Exploring Linear Voltage Regulation

RE: Exploring Linear Voltage Regulation

fmilburn — Sat, 12 Sep 2020 19:47:13 GMT

[mention:4f57fc9d538949ad9eb336ddb9469bb8:e9ed411860ed4f2ba0265705b8793d05]

I did a crude test to see how it responded to a change in output load. This was done by plugging in the smaller resistor in parallel and triggering a screen capture in single shot mode on the 'scope. Input voltage of Tenma 72-2685 was set at 9V.

Starting load 470 ohms, ~ 11 mA draw

Step change to 47 ohms, ~ 110 mA draw

My probing technique is awful. Here is a screen shot from the 'scope.

[View:/resized-image/__size/620x474/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-fdd45506-20d7-4e0a-8f56-91dc85b47b85/8322.contentimage_5F00_192330.png:620:474]

The green trace is the input from the bench power supply and the yellow trace is the regulated output. Major divisions in time are 500 ns. There is unwanted capacitance in the breadboard and my lazy probing technique is text book don't do it like that. The power supply took about 2.5 us to get 80 percent recovery. I don't know how useful this test is though...

RE: Exploring Linear Voltage Regulation

DAB — Sat, 12 Sep 2020 17:45:40 GMT

Nice walk through of the circuit.

Good job.

DAB

RE: Exploring Linear Voltage Regulation

Andrew J — Sat, 12 Sep 2020 17:44:59 GMT

Excellent posting Frank

RE: Exploring Linear Voltage Regulation

dougw — Sat, 12 Sep 2020 14:58:59 GMT

To achieve better regulation, the current through the zener could be made constant.

As a bonus exercise, what would the members suggest is a simple way to do this?

RE: Exploring Linear Voltage Regulation

dougw — Sat, 12 Sep 2020 14:43:56 GMT

the robot needs a name...

RE: Exploring Linear Voltage Regulation

colporteur — Sat, 12 Sep 2020 14:30:30 GMT

Great tutorial JW. Skipped the video in the interest of time. I'm curious (i.e. never seen it before) the reference on the schematic to PWR_flag? Is that a European convention?

RE: Exploring Linear Voltage Regulation

jc2048 — Sat, 12 Sep 2020 11:56:52 GMT

Nice robot.

I didn't watch the video. Sorry, video is not really my thing.

It is good for 625 mW and continuous DC collector current of 200 mA.

I'm sure you understand, but for anyone who doesn't they are separate limits: you don't necessarily get both at once. In your circuit here you drop 4V across the transistor, so the maximum current before you hit the dissipation limit is 625mW/4V = 156mA [and, in practice, you don't really want to be running the transistor at that high a temperature anyway].

One old way of dealing with the reference voltage changing with input voltage was to power it from the regulated output instead. Obviously, if you do that, you need to be careful of the stability, and also take care that it will actually start up reliably and doesn't get stuck.

What was the stability like? Did you try 'kicking' the output and seeing how it responded?

RE: Exploring Linear Voltage Regulation

jw0752 — Sat, 12 Sep 2020 05:02:40 GMT

Hi Frank,

I really enjoyed your power supply experiment. When ever an exercise like this is presented on the forum I like to see if I can duplicate it on my bench. It seems I can learn from reading but it sinks in much better if I actually go hands on. You mentioned how you hate to use the MOSFETs and probably other TO220 devices on the bread board. Here is a trick that I use to overcome damage to the bread board from the wide leads.

[View:/resized-image/__size/620x465/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-fdd45506-20d7-4e0a-8f56-91dc85b47b85/7762.contentimage_5F00_192323.jpg:620:465]

Those are female square pin headers that I have trimmed down to 3 pins. The TO220 device plugs in very easily with no damage to the header and the pins of the header plug into the bread board and do not seen to damage it either. I have some small TO220 heat sink clips that I use if there is going to be and heat generated.

Thank you for your posting and I always am happily surprised when a little gratuitous lego robot is introduced.

John