Re: "High" Voltage regulation
- From: John Larkin <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Mon, 04 May 2009 13:12:31 -0700
On Mon, 4 May 2009 11:09:05 -0700 (PDT), James Rollins
<james.rollines@xxxxxxxxx> wrote:
On May 4, 9:07 am, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On 4 May 2009 09:13:37 GMT, Jasen Betts <ja...@xxxxxxxxxx> wrote:
On 2009-05-04, James Rollins <james.rolli...@xxxxxxxxx> wrote:
You may as well use a single series fet+resistor, pwm controlled, and
one output cap. Or just use a linear regulator. All are about equally
efficient.
John
If you don't disconnect the load there will be a voltage spike and
also a voltage dividing effect. i.e., the load is connected to the
voltage source directly and depending on the ratio of the two
resistors the load will generally see a higher voltage than you might
want. Hence the reason why the load is disconnected. If the voltage
supply resistance is too small then it requires faster rise/fall times
to quickly stop charging the capacitor as it will end up charging up
much faster.
your circuit avoids neither of those problems.
The same problem still exists with your idea though. The fet's gate
will need to be held at a voltage that is within the source/drain of
usually around +-20V max. But if the fet is sorta "floating" I am
unsure how to accomplish such a task. At least in a way that keeps
with the simplicity of the design.
I've thought about using a simple linear regulator idea but
unfortunately similar problems as well as other problems exist. Mainly
in this case the regulation seems much poorer and it is less
efficient. Although I'm not too interested in efficiency as I am
regulation. Trying to find cost effective HV bjt's is a bit of a
problem as compared to fets.
a linear series regulator is no less efficient than a series resistor for
dropping voltage, but it handles load fluctuations better.
you should do an energy audit on your design.
One of my products has a power switcher (variable output, 25 to 200
volts) using a series switching fet and a BIG power resistor feeding a
BIG output cap. A microprocessor/ADC checks the output voltage once
every millisecond and turns the fet on or off. Works great, and keeps
the room warm. It's about as efficient as a linear reg, but simpler,
and the heat's mostly in the resistor, not in the fet.
Sort of a delta-sigma regulator.
John
Similar to what I'm suggesting doing. I assume though your load is
very large compared to mine. At most I would be dissipating
1000^2/10^5 = 10W. I'm mainly doubling up so that when the fet is off
for one capacitor it is on for the other sot hat the load is never
disconnected from a capacitor as I need to supply it continuously. As
I mentioned one could probably do this just by adding a diode and
capacitor after the first capacitor so that it acts as a temporary
storage while the other capacitor is being charged.
How do you drive the gate of the fet with the uP?
Optoisolator, with a small stock DC/DC converter to supply floating
power for the gate driver. The whole rig just precharges a capacitor
bank before we kick in the BIG power supply!
John
.
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- From: James Rollins
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- Re: "High" Voltage regulation
- From: James Rollins
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- Re: "High" Voltage regulation
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