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Kerry Design mini GRHV\GRLV and JoaMat mini T2 Group Buy

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GR78xx build notes:

Writing direction on the opamp and voltage reference match the writing direction on the pcb

I suggest checking the led orientation with a multi-meter in diode test mode, finding out which way round the multi-meter leads need to be to make the diode light and then marking either the positive end of the led with a red pen or the negative with a black pen whilst holding the led with twisters - if you don't hold the led with twisters it has a nasty habit of sticking to the pen tip. The leds face opposite directions. Positive and negative ends are marked in the picture with red and black lines respectively. All transistors are shown with their case markings. Its a good idea to solder the leds in first and then check. D2 has the end closest to the Vin pins connected ground and so its easy to check its orientation is correct, the other led is opposite orientation.

The  DN2540 is a depletion device so if you measure resistance between pins, two of the pins will appear to be shorted - this is normal and shown on the picture. The tab is also electrically connected to the centre pin...

The top left pin of the hn4a51j is also connected to the bottom middle pin on the ocb and will therefore also measure as a short.

The pmsta devices have 3 digit case codes the first digit being the place of manufacture, the kst devices have two digit codes. Be aware Both the pmsta42 and kst42 have codes 1D but the pmsta42 has a t or other letter before the 1D for the manufacturing location.

voltage ref should have 10V between pins 4 and 6

If you test the board by itself it must have capacitance connected to the output in excess of 20uF in order to regulate and not do strange things like increase the output voltage when the load increases. 

When setup for 15V output, input voltages bellow about 1.7V should result in very little current draw <1mA and no leds lit . At around 1.7V input D2 show glow dimly and increasing the input voltage should result in D2 glowing brighter, the current draw increasing and the output voltage increasing. When D2 is fully bright the current draw should be about 10mA.

At about 17.5V input D1 should begin to light . Increasing the input voltage further will make D1 brighter and the current draw increase towards 10mA current the draw when the led is fully bright. At around 18.3V input the output should stabilise at around 15V and increasing the input voltage further should have no effect on the output voltage or current draw. The second 78xx I built required 0.2V more to regulate fully despite having a 8mV lower output.

Load testing

Expect approximately a 23mV decrease in output for each 100mA of load current drawn from the gr78xx. At 200mA the components on the board should be warm but easy to touch and leave your finger on. The MJW211 should also be a little warm. NOTE the metal tab of the MJW is live so don't short it to something.

Voltage drop under load test, no heat-sinking, MJW211 close up against the pcb, 18.3V input. The drop in output voltage is the same using a 47uF output cap as 220uF.

100mA 23mV drop

200mA  46mV drop

300mA  69mV drop

400mA  93mV drop

500mA 116mV drop (note tab of mjw gets too hold to touch for more than a moment after a few minutes of this load. heat-sinking recommended)

The second 78xx I built had voltage drops within 2mV of the first. The voltage drop under load is a bit more than a traditional 7815 to-220 voltage regulator under the same conditions. Removing the load results in the output voltage of the gr78xx going back to within 1mv of the original no load output almost instantly, even from the hot 500mA load. the voltage drop is fairly linear with load. Otuput voltage drift under constant load as the device heats up or cools down is very low.

666360410_gr78xxfrontpopulated.thumb.jpg.23e8fe9b62f202b186d086afa3b98e2b.jpggr78xx back populated.jpg



79xx build notes

All polar caps, Zener and LEDs are in the opposite orientation to the 78xx, All resistors are in more or less the same positions and orientations as the 78xx, all transistors that are xx42xx become xx92xx and visa versa. NOTE in the BOM Q6 and Q4 appear to be the same on both the 78xx and 79xx however, on the silk screen the physical positions of Q4 and Q6 swapped in all other cases the transistors change in the BOM rather than the silkscreen designations moving. The opamp and LT voltage reference are in the same orientation as the 78xx. The HN4A51J becomes  HN4C51J and the  MJW211  changes from 94 to 93. All positions that hold a KST device continue to do so and the same is true for the PMSTA. Only the type of device swaps from NPN or PNP i.e. from kst42 to kst92 and visa versa or pmsta42 to pmsa92 and visa versa.

The 79xx has similar load behaviour to the 78xx.







Edited by jamesmking
R1 incorrectly positioned in 79xx, spotted by Joamat
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Just got a few boards in.  From left to right... GRHV78xxx, GRHV79xxx and to the right is a new experimental digital alternator.  It’s stackable for balanced  

Look what I just found at my door step...  

Quick update on the status of the GB - we are in the process of testing the boards before sending them to the fab house for estimates. Will provide another update as progress is made.

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  • 2 weeks later...

I've not received them yet either. I suspect they are stuck in customs. Either that or the local post dropped them off at a pickup point, forgot to tell me about it, and happily shipped them back after a week, which has happened before. Or they've disappeared...

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1 hour ago, Discom said:

I've not received them yet either. I suspect they are stuck in customs. Either that or the local post dropped them off at a pickup point, forgot to tell me about it, and happily shipped them back after a week, which has happened before. Or they've disappeared...

Yes, these are the options about here(Hungary). Not usual to lose something but the times are not usual too.


12 minutes ago, MLA said:

Mine just cleared customs...

So there was some delay we will see. Thanks for the answers!

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Thanks for letting me know John!

Hope all will receive your packages soon. I have no clue how much time the packages take to reach different countries/recipients based on past experience - there seem to be quite a bit of variance. Sometimes the customs plays a part and I was also warned that the COVID pandemic may cause some delay as well. 


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