a preferred way to do this, or is using an optocoupler acceptable?

 

[DaveE]

There are about a million ways to do this level conversion. A web search may be your best bet. It's hard for us to say what's acceptable, that depends on your detailed requirements. FOD3180 should be OK, I think. A schematic would be helpful for us.

The 555 can source or sink lots of current (200mA typ.). Whatever your problem is with the FOD3180, it's probably not that.

BTW, ever since I saw the 7555, I NEVER used a 555 again, although they do work OK, sort of.

 

[imsmooth]

Is there a hex inverter that has a low voltage value for logic HIGH when running off 15v? The 4069 has a value near 5v when running off 15v so it does not work for me.

 

[DaveE]

Is there a hex inverter that has a low voltage value for logic HIGH when running off 15v? The 4069 has a value near 5v when running off 15v so it does not work for me.

Yes, honestly, too many to easily choose one. Have you looked at digikey? They have some really good search tools.

 

[DaveE]

Here's the OG TTL to CMOS IC
CD4504B

 

[imsmooth]

Yes, honestly, too many to easily choose one. Have you looked at digikey? They have some really good search tools.

Yes. I was looking at Digikey and there were so many. That's why I thought to ask if someone else knew one off the top.

What I am trying to do is build a feedback as in this link:
https://autotuningmainsinductionhea...ains-high-power-half-bridge-induction-heater/

He is using the 555 for a baseline signal and overpowering it with the current transformer's signal. This is getting fed into the hex for a square output to the inverter.

The 555 and hex inverter are using 5v and then getting bumped up to 12v later. I wanted to bump it up where the hex inverter is located by that IC running off 15v. Would the optocoupler be reasonable, or is the hex better?

 

[DaveE]

Yes. I was looking at Digikey and there were so many. That's why I thought to ask if someone else knew one off the top.

What I am trying to do is build a feedback as in this link:
https://autotuningmainsinductionhea...ains-high-power-half-bridge-induction-heater/

Did you read this part?

"Before I go any further, just a word of warning. This project utilizes unprotected mains and generates high voltages, high alternating magnetic fields, and very high temperatures which can be dangerous resulting in injury which can be serous or fatal especially in untrained hands. Please regard the information in this page for academic purposes only."

Would the optocoupler be reasonable, or is the hex better?

Either will work if implemented properly. Also 555's work well from 15V power supplies. If you can't or won't do the work to figure this out yourself, then you probably shouldn't be starting out with hazardous circuits.

Good Luck, I'm done.

 

[imsmooth]

Did you read this part?

"Before I go any further, just a word of warning. This project utilizes unprotected mains and generates high voltages, high alternating magnetic fields, and very high temperatures which can be dangerous resulting in injury which can be serous or fatal especially in untrained hands. Please regard the information in this page for academic purposes only."Either will work if implemented properly. Also 555's work well from 15V power supplies. If you can't or won't do the work to figure this out yourself, then you probably shouldn't be starting out with hazardous circuits.

Good Luck, I'm done.

Yes I did read that part, but that is referring to his tank circuit. My tank circuit does run off an isolated power supply which I have been using for the last 15 years. I want to try his circuit to see if I can get resonance using hardware vs software control.

I can't use 15v on the 555 because I need it to get overpowered by the current transformer's signal. At 15v the circuit won't override the signal until a much higher tank current.

I'll probably just use 5v for both and use the logic output to drive my 4421/4422 which will run off 15v.

 

[Baluncore]

I have a 555 running off of 5v. I want this signal to control another IC running off of 15v so the output toggles between 0 and 15v.

You must look at, (and understand), the internals of the 555, not the published circuits that are confusing.
I think of a 555 as having two outputs.
Pin 3 is the regular high-current bipolar output.
Pin 7 is an open collector output, called disch.

You could modify the circuit to make a square wave oscillator using pin 3, (not pin 7), to drive the frequency selecting pot circuit. Keep pins 2 and 6 connected to the same capacitor.

Pin 7 is then separate and available, so it can drive the higher voltage logic, with a pull-up resistor to the +15V supply.

 

[imsmooth]

You must look at, (and understand), the internals of the 555, not the published circuits that are confusing.
I think of a 555 as having two outputs.
Pin 3 is the regular high-current bipolar output.
Pin 7 is an open collector output, called disch.

You could modify the circuit to make a square wave oscillator using pin 3, (not pin 7), to drive the frequency selecting pot circuit. Keep pins 2 and 6 connected to the same capacitor.

Pin 7 is then separate and available, so it can drive the higher voltage logic, with a pull-up resistor to the +15V supply.

Thank you. What I'm trying to do is drive the higher logic with no more than 5v. All the inverters I've looked at have different threshold depending on the value of Vcc powering the chip. The mosfet drivers 4421 and 4422 seem to need a low threshold current to switch logic states. It also has an internal signal clamp at 4.7v so it should respond the way I need with the 5v logic signal.

 

[Baluncore]

What I'm trying to do is drive the higher logic with no more than 5v.

Are you saying that the two circuits have different zero volt references?

When designing electronics, the schematic diagram surpasses written language.

 

[imsmooth]

I have a different question related to this feedback circuit. A signal using a current sense transformer on the induction tank is converted to a 5v square wave and drives the inverter. I would like to implement detuning to a higher frequency if the current is too high. Going to a higher frequency would drop the current. I currently have a software-controlled system that does this, but I would like to do this with just hardware.

I was initially thinking of just a hard cutoff:

A CST would exceed a cut-off voltage with some Zeners. This signal going into a logic gate along with the feedback signal would cut off the signal.

I would prefer to detune, but I do not know where to start. Is this possible?

Here is the feedback circuit again.
https://autotuningmainsinductionhea...ains-high-power-half-bridge-induction-heater/

 

[Baluncore]

I was initially thinking of just a hard cutoff:

A CST would exceed a cut-off voltage with some Zeners. This signal going into a logic gate along with the feedback signal would cut off the signal.

I would prefer to detune, but I do not know where to start. Is this possible?

Anything is possible.
What do you mean by the term "cut-off" ?
What do you mean by "detune" ?

Do you want, what is now the 555 output frequency, to rise or fall gradually, so as to regulate the tank current ?
Or do you want each half cycle of the tank driver to end when a specified current has been reached ?

 

[imsmooth]

Anything is possible.
What do you mean by the term "cut-off" ?
What do you mean by "detune" ?

Do you want, what is now the 555 output frequency, to rise or fall gradually, so as to regulate the tank current ?
Or do you want each half cycle of the tank driver to end when a specified current has been reached ?

By cutoff I mean when the CST reaches a threshold voltage this will then initiate raising the tank frequency above the resonant value. If the current is above, say, 40A @ 75khz the CST will have a 40v value. The circuitry will then push the frequency higher until the CST value falls below 40v.

The 555 simply gets the circuit going. The feedback from the CST should be providing the drive to keep it going, so I don't think modifying the 555 will give me the desired result.

 

[Baluncore]

To change the self-resonant frequency, you would need to change the value of capacitance across the tank circuit.

By off-tuning the tank, without a change of LC, you will reduce the tank power, by reflecting energy back to the drivers, which will probably not be good for them.

PWM of the drivers, could reduce the current circulating in the resonant load. Once the circuit is oscillating, it might be easier to control the on-time of the drivers, to regulate the energy delivered by the drivers.

 

[imsmooth]

To change the self-resonant frequency, you would need to change the value of capacitance across the tank circuit.

By off-tuning the tank, without a change of LC, you will reduce the tank power, by reflecting energy back to the drivers, which will probably not be good for them.

PWM of the drivers, could reduce the current circulating in the resonant load. Once the circuit is oscillating, it might be easier to control the on-time of the drivers, to regulate the energy delivered by the drivers.

Would you have any idea if commercial induction units use software or hardware to control the driving frequency?

 

[Baluncore]

Would you have any idea if commercial induction units use software or hardware to control the driving frequency?

That will depend on the application.

The frequency should be the natural frequency of the resonant LC circuit.

I would expect new designs to be entirely digital, with a microcontroller measuring and adjusting the current in the tank circuit, by changing the duty cycle of the drivers. That microcontroller should start the oscillation, then the frequency should rise and fall as the heating load is changed.