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What I would like to accomplish: I am trying to add current regulators into a home built dual rail linear regulated power supply. I previously asked this question about transformer fusing and received useful responses from the EE Community. The supply is mostly complete now and I also added a current source using the following schematic off the LM317 datasheet:

Current Source using LM317

I adjusted the resistor values though to ensure that the current source stays well below my max current (.35Amps on each secondary of the transformer).

I would like to also build a current regulator on the negative rail using either Figure 12 or Figure 15 from the LM337 datasheet:

Example from LM337 Datasheet Example from LM337 Datasheet

Problem: I may not understand exactly what is going on with the LM337 schematics, but I cannot figure out how to connect this circuit up correctly, especially after the LM317 current regulator was straight forward.

Where do I place the load? I think this is supposed to be a Current Source where the load goes between V-in and V--. I appreciate any help you can provide in understanding how the LM337 current regulator configurations are supposed to work.

Community
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Dave Guenther
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  • The LM317 circuit, after you put the resistor in, is just a two-terminal limiter. It will work in series with a load regardless of whether the series connetion is (+)-load-regulator-(-) or (+)-regulator-load-(-), and regardless o f whether (+) or (-) is ground. So, there's no reason to do an LM337 variant. – Whit3rd Mar 03 '17 at 22:30

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Use them exactly as you used the 317, -ve supply input to Vin, load between ground and ADJ, resistor between ADJ and VOUT. As shown in the schematic below:

schematic

simulate this circuit – Schematic created using CircuitLab

They are shown the way they are shown in the data sheet because current flows from ground, out of Vin and into your -ve power supply pin - remember conventionally we say that current flows from +ve to -ve

Icy
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  • I just tried placing the load between ADJ and Gnd and it worked. To make sure I understand what's going on, is this current regulator operating as a current sink? – Dave Guenther Dec 15 '15 at 16:18
  • Yes (ish) that's not really a useful way of looking at it. The load and regulator components together are a current sink, the regulator (and associated resistor) is really acting as a variable resistance that will get higher when the current limit is reached. – Icy Dec 15 '15 at 16:26
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    @DaveG - but also note that you should not do this as an add-on current limiter for a voltage supply. Adding this circuit will cause very considerable voltage losses at the load. At the least, you have the drop across the resistor, plus the dropout voltage (~1.5 to 2 volts). – WhatRoughBeast Dec 15 '15 at 17:21
  • Thanks @WhatRoughBeast, definitely don't plan to make this a current limiting device, rather a way to control current regardless (for the most part) of voltage. – Dave Guenther Dec 15 '15 at 18:06