Universal Power Supply
Low Voltage Section
The low voltage section nominally provides 12VDC at 200mA, however the voltage and current may be set over a wide range. The voltage may be set anywhere between 6V and 12V.
the supply in my system the ripple on the input to the High Voltage CCS is
70Vp-p with the positive peak at 325V and the negative peak at 255V. The output
DC from the supply is 215V. The significant number is that there should be at
least 20V between the negative peak of the input to the CCS and the output of
the CCS (255 - 215 = 40 in my system.) So with things as they are the supply
adjustment is limited to 235V. To go to 250V on the output you will need to
adjust the negative peak to 270V or more. This can be achieved in two ways.
First, the input AC can be increased (thereby raising the value of both the
positive peak and negative peak) and second; the capacitance in the filter can
be increased (thereby reducing the ripple and increasing the value of the
negative peak). In my system the AC is 250-0-250 and the capacitance is 3.6uF.
The AC could be increased to somewhere in the range from 275-0-275 to 300-0-300.
The capacitance could be increased to somewhere in the range of 4.7uF.
The output voltage is set by the ratio of R12 and R13 to give 2.5V at their junction. They are currently 845K and 10K for 215V.
The stock Rset should work for 25-30mA with the supplied heatsink.
For the low voltage section of the supply, the voltage can be adjusted by the ratio of R3 and R4 to give 1.25V at their junction. They are currently 1K and 115 Ohms for 12V.
For use as a filament supply there are six concerns.
1. If the voltage is below about 10V, consider changing the relays to lower voltage units.
2. The time constant of the timers will change with the voltage.
3. The diodes should be changed to SB540.
4. Capacitor C4 will need to be increased.
5. A larger heatsink will be needed.
6. Current is limited by the choke to 2.2A
To determine the voltage needed, figure it the normal way and then to keep the MR characteristic increase it by 50 to 100%. The value of C4 will have to be chosen empirically: choose it for maximum ripple so that the negative peak is 2V greater than the regulated output voltage.
If the LV is to be biased above ground then use R15, R16, R17 and C20. R15 and R16 are 10K suggested, R17 is 3K suggested. C20 1500uF, at appropriate voltage suggested. You will need to cut the trace which bridges both ends of R17.