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unregulated dc-dc converter

Started by ***Marco*** February 25, 2016
Hi all,

I'm trying to figuring out how a circuit which employs an unregulated 
Dc-DC converter works. I've never used one before, so I'm asking for 
some clarifications.
The dc-dc converter is the PICO 5A250S 
(http://www.picoelectronics.com/dcdclow/pe62_63.htm). As the datasheet 
states, I'm expecting that for input voltages in the range 4-6.5 V the 
output is 250 V.
But should I expect that te output follows linearly the input for 
voltages less than 4 V?
Are these kinds of devices the same as "proportional" dc-dc converter?
The question arises from the fact that the circuit I'm examining (from a 
ultrasound pulser) uses a feedback circuit around the DC-DC converter to 
get output voltages in the range 20V - 230 V controlled by an input 
voltage in the range 0.5 V - 4V.
Thanks

***Marco***
Look up Royer converter

It's a self oscillating 50% duty cycle converter 

Cheers 

Klaus 
On Thu, 25 Feb 2016 22:59:31 +0100, ***Marco*** <klaus_my@hotmail.com>
wrote:

>Hi all, > >I'm trying to figuring out how a circuit which employs an unregulated >Dc-DC converter works. I've never used one before, so I'm asking for >some clarifications. >The dc-dc converter is the PICO 5A250S >(http://www.picoelectronics.com/dcdclow/pe62_63.htm). As the datasheet >states, I'm expecting that for input voltages in the range 4-6.5 V the >output is 250 V. >But should I expect that te output follows linearly the input for >voltages less than 4 V? >Are these kinds of devices the same as "proportional" dc-dc converter? >The question arises from the fact that the circuit I'm examining (from a >ultrasound pulser) uses a feedback circuit around the DC-DC converter to >get output voltages in the range 20V - 230 V controlled by an input >voltage in the range 0.5 V - 4V. >Thanks > >***Marco***
"Unregulated" typically means that the output is proportional to the input for all inputs in the operating range. Outside the spec range, it might not work at all. It probably won't work at 0.5 volts in. Practically guaranteed to not. The output will be in the specified range if both the load is the specified value and the input voltage is the specified value. Your feedback loop might still work. Try it. Aren't those Pico things awfully expensive? -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Il 26/02/2016 00.47, John Larkin ha scritto:
> On Thu, 25 Feb 2016 22:59:31 +0100, ***Marco*** <klaus_my@hotmail.com> > wrote: > >> Hi all, >> >> I'm trying to figuring out how a circuit which employs an unregulated >> Dc-DC converter works. I've never used one before, so I'm asking for >> some clarifications. >> The dc-dc converter is the PICO 5A250S >> (http://www.picoelectronics.com/dcdclow/pe62_63.htm). As the datasheet >> states, I'm expecting that for input voltages in the range 4-6.5 V the >> output is 250 V. >> But should I expect that te output follows linearly the input for >> voltages less than 4 V? >> Are these kinds of devices the same as "proportional" dc-dc converter? >> The question arises from the fact that the circuit I'm examining (from a >> ultrasound pulser) uses a feedback circuit around the DC-DC converter to >> get output voltages in the range 20V - 230 V controlled by an input >> voltage in the range 0.5 V - 4V. >> Thanks >> >> ***Marco*** > > "Unregulated" typically means that the output is proportional to the > input for all inputs in the operating range. Outside the spec range, > it might not work at all. It probably won't work at 0.5 volts in. > Practically guaranteed to not. > > The output will be in the specified range if both the load is the > specified value and the input voltage is the specified value. > > Your feedback loop might still work. Try it. > > Aren't those Pico things awfully expensive? > >
Thanks for the replies. The voltage is set by software, I've re-measured: - 0.6 V at input for 20 V at the output - 3.8 V at input for 230 V at the output I've also the same your impression that these devices are too expensive. Actually, the presence of this component on the board has led me to investigate the associated circuitry and try to understand what was special with it. I've never done anything similar before, but I think I've seen some circuits which grant the same performances with cheaper components, probably at the expense of dimensions and complexity. Bye Marco
On Fri, 26 Feb 2016 23:21:45 +0100, ***Marco*** <klaus_my@hotmail.com>
wrote:

>Il 26/02/2016 00.47, John Larkin ha scritto: >> On Thu, 25 Feb 2016 22:59:31 +0100, ***Marco*** <klaus_my@hotmail.com> >> wrote: >> >>> Hi all, >>> >>> I'm trying to figuring out how a circuit which employs an unregulated >>> Dc-DC converter works. I've never used one before, so I'm asking for >>> some clarifications. >>> The dc-dc converter is the PICO 5A250S >>> (http://www.picoelectronics.com/dcdclow/pe62_63.htm). As the datasheet >>> states, I'm expecting that for input voltages in the range 4-6.5 V the >>> output is 250 V. >>> But should I expect that te output follows linearly the input for >>> voltages less than 4 V? >>> Are these kinds of devices the same as "proportional" dc-dc converter? >>> The question arises from the fact that the circuit I'm examining (from a >>> ultrasound pulser) uses a feedback circuit around the DC-DC converter to >>> get output voltages in the range 20V - 230 V controlled by an input >>> voltage in the range 0.5 V - 4V. >>> Thanks >>> >>> ***Marco*** >> >> "Unregulated" typically means that the output is proportional to the >> input for all inputs in the operating range. Outside the spec range, >> it might not work at all. It probably won't work at 0.5 volts in. >> Practically guaranteed to not. >> >> The output will be in the specified range if both the load is the >> specified value and the input voltage is the specified value. >> >> Your feedback loop might still work. Try it. >> >> Aren't those Pico things awfully expensive? >> >> > >Thanks for the replies. >The voltage is set by software, I've re-measured: >- 0.6 V at input for 20 V at the output >- 3.8 V at input for 230 V at the output > >I've also the same your impression that these devices are too expensive. >Actually, the presence of this component on the board has led me to >investigate the associated circuitry and try to understand what was >special with it. >I've never done anything similar before, but I think I've seen some >circuits which grant the same performances with cheaper components, >probably at the expense of dimensions and complexity. > >Bye >Marco > >
This is an electronic design group, so some of us would be inclined to design your whole loop from parts. But that would take a bit of engineering, which might not be optimum for your situation. If your load is small, you could start with a fixed HV and linear regulate it down, especially good if you need multiple regulated outputs. Or build a boost regulator using a standard chip, like an LTC3803. The LTC and a transformer and some diodes and such might cost $6 or so. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com