[hpsdr] thor

[Kjell Karlsen]

Hello all.

All the Switch mode PSU´s I know have a transformer to insolate the mains  
 from the equipment. The mains are rectified and then regulated with a  
transistor (FET) via a transformer. By using a higher frequency for the  
switcher, it can be smaller than one for 50 or 60 Hz. The feedback is with  
an optocoupler or inductive in some way. It is not permitted to connect  
the unit directly to the mains without a galvanic insulstor in between.  
This also apply to a washing machine..... (and for safety, also for home  
built equipment!!)
The Motor in the washing machine runs directly on the mains, but the  
galvanic insulation is intact.

73, Kjell LA2NI





På Fri, 21 Aug 2009 19:36:33 +0200, skrev Graham / KE9H  
<KE9H at austin.rr.com>:

> ***** High Performance Software Defined Radio Discussion List *****
>
> Steve:
>
> I think that in the context of European Electrical Safety rules,
> which are the most stringent globally, that it is possible
> to do off line switching, but when you do that, all parts of
> the electrical system connected to the off line switcher power
> supply become subject to the voltage breakdown isolation and
> isolation tracking distances for the primary or line side of the power
> supply.  From memory, this means that all parts of the circuit need
> to observe some two centimeters isolation clearance to ground
> and to any operator connected conductive surfaces, etc.
>
> So, technically, you can do it.  And Phil's washing machine
> probably complies.  But since I personally would find it
> challenging to build a RF PA where all connections to the power
> supply, including the power supply ground, had to be isolated
> from the real/safetyRF ground by some 2 cm tracking distance, I would
> personally use a power transformer and restrict the safety
> compliance issues to the primary side of the transformer.
>
> The rules apply to commercially manufactured and sold items.
> I have no idea how the regulations apply to home built
> equipment.
>
> --- Graham / KE9H
>
> ==
>
> Steven Doyle wrote:
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> Hi Alex,
>>
>> We are considering rectifying striaght off the mains, but the prototype  
>> has a transformer, noise issues asside the main reason being the  
>> voltage at the FET drain can typically reach 3-4 times the supply  
>> voltage which exceeds the break down voltage of most of the popular  
>> power FETS. We are using a 120VDC supply in the prototype.
>>
>> I wasn't aware of any legal issues with rectifing stright off the  
>> mains. I will investigate this.
>>
>> 73s
>>
>> Steve
>> G1YLB
>>
>>
>> ----- Original Message ----- From: "Phil Harman" <phil at pharman.org>
>> To: "Murray Lang" <murray.lang at westnet.com.au>
>> Cc: <hpsdr at openhpsdr.org>
>> Sent: Friday, August 21, 2009 3:13 AM
>> Subject: Re: [hpsdr] thor
>>
>>
>>> ***** High Performance Software Defined Radio Discussion List *****
>>>
>>> Hi Alex,
>>>
>>> That is exactly what is planned. Basically you build a switching PSU
>>> running at say 200kHz.  You use the your modulation envelope signal to  
>>> PWM
>>> the PSU and that gives you a DC voltage that varies in sympathy with  
>>> the
>>> modulation.
>>>
>>> At bit like the AM modulators we built years ago. There is one  
>>> significant
>>> difference.If you think of the envelope of an SSB two tone test signal
>>> then as the envelope passes through zero volts the signal rapidly  
>>> changes
>>> direction. You need a wide enough  LPF to pass this signal but still  
>>> able
>>> to attenuate the (200kHz say) switching frequency.
>>>
>>> This is one of these techniques that 'works beautifully on the white
>>> board' :-).
>>>
>>> Not sure about Murray's comment on rectifying the mains directly. Our
>>> washing machine does this and does not have a mains transformer to be  
>>> seen
>>> - and produces the most QRN of any device I've ever come across!
>>>
>>> 73's Phil...VK6APH
>>>
>>>
>>>
>>>> ***** High Performance Software Defined Radio Discussion List *****
>>>>
>>>> alex wrote:
>>>>> ***** High Performance Software Defined Radio Discussion List *****
>>>>>
>>>>> why bother having a separate modulated psu, why not run the pa off
>>>>> rectified mains and modulate the duty cycle.
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>>>>>
>>>> Hi Alex,
>>>>
>>>> I don't know about the US, but in Australia I think it is illegal to
>>>> rectify the mains directly. There must be a transformer first.
>>>>
>>>>
>
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