Gen1 DCDC Converter Troubleshooting and Repair

[eldenh]

It looks like I mislabeled the terminals. The central terminal of Q101, Q104 and Q110 are at 59v.

 

[kiev]

Q104 and Q103 are the upper FETs in the H-bridge. The ODD numbered side feeds the -1 terminal of TR103; the EVEN numbered side feeds the -2 terminal.

So the question is what does it take to boot strap IC101 the switching regulator controller to start switching Q110?

The datasheet indicates it uses a 26V supply and start up threshold of 11V.

In the pictures you can see the bottom layer has a HV resistor divider network. It is self-switched by Q109 to create a voltage labelled as "Vsub" on the top layer in a little box with 2 vias over by IC101. It is carried around on internal traces.

This Vsub provides the "collector" voltage to pin 10, and passes thru R125, 51Ω, to provide the Vcc for IC101 on pin 11. Ground is pin 6 and it connects to the HV(-) terminal.

So check the voltage at Vsub with respect to HV(-) , IC101 probably won't start switching until it hits 11V.

There are 2 more HV resistor divider networks on the bottom layer, appear to be associated with IC102 op amp, and somewhere else--there are some internal traces.

[edit]
So the HV resistor divider networks: the first one drops the HV(+) across R117-120 for a total of 204kΩ and feeds a zener diode ZD101 (can't read the marking) on the base of Q109 ; the second one drops across R121-124 for 188kΩ to the collector of Q109. i think the action here is to self start Q109 to provide the power supply Vsub. There is a diode D101 (blocking diode?) on the emitter of Q109 before the Vsub via.

Vsub is the voltage on C122, 47uF 35V.

The third divider drops 900kΩ across R139-141 and runs to some internal plane on vias. It is also dropped across 130Ω R142 to feed ?

There is an ON/OFF pin 13 of IC101, but i'm not finding the source--it is carried on an internal trace...

 

[eldenh]

Kenny, it looks like you stayed up late working on this! I decided I would have to take the PC board off the check on the back side too. After examining it, I chose to power up again with 59v. I found that the ZD101 is at 2.56v and the output from D101 is 1.37v which is what i'm finding pin 11, VCC, of IC101. Since the spec sheet calls for 11.5 to 24v, it seems that ZD101 may be defective.

 

[kiev]

Continuation,

i found the ON/OFF.

IC101 has an internal reference voltage regulator, +5V output on pin 14. The board vias and traces that i couldn't seem to follow are coming from that pin.

When the Vcc on pin 11 is greater than 11V, but less than 26V, the internal reference 5V is created and available on pin 14. On this board they have connected pin 14 to the ON/OFF control pin 13, so it should start right up given a proper Vcc.

 

[kiev]

... I found that the ZD101 is at 2.56v and the output from D101 is 1.37v which is what i'm finding pin 11, VCC, of IC101. Since the spec sheet calls for 11.5 to 24v, it seems that ZD101 may be defective.

i tried to measure mine in-circuit--it was breaking over at about -0.5V, and had about 1V of forward drop. So your's is probably okay.

2.5V should be enough to turn on Q109, but i'm not seeing how it could create 11 to 26V for the chip supply.

Need to get this drawn up and look at the datasheets...

[edit] i'm seeing a faint impression of "182" on the zener, maybe that's the Vz = 18.2V

Q109 turns on at about 0.6 according to datasheet, so my measurement was likely just biasing that junction in the device and not the zener. if i have time i will remove it and test it separately, but it doesn't matter unless it is shorted the Q109 will be turned on if HV is high enough.

 

[eldenh]

Can anyone determine the correct voltage for ZD101?

 

[coulomb]

... I found that the ZD101 is at 2.56v and the output from D101 is 1.37v which is what i'm finding pin 11, VCC, of IC101. Since the spec sheet calls for 11.5 to 24v, it seems that ZD101 may be defective.

i tried to measure mine in-circuit--it was breaking over at about -0.5V, and had about 1V of forward drop. So your's is probably okay.

My understanding is that zener diodes below about 3.3 V are really useless, and even 5.1 V is a bit dodgy. So I doubt that it's a less than 1 V zener. More likely, the rest of the circuit is loading it down.

I think to get the voltage to IC101 up with 59 V applied (and I think it's worth a bit of effort doing this), some of the resistor chains will have to be temporarily shorted. But there seem to be three separate chains, so some tracing will likely be needed.

To find the voltage of ZD101, I think applying about 12 V limited to about 25 mA directly across it with nothing else powered should be fairly safe. But the rest of the circuit could well load it down too much. But it might give you an idea, like oh it's more than 5 V. I wonder if it might be compared with Vref to generate a sort of "power good" or "DC-DC operating OK" signal, or at least one input into the power good logic.

 

[eldenh]

ZD101 is connected to the HV+ by about 205k. It appears the voltage out of Q109 is connected to VCC of IC101 by a diode. The spec sheet lists max VCC of 26v and recommended 11.5 to 24 with 15 normal. Without proper test equipment, I've been making do with a 12v battery and a 58.7v bicycle battery charger.

 

[coulomb]

ZD101 is connected to the HV+ by about 205k.

Ah, That's probably R117-R120 (51 kΩ x 4 = 204 kΩ). Perhaps consider shorting one or two of these temporarily.

It appears the voltage out of Q109 is connected to VCC of IC101 by a diode.

OK. So perhaps Q109 turning on, perhaps partially, is what "bootstraps" IC101. IC101 gets its power from the "logical OR" of Q109 or another path via another diode. That other path is probably one of the secondary windings of TX105, suitably rectified and filtered. So once IC101 is driving the MOSFET and transformer (probably actually a multi-winding inductor), it can power itself from the HV source. At that point, something will likely happen to turn off Q109. Perhaps there is a capacitor in the base circuit of that transistor that turns it off after a few hundred milliseconds.

Without proper test equipment, I've been making do with a 12v battery and a 58.7v bicycle battery charger.

Hopefully, that's a dumb battery charrger that doesn't need to see an actual battery there. Elcon charrgers for example won't turn on their output relay unless a battery is detected. An actual current limited power supply would be much better, since it can be programmed not to supply more than a few watts of power, which hopefully reduces the chances of something burning up. But of course, you have to work with what you have.

 

[kiev]

It appears the voltage out of Q109 is connected to VCC of IC101 by a diode.

OK. So perhaps Q109 turning on, perhaps partially, is what "bootstraps" IC101. IC101 gets its power from the "logical OR" of Q109 or another path via another diode. That other path is probably one of the secondary windings of TX105, suitably rectified and filtered. So once IC101 is driving the MOSFET and transformer (probably actually a multi-winding inductor), it can power itself from the HV source. At that point, something will likely happen to turn off Q109. Perhaps there is a capacitor in the base circuit of that transistor that turns it off after a few hundred milliseconds.

Mike, you are a really smart guy with a great ability to explain the details without a board or schematic in hand. As always, i appreciate your observations and analysis.

After reading what you wrote i went back to look at the board and you are spot on. The resistor chains and Q109 on the bottom layer can only get so far on generating a startup voltage even with a 360V supply, in fact it may function just as a "Pre-charge" circuit for filling the Vsub reservoir of capacitor C122. Vsub is the supply voltage created on the "hot side" secondary by the switching action of Q110, and it is used as the Vcc for the IC101 chip.

Here is a simulation run with a 15V zener and no load on the test point that would be pin 11. The voltage can be adjusted by changing the zener value--it's going to level off at a little below the zener.

And this is with a bit of load added to represent the drain on Vcc at pin 11,

 

[kiev]

i'm not sure there is much value in trying to get it "running" on the bench quite yet, there is the third resistor chain that sets some voltages used by the op amp to send input signal to IC201. Until that is understood it could give a false indicator or cause possible damage. See sketch in post down below.


[edit] elden has been able to see that the zener is marked "182".
If it reads a normal diode drop in the forward direction i would think it is okay. i don't think it would stop the circuit unless it was shorted, so it is not likely the root cause.

 

[eldenh]

Thanks for all the help! I picked up a better lense and can now read the numbers on ZD101 as 182. As I see it, IC101 requires 11v to start and it can't bootstrap it's power until it starts, so the fact that I have only 1.3v on pins 10 & 11 seems significant.

 

[kiev]

Yes but the circuit was designed for ~300 to 360 VDC on the HV(+); 59V is not enough to meet the criteria, see the simulation, they were run at 360. At 59 it will be much lower due to the resistor chains dropping the voltage.

 

[kiev]

Since you have the board out, one thing that you could do is measure across all the resistors and make sure they read close to the value marked.

Also you could check for continuity (beeper function on meter) across all those little ceramic capacitor--they should measure open but they can short out when they fail.

And then there is the diode check function across all the diodes looking for shorts instead of ~0.3 to 0.6 V diode drop depending upon type.

A failure of any of the passive components could cause it to not work, so checking these might find the culprit or rule them out. Both are good things.

 

[kiev]

fleshed out the HV input section--should be everything on the HV side of the isolation gap for startup and switching of the TR105.

 

[eldenh]

D103 reads 167 ohms both ways. C123 reads 104 ohms. I haven't checked the resistors yet and have been checking only the HV section initially. Most of the diodes in the Q101 to Q104 driver section appear to have a resistor in parallel. Q109 doesn't seem to be a junction transistor, the central lead checks as a diode to the left lead but always open to the right one.

 

[kiev]

D103 reads 167 ohms both ways. C123 reads 104 ohms. I haven't checked the resistors yet and have been checking only the HV section initially. Most of the diodes in the Q101 to Q104 driver section appear to have a resistor in parallel. Q109 doesn't seem to be a junction transistor, the central lead checks as a diode to the left lead but always open to the right one.

There are 2 resistors in parallel to D103 so that is ok, same with C123.

Q109 should read a 0.59V diode drop from the left (+) to the center(-) and from the left to the right(-). If you reverse the meter leads then there should be no reading from left(-) to center(+) and a high value like 2.3V from left to right.
left is the base, center is collector, right is emitter. Should be a link to the datasheets in post #4 on the first page of this thread.

Q105-108 are PNP transistors and should have diode drops between the left(-) and center(+), and left and right [base,collector, emitter] using the opposite polarity as used to measure on Q109 (an NPN transistor).

 

[eldenh]

I'm learning about surface mount devices! Q109 checks out, but Q105-108 don't. I get 350mv to center and 526mv to right with black lead to left lead, but 352mv and 869mv with red to left lead. I assume those readings involve the diodes that are in their circuits.

 

[kiev]

The transistors are probably okay from those readings; it won't be a clean check because of all the components connected in the ciruit provide a parallel path. But if it were to measure nearly zero volts such as due to a dead short, then that would raise the alarm flag. Just looking for bad components that are either shorted when they shouldn't be, or open circuit when they should have some resistance.

It looks that only the two 12V lines and ground, plus the 2 signals, DCSW and SDW, are needed to make the DCDC run. If possible it would be good to verify continuity of the 2 signal wires from the E-03 connector back to the EV-ECU under the rear seat.

[edit] i'm finding some labelled test points on the top layer of the board that could be used with a volt meter while the board was installed and powered up in the car. i'll have to ring these out to know what they would report, but for example; TP201 located in the corner near the circled-6 screw hole, reads the TR105 secondary voltage of C212 in the middle of the board. This voltage is used to pulse the isolation transformers to create the gate drive voltages for Q101-104. And the test point labelled Vsub is the TR105 secondary voltage on C122.

Other TP: TP202 and 203, these are the gate drive signals to Q201 and Q202 to pulse the Isolation transformers. TR101 is used to control the gate drives of Q104 and Q101; TR102 is for Q103 and Q102. These are the top and bottom pairs of the H-bridge needed to create an AC for the stepdown power transformer TR103.

TP217 looks like the temperature sensor mounted to the heatsink on connector CN203.

CS201 somehow related to the current sensor.

LV section:
There are about 8 ICs, 23 transistors and 11 diodes in the isolated LV section near the CN201 connector. i can't imagine what it does or why it's needed considering the HV section appears to have it's own boot strap and secondary voltages. Probably current sensing on the output and a way to regulate the PWM.

Look the board over really closely looking for signs of heat discoloration or charring, broken or blown components, cracked solder joints, etc. Get a bright light and a magnifying lens to make a detailed search of every bit of both sides of that thang.

 

[eldenh]

Thanks for the explanations. I feel very lost without a schematic and question how well I'd understand it if I had one. I checked the two lines to the EV-ECU and find read voltage on them. I can see any apparent damage or problem on the board.

It can't require 360v to run the HV section, or it wouldn't work when the battery is getting low. I've seen that it would function normally when down to turtle. If the fact that it doesn't function with my 59v, 2A supply, might it be worth trying to supply about 12v to get IC101 running when using the 59v on for HV?

Where did you get 1k and 100nF to model IC101? I read the data as 10ma normal. What is the function of TR104?