i have a spare 58Vac {unloaded} primary winding which im planning to use for both negative bias voltage for grid bias and also positive heater lift for a srpp driver stage. i came across this cct which can do what i want but needs some tweeking. can i reverse the voltages polarity in such a way that the top fullwave rectifier does the -ve bias and the bottom halfwave rectifier doing the +ve bias? thanks for any help.
yes...i wish to switch the polarity around so that negative appears at the top and positive at the bottom half.
You can look at the two parts (pos & neg) separately. Temporarily remove the neg stuff (Rrc, Crc, Rbias, bottom 100u cap), now look at the pos stuff you have left. Can you change that to neg?
Now remove the pos stuff and look at the neg part you have left. What needs to be changed to make it pos?
If you separate out the two parts it becomes clear.
Jan
Now remove the pos stuff and look at the neg part you have left. What needs to be changed to make it pos?
If you separate out the two parts it becomes clear.
Jan
Just rotate all the diodes in the schematic 180º . You can get the voltages you want by adjusting the resistor values but you'll have to add some filter sections to get usefully smooth DC.
I'm not a spice user but the question interested me and wanted to see what the ratios might be. I'm sure you can do better than this but at least spice shows that it should be possible to get to the voltages you are looking for, though the startup time is very slow with these values. Maybe Jan can give some critique?
I'm not a spice user but the question interested me and wanted to see what the ratios might be. I'm sure you can do better than this but at least spice shows that it should be possible to get to the voltages you are looking for, though the startup time is very slow with these values. Maybe Jan can give some critique?
No your concept is right on the dot, the resistors have to be twiddled depending on the load current hich probably is light.
I was just hoping he would discover the nice symmetry himself. 😎
Jan
I was just hoping he would discover the nice symmetry himself. 😎
Jan
thanks for the spice simulation on the power supply, which at least proves that it is a workable circuit. i was originally also wondering if both the rectifier sections be orientated 180deg off.. just as what you had shown but with an addition of reversing the electrolytic cap as well to suit the -30v side. btw the voltage graph shows the opposite ....ie target is -30V on top and +75V at the bottom.
im also trying to understand the function of Crc and Rrc which apparently is put as a voltage divider (from the marshall jdm 900 bias cct). there they also used a 56k resistor (versus 1k, R1 in the simulation). what would the effect be if its raised from 56k or even lowered from there?
Jan, yes the circuit it for heater and grid bias only hence is a very low load. its also not symmetrical as its -30 on one side and +70 on the other. cheers
im also trying to understand the function of Crc and Rrc which apparently is put as a voltage divider (from the marshall jdm 900 bias cct). there they also used a 56k resistor (versus 1k, R1 in the simulation). what would the effect be if its raised from 56k or even lowered from there?
Jan, yes the circuit it for heater and grid bias only hence is a very low load. its also not symmetrical as its -30 on one side and +70 on the other. cheers
Dumb question time.
What actual voltages do you need?
Just reversing the diodes simply gets you -ve 70 volts and +ve 30 volts, see the plot on Hearinspace's working...
I would assume without seeing the full schematic, you want a positive 70 volts (elevation) and negative 30 volts (-ve bias)? err, which is what the original circuit gives you?
What actual voltages do you need?
Just reversing the diodes simply gets you -ve 70 volts and +ve 30 volts, see the plot on Hearinspace's working...
I would assume without seeing the full schematic, you want a positive 70 volts (elevation) and negative 30 volts (-ve bias)? err, which is what the original circuit gives you?
Puginfo: It was late at night and my interest in your supply problem prevailed over clear reading of your first post. Typical heater bias doesn't need a dedicated power supply. Just a divider from mid filter chain with capacitor across the lower resistor in the B+ supply is enough. You can just use your secondary for the -Vg supply directly and save yourself the tweaking time of the more complex circuit. Plus you can do it with a potentiometer so the grid bias becomes adjustable.
Here's what happens if R1 is upped to 56KΩ
Here's what happens if R1 is upped to 56KΩ
Thanks Jan. It's nice to get that feedback from you. I apologize for interrupting your intended process, I had started on the sim well before you posted and (re-learning how to use LTspice at the same time) had too much time in it to want to drop it.
You can replace R1 with a diode, creating a "half-wave doubler" which will deliver the same voltage as the full-wave bridge, though at less current capacity.
K.I.S.S.
Today's cap prices are so low, you can use several/many to mask the racket of half-wave rectification. Do once each way, transformer shift tends to null; anyway the loads here are SO small that it hardly matters. And analyzing two half-wave is tons simpler than a mix of bridge and cap-fed rectyfiers.
Today's cap prices are so low, you can use several/many to mask the racket of half-wave rectification. Do once each way, transformer shift tends to null; anyway the loads here are SO small that it hardly matters. And analyzing two half-wave is tons simpler than a mix of bridge and cap-fed rectyfiers.
i went with PRR's half wave rectification circuit. very simple, good voltage flexibility and its also symmetrical on both halves. for the voltage trimming part which comes after the half wave rectification caps, i used 2 trimpots wired parallelly....(both wipers joined). now, i got a wider voltage range (10 volts, +/- 5 volts each way) & finer voltage granularity (0.1V incremental possible) to play with. thanks for all the help.