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A PSU controller on a shoestring
A PSU controller on a shoestring
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Old 29th November 2018, 05:58 PM   #1
Elvee is offline Elvee  Belgium
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Default A PSU controller on a shoestring

This PSU handles a number of functions for battery-operated devices:

It is basically a LDO regulator, but it also performs the ON/OFF function with a single push-button, the power indication, lo-bat indication and short-circuit protection.

It is absolutely minimalistic, comprising only 2 discrete transistors.

This pic shows the core of the circuit subjected to simultaneous input and load ripple:

A PSU controller on a shoestring-2qreg1-png

To create the toggle function, a few components are added:

A PSU controller on a shoestring-2qreg2-png


When the circuit is off, the current consumption is ~1µA.
The component values are suited for an output current of 50~100mA, but by scaling the resistors values, any value can be obtained: multiply them 100 times, and you have a micropower regulator.
The reference voltage is generated by the red LED: its tempco compensates the Vbe of the transistor.
This LED also serves as a power indicator (use a low-current type), and as a lo-bat indicator: when the battery voltage is too low, Q2 steals all the available current for Q1's base.
The circuit is short-circuit protected because it is based on regenerative action: if the output current exceeds Q1's capability, the circuit trips and turns off, and cannot be turned on again until the short has been removed.

The following pic illustrates the toggle operation:

A PSU controller on a shoestring-2qreg3-png
Attached Images
File Type: png 2Qreg1.png (66.3 KB, 233 views)
File Type: png 2Qreg2.png (11.1 KB, 233 views)
File Type: png 2Qreg3.png (64.3 KB, 239 views)
Attached Files
File Type: asc 2Qreg3Vtog.asc (2.5 KB, 2 views)
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Old 30th November 2018, 01:20 PM   #2
Ketje is offline Ketje  Belgium
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Nice and simple. Only for turn-off you have to push long enough specialy with low or no load.
How about like this ? No current ( exept transistor leak ) after turnoff.
Mona
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Old 30th November 2018, 10:24 PM   #3
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by Ketje View Post
Nice and simple. Only for turn-off you have to push long enough specialy with low or no load.
How about like this ? No current ( exept transistor leak ) after turnoff.
Mona
You are right, of course:
a)The time constant of the <output load> times the <output cap> cannot exceed ~60ms without an adaptation of the pushbutton RC network.
I opted for 2.2µF because it is easily available as a MLCC format, but higher values should be possible (with the caveat that ON/OFF actions will have to be separated by at least a few seconds).
This regulator was designed for a small portable GM-counter, consuming a few milliamps in the idle state, thus the RC time constraint was easily met, even with larger values of the output cap and smaller values of the pushbutton cap, but I published a more general version, however you are right to point out the fact that it won't turn off for light- or no-load conditions.

b)Yes, I am perfectly aware that an additional active element would considerably ease matters, but I opted for the bare two-transistor version simply because of my silly manly pride: real men can do it with just two transistors....
Obviously, this is for leisure only: when I did that kind of design as a paid work, I prudently left my pride aside.... I can imagine you are more or less in the same situation.
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Old 30th November 2018, 10:32 PM   #4
Ketje is offline Ketje  Belgium
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Quote:
Originally Posted by Elvee View Post
Obviously, this is for leisure only: when I did that kind of design as a paid work, I prudently left my pride aside.... I can imagine you are more or less in the same situation.
Well, i'm in a home on my bed, with nothing else to do
Mona
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Old 1st December 2018, 08:20 PM   #5
Elvee is offline Elvee  Belgium
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Then, we both are cranky old farts having pointless, yet interesting discussions.
I am sure you had a fulfilling and varied career.

I hope your home is nice and comfy
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Old 9th December 2018, 04:27 PM   #6
Elvee is offline Elvee  Belgium
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Here the PSU in its environment:

A PSU controller on a shoestring-gmc1-jpg

(just 1 or 2 square centimeters on the top right; the rest is the HV converter, pulse amplifier & processor, integrator, etc)

This is the finished GM detector: the current drain is ~5mA from 3 AA batteries:

A PSU controller on a shoestring-gmc2-jpg
Attached Images
File Type: jpg GMC1.jpg (304.1 KB, 142 views)
File Type: jpg GMC2.jpg (151.6 KB, 149 views)
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Old 9th December 2018, 11:53 PM   #7
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by Elvee View Post
This PSU handles a number of functions for battery-operated devices:

It is basically a LDO regulator, but it also performs the ON/OFF function with a single push-button, the power indication, lo-bat indication and short-circuit protection.

It is absolutely minimalistic, comprising only 2 discrete transistors.

This pic shows the core of the circuit subjected to simultaneous input and load ripple:
Impressively simple. C2 (100nF), first schematic, is that added to slow down the loop?

Now I may have the attention of two particularly skilled "old farts", I like to ask you a question: A member recently wanted to use a 1KVA transformer after a Variac (looking for a lab/bench power supply for amplifier testing ,posting #25) but the manufacturer stated that the transformer will not transfer much power below 75% of nominal input voltage. Does that sound correct? High level of remanence?

Zalig Kerstfeest
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Old 10th December 2018, 06:15 AM   #8
PRR is offline PRR  United States
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> the finished GM detector

A "Geiger Counter"?

Here's a clever (no range switch) compact job from long ago.
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Old 10th December 2018, 10:13 AM   #9
Ketje is offline Ketje  Belgium
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Quote:
Originally Posted by FauxFrench View Post
Impressively simple. C2 (100nF), first schematic, is that added to slow down the loop?
No, to speed up.The emitter is connected to the +rail via D1=reference voltage and the base with C2 to the minus rail.
Quote:
the manufacturer stated that the transformer will not transfer much power below 75% of nominal input voltage. Does that sound correct? High level of remanence?

Zalig Kerstfeest
The transformer has a max current independent of the output voltage, so the VxA power will be less with less voltage.
Joyeux Noel.
Mona
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Old 10th December 2018, 10:19 AM   #10
Ketje is offline Ketje  Belgium
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Quote:
Originally Posted by Elvee View Post
This is the finished GM detector: the current drain is ~5mA from 3 AA batteries
Well, now you are ready when something goes wrong at Doel or Tihange
Mona
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