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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 12th Mar 2017, 5:27 pm   #21
paulsherwin
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Default Re: Dropping 40V Down to 9V volts

You won't need to heatsink it if the current is low.
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Old 12th Mar 2017, 5:28 pm   #22
sp10mk11
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Default Re: Dropping 40V Down to 9V volts

ah ok but I would be able to bolt it to the chassis?
Gary
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Old 12th Mar 2017, 5:32 pm   #23
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Default Re: Dropping 40V Down to 9V volts

No, not without an insulator. It's connected to the output pin as with similar voltage regs.
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Old 12th Mar 2017, 6:06 pm   #24
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Default Re: Dropping 40V Down to 9V volts

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Originally Posted by sp10mk11 View Post
ah ok but I would be able to bolt it to the chassis?
Gary:
If its only pulling say 10 or 20mA theres no need to bolt it down it won't get hot enough to worry about. I'd assume you'll use a bit of veroboard/stripboard to mount it and it's associated components on so why not just bolt the wee bit of board down on a short standoff? Heck a nut would likely be thick enough to keep the board clear of the chassis.
I'd use the recommended circuit with decoupling capacitors on input and output.
It could save annoying oscillations.

A.
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Old 12th Mar 2017, 7:39 pm   #25
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Default Re: Dropping 40V Down to 9V volts

The LM317AHV would also fit the bill. Its a high voltage variant of the well known LM317 and has a 60 volt input to output differential rating.
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Old 12th Mar 2017, 8:12 pm   #26
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Default Re: Dropping 40V Down to 9V volts

When you're bringing the voltage down a long way and only taking a light current, watch out for the current taken in the voltage programming resistors - typically 10mA because this can take as much power and create as much heat as the wanted output, if the output current is similar.

There are some regulators with particularly low currents on their reference pins, so you can scale down the programming resistor current and make the thing a good bit cooler.

David
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Old 12th Mar 2017, 8:55 pm   #27
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Default Re: Dropping 40V Down to 9V volts

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It is to power an FM tuner so it does not have to be a high current job
How much current does the tuner take? Without this it's all guessing.
 
Old 12th Mar 2017, 9:08 pm   #28
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Default Re: Dropping 40V Down to 9V volts

"How much current does the tuner take"
I do not actually know it is run off a 2 watt 1K resistor
Gary
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Old 12th Mar 2017, 10:24 pm   #29
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Default Re: Dropping 40V Down to 9V volts

Hi

CPC have the TL483 voltage regulator available singly.

http://cpc.farnell.com/texas-instrum...rfnonsku=false

Regards
Symon
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Old 12th Mar 2017, 11:25 pm   #30
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Default Re: Dropping 40V Down to 9V volts

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"How much current does the tuner take"
I do not actually know it is run off a 2 watt 1K resistor
Then it's easy to calculate Gary.
Just measure the Voltage across the resistor in series with the supply and apply Ohms law.

A.
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Old 13th Mar 2017, 8:10 am   #31
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Default Re: Dropping 40V Down to 9V volts

The LM317AVH goes up to 57v, output is connected to the body like most 3 pin adjustable regulators.

Andy.
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Old 13th Mar 2017, 8:37 am   #32
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Default Re: Dropping 40V Down to 9V volts

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Originally Posted by Radio Wrangler View Post
When you're bringing the voltage down a long way and only taking a light current, watch out for the current taken in the voltage programming resistors - typically 10mA because this can take as much power and create as much heat as the wanted output, if the output current is similar.

There are some regulators with particularly low currents on their reference pins, so you can scale down the programming resistor current and make the thing a good bit cooler.
Good point, although the TL783 takes only 110uA at its reference input so 1mA through the programming resistors would be fine - particularly as the reference current is pretty constant so can be adjusted-out.

However, there is a minimum load of 15mA. Many people (me sometimes!) achieve this by using low-value programming resistors, so that the output doesn't rise off-load. But, if you have a permanent load, the problem goes away.

So in this application, just don't have a big output capacitor, disconnect your FM tuner with the 40V still supplied, and then reconnect it. Or if you think you might, have a Zener diode across the output of a couple of volts higher than the programmed output voltage, which will hold things down off-load, but have no effect on-load.

Dr Wobble and Mooly's suggestion of LM317HV would also be a good candidate, the same applies here too!
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Old 23rd Mar 2017, 4:34 pm   #33
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Default Re: Dropping 40V Down to 9V volts

I bought a TL783 and it works perfectly so thanks to all who contributed and gave advice.
Gary
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