I'm working on. I've taken some old ideas I've drawn and added to them.

I'm starting with a modular 48V 2.06A power supply. I'm thinking of using it to feed these circuits.

Basically there will not be a fixed current limit, it should boost the total current available with lower power supply voltage settings. Max voltage out will be 24V at 3A, going to almost 10A when set to 5V.

There will be an indicator that shows when the power draw exceeds the 48V Power Supply module.

I've broken it down into 4 boards, I'll probably merge the last two. I'm going to draw up some PCB layouts next.


Board 1 - On board power supply



Signals

+48V / Input
+28V / Output
+51.5V / Output
-3.5V / Output
Ground
+DVM1 PM PS / Output
-DVM1 PM PS / Output
+DVM2 PM PS / Output
-DVM2 PM PS / Output


BOM

U1 - LM317
U2 - 555
CR1.2 - 1N4454 Silicon Diodes
D1,2 - Blue LEDs
ZD1 - 15V Zener Diode
SD1-8 - Shottky Diodes, Low Power, Optional
C1,4,6,8 - 0.1uF Caps
C2 - 1uF Cap
C3 - 220uF Cap
C5 - 1nF Cap
C7,9 - 10uF Cap
C10,12,14 - 10uF Cap, Optional
C11,13 - 0.1uF Cap, Optional
XFM1 - Torrid Transformer, Hand Wound, Optional
R1 - 120 o
R2 - 56Ko
R3 - 2.7Ko
R4 - 1Ko
R5 - 10Ko
R6,7 - 330 o


Board 2 - 48V 2A Current Regulator




Signals

+48V / Input
+51.5V / Input
+48VLIM Out / Output
Ground


BOM

U3 - LM393
U4 - 7555, CMOS 555
Q1 - P-Channel MOSFET
Q2 - NPN, 2N2222A
D3 - Red LED, Indicator
ZD2 - 36V 5W Zener
SD9 - Shottky Diode, 50PIV 2A Min
C15,17,18,20,22 - 0.1uF
C16,21 - 220uF
C19 - 10uF
L1 - 220uH Hand Wound Torrid
R8 - 100 o Variable Trimmer
R9 - 22Ko
R10 - 2.4Ko
R11 - 10Ko
R12 - 10 o
R13 - 0.1 o 1W
R14,16 - 1Ko
R15 - 4.7Mo


Board 3 - Preregulator



Signals

+48VLIM / Input
PreReg / Output
PS Output / Input
-3.5V / Input
Ground


BOM

U5 - LM393
U6 - 7555, CMOS 555
U7 - LM317
Q3 - P-Channel MOSFET
CR3,4 - Silicon Diode, 1N4454
ZD3 - 5.1V Zener
ZD4 - 12V Zener
SD10 - Shottky Diode, 50PIV 10A
C22,24 - 220uF
C23,25,26 - 0.1uF
L2 - 220uH, Hand Wound Torriod
R16,17,21 - 10Ko
R18 - 100Ko
R19 - 10 o
R20 - 2.2Ko
R22 - 120 o


Board 4 - Main Regulator



Signals

+28V / Input
-3.5V / Input
PreReg / Input
+PS Output / Output
Ground
+ DVM, Current Meter
- DVM, Current Meter
+ DVN, Volt Meter
- DVM, Volt Meter
Q4 Base
Q4 Emitter
Q5 Base
Q5 Emitter
R2 +, Current Adjust
R2 -, Current Adjust
R6 +, Voltage Adjust
R6 -, Voltage Adjust
+D4. Indicator
-D4. Indicator


BOM

U8 - 1465, Fast Linear Op Amp
Q4 - PNP Darlington
Q5 - NPN Darlington
D4 - Green LED, Front Panel
C27 - 0.1uF
R23 - 0.1 o
R24,28 - 10Ko Pot, Front Panel
R25 - 500Ko Trimmer
R26,29 - 10Ko
R27 - 13Ko
R30 - 10Ko Trimmer
R31 - 5.1Ko

 

What do you plan on using this on Wendy ??

 

I have a one question, is that +51.5V rail really necessary? I think you should be able to reference and level shift everything to be below the 48V rail and eliminate that. Adding a divider to the output of R13 lets you shift that sense voltage safely below 48V and into the common range of the opamp, without the need to up the positive supply rail.

 

The current limiter on board 2 requires that the comparator be able to sense to the 48V rail accurately, down to the last uV. The 51.5 V for the power supply to it will allow this to happen.

It is a general variable power supply with decent output specs. My Veleman power supply is acting up, I've repaired it once but without schematics I'm not willing to reverse engineer it to figure out the schematics.

 

The current limiter on board 2 requires that the comparator be able to sense to the 48V rail accurately, down to the last uV. The 51.5 V for the power supply to it will allow this to happen.

It is a general variable power supply with decent output specs. My Veleman power supply is acting up, I've repaired it once but without schematics I'm not willing to reverse engineer it to figure out the schematics.

Hey if you have a model # or something for the PS so I can try to find a schematic for it ,if you want me too and it wouldn't be much trouble at all..

 

Wendy
On board 1 are you using blue leds as 3.5 volt zener diodes??

 

The current limiter on board 2 requires that the comparator be able to sense to the 48V rail accurately, down to the last uV. The 51.5 V for the power supply to it will allow this to happen.

The current limiter just measures voltage on R13, so if you move the setpoint a bit lower, and divide the 48V after the sense resistor by adding a resistor from junction R14-C15 to +36V, then you still have the same accuracy without the need for that supply rail.

 

R13 must be on the rail, all else follows from that. It is part of the main current path of the supply. Given I will have the negitave voltage generator (-3.5V) the extra parts count to add the voltage drop resistors for board 1 is about the same.

 

Wendy
On board 1 are you using blue leds as 3.5 volt zener diodes??

Yes.

 

Hey if you have a model # or something for the PS so I can try to find a schematic for it ,if you want me too and it wouldn't be much trouble at all..

Sure, and thank you.

This one...

https://www.vellemanusa.com/products/view/?id=522797

It uses 741 op amps of all things, it is easy to service. I'll give it that.

 

The current limiter just measures voltage on R13, so if you move the setpoint a bit lower, and divide the 48V after the sense resistor by adding a resistor from junction R14-C15 to +36V, then you still have the same accuracy without the need for that supply rail.

Something else I'll mention in passing, this scheme I don't have to compensate for resistor tolerances.

 

Something else I'll mention in passing, this scheme I don't have to compensate for resistor tolerances.

That doesn´t make much sense since either way you are setting the trip point with a trimmer pot so the absolute value of those reistors doesn´t matter.

 

If I have to move the trimmer to 1Ko just to compensate it becomes a lot more finicky. 5% may not sound like much, but it adds up.

 

Seems like a lot of "stuff" to make a power supply.
I haven't tried to decipher it. Does it go to zero volts on the output? Is there current limit on the output as well as the 48 volts?
The extra transformer is for some non- isolated gauges?

 

While I'm not totally comfortable with board 2, the rest is pretty standard. It also has a full current limiter / regulator, which if works could be used directly for LEDs without the usual surge issue. The current is adjustable, but it doesn't have a rated maximum. I figure it can handle up to 3A at 24 V, or 9A at 5V, give or take.

The extra transformer is indeed for panel DVMs, most of which require a isolated DC power supply to power (isolated as in isolated from the voltage being measured). If you use analog panel meters it is totally unnecessary.

I am expanding on an idea I had a while back. The problem with analog op amps is the input rail to rail issue. By powering the op amps with a greater power supply voltage, both positive and negative, than the inputs will never be near a power supply rail. This is done by board 1.

The analog power transistors will only see 15W max. This is done with board 3.

Board 3 addresses a problem usually handled by multi-tap transformers, which is not feasible for a external sourced power supply. It drops the voltage down to a point where the analog transistors will only dissipate 15 watts worst case. If I just feed 48V and 2A through the transistors and short the output one of the transistors would dissipate almost 100W. With multi-tap transformers you switch which windings to use to bring the apparent wattage down, usually using a relay judging from the sound my Velleman makes.

Board 3 drops the input voltage with a switching power supply to 5V of what is needed for the output. Even when powering a circuit at 20V at 4A it should run very cool temperature wise. Heat is always the enemy.

Board 4 is very basic and very simple. A really simple current regulator followed by an equally simple voltage regulator. They would normally run very hot, except for the accessories.

 

Do C6 & C8 need a path to ground via diodes?

 

@Wendy
Thanks for the edit, but to answer the question - a handful.
I don't mean to yank your chain, but it seems like with 2 integrated regulators. 2 switching regulators and 2 power stages to make a 24 volt supply there must be some room to simplify it.
I suppose we could start a contest.

 

I'm after a certain type of performance. Low heat, analog performance do not usually go together.

That and current boosting. Like I said, board 2 is a bit of overkill, but the rest should be pretty decent. I could make simpler, done that with a LM317 decades ago.

 

Do C6 & C8 need a path to ground via diodes?

Not sure what you mean, I only need the AC component, which is rectified to create a low voltage.

 

I'm after a certain type of performance. Low heat, analog performance do not usually go together.

Well, yes, but the functions of board 2+3 and a bit from board 4 could be merged into one switcher, that would be current limited to 2A at the input and provide a voltage limited current source, and feed that to the final linear reg.
Also, you mentioned that the linear regs should not be dissipating more than 15W, but I think that at high output current and low load impedance you might be getting more than that in Q4.