Switch 55-60v 16mA advice, optocouplers?

Other Hardware General Electronics
1

Hi crew,

I'm wanting to switch the high side of my ebike controller which is about 55-60v at 16mA. I want to switch it using a 3-3.3v signal.

I was thinking of using a p mosfet, but after measuring the current I think I can get away with something a bit simpler...

Would an optoisolator/optocoupler work for this okay?
What specs should I look for?

My local electronics store has:
MOC3020/MOC3021 are these appropriate for the task?

2

Those two optocouplers both have triac outputs.
They are for use on AC, but totally unsuited for DC. Once triggered a triac will continue to conduct until the current is reduced to zero (or some low value).

1 Like
3

why not use an ssr
https://www.aliexpress.com/item/1005005821892767.html?src=google

4

SSR are too large. Im currently using a 3.3v relay for the job, but I really want something smaller as space is very limited.

Ive done a search:
https://au.element14.com/w/c/optoelectronics-displays/optocouplers/transistor-output-optocouplers?sort=P_INVENTORY|1&no-of-channels=1-channel&collector-emitter-voltage-v-br-ceo=70v

What about FOD817?

5

Something like this would not take up much space:
image

6

No that won't work.

7

At 16mA, you do not need a SSR with any heat sinking. Look at Digikey and other distributors for the physical size you need.

8

An SSR can be as small as an opto coupler.
Google "optofet" or "photofet".
My local supplier stocks this one. 5mA in 60V/500mA out.
Leo..

2 Likes
9
10

Thanks guys! I had no clue SSR could be that small!
I'll pick the jaycar one up as we have that in australia!
It looks perfect for the job

11

Don't forget the current limiting resistor for the LED.
Vf of an opto LED is normally ~1.3volt, so the resistor drops ~2volt with 3.3volt-logic.
330 ohm will do, which drives the opto LED with ~6mA.
Leo..

12

Thanks! I was just looking at what was required to get this going too!

13

Looking at the circuit diagram. I assume I connect my battery to drain, then source becomes the switched output, like a p channel mosfet...

Is there a difference between the drain pin 4 & 6?

14

There are two N-channel fets back2back between pin 4 and 6.
So polarity doesn't matter if you use 4 and 6 as a switch.
Leo..

15

So for clarity:

  1. Use pins 5 and either 4 or 6, if I care about polarity for some reason.
  2. Use pins 4 and 6, if I just want a simple switch, no polarity.
16

From the Datasheet:

3.4 Repetitive peak off state-voltage 60Vdc min

You should allow some margin for derating. This is on the edge of failure.

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