Variable DC-DC converter

[Lavanya R]

Hi All,

Does my attached circuit can work as variable DC-DC converter. If not help meto make the circuit as intended.

Thanks in advance
IC1 & IC2 is 555 timer
IC3 is IR2110

 

[Anna Conda]

source of Q1 goes to drain of Q2. else the 2110 won't work very well...

 

[ravindragudi]

The Q1-S to be connected to Q2-D and undo the connection of GND from Q2-D. In this way the converter can function like Buck converter.

 

[Lavanya R]

Been tried as mentioned by ravindragudi and connected inductor in series with junction point of Q1 source and Q2 Drain does not functions as buck converter.

FYI, the circuit has to be variable buck converter

 

[ravindragudi]

It will be helpful if you provide more details on the things you tried, how the input supply to DC-DC converter is given, waveforms @ gates of Q1, Q2 and output waveform.

 

[Lavanya R]

It will be helpful if you provide more details on the things you tried, how the input supply to DC-DC converter is given, waveforms @ gates of Q1, Q2 and output waveform.

The supply to the DC-DC converter is been given by 2 channel DC supply in which one channel supplies power 15 V to IC1, IC2 & IC3. The other channel is been used to power up the MOSFET.

Moreover after supplying power the signal at L0 pin (IR2110 IC) is available. but no signal at Vs, Vb, & H0.

Across pin HIN and LIN, the signals are available.

- - - Updated - - -

also I use 100nF ceramic capacitor and 1N4148 diode in Bootstrap circuit.
Does the voltage rating of cap and diode affects the working of DC-DC converter.

what should be the voltage rating of cap & diode if totem pole (MOSFET) supply is 10-100v DC?

 

[Orson Cart]

Connect Vs to 0v for test only, no supply on the mosfets, and check all the signals on the way thru...

 

[ravindragudi]

Moreover after supplying power the signal at L0 pin (IR2110 IC) is available. but no signal at Vs, Vb, & H0.

Across pin HIN and LIN, the signals are available.

I think the supply to IR2110 driver IC is not correct. Look at the functional block diagram of this driver. The SD, VSS and COM have to be connected to ground in your circuit. The VB is supply for high side MOSFET and Vcc is supply for low side MOSFET. VDD is logic supply so it can be 5V. With these changes check if the circuit is functioning as intended.
Also VB is the supply so, if there is no signal here, means there is no power input given

 

[Lavanya R]

What happens if VS pin is not connected to junction point of Source of Q1 and drain of Q2?

Also I use 100nF ceramic capacitor and 1N4148 diode in Bootstrap circuit.
Does the voltage rating of cap and diode affects the working of DC-DC converter.

what should be the voltage rating of cap & diode if totem pole (MOSFET) supply is 10-100v DC?

 

[ravindragudi]

The cap and diode have to be rated for the max voltages/ currents seen by them during switching as well... that means you have to select these parts with voltage rating of at least 1.5x of 100 volts and current of 1.5x of gate drive requirement.
Refer to this application note which details this - http://www.irf.com/technical-info/appnotes/an-978.pdf

Also attached is a simple Buck converter using this IC. This may be useful for you.

 

[ravindragudi]

I missed the Q about Vs pin in last post ... Vs pin is reference signal for the signal on the gate of high side mosfet. That means voltages on Gate will be with respect to floating supply at Vs and hence has to be connected to S of high side mosfet. Otherwise transistor may not function properly.
Also referring you a video link to get understanding on IR2110. https://www.youtube.com/watch?v=wgsTXbHLbmI

 

[Anna Conda]

The 1N4148 is too small for this app, ideally you want a 1A diode rated above the maximum DC bus voltage, the 4148 will tend to fail short, then possibly open, this can kill the 2110....

 

[Lavanya R]

then UF4007 can suit this application.. can u tel wat abt the voltage ratings of capacitor?

 

[Lavanya R]

Also I tested the complete circuit as attached.. The output votage across the inductor is 5V pulsating DC..
I supplied supply voltage of 20v to Drain but the output is 5V...

Help me out to get the proper output

 

[ravindragudi]

You have not mentioned what's the output voltage you are targeting. And this circuit is buck converter - if you give more than 5V at input you will get the 5V at the output - you have to choose proper capacitor filter at minimum to see a proper DC voltage here.
Also attach some scope shots to give us more information about what's happening in the circuit. Don't forget to share the recent schematic that you are working on this now.

 

[Lavanya R]

I intend this circuit to work as variable buck converter. So based on PWM signal the output voltage should vary. for Eg, say I supplied 20V to drain so if PWM is 100% then output should be 20V if it is 50% then 10V.

- - - Updated - - -

this is my recent schematic in which Im working.

 

[ravindragudi]

Though you have not shown in schematic, I assume that you have connected Vss, SD and COM to ground. Also you are still showing 1N4148 diodes, i guess you replaced them with proper diodes as said by Anna Conda.
You are not mentioning about the switching freq, required Vout. The Vout will depend upon L, C, fs and Vin max. Refer to this TI app note and calculate the L and C and experiment again.

**broken link removed**

 

[Lavanya R]

I think diagram is not properly visible. You are right I connected SD,VSS and COM to ground and I replaced 1N4148 diodes with UF4007.
Inductor value is 400uH, 4A
Capacitor value is 100uF and 100V
Switching frequency is 300Hz
and Supply voltage to Drain terminal varies from 10 to 100V
The Vout has to be pulsating DC. If PWM signal duty cycle is 50% then output voltage should be 50% of input.

 

[Orson Cart]

Not at no load....

 

[ravindragudi]

I think diagram is not properly visible. You are right I connected SD,VSS and COM to ground and I replaced 1N4148 diodes with UF4007.
Inductor value is 400uH, 4A
Capacitor value is 100uF and 100V
Switching frequency is 300Hz
and Supply voltage to Drain terminal varies from 10 to 100V
The Vout has to be pulsating DC. If PWM signal duty cycle is 50% then output voltage should be 50% of input.

With change in duty cycle approximately by same factor of duty cycle change, the output should vary. Be aware that efficiency is also a factor in determining Vout, there may be delta change in efficiency with change in duty cycle.

Have you done the calculations for selecting the L and C for given input and output? I am not seeing the co-relation between the values you mentioned and the Vout you are getting. First thing is you have to calculate the L and C. Also is fs 300 Hz or 300k Hz?