Re: 100kHz SMPS control
- From: Jamie Morken <jmorken@xxxxxxx>
- Date: Sat, 15 Dec 2007 23:18:05 GMT
Nico Coesel wrote:
Jan Panteltje <pNaonStpealmtje@xxxxxxxxx> wrote:
On a sunny day (Sat, 15 Dec 2007 11:29:37 GMT) it happened Jamie Morken
<jmorken@xxxxxxx> wrote in <BUO8j.1099$hQ3.685@pd7urf3no>:
Hi,>from all of the switching noise.
I was initially thinking of designing a 100kHz SMPS with using 200kHz
ADC feedback of the output voltage and current fed into a DSP which
would directly interface to the fet drivers, and using cycle by cycle
regulation based on these readings, but I think this may be very
difficult to read these signals cleanly without them being noisy
You would need to sample much faster, if you want to monitor
for example the rising current in an output switch, so you
can switch off if it exceeds some level, you need to sample at at least
(estimate) 20x during the max on time, say 10MHz would be OK perhaps.
i /------------ I max, max allowed current in switch
/
/
/
/
/
/ t 0 5 us .......
sample points
It is then much simpler to use an analog comparator at I max on
an input pin of the micro.
That is not really necessary. Sampling once at the end of the on-time
is enough. The input voltage is known and the inductor is known. From
this you can calculate a maximum on-time that will not destroy the
inductor or the switch.
The 100kHz transformer I have only has 50uH primary inductance with
500VDC what would the maximum on time be for it?
cheers,
Jamie
.
To limit the output current, you can measure the voltage across a
sense resistor or the MOSFET. I recently built a circuit based on this
method. To sense the MOSFET current I use an RC timing constant which
is discharged through a diode into the MOSFET. The voltage across the
capacitor is the diode forward voltage + the MOSFET across the MOSFET.
- References:
- 100kHz SMPS control
- From: Jamie Morken
- Re: 100kHz SMPS control
- From: Jan Panteltje
- Re: 100kHz SMPS control
- From: Nico Coesel
- 100kHz SMPS control
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