# Minimum Output Operating Voltage of Solid State Relay

I'm wondering if someone could explain why a solid state relay has a minimum voltage that it can switch on or off. For example I'm hoping to use an SSR-10DD (http://www.fotek.com.hk/solid/SSR-3.htm) solid state relay, however the spec sheet mentions a minimum of 5V on the output side. I was hoping to use it to switch around 3V. Why would it require a minimum of 5V?

Update:

• V_input range = 5V from an Arduino output pin
• I_Output current range = Signal only, so less than 10ma
• Target load type = Signal
• Reason for isolation = want to avoid all possibility of damaging existing circuit

More details about what I'm trying to achive can be found in this question: Connect Arduino to existing circuit with seperate power supply

• what current???? – Tony Stewart Sunnyskyguy EE75 Oct 19 '16 at 2:48
• I've updated my question. The current would be negligible since I'm switching a signal only. – Harry Muscle Oct 19 '16 at 15:35
• I understand the rack mounted modules limits options for minuscule optoisolated switching, but in this case all one needs is a board to mount the connectors for this chip as a low side switch for 5V for $0.40 with 3kV isolation digikey.ca/product-detail/en/lite-on-inc/6N137S-TA1/…. or buy similar on boards online for$5 with many ports – Tony Stewart Sunnyskyguy EE75 Oct 19 '16 at 16:40
• created 2nd answer better for you – Tony Stewart Sunnyskyguy EE75 Oct 19 '16 at 17:15

Harry I don't know if you know anything about transistors but I think you have chosen the wrong part for your application.

This active Opto circuit needs enough voltage to drive the transistor base current to saturate the switch.

Try again.

PLEASE Specify the following;

• V_input range,
• Control V,I range options
• I_Output current range
• target load type. ( reactive , resistive/ motor/ micro etc)
• reason for isolation ( kV? EMI? both?
• I've updated up original question with the additional details you asked for. – Harry Muscle Oct 19 '16 at 15:32

SSRs use SCRs or TRIACs on their switch outputs. These components have a dropout spec that gives the ON voltage supplied to a load whereby the switch component will no longer stay on.

• AC SSR's use Triac's DC SSR's use single transistor's ( open collector or open drain) – Tony Stewart Sunnyskyguy EE75 Oct 19 '16 at 3:22
• @TonyStewart.EEsince'75 Does using a pair of SCRs count as a triac? (It's what I'm doing here as part of my AC 40 A split phase H1/H2 hybrid switch -- no physical triacs present, just SCRs.) – jonk Oct 19 '16 at 4:22
• natch 4 Q's in a Triac or 2 SCR's with equal quadrant sensitivity hopefully. – Tony Stewart Sunnyskyguy EE75 Oct 19 '16 at 4:24
• @TonyStewart.EEsince'75 It's a hybrid system. The TYN640's are ON only long enough to allow the mechanical relays to engage. Then they are no longer triggered by the MOC3083s until it's time to release the mechanical relay. There are other components of course which allow some adjustment. My first question here shows an earlier schematic of part of it. – jonk Oct 19 '16 at 7:56
• Just to confirm, the dropout spec you mention is not the same thing as the voltage drop, correct? In other words, if I put 3V across the outputs of the relay I mentioned which has a voltage drop of 1.6V I would get 1.4V across it, however, because the 3V is lower than the dropout voltage I would actually get no voltage/current flowing. Just want to make sure I understand correctly. – Harry Muscle Oct 19 '16 at 15:35

Harry, I know you would like to buy a rack mount or other std mount for this simple application, but all you need is a tiny shielded Reed relay with 3 to 5V control input from logic. SEEED Co. has over 500 products with gas sensors, indicators, interconnect cables and guys like Mouser may carry them. \$5 or less. Then use twisted pair output to reduce noise ingress on high impedance load. Reed Relay board with screw terminals out and input jack, very reliable

... however the spec sheet mentions a minimum of 5V on the output side. I was hoping to use it to switch around 3V. Why would it require a minimum of 5V?

Figure 1. Block diagram.

The 5 V minimum output voltage requirement is probably required to power the output circuit driver. The datasheet says that 1.6 V will be dropped between 1 and 2 so with a 5 V supply there will only be 3.6 V available for the load.