DC SSR

[snething]

Here is the DC SSR I have been working on. The layout, size and operation are similar to the coop AC SSRs. I have consulted with Wjohn and Pshort on the design and they have assisted me on several improvements.

My design thoughts were keeping the DC SSR flexiable. My control interests are DC motors for animation, LED floods and other DC items like valves or special effects.Â*I think the Halloween builders will use it the most.

I planned to be able to use a wide range of control voltages but will most likely only use 5v and 12v, but as I read the spec of the Mosfet it would handle higher voltages.

Input power would come from a modified PC power supply.

I used an optoisolator in the circuit to keep the computer and the control board from any damage. Hard to say how/where the controled item will be and what conditions it will be used in. This way I only risk the DC power supply and the rest of the show can go on if there are any problems.

When I received the parts I set up the circuit on a breadboard and tested the design. Works great!Â* I then decided to test PWM.Â* I used the output of a servo PWM circuit I built, using a 555 timer, as the control input.Â*I hooked up a stip of LEDs to the output of the DC SSR and they dimmed smoothly across the PWM range of the servo circuit.Â*

I have etched a board, assembled and done some testing. This design will work for my needs. I hope it will help with other holiday projects in the works.

The attached PDF contains a schematic, board layout and parts list.

A big thank you to Wjohn and Pshort and Thanks for your interest

Scot

[RJ]

Glad you got it going. Have fun.

[snething]

Here is the expressPCB file for the DC SSR

Scot

[wjohn]

as noted,

I have been working with Scot on the design, and putting togther a DC SSR COOP.

Here is the work so far, the schematic is as per the one published by Scot, with a few minor mods.

Feedback appreciated,

John.

[P. Short]

I'm far from an expert on these matters, but most of the MOSFETs that I've looked at require much more than 5V to approach their maximum current (or minimum RDS) specs. Also, the regulator is overkill, I think...a zener diode and resistor would work just as well, and even those aren't needed if the input voltage is below 20V or so.

--

Phil

[synnie]

Hi all, would these DC SSR's be able to handle a voltage of between 24- 48VDC?.Am looking to switch LED strings if possible. Ta Synnie

[synnie]

Hi all, would these DC SSR's be able to handle a voltage of between 24- 48VDC?.Am looking to switch LED strings if possible. Ta Synnie

[wjohn]

I'm far from an expert on these matters, but most of the MOSFETs that I've looked at require much more than 5V to approach their maximum current (or minimum RDS) specs. Also, the regulator is overkill, I think...a zener diode and resistor would work just as well, and even those aren't needed if the input voltage is below 20V or so.

--

Phil-

Hi Phil,

ther are some MOSFETs that are designed for Logic Level

http://www.fairchildsemi.com/ds/RF/RFD14N05LSM.pdf

These are N-channel power MOSFETs manufactured using the MegaFET process. This process, which uses feature sizes approaching those of LSI integrated circuits, gives optimum utilization of silicon, resulting in outstanding performance. They were designed for use in applications such as switching regulators, switching converters, motor drivers and relay drivers. This performance is accomplished through a special gate oxide design which provides full rated conductance at gate bias in the 3V-5V range, thereby facilitating true on-off power control directly from logic level (5V) integrated circuits.

[P. Short]

Those look like they will work fine.

--

Phil

[klanger]

where we at with the dc ssr?

[wjohn]

Gents,

My most extensive testing to-date. this is based on a standard COOP AC SSR, and the DC SSR that James and I worked on. it is not a test of the design proposed by Phil.

I have been using the DC SSR on my GRINCH during the Halloween show period and it has been working fine. A PCB is been developed, and there were 20 made in the first batch. The DCSSR is optically isolated from the Controller (just like the AC version), and can switch DC voltages of 5 to 30 V DC, and up to a couple of amps per channel. The limit is the heatsink on the MOSFET.

Some results from testing today.

The Test Setup was:

LAPTOP PC > REN Power Supply > RENC > GRINCH > DCSSR or AC SSR. This setup uses the RENC and provides a PWM waveform to the connected SSRs.

The Lamps connected were:

AC SSR: Channel 1: 12 V 20W MR16 Halogen globe
Channel 2: 12 V 1 W MR16 LED Globe
The supply voltage to the AC SSR was 12 VAC 50 Hz via a transformer.

DC SSR: Channel 1: 12 V 1 W MR16 LED Globe
The supply voltage to the DC SSR was 15V DC via a Lab power supply.

Dimming Tests.

Using the Vixen function to Test Channels, I selected all 64 channels on the Test sequence, and dimmed them using the slider built into the current Vers 2.3 beta.

Results.

AC SSR.

12V Halogen globe.

Range 0 – 20%. No visible effect.
21%. First Filament glow observed.
25% reflected light observed (The condition was when was light observed, reflected off a white surface, without directly look at the globe filament.)
25 – 80% Dimmable range.
80 – 100%. No perceivable change in reflected light output, for increased drive above 80%.

12V LED MR16 globe (Yellow)

Range 0 – 18%. No visible effect.
18%. First LED glow observed.
22% reflected light observed (The condition was when was light observed, reflected off a white surface, without directly look at the LEDs.)
22 – 70% Dimmable range.
70 – 100%. No perceivable change in reflected light output, for increased drive above 70%.

DC SSR.

12V LED MR16 globe (Yellow).

Range 0 – 3%. No visible effect.
3%. First LED glow observed.
3% reflected light observed (The condition was when was light observed, reflected off a white surface, without directly look at the LEDs.)
3 – 95% Dimmable range.
95 – 100%. No perceivable change in reflected light output, for increased drive above 95%.

Other observations.

The DC controlled LED tended to turn on with a fairly visible step, at 3 %, compared to the LED junction glow at 18% for the AC SSR powered LED Globe.

The dimmable range for the LED Globe was wider on a DC SSR, than an AC SSR.

Standard Code test. It was possible to dim the AC SSR LED, using standard RENARD code (non-PWM). It did not dim the DC SSR.

Conclusion and recommendations.

It is possible to dim LEDs. Due to the different characteristics of a LED to a globe, you need to take this into account when choosing to use LEDs, and what method to dim them.

The most straight forward dimming scenario is to use a 12 VAC source, and use a modified SSR to dim a 12 VAC load (either Halogen or LED). The advantage is the SSR boards are already fielded and only require a simple mode to the Gate Resistors to ensure reliable TRIAC triggering. The Disadvantage is that you need to provide a suitable AC 12 V source.

The most controllable scenario, based on my testing is the DC SSR. The dimming range was broader than the ACSSR controlled LEDs. The advantage to this scenario is the cheaply available DC powersupplies that can be salvaged and put to use powering the DC globes. It would be possible to mix halogen and LED on the same controller, and achieve some good effects. The disadvantage is that a separate DC SSR is required.

[NogginBoink]

Is the voltage regulator really necessary?

(It's certainly nice to have pads on the PCB for it, but I'm curious what results you'd get if you tested without the regulator and used the host controller for power.)

[P. Short]

The regulator is on the isolated side of the opto-isolators, you can't use the host controller for power and still maintain isolation.

--

Phil

[NogginBoink]

OK, fair enough.

Is isolation required?

[wjohn]

Isolation = safety. Even though this is a DC SSR board design, it is still prudent to isolate the lights Power Supply from the PC and controller.

The GRINCH can sink 90ma @ 5 volts, and the 595 can be configured for 12 V sink. Each of those solutions is specific to the controller and has lmitiations with respect to voltage or load current.

The RENARDs can sink even less current (i think 80 ma per PIC), so that wont be enough.

The DCSSR design allows you to select the Light Voltage independant of the Controller, and the switch current is at least 1-2 amps, per channel, with a simple heatsink on the MOSFETs.

The regulator could have been a Zener and a resistor. I opted to go with a 7805 because the cost is not much (less than 60c) and they are dependable.

There is a separate discussion about 120VAC LED Strings that Phil is working on, this design is not intended for that solution, morso it was designed for LED MR16s and other types of Garden Lights.

John.

[P. Short]

Are you still using that K847PH quad opto? It seems very slow in saturated mode (which is how it's being used).

--

Phil

[NogginBoink]

Isolation = safety. Even though this is a DC SSR board design, it is still prudent to isolate the lights Power Supply from the PC and controller.

The GRINCH can sink 90ma @ 5 volts, and the 595 can be configured for 12 V sink. Each of those solutions is specific to the controller and has lmitiations with respect to voltage or load current.

The RENARDs can sink even less current (i think 80 ma per PIC), so that wont be enough.

The DCSSR design allows you to select the Light Voltage independant of the Controller, and the switch current is at least 1-2 amps, per channel, with a simple heatsink on the MOSFETs.

The regulator could have been a Zener and a resistor. I opted to go with a 7805 because the cost is not much (less than 60c) and they are dependable.

There is a separate discussion about 120VAC LED Strings that Phil is working on, this design is not intended for that solution, morso it was designed for LED MR16s and other types of Garden Lights.

John.

Thanks for the detailed explanation. I love the education I get here!

[P. Short]

My experiences with MR16 LED spots from the WireKat group buy over at PC are as follows:

AC Control (standard Coop SSR using BTA08-400B triacs with 12VAC)

0-12% - nothing visible
12%-16% - flickering
16%-45% - dimming range
45%-100% - no further changes

There is a newer version of the firmware (20070823) the only flickers on the first visible level.

DC Control (simple BJT transistor on output of Renard using the DC firmware build)
0-5% full dimming range (off to full brightness)
5%-100% - no further significant changes

--

Phil