Can I use linear adapter in place of switching adapter

[mockingbird]

I have a TP-Link WR-740N which I preemptively re-capped, and I want to use a reliable adapter with this so I don't have to service it in a few months.

The router's adapter is 9V 600mA, and I have a GE 9V 800mA adapter. The GE adapter's internals consists of the big copper transformer, and a small PCB with a 16V 2200uF input cap, four diodes, and one resistor.

Can I safely use this adapter, or do linear adapters have more ripple than switching adapters?

[budm]

Re: Can I use linear adapter in place of switching adapter

Your original power supply is regulated output switching power supply, your linear power supply is rated at 9V when you draw 800mA, so if you do not draw 800mA from it, the output can be as high as 12~14VDC, you can check the output and see what you are getting right now, unless the GE is labeled with REGULATED output.

[mockingbird]

Re: Can I use linear adapter in place of switching adapter

You're right. I'm getting some 14.55 volts.

...What if the voltage regulator in the router can handle more than 15V, would it then be safe?

[budm]

Re: Can I use linear adapter in place of switching adapter

I am not sure what kind of power supply it has inside your router, it may have sub-power supplies that take the 9V down to 5V, 3.3V, ETC. If they are linear regulator, there will be more power dissipation on them since it will have more voltage drop across the regulators due to higher input voltage.

[mockingbird]

Re: Can I use linear adapter in place of switching adapter

The only power logic I see is a 34063, which takes 3V to 40V, and there's a small SOT-23 right next to it that says "H72P" which I can't find any info on.

The only other chips on the board is the RAM, Atheros SOC, and the flash. Everything else is passive. All three electrolytic caps are 16V.

[budm]

Re: Can I use linear adapter in place of switching adapter

Do you have the pictures? What you do (taking chances) is to use this GE and see if the voltage does drop down to around 9V when loaded by this router.

[mockingbird]

Re: Can I use linear adapter in place of switching adapter

From the OpenWRT site:


Input is on the right. Don't worry, I replaced those Leaguer capacitors with Nichicon HM and HN.

What you do (taking chances) is to use this GE and see if the voltage does drop down to around 9V when loaded by this router.

Sounds good. I want to replace the "Jun Fu" input cap in the GE adapter first.

[budm]

Re: Can I use linear adapter in place of switching adapter

OK, it does have switching power supply inside, big round inductor, more likely to be switching buck regulator (you can check the DC on the cap right next to the inductor to see if it is less than the input voltage). So you may be OK with your GE adapter.

[severach]

Re: Can I use linear adapter in place of switching adapter

I find that equipment where all power goes through a switcher doesn't care much about the voltage or the power quality so long as the watts are available. Lower than what blows a cap and higher than the minimum needed to power up all the switchers.

I like putting transformer based power bricks onto equipment that needs to be reliable.

Note: an AC adapter into a DC device spells instant death to the switchers unless the device starts with a full wave bridge. Some do.

[mockingbird]

Re: Can I use linear adapter in place of switching adapter

I like putting transformer based power bricks onto equipment that needs to be reliable.

That's the idea here... Since the router takes less than 1 amp, I thought why not use one of the hundred transformer adapters I have lying around here, instead of fiddling with the cheap adapter TP-Link supplies.

What do you mean by your last statement? Are you talking about an AC to AC step-down transformer?

[budm]

Re: Can I use linear adapter in place of switching adapter

I have a lot of Linksys Router, modem, AP, etc. They are designed to run with regulated 5V 2A swtiching power supply or 12vdc 1A linear un-regulated power supply, and so far the linear wallwart out last all the 5V swithcing power supply. So I am using 12v linear PS for all my equipment, but I still have to replace bad caps inside these units due to the SMPS inside the units.

[mariushm]

Re: Can I use linear adapter in place of switching adapter

I suspect the voltage in those is at best 3.6v - the controller probably uses 3.3-3.6v, the leds needs at least about 2.2v to light up and they'll light up at 3.3v, there's probably also a linear regulator for 1.8v or 2.5v (memory)

It's best to measure the voltage on that small sot chip pins, right below the pair of capacitors, and the voltage on the capacitor below the inductor. You'll see they're probably both below 5v

You can probably run it from 5v linear power supply (a transformer, bridge rectifier, capacitor) but the switching regulator may be unstable with such low input voltage. you have to test, or check the datasheet of the controller if you can read the code on it.

If you get around the switching regulator, that's another story. But that would involve probing the traces from the dc jack to see where they go and basically use linear regulators to get smaller voltages from your 5v and then solder the wires directly on the output of that switching regulator.

[budm]

Re: Can I use linear adapter in place of switching adapter

5V Wallwart will put out about 7~8V without the load (he has 9V 800mA that puts out 14V no load, 9V at 800mA load) it will have to be loaded at full load to get the output to be 5V. He can easily mesure the 2 output DC filter caps to see what the switching regulator puts out. It looks like the IC drive the MOSFET next to it. The Linksys 12V 1A adapter puts out almost 18V at no load.

[mockingbird]

Re: Can I use linear adapter in place of switching adapter

Just tested this.

Measuring via the two solder points on PCB connector where the adapter plugs in, I get 13.7 volts. The pair of two caps gets about 13.4V, and the lone cap gets about 3.4V.

Also, That Jun Fu cap in the wal wart had a 1992 datecode (The adapter itself is dated from '93), so I replaced it with a Panasonic FK equivalent I had. Voltage (With no load) dropped on the adapter to a very stable 14.4V after replacing the cap. I'd like to see a switching adapter last 20 years.

Router works fine, using a custom OpenWRT build I obtained from here. The speed is excellent, signal is pretty good for only 50mw (TX Adjust cannot be increased for Atheros SOC AFAIK). Pretty good little $15 router if you're willing to invest a little time in it.

[severach]

Re: Can I use linear adapter in place of switching adapter

Are you talking about an AC to AC step-down transformer?

While equipment that starts with all switchers doesn't mind a wide range of DC voltages, reversed polarity or an AC transformer destroys the switchers instantly.

Equipment that requires 3.3v DC transformers usually do not start with switchers and not only require 3.3v, it must be regulated. Think Buffalo and Cisco.

[mockingbird]

Re: Can I use linear adapter in place of switching adapter

I reversed the polarity accidentally on the thing, it still worked.

It's been in service for the past week, haven't heard any complaints...

Check those linear wall-warts for a bloated main cap. I have a switch that was dropping packets because of this.

[999999999]

Re: Can I use linear adapter in place of switching adapter

It looks like that particular router has a series diode "D5" that would protect it against reverse polarity or AC supply input, right after the power switch and an inductor, right before the bulk caps ahead of the switching circuit.

While I'd expect what you have set up to work, it leaves less margin for protection from power surges than either a lower voltage unregulated supply or a switching supply.