Electronics > Projects, Designs, and Technical Stuff
High Voltage Bench Power Supply Design
H713:
Alright, the 1nF cap in parallel with R13 seems to have done the trick. I would do the square wave testing, but I successfully managed to properly nuke my proof-of-concept/prototype. :palm: I'm fairly confident that this is not a design issue, and more of a sketchy parts from who-knows-where issue. And no, the pass transistor did not short. I have yet to try this with the actual driver and pass transistors, so there likely will be some tweaking required. Square wave testing will be done then as well.
Meanwhile, I have an updated schematic and a version 1 PCB layout. Gerber files are attached and can be viewed in an online viewer. Feedback greatly appreciated, as my layout and routing skills are something I'd like to improve. I did try to keep the PCB a somewhat reasonable size whilst limiting myself to 2 layers for cost reasons.
blackdog:
Hi,
I have some remarks ;)
Split R2 in 15K than 4.7uF to ground en 33K to the drain of Q1, this wil help the hum suppression this wil be a small 30dB.
Is the SOA enough for Q1?
Place a 8.2V or a 10V Zener over R14 to protect the opamp in case of short circuit, anode to ground.
If you want to spend a little money, replease the diode D5 with a 10V reference.
The minimum output voltage will be a bit higher, but the power supply will become more stable and will get less noise.
Adjust the value of R14 to get the right ratio again.
If the current value of C5 just keeps the power supply stable, then something's wrong...
The 10nF of the pin-2 and the 100nF over the compensation connection of the NE5534 is really ridiculous... :-DD
Tip
If you come up with values for components that are far above the normal values during testing, then you know that something is not going right.
C5 is for normal use with gains lower than 3x about 22pF!
Above gains of 3x a capacitor in not necessary for the NE5534.
But...
This is not a normal circuit, you have extra gain in the loop, so compensation for a stable regulator wil be far more difficult.
Yes C7 helps :-) but that is nog good enough, and no do not make this capacitor higher in value!
You have to solve the problem where it arises and that is the gain or Q1.
Place a resistor and a capapcitor in series from the Drain van Q1 to ground, this wil lower the gain in the loop.
Try to find out for yourself which value's ar needed.
As a starting point you can take the value of R2 which is the dominant part of the impedance of the drain of Q2.
Q5 need a small base resistor, 100-Ohm or so.
You need a Zener to protect the Gate-Source voltage of the power MOSFets.
Place direct on the gate of Q1 en resistor, say 150-Ohm.
Kind regads,
Bram
H713:
If I remember right, the 100nF on the compensation pins was not really needed but I put it there anyways just so it made it onto the pcb in case I needed it later. 100nF is definitely ridiculous, same with the 10nF, I want to say that 1nF made it stable. I think I put the really large caps in just to see if it made it stable, and unsurprisingly it did not.
Good call on The gate protection zener, I totally forgot to draw that in.
duak:
H713, since you're going to layout may I suggest splitting R13 into two or three parts? I calculate that with a 500 V output, R13 would have to dissipate 2.5 W. It'll be easier to find smaller precise and stable resistors than one larger one.
When the voltage crowbar circuit trips, triac D10 will have to dissipate the 7.2 Joules of energy stored in C14 and C15. I doubt it will survive and will most likely short out. If the pass transistors weren't initially damaged, they'll probably overheat and short out too. A fuse in the +Vout line between C14 & D9 to limit the current should minimize damage. Note that the fuse should be rated for breaking the circuit voltage - these parts are usually sand filled to extinguish the arc that occurs at a higher voltage.
H713:
You aren't wrong with the crowbar, and I wasn't really expecting the triac to survive. It is a last resort to stop the full DC bus from being dumped into the load if a pass element shorts. I was going to have a small fuse in series with the output of the capacitor bank (separate to this board), so if the triac shorts I don't expect the pass transistors to blow. I already found a suitable 600v rated fuse holder and fuses on mouser.
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