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Old 22nd Jan 2023, 8:12 pm   #1
Electronpusher0
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Default HV Boost converter module

I have bought one of these modules to see if it can be adapted to use as a valve HT supply.
It is available from several suppliers including e-bay, amazon and Aliexpress.
Search for:
"DC12V to for 200-450V 70W High Voltage Converter Boost Step Up Power Supply"

I have traced the schematic, see attached. (the value of some of the capacitors is guesswork)
I am sure that the chip is a uC3848AN device. The chip is only marked with chinese characters which Google lens translates as "Select Electronics"

I am puzzled by the function of Q2, this seems to be switched hard on when the supply voltage exceeds about 3V and connects the input 0V to the output 0V.
If this is functioning as an undervolt protection then it is superfluous as the 3848 has a low voltage protection built in, it will only run if the input volts is above 7V.

Any thoughts welcome.

Peter
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Old 22nd Jan 2023, 8:38 pm   #2
Chrispy57
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Default Re: HV Boost converter module

Interesting that the fuse is also in the negative circuit, and the diode across Q2 will be conducting?
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Old 22nd Jan 2023, 8:50 pm   #3
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Default Re: HV Boost converter module

Quote:
Originally Posted by Chrispy57 View Post
Interesting that the fuse is also in the negative circuit, and the diode across Q2 will be conducting?
True, I had not noticed that the diode would be conducting. The diode is an integral part of the mosfet.

I have double checked that part of the circuit and it is correct.

Peter
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Old 23rd Jan 2023, 12:25 am   #4
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Default Re: HV Boost converter module

It is for polarity protection in case somebody swaps the +/- input supply.
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Old 23rd Jan 2023, 8:30 am   #5
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Default Re: HV Boost converter module

That makes sense.

For my application I can link it out then.
That would free up the MOSFET to connect in parallel with the output device. With another gate resistor to prevent parasitic oscillations of course.
I am also going to try adding an overwind to get a negative supply for grid bias.
See proposed circuit.

Peter
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Old 23rd Jan 2023, 9:45 am   #6
vinrads
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Default Re: HV Boost converter module

Hi Peter good luck with it, the one I tried wiped out most of the AM bands, Mick.
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Old 23rd Jan 2023, 12:25 pm   #7
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Default Re: HV Boost converter module

Are the resistor values in the output divider string right?

dc
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Old 23rd Jan 2023, 12:59 pm   #8
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Default Re: HV Boost converter module

These converter modules are somewhat noisy but with a few outboard components like ferrite chokes and feedthrough capacitors and additional screens they can be made RF- quiet enough to be incorporated into receivers without any major problems. I used one of the smaller ones recently to replace the failed vibrator power supply in my 1950s era R209 comms receiver.
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Old 23rd Jan 2023, 2:16 pm   #9
AdrianH
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Default Re: HV Boost converter module

Well as it says 40 watts continuous I thought I would buy one to try out on my TX unit, nothing to lose for that cost.

Thanks for the circuit as well.

Adrian
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Old 23rd Jan 2023, 5:11 pm   #10
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Default Re: HV Boost converter module

Quote:
Originally Posted by dave cox View Post
Are the resistor values in the output divider string right ?

dc
Sorry R10 is 240K, an error in transfering from my hand drawn paper schematic.

Peter
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Old 24th Jan 2023, 2:58 am   #11
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Default Re: HV Boost converter module

Re post #5 pdf - Why have you got a 5k resistor - R13 - in the source of the FET you've reallocated?
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Old 24th Jan 2023, 4:09 pm   #12
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Default Re: HV Boost converter module

Quote:
Originally Posted by Electronpusher0 View Post

Sorry R10 is 240K, an error in transfering from my hand drawn paper schematic.

Peter
Thx Peter
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Old 24th Jan 2023, 4:13 pm   #13
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Default Re: HV Boost converter module

Quote:
Originally Posted by Terry_VK5TM View Post
Re post #5 pdf - Why have you got a 5k resistor - R13 - in the source of the FET you've reallocated?
It should be connected to the gate? So the the two Q2's in parallel


dc
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Old 24th Jan 2023, 5:37 pm   #14
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Default Re: HV Boost converter module

Quote:
Originally Posted by dave cox View Post
Quote:
Originally Posted by Terry_VK5TM View Post
Re post #5 pdf - Why have you got a 5k resistor - R13 - in the source of the FET you've reallocated?
It should be connected to the gate? So the the two Q2's in parallel


dc
Quiet correct, too much haste.

Peter
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