DC SSR VReg, 78L05: Vin=12v & Vout=11.35V??

[stempile]

I checked out this thread regarding DC SSRs. I am noticing something different however.
http://www.doityourselfchristmas.com/forums/showthread.php?t=3034


After building the John's DC SSR with the specific 78L05 VReg (863-MC78L05ACPRPG), I notice the VReg was getting warmer then I had expected and that it was pulling 40mA without a load. I checked the voltage across it, Vin=12, Vout=11.35. I have the output cap on, but not the 'hacked' on input cap as suggested by the thread noted above.

Suspect of the VReg, I pulled it off and bread board it and another one. Same thing. The device markings are: "MC78L 05ACP 714". That appears to match the data sheet for the part number listed above.

I would expect to get Vout=5v. I am concerned that he higher voltage on the Vout may have cooked the opto-iso?

?What am I missing in regard to this VReg?

Thanks
ms

[stempile]

My SSR build appears to be working. Also the temp of the Vreg held constant, but still I am confused about the voltage. Likely I am not measuring it correctly...

Thanks

[ErnieHorning]

I can’t tell for sure looking only at the picture in the Wiki, but from the orientation of the power pins, the opto IC and the brown shading of the traces below, it looks to me that the silkscreen for 78L05 part is backwards. The 78L05 will operate just as you describe if it’s inserted backwards.

[stempile]

Thanks Ernie. I flip the Vreg around as you suggested. Now with no load its not pulling any mA and the output voltage across is 5v. I need to look at the specs for the MOSFETs to see if with the higher voltage I might have caused damage while testing.

ms

[jpb]

I can’t tell for sure looking only at the picture in the Wiki, but from the orientation of the power pins, the opto IC and the brown shading of the traces below, it looks to me that the silkscreen for 78L05 part is backwards. The 78L05 will operate just as you describe if it’s inserted backwards.

I noticed with my first two that if I put the voltage regs in as per the wiki and the silk screen they cooked themselves. I put it down to my own ignorance but now that it has happened to others ....

[stempile]

I noticed with my first two that if I put the voltage regs in as per the wiki and the silk screen they cooked themselves. I put it down to my own ignorance but now that it has happened to others ....

I updated the wiki to reflect the construction note as well as the errata. Not seeing the original part list, my guess is that John used a different Vreg in the design and picture then what is listed in the current BOM.
http://christmasinshirley.com/wiki/index.php?title=4_Channel_DCSSR_Assembly_Instructi ons

I check voltages and temp when I am building for the first time. The temp of the Vreg and the trace leading up to it was hot to the touch with no load. I got lucky it didn't get cooked cause I only had it powered for short amounts of time for testing.

ms

[scorpia]

could someone please post a pic of the completed board with the correct regulator in it please.

its allways good to see a pic.

Peter

[stempile]

could someone please post a pic of the completed board with the correct regulator in it please.

its allways good to see a pic.

Peter

I will tonight. I finished making a new set last night that also included some clear shrink tub to prevent the MOSFETs from touching tabs (the drain).

ms

[stempile]

Attached is an almost complete DC SSR. Ran out of the 470 resistors so there are 4 holes for those. Also I used a different cap then the what the BOM called for and a different LED. Those parts came out of my supply.

Notice the Vreg and notice the clear shrink tube on the tabs of the MOSFETs. See my other post regarding the shrink tube.

ms

[rstehle]

Just for clarification, if the vreg is installed according to the pic in the Wiki, it will be wrong? It needs to be reversed as per the pic in the previous post?
Thanks,
Randy

[stempile]

Just for clarification, if the vreg is installed according to the pic in the Wiki, it will be wrong? It needs to be reversed as per the pic in the previous post?
Thanks,
Randy

Depends on what part you have. 78L05 VReg (863-MC78L05ACPRPG) is what has been discussed in this thread.

I am not willing to post my picture on the wiki because I only used a couple parts from the Wiki BOM. The Vreg, Opto-iso and MOSFETs were from the BOM. Everything else was from my stock.

ms

[rstehle]

Jeez, this is like a Presidential Debate (hard to get a straight answer.....LOL). I just need to know if I have to reverse my vregs? My DC SSR's are built from the BOM in the Wiki. Is the orientation of the vreg in the photo in the Wiki correct based on using the part # in the BOM?

[stempile]

rstehle -

Please keep in mind the WIKI is a living document. Any member of the of forum can and should make changes to it when mistakes or improvements are found.

The BOM changes from time to time as parts become unavailable or others find a better / cheaper combination of parts to use. Also John designed this board to be flexible so a variety of Vregs may have been listed since the initial development.

I don't know what part number you have for sure because the BOM might have changed between your ordering of parts and my order. I have not been tracking the changes.

Part number 78L05 VReg (863-MC78L05ACPRPG) was listed a month ago on the BOM when I ordered, it should be placed like the picture I posted to the thread. Its important that you verify your part numbers.

I don't know the orientation for other parts and I don't know what parts are used in the wiki picture. I am sure it worked for John when he took the wiki picture so I am guessing the BOM has changed since the wiki picture was taken.

Keep in mind you should place the part and test the voltages across Vout and GND. If it comes out 5v then you are good, if something else then you have to change it. Test it with 6v the first time. Its likely at 6v not to cause much or any damage if it is in backwards.

Good Luck.
ms

[rstehle]

Matt, that was a great explanation. Thank you! I used the same part number for the vreg as you did. Guess I'll heat up the ole soldering iron...........
Thanks again,
Randy

[ErnieHorning]

If you’re using a part with ‘78L05’ anywhere in the part number and it physically looks like the part shown in the wiki picture (TO92), it must be installed backwards to the silkscreen, just like the part in Matt’s picture. That part has been around for more than 30 years and to the best of my knowledge, has never been made with the leads in the reverse order.

My guess is that when John tested the circuit, he used a low voltage somewhere around 8 or 9 volts. The regulator got hot also but, like Matt discovered, the circuit still worked fine. The first time that I use the ‘L’ version I hooked it up backwards too. I was using 18 volts for input and it promptly blew the black part across the room. It was pretty obvious, something was wrong.

If you’re using the TO220 style part, it should be installed next to C1 in the same orientation as the silkscreen.

[wjohn]

bugger,

Notch that up as another mistake!

Pinouts of the TO-220 case are

IN -1
Gnd - 2
Out - 3

while the TO92 are:


OP GND IP , with the flat side facing you.

[stempile]

bugger,

Notch that up as another mistake!

Pinouts of the TO-220 case are

IN -1
Gnd - 2
Out - 3

while the TO92 are:


OP GND IP , with the flat side facing you.

No worries! They are still solid boards that are high quality! Mine work great!