How do I get more current?

[AllanBertelsen]

Hi

I build a Switching power supply based on PQ1CG2032. (Like fig 15 in https://www.electro-tech-online.com/custompdfs/2008/05/pq1cg2032_e.pdf )
It is working fine but the PQ1CG2032 becomes hot.

Then I saw a way to boost the output current capability for a linear regulator by using a PNP Darlington transistor in this article Silicon Chip Online - Low-Voltage Adjustable Regulator .

Now my question is. Can this technique also be used to boost the output current capability for a switching power supply?

 

[erosennin]

What kind of conditions are you running it at?
You should probably use a heat sink, if you're using it at its limits.
As far as I'm aware, you can't use that bypass method on a SMPS.

 

[AllanBertelsen]

I use it to feed a picoPSU running a ITX motherboard.

It’s for a rower-robot. I'm using two acid/lead batteries as power supply as the motors are using 24 volts. So my switching power supply are converting 24V to 12V.
It got a heatsink, and using a fan the PQ1CG2032 are cooled effective.

I’m just worrying when I add web-cams, HD and other items to the computer.

 

[erosennin]

Well it is a 3.5A device... If it's a 3.5" HD, you will need about 0.6A@12V and 0.5A@5V so that's nearly 10W... web cams aren't too bad around 0.4A... but it all adds up.
Also depending on your motors as well... so, you will probably be better off using mulitple PQ1CG2032 devices, or using a higher capacity regulator. 'Just in Case'

 

[AllanBertelsen]

Well, the PQ1CG2032 got over current protection. So far it has not shot down. So when I just get rid of the heat I can continue to add components to the computer (trial and error). The fan uses 0.16A. Not much but I would have preferred a fanless solution. I was hoping that the bypass method could fix the problem using a few cheap components.

 

[ZONEZERO]

Check this out! **broken link removed** . Look specificly at the output of this circuit. Hope this gives you ideas. The more tranststors the more current. How high can you go? LOL Take care and have a great day!

 

[Papabravo]

With an SMPS there are a couple of things to keep in mind.

1. The output power will always be strictly less than the input power
2. More output current generally requires beefier magnetics.
3. If you are at less than 85% efficiency you may be able to squeeze a bit more current out with a redesign.
4. A well designed heatsink is essential.
5. PCB layout is critical to obtaining good performance.

 

[AllanBertelsen]

This is my regulator

To be very specific, here is a pdf showing my regulator. I would be pleased to get comments on the design. That goes for heat-sink, pcb layout and the possibility to squeeze a bit more current out with a redesign.

Thank you for the comments so far.

 

[Papabravo]

You must be joking!

A crappy single sided PCB with wimpy traces!
An undersized inductor that maxes out at 2.8 A!
This PCB copies the test circuit from the datasheet! Test circuits are just that, they are seldom if ever a recommendation for an application.
The 90 uH inductor from Toho and the one from Digi-Key may actually differ in characteristics other than inductance which are compromizing the circuit.
I don't know if the diode you are using may also be causing problems dur to reverse leakage current or recovery time.

The heatsink looks OK, but more parallel fins on the backside would help.

In short this circuit was copied from a datasheet without understanding it or the components and now you're stuck with it. Without being able to see the wave forms I'd be hard pressed to make more specific recommendations.

You have no choice but to look for an alternative; this thing is a joke when it comes to high current switching power supplies.

 

[AllanBertelsen]

This is actually working.

You must be joking if this kind of comments is meant to help others.

Don't answer if you only have bad things to say.

Serious answers would be much appreciated.

 

[Papabravo]

According to your original post(s) the design is not meeting your requirements. It is running hot and you would like to increase the available current. You asked for comments and I thought you wanted an honest assessment. It is my purpose to get you where you want to be. In order to do that I need to point out the limitations of the design. You need to decide if it meets your requirements to an acceptable level. If it does, then we are done, and if it does not then you need to explore alternatives.

I understand that you may have a level of pride associated with desinging and building something like an SMPS for the first time. People on these forums have widely differing opinions on the boundaries of criticism that are acceptable. Many people link themselves inextricably to their designs such that an attack on the one is viewed as an attack on the other. Please be assured that I have no earthly reason to attack you personally. It is a fact of life that we learn the most from our efforts that come up short. I'll let you in on a little secret. My first SMPS design was a costly and unmitigated disaster. I learned a valuable lesson from that experience. I hope you can reevaluate my comments in that light.

 

[AllanBertelsen]

So now Papabravo you changed your first response to include some fair comments and not only that what I made was a crappy single sided PCB with wimpy traces. That’s somewhat better. I have been studying a bunch of these circuits. Both from datasheets and from professional implementations as fx **broken link removed** page 20. So the engineers at sharp are just a bunch of amateurs according to you. They use the circuit from the datasheet. Puhh!

My first goal was to feed an old laptop. The components were bought for that SMPS corresponding to the power supply of the laptop. That goal was reached. Now I want to replace the old laptop by a new computer. Then the requirement seems to be a little higher. Hoping that adding a few components to the existing design would help the SMPS to meet these requirements would hopefully not be a crime of a simple amateur.

The question was: Could a PNP Darlington transistor be used as in this article Silicon Chip Online - Low-Voltage Adjustable Regulator to boost the current? Now I’m not an electro engineer. That’s why I ask this forum. And don’t try to tell me that single-sided pcb’s are good for nothing. That’s just not correct. I have seen a lot of exiting project where components just were soldered together.

 

[Papabravo]

The answer to your original question, as has already been stated, is no. You cannot use the same bypass arrangement with an SMPS that you would use for a linear supply.

An SMPS is a challenging and complex circuit. You cannot rely on the test circuits from a datasheet to be suitable for an application period. If you choose to do so then you get what you deserve. There are details of the design and the component selection that are not obvious from the schematic.

I made no claim about the capabilities of the engineers at Sharp. I do claim that users are responsible for the results of appropriating a circuit diagram from a datasheet and substituting components without undertstanding the implications of doing so. Clearly you did very little in the way of analysis of this design.

Single sided circuit boards may be appropriate in many contexts. It is my opinion that an SMPS with more than 1 A of output current is not one of those places. You need thick traces and very low impedance pathways to squeeze performance and efficiency from an SMPS. You need very careful consideration of the magnetics, the diode, and the ESR of the capacitors. We can discuss these things if you like, but you seem more interested in defending your design than in figuring out how to improve it.

So, all thing considered, you might as well solve your own problems since you don't seem disposed to listen or learn.

 

[AllanBertelsen]

Papabravo I certainly want to learn. I just don’t get much out of being told that what I made was crappy single sided PCB with wimpy traces. That is not useful information. I want facts not insults. But don’t answer this Papabravo. It won’t lead to anything productive anyway.

But I would appreciate a second opinion. How do I measure the efficiency? The inductor does not produce any heat, should that be expected if it is driven to the limits? For the lesser demanding setup you could say PQ1CG2032 is oversizes in relation to the inductor. Now when the requirements are higher, would an inductor meant for a higher current then lower the heat from the PQ1CG2032?

 

[Papabravo]

I disagree. I think it was a very useful comment, and I encourage any other supporters of the design, and the single sided PCB, to line up and take a whack at me. Be my guest.

 

[Hero999]

Papabravo is right, your crappy PCB with wimpy traces won't cut the mustard.

How do I measure the efficiency?

Perhaps you haven't thought about this question or you've misworded it (don't be offended I know English isn't your first language).

No offence but if you can't answer that then perhaps you shouldn't be trying to design an SMPs.

The inductor does not produce any heat, should that be expected if it is driven to the limits?

I haven't looked at the datasheet for the inductor. The inductor needs to be rated for the peak current, not just the average current, just because it doesn't get warm it doesn't mean that it's not saturating.

There are other things to consider like the core material. Your inductor looks like it might be an RFI suppressor which is totally useless for an SMPs.

 

[AllanBertelsen]

Thank you for all the offences. I really feel welcome in this forum. How can you explain that this crappy PCB does work fine for my laptop if it is so lousy? Could you please be serious?

The inductor is a switchmode high frequency toroidal indoctor FIT68-1.

I put on a load.
At the output I measured 12V and 0,26A. That’s 3,12W.
At the input I measured 19,6V and 0,19A. That’s 3,72W.
The output effect is 84% of the input. Is this the efficiency?

 

[Hero999]

Yes, efficiency is power in over power out.

Assuming your figures are correct (3.12W does seem a bit low for a laptop), 84% doesn't sound bad so your PCB can't be that bad after all.

This brings me back to the question raised before: if you're so happy with your SMPs, then why are you asking for advice?

 

[AllanBertelsen]

The load was not the laptop. A laptop's load is going up and down all the time, so it would not make any sense make measurements on a laptop. I used a resistor as load.

The reason that I want to modify the SMPS is that the laptop has to be replaced by an Intel D201GLY motherboard. This enables using Linux installed on an usb-pen as well as more power for doing visioning with webcam and the opencv library.

This mb requires a bit more power than the laptop.

 

[crutschow]

Papabravo, I agree with AllanBertelsen that the dismissive and condescending manner of your criticism is not conducive to a good exchange of technical information. Crappy and wimpy are not very useful technical terms. You may be a expert on SMPS (and I reserve judgment on that), but that's no reason to be arrogant about it.

And I disagree with your opinion of demonstration circuit boards. They are usually designed to achieve the maximum performance from the parts, since a customer may be using it to determine if it's appropriate for his own application. A bad design of the demo board would likely kill a sale. It would be like a car dealer letting you test drive a car with a engine that's out of tune.