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Overvoltage protection

Greetings, my assembly contains the following HF amplifier (50 ohms in/ out), whose max input power is 3W (about 12 volts on the input),

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but the HF300-0130 does not contain any overvoltage protection, so any overshoot could potentially kill it. Does anyone have recommendations on what I could use to provide some kind of overvoltage protection or voltage clipping to ensure the input never goes above 12v (3 watts)? This has to be 50 ohms impedance matched, fail-free, low noise and without introducing any transients (all risetimes should be less than 1usec).

Reply to
Louis Bouchard
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input),

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The datasheet says "Max=3Watts RF input" (not voltage). Just use a variable attenuator that can handle the max power. M/A COM makes some.

Reply to
maxfoo

Put a transzorb across the supply terminals, and a fuse in line from the power supply to it (and the +12 power to the board.)

Googls "transzorb" - I'm not with the company, just a satisfied customer.

Good Luck! Rich

Reply to
Rich Grise

ummm. the supply voltage is 50volts not 12 volts. AFAIK no one makes a

50 ohm matched transzorb that works at HF , Please provide google link... ;^D
Reply to
maxfoo

^^^^^^^^

...

Max Foo, you need to learn to read. The supply voltage is 12V, the impedance of the signal is 50 ohms.

Good Luck! Rich

Reply to
Rich Grise

READ the datasheet! the link the OP provided. supply voltage =52Volts, Current= 13Amps It's a 300Watt HF amplifier. where are you seeing this 12Volts on the spec sheet. The OP is confusing voltage protection with max input power...

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Reply to
maxfoo

power...

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Okay, the confusion may be the 'overvoltage' terminology. The dc supply is

52vdc 13 amps, and this is always constant (no need for overvoltage protection on the dc supply end), as the power supply is a very good one. The protection that is needed is on the 50 ohms RF input. The amp can be damaged if this exceeds 3W input. So 3 watts input into a 50 ohms port corresponds to 12 volts (Pmax=Vmax^2/R50ohms). That's where the 12 volts comes from. This amp is being fed by a 5W preamp, so the goal is to limit the output of the 5W amp, or, equivalently, to limit the input of the 300W amp. The attenuator solution proposed earlier will work, but I'm not sure it's the most efficient in terms of noise- adding passives (e.g. resistors) usually adds more noise. I was thinking about clipping the input to 12 volts, but I'm not sure this would be any better.
Reply to
Louis Bouchard

power...

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Clipping will to the job (O.V. protection) but when the input is driven above the clipping limit, you will get noise (harmonics). You might have to add some filters downstream of the protection stage to keep the generated harmonics out of the amplifier.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
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Reply to
Paul Hovnanian P.E.

power...

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Harmonics are o.k., as long as they don't exceed 12 V. Would you recommend a particular produce as voltage limiter device, which can work in a 50 ohm transmission line? (I have only used voltage limiters for dc operation)

Reply to
Louis Bouchard

a

power...

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Agilent makes power limiters but they are not cheap ($600-$1000).

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Reply to
maxfoo

Well, you seem to be unexperienced with RF. A +/-12V limit will *not`* be

2.88W into 50R(exept for a square wave). And the 52V/13A supply is the abs. max. rating, better to stay with the 48V given in the datasheet. To protect your amp you can reduce the supply voltage of the preamp, so it delivers the required power and drives the power stage to the specified level at onset of clipping at the operating frequency. If you cannot access the preamp, a variable 5-10W pad is the best solution. The noise floor will *not* be higher, since it will come from the preamp and will be attenuated as well. Much more important to match the load, whatever it is. 
--
ciao Ban
Apricale, Italy
Reply to
Ban

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