AC/DC and Isolated DC/DC Power Forum - Recent Threads

UCC28019 and UCC28019A

John2012 — Mon, 29 Apr 2013 20:33:52 GMT

Hello,

What are the differences between UCC28019 and UCC28019A?

After half hour reading the datasheest, I couldn't tell, thought to ask a quick question as I'd like to buy it today.

anybody can help?

Thank you,

UCC28251 current sharing

Alen Petrossian — Thu, 23 May 2013 22:26:24 GMT

Hello,

I have a question regarding using the UCC28251 controller for Half –Bridge with synchronous rectification.

Can I connect the outputs of multiple converters in parallel for current sharing (with no or-ing diodes)?

Thank you in advance.

UCC28061 / UCC28063 spontaneous gatedrive turn-on after turn-off

Floris Schropp — Tue, 16 Apr 2013 09:49:30 GMT

I'm working on a 10 KW 2-phase BCM buck converter based on the UCC2806x but got stuck. I've 'folded' the math and ins/outs so it works for buck application, and the circuit is working quite happily for a range of in- and outputvoltages. For any other range, strange things happen. This range is not clearly defined, but lies in the range of Vin=2xVout. Above and below is no problem (30KHz switching freq. works just as nice as 120KHz)

What happens is that immediatly after the gate driver (IRS21850 single high side) is turned off and current starts falling, the controller turns the gate on again, thus ramping current further up until it hits the current limit of the lab supply used. Most of the time the gate drivers don't survive. The same thing happens when GDB is disabled, when VINAC, VSENSE and HVSEN are externally controlled and when seperating or not seperating PGND and AGND.

I've looked at it with a few colleagues, redesigned grounding and signal routing and ruled "everything" external out. The feedback may not look stable, but this is pickup. Gate B is completely disabled and remains so, even when A decides to turn on. When connecting gate B to Comp, the controller works fine until A starts misbehaving and then chaos happens, as can be expected. So, for tests, i've disabled B.

Green = Gate of MOSFET A vs GND (so a bit dirty, sorry for that, we've not kept every screenshot)

Blue = ZCD winding of A vs GND before RZCD

Purple = IL,A

Then we have (different scope, different day)

Top: VGS (diff probe) MOSFET

Bottom : output of Controller GDA

Clearly, the controller is first to turn on again. Not the FET, not the Driver, not the Current Sense winding, but the Controller itself. I've got more scope shots of all the other signals to reaffirm this statement.

I could list everything i've done, but in the beginning there was almost no decoupling and/or limiting switching speed and long wires. Now everything is limited, filtered and built on the controller itself. I've used other power supplies, coax or twisted wire. I've also eliminated reflections and ground bounce from controller to gate driver. All signals, supplies and ground became cleaner and cleaner, but no difference in behaviour.

Why does the controller decide to switch on again, with no apparent external cause?

led lihting

praveen vp — Wed, 22 May 2013 04:56:30 GMT

hai everybody

iam praveen work in marc weighing system kerla,india

we are to design ome led lighting products . we select one ic tps61500

in thi ic there is an option for analoge dimming and pwm dimmin seperately.

for pwm dimmig the what is the optimum frequency and it is possible to give with out a micro controller using simply a 555 timer ic .

or it simply connected to the vcc.

we are thinking to connect 10 white led's in series with a current of 200 ma .(3w,5w,7w led lights)

thankyou

SMPS for input 85V to 325VAC and output 15V, 10A

Atul Bhakay — Wed, 22 May 2013 08:49:52 GMT

Hi, Kindly provide design details and circuit diagram for 15V, 10A SMPS with input of 85V to 325VAC

Regards Atul Bhakay

Lead Acid Battery Charger for 12V, 7.2AH battery

Atul Bhakay — Wed, 22 May 2013 08:33:06 GMT

Hi, Kindy suggest design with circuit diagram for above battery charger with input of 85V to 265VAC

Regards Atul Bhakay

UCC28950 VREF OUTPUT NOT CORRECT

John Wiemeyer — Fri, 17 May 2013 15:28:16 GMT

Hello,

I’m having a little trouble getting the UCC28950 working properly and would like a little tech support. In particular, the Vref output is ~7v, but according to the spec it should be 5v.

I have attached a schematic showing the pwm ic circuitry. All the delay resistors are 20kohms, and the master clock resistor is 60k ohms (100khz). The Rt_master now goes to Vref instead of AGND as shown below. The IC appears to function correctly with burst mode pulsing (not connected to real signals yet), but the voltage from Vref is ~6.8v instead of the specified 5.0v. Not shown is a 1ufd cap now connected to Vref.

Regards,

John Wiemeyer

(Please visit the site to view this file)

Isolated DC/DC power supply

Stan Gibson2 — Thu, 23 May 2013 21:16:57 GMT

I have been told that TI has an old Burr Brown part that is a 5V input, 5V output 2W isolated supply. Something like part number DCP020505P only with regulation. Does TI have something like this or similiar? We actually need something like this that can handle 1 to 2 Amps. We can settle for a DC/DC convertor that has a higher input requirement, but the output must be isolated. Please let me know. I found a datasheet for a Burr Brown part called a 724, which is also very close to what we need but I am not sure TI supports that any more.

Difference between LM25118 LM5118 and functional difference of automotive grade

Karan Rao — Thu, 23 May 2013 20:14:42 GMT

Greetings

This is my first post here.

Q1. What is the difference between the two devices LM25118 and LM5118, design report suggest no difference?

Q2. What is the difference between Q1 or automotive grade and regular device. Can I use the same design for both controllers? - I am guessing that, the reliability is the only difference, is that a right assumption.

Thanks

Regards

UCC2804 Note Question

Eric Kohnke — Thu, 23 May 2013 19:16:14 GMT

Can someone clarify note 2 with respect to the Vcc voltage on the UCC2804 datasheet page two ? I am getting hit by reliability because we have 11.74V on the Vcc pin. They way I read this note is that as long as I am below 30mA the 12V maximum does not apply.

Note 2 states In normal operation Vcc is powered through a current limiting resistor. Absolute maximum of 12V applies when Vcc is driven from low impedance source such that Icc does not exceed 30mA. We are less than 5 mA.

Then the note states:

The resistor should be sized so that the Vcc voltage, under operating conditions is below 12V but above the turn on threshold.

current sensing

Eirik Sundal — Thu, 23 May 2013 17:16:39 GMT

Hi guys,

I am designing a buck regulator for battery charging. I have done quite a lot of testing on my current design and found that it gets unstabile at high voltages and light loads. The controller I use is the uc3823a HIGH-SPEED PWM CONTROLLER. I use it in voltage mode but now I also want to implement current sensing. How to do this, or is this even possible for this controller?

Thanks for replies

UCC29421PW rare error

Daniel Ciu — Thu, 23 May 2013 09:09:47 GMT

Hi all.

I'm using the UCC29421PW as a controller for DC converter.

recently I observed an error during running, that I would like to understand better and know if someone is familiar with it and may know its source.

the topology I used is as follows:

pins RSEN PGND CP ISENSE GND PFM FB are connected to ground.

pin RT is connected to ground through a 100kohm res.

pins VOUT and VPUMP are connected to a scope.

pins VIN RSEL are the VCC.

pin SYNC/SD is connected to a voltage source.

it happens about 25% of the time that after I shutdown the VIN voltage , the PUMP pin some how drive a high value to the gate of transistor and get stucked liked that, so shortning the inductor connected to the vin , thus no more supply voltage arrives to the UCC29421PW.

after looking at some tests points , it seems that when VOUT get down to 2.5V , the PUMP pin trigger this situation , thus not allowing increase VIN more than 300mV resulting from the RDSON and the inductor resistance and the high current floating to ground through them.the situation is stucked like that until reseting .

also I noticed it is temperature dependence.

1. has some one noticed this situation?

2. is PUMP pin should be connected that way ?

3. any further ideas of what could lead to that will be gladly recieved.

Thank you!

UCC27531EVM-184 evaluation module

Thilak Senanayake — Thu, 23 May 2013 02:19:59 GMT

Please let me know the maximum switching frequency of the UCC27531EVM-184 evaluation module.

MOSFET driver for high-voltage without bootstrap setup nor shared grounds

nano-eng — Wed, 22 May 2013 14:59:37 GMT

Dear TI forum,

I'm a newbie to power design engineering and I'm trying to design a system that would allow me to drive a couple of N-MOSFET devices set in a totem configuration for high voltage configurations (variable rails set between -300V and +300V). The system has the following requirements

We want to have a system where a single digital PWM line (TTL level) controls both gate drivers with non-overlapping characteristics to prevent any kind of condition where the high-rail and the low-rail sources are short circuited. As such, we thought about using a MOSFET driver.
Isolation is a key characteristic that has to be provided so no bootstrap setup is allowed.
The high-rail voltage can variable be set between (positive)300V and 0V. The low-rail voltage can as well be modified to have a value between 0V to (negative)300V. As such, we decided to use ST's STB8NM60 N-MOSFET transistors for the output stage since those devices can operate up to 650V.
We found that Analog's ADuM7234 could be used to implement a possible solution. However, due to inherited limitations in the control stage (namely, the fact that there is only one PWM line to control the totem pole setup) doesn't allow us to go in that direction.
The block diagram shown below presents the overall configuration we want to achieve. The frequency for the PWM signal should not be greater than 10KHz in a 50% duty cycle.
We were wondering if TI has any device that could meet the requirements listed above. We searched TI's catalog and found TI's LM5106. However, it has several limitations regarding our system's specs. We are mainly concern about the bootstrap requirement and its upper boundary (118V) which will not meet our system's needs.

Please, don't hesitate to contact me if you need more info.

I appreciate any help you can provide me with.

Thanks in advance!

The diode in the circuit LM26480

Dmitriy Vlasov — Wed, 22 May 2013 09:29:26 GMT

Need to put a diode in the circuit LM26480 SW to GND pins ? The diode is in the document AN-1800 Evaluation Kit for LM26480 - Dual DC/DC Buck Regulators with Dual Low-Noise Linear Regulators Figure 10 LM26480 Evaluation Board Schematic. In PCB Evaluation Board no diode. In no other documentation diode. The diode is a classic scheme BUCK . Do I need a diode?

LM25576: Suitability for Switchable Output Voltage Supply

Paul Alciatore — Wed, 22 May 2013 04:44:47 GMT

I am doing a design for a supply with switchable output Voltages in the range of 2 to 14 Volts. Switching would be accomplished with power on and load connected. Load current from 0 to 1 or 2 Amps. My preliminary plan is to design the feedback divider for the lowest desired Voltage and mechanically switch additional resistors in parallel with the low side resistor to change to higher output values. Input will probably be filtered 18VDC but this can change.Circuit specs are fluid at this point.

I am looking at the LM25576 for this design. Is this a good choice or is there a better device that I can look at?

One point of concern is the statement in the LM25576 data sheet that there is a minimum load current for CCM (continuous conduction mode). I am not sure what would happen if the load current is lower than this value. Would it go out of regulation? Would the ripple increase?

MC33063AQDRQ1 VIpk Current-limit sense voltage

Toshio Ushikubo — Mon, 25 Mar 2013 04:38:21 GMT

Hello,

Please give me the following information of MC33063AQDRQ1.

1)Datasheet specify VIpk Minimum and Maximum value only at 25°C.
Please give me any VIpk distribution data at full temperature range(–40°C to 125°C).

2)Datasheet page 3 specify that VIpk typical is 300mV, but figure 4 explains VIpk is 330mV at 25°C.
Please let me known why each value at 25°C are different.

3)Pleas give me statistical distribution data of VIpk.

Regards.

UCC28811 switch off at low line

Ronald Jansen — Thu, 16 May 2013 14:11:15 GMT

Hello,

I designed a single stage PFC LED-driver with a UCC28811. I found that the input current has jumps around the zero crossing. I zoomed in on this in the below image.

I found that these jumps are caused by the fact that the controller shuts down during appr 500us around each zero crossing. The below image shows the buffer voltage versus the MOSFET gate voltage. As the controller shuts down the buffer is never completely drained to 0V. Because of that there is a current jump when the line voltage gets higher than the buffer voltage and the buffer starts charging again. Then at 900uS there is a second current jump when the controller resumes operation.

I have also seen this behaviour at other UC28811 designs, but with this design it is much longer. Also here I see that the buffer voltage remains at appr 20V for 500uS, whereas in other designs it starts increasing directly after that (see image below)

I am now trying to find out what is different in this design and if there is a way to improve this behaviour. In the other design I can see that around the zero-crossing the FET on-time is very short (see image below).

I am not sure why this is. It should have a pretty fixed on-time.

My guess is that in my design the on-time gets so short that the pulses actually disappear. What I don't know is why. As you can see in the images there is a sudden drop in pulse duration around the zero crossings.

Does anybody know why this happens and if there is something I can do about this?

dc/ac invertor

or sam — Sun, 19 May 2013 13:44:51 GMT

I want to deliver electricity wireless between 2 coils.

from what I understood I deliver the power between the coils in high freq then I need to make dc from it - (I will use rectifier + capacitor) but then I want to generate a 10 hz sin.

I understand I need inverter I havent found any small components (I need +-2v sin wave). can you direct me to such component? - I need it to be passive as possible.

is there another way to convert my 1Mhz signal to 10Hz without using inverter?

thanks in advanced,

which is the better topology for 235Vdc/1A

mahesh jalgaonkar — Sat, 18 May 2013 10:56:27 GMT

Sir,

please can anyone help me to choose the correct topology for 235Vdc/1A output.

Input requirement is 230Vac +/- 20%

And please suggest me some IC for good efficiency and price.

I already work with flyback, PFC and forword converter.

LM5104 issues

Emanuele Grasso — Mon, 06 May 2013 10:02:12 GMT

Hi.

I am using the LM5104 to drive an half bridge with an inductive load, whose schematic is attached.

The main problem is a strong swinging on the load voltage. I have experienced the same problem

by changing the layout of the PCB many times, by using different resistors connected to the RT pin,

and different sizes of the bootstrap capacitor. I also tried to use an external "optional" recovery

bootstrap diode, and this increases the swinging really a lot. Moreover, the swinging has a fixed

frequency of 14 MHz which I can not really explain.

Any suggestions on how to improve the circuit behaviour, as at the moment it is not useful at all ?

Thanks

What is the best PWM for 200v v to 15v DC to DC at 150C

Ruben Aguila — Wed, 08 May 2013 17:08:50 GMT

I need a PWM controller that can work up to 150C.

I designed a 200v to 15v DC to DC flyback converter using the UCC28700 PWM, but it works only up to 140C then the PWM thermally shuts down.

Is there another PWM with no internal thermal shutdown that can be used in my application?

Power supply voltage .

Abhilash P K — Fri, 17 May 2013 04:57:07 GMT

Why people always 3.3 vpower supply and not 3v? Is it any reason for that? Just curious to know that.

Solar battery charger

Chito Condes — Fri, 17 May 2013 06:56:26 GMT

Warm greetings to all.

I am looking for a schematic diagram complete with parts identification, so I can build a charger for a 12-volt lead acid battery. I will be using solar cells as

a source of power. Can anyone tell me where I can find them and where to buy the required parts? Please reply to cscondes@gmail.com

Thank you and best regards.

LM5113 GaN FET driver? Isolation?

phil86 — Sun, 12 May 2013 10:55:32 GMT

Hello

Has anyone successfully used the LM5113 yet?

My question is whether I need to isolate the HI and LI inputs from my uC. (I am doing a DC 48 V to DC 12 V conversion with a synchronous buck topology). My uC is not connected to any PC or similar but is there any thread that HI or LI is on a higher potential then 4 V. The block diagram on page 2 is rather vague.

In other words, what is the maximum potential I can expect on LI and HI with respect to ground (if I feed them with a 3.3V PWM signal) ?

Thank you

phil