Turning on and off a SMPS with DC control

[Ultron81]

Hello,

I have equipment at work that had a power supply fail. This power supply had a remote option, allowing it to turn on and off remotely without switching the AC input. Unfortunately, I can't find a supply with remote capabilities as they seem to be a custom order, and off the shelf replacements dont have this.

The supply is a 240W 24VDC output. I found a replacement of the original supply, but without the remote option. It's a Cosel LEP240F-24.

The remote line used for control was a 24VDC supply with a 3.3k ohm resistor in series, which originally went through the remote circuit on the old supply, and then into a 75452BP driver. The driver has a rating of up to 300mA collector current.

My thought of controlling the SMPS with the old remote line was to use a Opto-Triac or a SSR. The SMPS has a max input current of 3.3A at 100V, 1.7A at 200V. The input voltage to the supply is 200VAC.

I've never used an Opto-Triac in a circuit before, would this be a good idea to use in this type of circuit? Is there anything else I need to worry about, like a snubber?

I attached a drawing. My guess is I will need to add some series resistance to drop the current going through the LED.

Thanks!

[mawyatt]

Why not just a simple 24V Relay?

Best

[Ultron81]

Why not just a simple 24V Relay?

Best

The 3.3k resistor is the problem. The power supply is part of a 3rd party rack that has a ton of other supplies and a control board, where the 3.3k resistor is located. It's very hard to get to the resistor, so I'm trying to find a solution around it.

The only other thing I can think of is making a voltage divider and using a 12V relay instead.

[PCB.Wiz]

My thought of controlling the SMPS with the old remote line was to use a Opto-Triac or a SSR. The SMPS has a max input current of 3.3A at 100V, 1.7A at 200V. The input voltage to the supply is 200VAC.

A single component opto-triac will struggle to manage the current, but a SSR module that has multiple parts (Opto triac + 2 x SCR or larger triac) would work fine.

The serious bolt down module ones like Cosmo KSD210AC8 look to be suitable.
10A gives some inrush headroom, and it says Vin=4~32V gives 5~12mA, so the ~6mA from your 3.3k/24V looks just ok.

[Psi]

Yeah, SSR module seems like the tidiest way.
Easier to get nice modular SSRs you can mount easily than opto-triacs

[NiHaoMike]

You'll want a zero cross SSR for minimum inrush. Alternatively, you could switch the output. 3D printer MOSFET modules are readily available for switching 24V.

[Ultron81]

Thanks, I ordered an SSR module and one of these SIP package versions to try - https://www.littelfuse.com/assetdocs/littelfuse-integrated-circuits-cpc40055st-datasheet?assetguid=de3d1170-6a6f-4689-b821-ff1140bd00ea

For some reason, I always thought switching off the load on a SMPS was not good, so I figured switching the input would be better.

[Psi]

Switching off the load on a SMPS is fine, unless it's something custom that says not to do that.
Minimum load requirements are usually only to ensure the output voltage stays within the specification.

Switching the AC input off is better for power savings since SMPS all draw some current even with no load.