pmroz
Well-known member
Hi all, need someone to check work re: Bauman's +-18/48v/5v PSU, for 3*1*2 etc boards. This is my first DIY attempt, trying to grind out the math so concepts will sink in.
Schem...
http://www.thediypill.phx.com.br/forumfiles/psu312sch_v1.pdf
Trying to calculate value of R1 and find proper V for smooth DC at REG+
i'm using 3300uf for C1/C2
Fabio said in a post 'R1 = 22R if C1/C2 = 2200uf'
...also he wrote if i use 4700uf, R1 would be something like 10-12R
Toroid spec: Amveco 62085
22@ 2.27a, 44@ 1.136a 50Va
No Load current 8.0ma No Load V: 2x25.4 V
Vpeak after D1/D2 = 42.6V (rect drop) at 120hz,
Vavg = 27V, Veff = 29.2V
Iavg= 723ma, Ieff = 792ma
ripple freq = 120hz
Then i read with 'RC filter' after full-wave rectifier, multiply Vavg x 1.4? Is this right? That makes 37.2V..??? ..also there is Vripple equation..
can't figure why i would even want R1 there... then i see RC time constant. Okay, R1 is to make the caps discharge on the same cycle as DC ripple, for max smoothing. Do i have this right?
But what value for t? so i cheated and plugged in Fabio's numbers from before.
t= r x c = 99ms
...then with C1/C2 = 6600uf
r = .099 / .0066 = 14.66 = 15R
This seems to fall in range, given the 2 values above. But why 99ms?
cap reactance (.159/fc) = .20
impedance = 9
ohm's law- circuits with reactance and impedance:
I = E/Z =27/9 = 3a ???? dunno if this formula applies
which value for I to check V at REG+ ?,
plug in 15R with I to get V at REG+... I = lm317 max current = 1.5a
V at reg+ = 15 x 1.5a = 22.5V
that looks good, but wrong i suspect. Iavg x 1.4 = 1.01a
15 x 1.01 = 15.15V.... not so good.
or V= 15 x 3a (ohms law with resist and reactance) = 45V ???
or add impedance and R, 15 + 9= 24 x Iavg = 24.24V
Could someone clarify which values of I and V i should do these equations with? The Ac to Dc transition is throwing me off. Missing a crucial formula? if/why t=99ms? so many questions... this is probably 101 for most of you, but i gotta start somewhere...
...also, on schem, are C11/C12 there to show no load V to toroid? so 48V rail gets (in my case) 50.8V ?
Schem...
http://www.thediypill.phx.com.br/forumfiles/psu312sch_v1.pdf
Trying to calculate value of R1 and find proper V for smooth DC at REG+
i'm using 3300uf for C1/C2
Fabio said in a post 'R1 = 22R if C1/C2 = 2200uf'
...also he wrote if i use 4700uf, R1 would be something like 10-12R
Toroid spec: Amveco 62085
22@ 2.27a, 44@ 1.136a 50Va
No Load current 8.0ma No Load V: 2x25.4 V
Vpeak after D1/D2 = 42.6V (rect drop) at 120hz,
Vavg = 27V, Veff = 29.2V
Iavg= 723ma, Ieff = 792ma
ripple freq = 120hz
Then i read with 'RC filter' after full-wave rectifier, multiply Vavg x 1.4? Is this right? That makes 37.2V..??? ..also there is Vripple equation..
can't figure why i would even want R1 there... then i see RC time constant. Okay, R1 is to make the caps discharge on the same cycle as DC ripple, for max smoothing. Do i have this right?
But what value for t? so i cheated and plugged in Fabio's numbers from before.
t= r x c = 99ms
...then with C1/C2 = 6600uf
r = .099 / .0066 = 14.66 = 15R
This seems to fall in range, given the 2 values above. But why 99ms?
cap reactance (.159/fc) = .20
impedance = 9
ohm's law- circuits with reactance and impedance:
I = E/Z =27/9 = 3a ???? dunno if this formula applies
which value for I to check V at REG+ ?,
plug in 15R with I to get V at REG+... I = lm317 max current = 1.5a
V at reg+ = 15 x 1.5a = 22.5V
that looks good, but wrong i suspect. Iavg x 1.4 = 1.01a
15 x 1.01 = 15.15V.... not so good.
or V= 15 x 3a (ohms law with resist and reactance) = 45V ???
or add impedance and R, 15 + 9= 24 x Iavg = 24.24V
Could someone clarify which values of I and V i should do these equations with? The Ac to Dc transition is throwing me off. Missing a crucial formula? if/why t=99ms? so many questions... this is probably 101 for most of you, but i gotta start somewhere...
...also, on schem, are C11/C12 there to show no load V to toroid? so 48V rail gets (in my case) 50.8V ?