Hi, I'm new here & I've been working with electronics for quite a few years now but have never been to college for it yet (Very soon).

I am trying to build a Microcontroller controlled variable freq. (0-20khz) 120v signal generator and have ran into problems with getting an output from the high side of the IR2110. Ultimately I will be using 2x IR2110's arranged as a Full Bridge.

The Lo works perfect, whereas the Ho gives +10v weather the Hin is High or Low.

For a test I used the schematic provided in the IR2110 datasheet.

Using a PC power supply for a steady 12v Vcc
3.3v Logic Vdd ( i have also tried 5v & 12v for Vdd with same result)
3.3v PWM to Hin/Lin ( PIC -> 2n2222 @ 5v -> 2110, shows close to 3vpp on oscope )

Vss & COM connected to gnd. & the rest is identical to the dataheet.

Outputs:

(2110)
Ho +10.95v ( Never Changes )
Lo + 5.65 @ Pwm

(Mosfet Using 12v High supply)
High Side +12v ( Never Changes )
Low Side - 12v @ Pwm


For the test I am connecting PWM to Hin or Lin while the other is Gnd. I have also tried connecting both Hin & Lin together. All result in same results.

What am I doing wrong??
the datasheet used +15v for testing the high side, is 12v too low?

When I measured my old inverter's base pin for the high side it said 60v @ 60 Hz and the Low side was 9V @ 60 Hz.

How is the 60v base generated??

I understand i need to return to college, its just were moving this winter to florida, so im waiting till i get there before i start school again.

Thanks

 

Post your circuit diagram please.

What values are your bootstrap capacitors?

 

ok, well, i have rebuilt the circuit (again) on a pref board, and it works!

however, i am getting 6.01v Lo and a 5.38v Ho using .33 uF ceramic's for Bootstrap and 12v Vcc, 3.3Vdd & my PWM is 2.34v (2n222 @ 5v & 1.5vPwm In) @ 400hz

currently i dont have many parts laying around, so my values are most likely wrong. i dont quite understand how the bootstrap cap's & floating supplies work just yet.

On my old inverter, how does it produce a 60v Ho that drives the 2 high side mosfets? while the Lo is 9v. and do i need to produce that same 60v signal to drive the mosfets to switch 150vdc?

OR does the Ho require the high side mosfet & +HV (via Vs) in order to produce the 60v signal to drive its own base??

i am rather confused on this one, and right now it is my final hurdle to get past and my project is done.

Any & all help is much appreciated.

 

also, what voltage rating should the bootstrap cap's be?? i cannot find a reference to this anywhere??

 

In your schematic the load is connected between the source of the high and the drain of the low side MOS. The MOS are never switched on the same time and thus no power flows to the load. When the high MOS is on the low MOS is off and vice versa. Use only the high MOS or the low MOS to drive your load.

 

that was not my intended circuit, that was only the "test" circuit.

my intentions are to make a 120v modified sine wave inverter with a variable pwm output. i have the inverter that makes 120v @ 54khz pwm from 12v. no problem.

but now for switching the high side 120v with a 1.5v logic in a full H-bridge im a little flustered.

im pretty sure i have the circuit working as per instructions from another post here i have managed to get a 6v signal (Hin) from the Ho and a 9v Lo (Lin).

What i Dont understand is how the 6v is suppose to switch the 120v which requires what about 20-60v? (my old inverter produces a 59v Gate drive signal for the High Side).

here is the 2110 section of my circuit, it has 2 signals generated by a parallax propeller chip as shown in the schematic.

i would like to know how the 6v switches 120v
and what voltage value should the bootstrap caps be? 50v or 200v??
or
do i have something wrong?

 

It switches 120V due to the action of the bootstrap capacitor. This capacitor is charged with a voltage 15V above the high side MOS source by the IC.

 

Check out IR Application notes 978, it should have a formula for deciding what the bootstrap capacitor should be. Page 6.

 

Hi,

1. First of all, if you need 120v modified sine wave, the dc bus has to be more than 120v around 170v or so to allow for losses and voltage drops and well as the voltage drop due to "deadtime" in quasi sine generation. You can always change the dc bus to see how much output you get. This shouldn't be much of a problem since you can pw modulate the signal from the propeller chip.

2. Now about the bootstrap capacitor, this is charged with the Vcc, in your case 12v. So, if you have a 100v dc bus, the MOSFET is switched with 100v + 12v(stored in the cap) at gate, but this corresponds to 12v VGS as source pin is at 100v and gate at 112v. VGS required for maximum performance should be above 8v and below the Vgs breakdown voltage, usually 20v.

3. Maybe its an error in drawing the schematic, but there, it does not show the 12v connected to the vcc pin (pin3) for either IR2110s.

4. C3 should be much much more than 0.33uF. Since this is the bulk capacitor, it should be quite a higher value, actual value depending on your output power. Taking for example that your power is 300W, the current draw would be ~3A. So, I would use something like 100uF with a smaller 0.1uF 300V or more to play it safe and have a clean dc bus with minimal ripple.

5. You used 3.3v for Vdd for IR2110. I suggest you use 5v and if required amplify the input signal to a higher level using transistor.

6. For bootstrap capacitor you would be safe using anything above say 4.7uF. This does not come from any equation or such as those are quite complex to work out. While testing full bridge with IR2110 at 50Hz, I used several values from 4.7uF to upto 68uF all with success, but never went below 4.7uF as it seemed to be too less. But usually, I would use 10uF. And make sure you use a 0.1uF ceramic decoupling capacitor across the larger electrolytic capacitor. But if the capacitor is tantalum type, then ceramic capacitor across it is not required. (This info can be found in, I think, the IR application note, maybe AN978).

7. The capacitor voltage rating should be twice the Vcc voltage. Since you are using 12v, you would be safe with anything above 25v.