Phase detector

XOR gate!

John

Reply to
John Larkin
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Okay, I've got a Rube Goldberg thing going in my mind...

First of all, I have an SG3524 based driver circuit, running a half bridge that runs an induction coil. Driver schematic:

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Half bridge:
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(Cmatch + Ctank = 6.4uF, Lmatch = 35uH, Ltank = 1uH, supply = 110V.)

Well the circuit works as good as I can expect it to at this power level... what I'm racking my brain on is control. At the moment I manually adjust it to resonance for maximum power (or above resonance, giving the inverter a lighter, inductive phased load). As you can imagine... frequency varies quite a bit depending on load resistance, dimensions and permeability.

What kind of circuit would work here? I was thinking of detecting phase between the instant the tank reaches peak voltage and the time when the inverter switches off. At 50-100kHz (the larger model will be lower), that requires fractional-microsecond pulses, which aren't impossible but I'm not familiar with the circuitry (storage time doesn't like me..) to handle it. Then some sort of circuit to measure the time between the pulses and translate that to a current which controls the 3524's frequency (current draw from pin 6, which probably goes to a current mirror inside the chip).

Or if you have recommendations for chip(s) I have on hand that do all this automatically...I'm all ears...(which is basically limited to an MC1391 I pulled from a monitor, and various 74[LS] chips I have on hand).

Tim

-- "California is the breakfast state: fruits, nuts and flakes." Website:

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Reply to
Tim Williams

TC5081AP Phase Detector from Toshiba

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Reply to
John Walton

Amazing! Looks like a poor logical copy of the gating in an MC4044 ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

SNIP

Yeah, but I was able to snag a bag of TC5081's on EBay for next to nothing.

Intersil has a very nice phase-detector circuit on their website (AN9637) -- and it is very acurate. I built it using some TI cfb opamps (the intersil part was discontinued -- the transistor array is a bit tough to find). CFB opamps with disable function are preferred for ease of gain switching.

Basically, the CFB amps drive 1n4148's through 200R -- this clips the sine wave of both reference and signal to be measured -- each circuit feeds one side of the transistor array used as a comparator. Phase is proportional to the voltage averaged over time.

Reply to
John Walton

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Hm, so I can add a current loop toroid to the work coil supply, clip the signal with two 1N4148's in antiparallel, amplify (hm, rather one 1N4148 and a B-E junction) to get a "full height" square wave, and send this to a LTP against clock from the 3524? Does it matter in the closed loop that the

3524 isn't ever at 50% duty cycle?

And that makes a PWM error signal, which can then be averaged as you say and compared to a control voltage (power level) and sent to drive the frequency pin, no?

I like... almost uses fewer pins (as discrete transistors) than that 9-pin SIP alone. ;-)

Tim

-- "California is the breakfast state: fruits, nuts and flakes." Website:

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Reply to
Tim Williams

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