Frequency threshold controlled switch component

[avihaio]

Hello,
I'm looking for a component that "knows" to switch a power trace with up to 2-2.5A and up to 15V (7W if it's important) according to an input frequency.
In order to explain - I can do an analogy to a MOSFET that instead of a Vgs(th) it has a frequency threshold.
This "switch" should consider only the frequency but not the duty cycle.
I'd like to solve it with one component (and passive components) and not something complementary to a regular switch like a MOSFET.

Any ideas please?

Thanks,
Avihai

 

[FvM]

There's no such component on the market as far as I'm aware of.

But it's surely possible to design a multicomponent circuit with the requested behavior. May be a power ASIC.

The spec is incomplete, however. Are you imagining an AC or DC switch? Is the frequency input a separate port? What's the control signal level range? Is the switch supplied by 1. the power circuit 2. the control circuit 3. an auxiliary supply

 

[betwixt]

Do you want something that switches according to a frequency being higher or lower than the threshold or being a particular frequency?

For a specific frequency, my first thought is a PLL (NE556 for example) with lock detect controlling the power switch. If a high/low frequency determination is needed you either have to use a rather complicated digital filter or a fairly trivial software routine to measure the frequency, either way you need an ASIC or an MCU. There is no single component that can both do the measuring and switch the power but it should be possible to do it with only a few discrete components.

Brian.

 

[avihaio]

Thanks for your answer.
I need it as a DC switch with a separate port for the frequency (like the gate in a MOSFET).
The input frequency (PWM) should be 0-3V and powered by the input DC that is switched or an aux supply of minimum 3.3V.
An ASIC is not an option, but a multicomponent circuit maybe - but anyway I can't convert the frequency to a DC signal that will open a MOSFET.

- - - Updated - - -

Do you want something that switches according to a frequency being higher or lower than the threshold or being a particular frequency?

For a specific frequency, my first thought is a PLL (NE556 for example) with lock detect controlling the power switch. If a high/low frequency determination is needed you either have to use a rather complicated digital filter or a fairly trivial software routine to measure the frequency, either way you need an ASIC or an MCU. There is no single component that can both do the measuring and switch the power but it should be possible to do it with only a few discrete components.

Brian.

Hi Brian,
An higher than threshold frequency or a particular are both possible, but not lower.
I'd like to avoid a DC signal that is the switching signal, so a PLL is less convinient.

Thanks

 

[FvM]

but anyway I can't convert the frequency to a DC signal that will open a MOSFET

What do you mean with "can't convert"? The frequency threshold function can be easily implemented with a RCD circuit plus comparator or monoflops.

 

[BradtheRad]

* The 567 IC (tone decoder) is designed to do this job.

* Narrow bandpass filter, can be made from passive components. Twin-tee is a notch (bandstop) filter which inhibits the center frequency and thus can turn on a PNP transistor.

* Oscillating circuit which responds only to your target frequency.

 

[betwixt]

I'm seeing some conflicting requirements here.

You want something that switches power on when a signal it is monitoring exceeds a certain frequency,
You want to avoid a DC signal that operates the switch.

Are you saying you want a gentle turn on (in other words not a switch) that increases power starting from a particular threshold frequency?

Perhaps if you draw a graph of frequency vs. power it would help us understand your requirement.

Brian.

 

[avihaio]

What do you mean with "can't convert"? The frequency threshold function can be easily implemented with a RCD circuit plus comparator or monoflops.

can't = I don't want a DC signal on a trace that directly opens a MOSFET, even if it's created by a frequency.

I'm seeing some conflicting requirements here.

You want something that switches power on when a signal it is monitoring exceeds a certain frequency,
You want to avoid a DC signal that operates the switch.

Are you saying you want a gentle turn on (in other words not a switch) that increases power starting from a particular threshold frequency?

Perhaps if you draw a graph of frequency vs. power it would help us understand your requirement.

Brian.

I'll try to explain it differently. Let's say that it looks like this:

IN --------------|___|-----------OUT

|​

| FREQ​

So the logic will be:

if (freq>50kHz)

OUT = IN​

else OUT = floating/GND

so it's not a gentle turn on, but a binary logic (yes or no output power).

I hope that it's clearer.

Thanks again

 

[FvM]

can't = I don't want a DC signal on a trace that directly opens a MOSFET, even if it's created by a frequency

Then you should give up your project unless somebody provides you a single component frequency controlled power switch. Or design a respective enclosed switch module.

I'm off.

 

[avihaio]

Then you should give up your project unless somebody provides you a single component frequency controlled power switch. Or design a respective enclosed switch module.

I'm off.

Fair enough.
Thanks

 

[betwixt]

I feel FvM's frustration.

Given that no such single component exists, and in view of it's highly specialized requirement, probably never will - what do you propose turns the switch on or off if it isn't a binary logic signal?

As I see it, the task can easily be solved with a small MCU to measure the frequency and produce the binary logic signal, then either a MOSFET or bipolar switch to enable the power to the load. Less than 10 components would be needed and you could get a 'brick wall' response as the frequency threshold crosses.

Brian.