Can I Implemented H-bridge by two inverters?

Discussion in 'General Electronics Chat' started by CaptainJohnson, Feb 20, 2008.

  1. CaptainJohnson

    Thread Starter New Member

    Feb 20, 2008
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    Hi everyone.

    I want to design a chopper circuit to modulate the very low frequency differential signal to 1kHz signal in order to limit 1/f noise. I choose H-bridge to connect a transformer to do this job. My question is: Can I use two inverters to implement the H-Bridge?
    Two inverters are connected in parallel. Sources of two PMOS are connected to +ve signal rail and sources of NMOS are connected to -ve signal rail. The outputs of two inverters are connected to transformer which is used to isolate from op-amp.

    I find that if two inverters are controlled by two anti-phase clock, one of NMOS and PMOS will be turned on at either side (but not at same side). For a eg, in the first half cycle, the right side inverter is input '1' and left side is input '0'. Then NMOS at left side and PMOS at right side will be turned on, the rest MOS will turned off. So, the current will flow from right to left. Similarly, in the second half cycly, it will flow from left to right.

    Do I understand this operation correctly? I notice that there is no Vdd and Gnd in this part of circuit, instead there are differential signals. So does it mean this two points are floating?

    Sorry for my poor English and hope you guys could understand what I said.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    You need to consult the datasheets for the MOSFETs under consideration.

    It is highly likely that the MOSFETs will take different amounts of time to turn OFF than turn ON.

    If at any point in time you have both high and low side of 1/2 of the H-bridge turned on, you will shunt the supply to ground, likely resulting in a loud "BANG" and smoke.

    You must design your circuit so that it is not possible for both the high and low side on the same 1/2 of the bridge to be on simultaneously.

    A simple inverter, or pair of inverters, will not work.
     
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    If Capt. Johnson is talking about CMOS logic inverters, there should be no problem. They do have some shoot-through current, but it is not destructive (or they wouldn't work). I don't see why adding a transformer between two of them (with 2 in parallel on each side) will somehow make them suicidal.
    If he is planning to make inverters from power MOSFETs, then what you say is true.
     
  4. CaptainJohnson

    Thread Starter New Member

    Feb 20, 2008
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    Thanks for you guys reply.

    The reason I want to use two inverters to implement H-bridge is that I find the normal H-bridge are implemented by 4 same type transistors (NMOS), and the behavior of two sides of the bridge just looks like two inverters to be operated by a anti-phase clock.

    Since there are no "supply" and "gnd" connections to the inverters, instead of differential signal inputs, I seem to use CMOS logic inverter to work as a analogue circuit. Can this happen, if we don't consider the ON and OFF time issue for now?

    The reason I connect a transformer at output of two inverter is that I want to modulate the low frequency signals to 1KHz. If PMOS and NOMS at either side are turned on at same time, the differential signals will appear at two ends of the transformer.

    Hope my explanation not to make you guys mad.
    Cheers
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I don't understand where you are going to apply your analog signal. You need to post a schematic.
     
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