In effect, this is part 2 of my previous post entitled "2-v. 1-amp d.c. PSU".
The requirement here was to produce a basic unregulated HT PSU to provide a nominal 120-v.d.c. at currents up to 20 mA. To meet this design, a similar set of criteria was applicable as per the 2-v. 1-amp d.c. PSU, namely:
1. Use as many parts as possible that were 'readily available'.
2. Keep the design as simple as possible, but meeting the essential design requirement.
3. Aim for maximum reliability and ease of future servicing.
The final design is about as simple as could be produced that meets those criteria. Possibly the one unusual feature is the use of two high-voltage Zener diodes - but I have an ample stock of these, and the temptation was too much to withstand!
The mains transformer secondary voltage was a good deal higher than what I would have liked, but as it was a transformer that I was very unlikely to ever want to use for anything else - and that I have owned it for a very long time - it was simply pressed into use for this project. Ideally a transformer with a lower secondary voltage would have been a better choice: less heat produced in the power resistors; prospective constructors might like to bear this in mind.
The circuit is below:
[attachment=4538]
Test performance figures.
Load Vo Ripple, p/p Notes
N/L...........130-v.........10 mV
12 mA......127-v.........20 mV
15 mA......125-v.........20 mV............Design centre *
18 mA......125-v........ 20 mV
20 mA......124-v.........20 mV
25 mA......124-v.........20 mV............Design centre extended
45 mA......115-v.........40 mV............Design overload
* The particular wireless (Pye model 65A), for which this unit was specifically designed, requires 10 mA @ 120-v.
Notes.
Short-circuit protection relies on a simple 100-mA fast-acting fuse.
An over-voltage protection cct. was not considered necessary.
Several items run warm to hot: some external heat-sinking is required, but all components, especially power resistors, are dissipating power that is well within their rating.
Subsequent to these tests, both parts (LT and HT) of the eliminator were connected to the Pye wireless and a set on 'live' tests and measurements were made: details follow later.
Al. / April 12, 2012 //
The requirement here was to produce a basic unregulated HT PSU to provide a nominal 120-v.d.c. at currents up to 20 mA. To meet this design, a similar set of criteria was applicable as per the 2-v. 1-amp d.c. PSU, namely:
1. Use as many parts as possible that were 'readily available'.
2. Keep the design as simple as possible, but meeting the essential design requirement.
3. Aim for maximum reliability and ease of future servicing.
The final design is about as simple as could be produced that meets those criteria. Possibly the one unusual feature is the use of two high-voltage Zener diodes - but I have an ample stock of these, and the temptation was too much to withstand!
The mains transformer secondary voltage was a good deal higher than what I would have liked, but as it was a transformer that I was very unlikely to ever want to use for anything else - and that I have owned it for a very long time - it was simply pressed into use for this project. Ideally a transformer with a lower secondary voltage would have been a better choice: less heat produced in the power resistors; prospective constructors might like to bear this in mind.The circuit is below:
[attachment=4538]
Test performance figures.
Load Vo Ripple, p/p Notes
N/L...........130-v.........10 mV
12 mA......127-v.........20 mV
15 mA......125-v.........20 mV............Design centre *
18 mA......125-v........ 20 mV
20 mA......124-v.........20 mV
25 mA......124-v.........20 mV............Design centre extended
45 mA......115-v.........40 mV............Design overload
* The particular wireless (Pye model 65A), for which this unit was specifically designed, requires 10 mA @ 120-v.
Notes.
Short-circuit protection relies on a simple 100-mA fast-acting fuse.
An over-voltage protection cct. was not considered necessary.
Several items run warm to hot: some external heat-sinking is required, but all components, especially power resistors, are dissipating power that is well within their rating.
Subsequent to these tests, both parts (LT and HT) of the eliminator were connected to the Pye wireless and a set on 'live' tests and measurements were made: details follow later.
Al. / April 12, 2012 //
