PrathikP

modified 5 years ago

Tracking Pre-regulator

258

03:18:30

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A Tracking Pre-Regulator is a circuit that "Tracks" or "Follows" the output of the following regulator by a suitable voltage "gap", which is around 2V in this case. Such a circuit is used to reduce the power dissipation per device, achieve better ripple rejection or even better efficiency, in which case a Switching Pre-Regulator is used. 

"Tracking" is achieved by the NPN BJT and LED. When the voltage difference between the outputs of the 2 regulators exceeds V(be, knee) + V(ka, knee), the transistor begins to conduct, thus posing as a resistance parallel to the already present 100kohm resistor and lowering the effective resistance, thus keeping the output of the Pre-Regulator 2V about the output of the (Post?) Regulator. The 620ohm resistor is used to send an additional current of 0.7V/620R to ensure the LED runs at its rated current, thus providing the full voltage drop, and also to glow brightly and act as an indication LED.

Note: I've heard that LEDs are "noisy", so using some other voltage reference is probably better for very low noise applications.

published 5 years ago

hurz

5 years ago

The power dissipation in total is still the same, its just splitted on two speparated mosfets, while the second on has the easy job and the first the rest.

PrathikP

5 years ago

I know, I just can't make a switching DC DC converter

PrathikP

5 years ago

Anyways I'm not trying to reduce or split power dissipation here, just trying to show tracking.

hurz

5 years ago

i think buggzy had an implementation linear- combined with a switching supply, but CFS was an issue as usual in everycircuit

hurz

5 years ago

http://everycircuit.com/circuit/6069151443714048

hurz

5 years ago

BTW, i like e.g. DPS50xx devices but for many appilactions it needs a ripple free voltage, i connect an external little board with LM317 or a tuneable 7805 (5V or more). They also provide extra LCR filtering and ferrit beads.

PrathikP

5 years ago

Oh Im not trying to build a power supply for myself, if that's what you think. And if I do decide to build one (I will, eventually. Everybody does), I have DC-DC Converter ICs (LM2596, MC34063) with I can use.

PrathikP

5 years ago

DPS50xx is buck only, if I'm not wrong. That's sorta a deal breaker for me.

hurz

5 years ago

deal breaker? What do you mean??

PrathikP

5 years ago

We it means that I can't use the 20V laptop power supply/ 12V wall adaptor that I have and get 0-32V out. I anyways have a 35W SEPIC, which is sufficiently powerful for me and compact. And I can use a small 12V wall adaptor.

PrathikP

5 years ago

And the module itself costs $50. The case and power supply will add to the cost

hurz

5 years ago

stack two ac adapter and you get even more with a single buck. So what is so bad about a high efficient buck converter?

PrathikP

5 years ago

No the buck converter itself isn't a problem. Sure, it's a high performance device and all that but its expensive and is step-down only. Putting 2 adaptor outputs in series is fine, but it also means 2 mains connections, which means I need to use an extension chord. Bit inconvenient.

PrathikP

5 years ago

I'm not saying that its a bad product. I've seen reviews of it and it's pretty good, performance and interface wise.

PrathikP

5 years ago

I don't have a lot of space on my table

hurz

5 years ago

234W, at 12V @19.5A or 6.5A at @36V. A bit inconvenient. Normaly, 20V are with 6.5A much enough for most things, sometimes i stack two AC adapter. Sometimes its inconvenient to have 234Watt power at 95% conversion efficiency. I still dont understand the "deal breaker" for a 234Watt setup... Whats the price for a SEPIC converter at this power?

PrathikP

5 years ago

I don't want a 200W buck converter. It's inconvenient for ME. Me only.

PrathikP

5 years ago

I have a compact 12V wall adaptor and a 35W SEPIC, with is more that sufficient. It's fits in a small drawer along with all of my other equipment and components. And it takes up only a small amount of space on my table. And you don't easily get a compact 48V Power supply in a lappy power supply package. I've searched for it in Amazon and a local seller's website. You only get huge 48V 10A modules, and they don't come in a nice, safe plastic package with a proper mains connector.

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